METHOD FOR OPERATING A CONTINUOUS SEPARATION OF TARGET PRODUCT X IN THE FORM OF A FINALLY DIVIDED CR

专利摘要:
The invention relates to a process for the continuous separation of a product X in the form of a finely divided crystallizate formed of a liquid phase P containing the target product X and components different from the target product X by cooling suspension crystallation. in the secondary space continuously traversed by the liquid phase P of an indirect heat exchanger as part of the simultaneous continuous passage through the primary space of the indirect heat exchanger by a refrigerant as well as the continuous withdrawal of d 'a suspension of crystallizate S, having a degree of crystallization Y, of the secondary space, in which the adjustment of the degree of crystallization Y is carried out on the basis of a heat balance carried out continuously using a computer .
公开号:BE1018537A3
申请号:E2008/0500
申请日:2008-09-11
公开日:2011-03-01
发明作者:Joerg Heilek；Peter Schlemmer；Ulrich Hammon；Klaus Joachim Muller-Engel
申请人:Basf Se；
IPC主号:

专利说明:

A method of operating a continuous separation of a target product X in the form of a finely divided crystallizate
Description
The present invention relates to a process for the continuous separation of a target product X in the form of a finely divided crystallizate of the target product X from a liquid phase P containing the target product X as well as different components of the product. target X using an (indirect) heat exchanger having a secondary space and at least one primary space, wherein the secondary space and the at least one primary space are spatially separated from each other by at least one material separating wall which serves as a surface for the transfer of heat from the secondary space into the at least one primary space, into which a liquid phase P is introduced continuously into the secondary space of the heat exchanger, while the at least one primary space is traversed simultaneously by at least one fluid refrigerant so that it forms in the secondary space, while leaving a resistor phase an individual liquid R originating from the liquid phase P, a finely divided crystallizate of the target product X, which is suspended in the residual liquid residual phase R, which contains, in comparison with the liquid phase P, the different components of the target product X to the enriched state and whose target product content X reaches at least 70% by weight (relative to the total weight of the residual liquid phase R), while retaining a suspension S, having a degree of crystallization Y, of crystallized finely divided by the target product X into the residual liquid phase R and the suspension (of crystallizate) S is withdrawn from the secondary space of the heat exchanger continuously.
Methods described above are known for the continuous separation of a target product X in the form of a finely divided crystallizate of a liquid phase P containing the target product X as well as different components of the target product X to using a heat exchanger (cooler or crystallizer) having a secondary space and at least one primary space (see, for example, DE-A 103 32 758, WO 2004/035514, Research Disclosure Database Number 496005 and 479008 and the German application with the file number 2007 004 960.0).
By heat transfer from the liquid phase P conveyed to the secondary space through the material separating wall (heat transfer surface) separating the secondary space and the at least one primary space from one another in the refrigerant flowing in the at least one primary space, the liquid phase P cools until the saturation limit of the liquid phase P with the target product X is exceeded and the liquid phase P is opposed to the supersaturation by crystallization of the target product X.
The expression "degree of crystallization" of the (crystallizate) suspension S having the finely divided crystallizate in suspension in the liquid residual phase means in this application the mass fraction of the finely divided crystallizate contained in the suspension S. The degree of crystallization Y by division of the crystallizate mass γτικι-, υ contained in the suspension S for a degree of crystallization Y by the total mass ms of the suspension:
The degree of crystallization Y of the suspension S is therefore necessarily between 0 and 1. The value "0" corresponds to an exclusively liquid phase and the value "1" to an exclusively solid phase (that is to say that in both cases, there is no more suspension).
A crystallization separation of a target product from a liquid phase containing the target product X as well as different components of the target product X is applied in particular to separate the target product X from secondary products formed in the course of its manufacture. . In this case, the production of the target product X can already be done directly by chemical reaction in the liquid phase. But it goes without saying that the production of the target product X can also be done, for example, in the gaseous phase from which the target product X is then converted into the liquid phase as a rule by condensation measurements and / or absorption, normally together with secondary components accompanying the target product X in the gas phase.
The crystallization separation of the target product X can now in principle be carried out directly by a "precise" thermal separation process from the liquid phase produced as described in the context of the production of the target product X and containing the target product X and secondary components.
But, frequently, the aforesaid liquid phase is subjected, prior to the application of crystallization separation of the target product X, firstly at least to an "imprecise" thermal separation process in order to separate a partial quantity the aforementioned secondary components of the target product X.
In this case, an imprecise separation process is defined as a separation process, in which, thermodynamically, the composition of the phase containing the enriched target product X which is formed during the application of the separation process depends mainly on thermodynamically necessary for the composition of the mixture to be subjected to the separation process (see for example the Mc-Cabe-Thiele diagram). Part of the imprecise thermal separation process is simple distillation, rectification, absorption, fractional condensation, desorption, extraction, stripping, azeotropic rectification, etc.
In contrast, separation by crystallization is all the more a precise thermal separation process that the composition of the crystals that form is, thermodynamically, very largely independent of the composition of the initial liquid mixture (see also the documents DE-A 2005 009 890 and DE-A 103 00 816).
The advantage of imprecise separation methods is generally based on the fact that they can be exploited with higher space-time yields. However, the disadvantage of imprecise separation methods is that the separation effect which they make it possible to obtain is relatively limited.
The disadvantage of the precise separation methods lies in their normally relatively small space-time yields, whereas in the normal case there is a very high separation effect.
Given the aforementioned background, the two principles of separation are therefore often also applied in combination as follows.
On the product mixture obtained in the context of the production of the target product X, first of all at least one imprecise thermal separation process is applied and a liquid phase P which contains the target product X is produced here. already enriched in comparison with its weight fraction in the product mixture. This liquid phase P, which still contains, in addition to the target product X, secondary components different from the target product X, is then subjected to separation by crystallization of the target product X and the residual liquid phase R which remains (and which is denominated frequently also mother liquor), which contains the secondary components in the relatively enriched state, is returned at least in part to at least one of the previously described imprecise thermal separation methods. In this way, the advantages of the two principles of separation can be implemented simultaneously.
In many cases, a liquid phase P having a target product X and crystallization separating the target product X therefore contains (and this also concerns the liquid phases P concerned in the present application) at least two, often at least three or four, frequently at least five or six and very often at least seven or eight, possibly at least nine or ten different secondary components of the target product X (these secondary components are then contained, for the purposes of the present application, in the phase liquid P if they are detectable as components of this phase, for example, by gas chromatographic, liquid chromatographic or otherwise (for example, as water by Karl Fischer titration).
In addition to the characteristic secondary products conditioned by the manufacture of the target product X, the liquid phase P containing the target product X may also contain solvents or a mixture of solvents and / or, in the context of the separation of the target product X a mixture of reaction products, auxiliary agents used in the production of the liquid phase P (for example, absorption agents, extraction agents, etc.). In fact, the residual liquid phase R can be, for example, as much a melt of the target product X and impurities as solutions of the target product X and solvents (or solvent mixtures) and, as a rule, impurities.
To a process described above for the continuous crystallization separation of a target product X from a liquid phase containing the target product X as well as secondary components (constituents) different from the target product X usually joins a continuous process for the separation of the crystallizate of the target product X suspended in the suspension (crystallizate) S of the residual liquid phase R, the residual liquid phase R ("mother liquor").
Such separation can be effected, for example, by filtration, by sieve centrifugation and / or in washing columns, as disclosed, for example, in WO 01/77056, as well as in the state of the art which is quoted. Normally, a separation also involves a separate crystallization wash to remove mother liquor adhering to the surface of the crystals. Such washing may, for example, be with the crystalline melt previously separated and washed.
In order to ensure an effective continuous separation (both in terms of separation effect and space-time yield) of the crystallization of the suspension of the residual mother liquor (residual liquid phase R), it is essential that the separation device used for separation is adapted in its embodiment (in its concept) to the degree of crystallization Y of the suspension (of crystallizate) S and that Y remains as stable as possible during continuous operation.
The degree of crystallization Y of the suspension S thus influences, for example, all the technical flow properties of the suspension S. But it also influences, for example, also the internal structure of the crystallizate cake to be washed or the crystallized bed of wash and therefore also determines the washing effect and the pressures prevailing during washing. In particular, these can increase abruptly, for example, in wash columns with forced transport as a predetermined separation device in the case of an undesired increase in the degree of crystallization Y with otherwise identical mass currents in unfavorable cases (eg exponential) and causes a disconnection of safety or damage to the separation device. The degree of crystallization Y, however, also influences the permeability of the crystallizate cake or the crystallizate bed for the liquid residual phase R (the mother liquor remaining during the separation by crystallization). On the other hand, in the case of small degrees of crystallization Y when using push centrifuges, this can lead to an overflow of the crystallizate suspension. In hydraulic wash columns, too low degrees of crystallization Y may result in the loss of the stable crystallizate bed.
Depending on the respective separation problem (in particular the separation device used) as well as the type and size of crystals constituting the crystallizate, the ideal degree of crystallization Y is frequently in the range of 0.10 to 0.50, with a greater frequency in the range of 0.20 to 0.40 and, particularly frequently, in the range of 0.25 to 0.35 or 0.30.
During a continuous separation as described above of a target product X in the form of a finely divided crystallizate of the target product X, from a liquid phase P containing the target product X as well as components different from the target product X by using a crystallization method described in the preamble of the present application, it is therefore endeavored to keep as constant as possible the degree of crystallization Y established on the basis of the dimensioning of the device over the operating life of the process of seperation.
Advantageously, the product of the degree of crystallization Y by the number 100 over the operating time of the separation process should not deviate from the corresponding product of the desired theoretical value for Y or the stationary value of Y of more than ± 5, preferably more than ± 4, especially more than ± 3 and most preferably more than ± 2 or more than ± 1.
In the known processes, for adjusting the degree of crystallization Y as a control variable, the temperature of the suspension S withdrawn continuously from the secondary space of the heat exchanger is usually used.
This is due to the fact that the temperature of a liquid phase containing the target product X, in which, starting from this liquid phase (where the possibility of occurrence of supersaturation phenomena is not taken into account), the crystallization of the target product contained therein is used in the dissolved state, which depends on the total number of moles of the different compounds of the target product X contained (respectively dissolved) in addition to the liquid phase with respect to the molar amount of target product X contained therein.
The larger the total relative molar quantity mentioned above, the lower the onset temperature of the above-mentioned crystallization (or the crystallization formation temperature) is low. In the literature, this phenomenon is also referred to as "reduction of the molar crystallization point".
But, as with a growing degree of crystallization Y, the relative total molar quantity of the compounds, different from the target product X, respectively contained in the state still dissolved in the liquid residual phase increases to the extent necessary, the suspension S (of crystallizer ) removed from the secondary space of the heat exchanger is a Tsaus temperature even lower than its degree of crystallization Y is greater.
In the liquid phase P continuously fed with a composition unchanged over the operating period to the secondary space of the heat exchanger, the temperature of the suspension S removed from the secondary space is therefore a direct measure of the degree of Y crystallization of the suspension S (in particular, because of the large total surface of the crystallizate in the suspension S and the mixing (or suspension) normally caused in the secondary space of the heat exchanger , the suspension S, when removed from the secondary space of the heat exchanger, is usually largely in the state of equilibrium.
The temperature Tsaus can, for example, with the aid of a resistance thermometer immersed at the point of removal of the suspension S from the secondary space in the suspension S, be followed (determined) continuously. In the case where the Tsaus temperature deviates from its theoretical value corresponding to the desired degree of crystallization Y, for example, the temperature of the fluid refrigerant (TKein) conveyed to the primary space as a control variable of the The above discrepancy will be increased or reduced antagonistically as needed.
The disadvantage of this control structure for the degree of crystallization Y is however, inter alia, that it acts exclusively backwards. In fact, it is only if a disturbance or a modification of the stationary state of exploitation is noticed by a temperature Tsaus which varies and that, consequently, a modification of the degree of crystallization Y has occurred, that the system itself begins to return to its target value (its stationary value).
Another disadvantage of the regulation structure described above lies in the fact that, when the quantitative fraction of the components, different from the target product Y, contained in the liquid residual phase of the suspension S withdrawn from the secondary space of the heat exchanger decreases, the dependence of Tsaus temperature to the degree of crystallization Y becomes flatter. This is particularly disadvantageous when the content of the liquid phase P in different components of the target product X may itself be subjected to stationary operation at certain fluctuations (this is particularly the case when, during the manufacture of the liquid phase P, at least one imprecise separation method is involved). If these components are substances having a relatively low molecular weight (for example, H 2 O), these fluctuations in their weight fraction already correspond to both a relatively small fluctuation of the weight fraction of these components in many cases that these fluctuations are exerted on the respectively current value of Tsaus for a real degree of crystallization Y possibly unmodified so that the degree of crystallization Y varies detectably due to a disturbance or modification of stationary operation.
This results in a modification of TKein, with which the control system tries to bring Tsaus back to its theoretical value and in this case undesirably triggers a deviation of the degree of crystallization Y from its desired target value.
The disadvantages described by way of example of the control structure illustrated increase in particular quite seriously when, for example, due to a variable market demand for the target product X, the liquid phase stream P to be conveyed to the secondary space of the heat exchanger must be adapted to the modified market demand. 'Irwv'
In many cases, the market demand for the target product X (for example, for an organic target compound such as acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone) is not a large quantity. stable, but fluctuates over long periods of time. For example, it can increase abruptly. Rather than responding to such increased market needs with an additional production facility, these needs can also be addressed by increasing the space-time yield of target product X in existing production facilities. On the other hand, the space-time yield of the target product X in the same production facility will have to be further reduced during a slowing market demand.
Such a transition from a stationary operating state to another stationary operating state is possible in the case of a separation of the target product X by crystallization, as described in the preamble of the present application, of the liquid phase P which contains it, for example, by increasing or reducing the liquid phase current P conveyed to the secondary space of the heat exchanger according to an increasing or decreasing market demand for the target product X and simultaneously adapting the passage of the at least one fluid coolant in the at least one primary space of the heat exchanger so that an increased or reduced stream of crystallizate suspension S can be extracted from the secondary space of the heat exchanger heat. Maintaining the degree of crystallization Y of the suspension as much during the transition in the new stationary operating state as, also, in this stationary operating state, is also advantageous in this case for the reasons already detailed herein. request.
A control structure with the sole use of Tsaus as a control variable for regulating the degree of crystallization Y of the suspension S is not suitable, however, as one imagines, for a variation in the operating state that the we will realize as described.
This is due, on the one hand, to the fact that the modification of the level (of the intensity) of the liquid phase current P to be conveyed to the secondary space of the heat exchanger, as a rule, is accompanied by a modified spectrum of components, different from the target product X, contained in the liquid phase P, this modification being able to concern as much the quantity of the individual components as their type as well. This behavior therefore makes that, normally, the adaptation of the liquid phase current P must also be done in existing production facilities. This adaptation, however, usually requires reaction conditions that are necessarily modified during the production of the target product X (for example, a modified reaction temperature, a modified feedstock of the catalytic bed with a reaction gas mixture, modified acidity of the reaction gas mixture, etc. .), which as a rule affect the spectrum of the secondary components of the target product X both qualitatively and quantitatively to a certain extent and may, with the same degree of crystallisation Y of the suspension, S, a temperature Tsaus possibly modified. Moreover, the temperature Tsaus is sensitive to a change in the level of the liquid phase stream P conveyed to the secondary space of the heat exchanger when this modification has already caused a change in the degree of crystallization Y. This behavior would also be correct if any other property (eg, viscosity, electrical conductivity or optical property) of the suspension S was considered as the sole regulator for regulating its degree of crystallization Y.
This background justifies the object of the present invention which is to provide a better control structure for the degree of crystallization Y in a process as described in the preamble for the crystallization separation of a target product X, which exhibits the described disadvantages of a regulation structure based only on Tsaus, but in any case still to a reduced extent.
According to this background, the invention relates to a process for the continuous separation of a target product X in the form of a finely divided crystallizate of the target product X from a liquid phase P containing the target product X as well as that different components of the target product X by means of an (indirect) heat exchanger having a secondary space and at least one primary space, in which the secondary space and the at least one primary space are spatially separated; one of the other by at least one material separating wall (solid) which serves as a surface for the transfer of heat from the secondary space into the at least one primary space, into which a liquid phase P is introduced continuously into the secondary space of the heat exchanger, while the at least one primary space is traversed simultaneously by at least one fluid refrigerant so that it forms in the secondary space, while leaving a residual liquid phase R remaining from the liquid phase P, a finely divided crystallizate of the target product X, which is suspended in the residual liquid residual phase R, which contains, in comparison with the liquid phase P, the different components of the product, target X in the enriched state and whose target product content X reaches at least 70% by weight, while maintaining a suspension S, having a degree of crystallization Y, of finely divided crystallizate of the target product X in the liquid residual phase R and is removed from the secondary space of the heat exchanger continuously the suspension (crystallizate) S, which is characterized in that, to adjust the degree of crystallization Y desired suspension S removed from the secondary space of the heat exchanger, the difference obtained (or balanced) at the respective operating point (in the context of a heat balance) is made using a computer between the heat flow of crystallization QKrY corresponding to the degree of crystallization Y and calculatedly developing in the secondary space and the difference formed between the heat flow Qms otherwise removed in total from the secondary space of the heat exchanger and the total Qein heat flow in the secondary space of the heat exchanger.
The process according to the invention is particularly suitable when the content of the residual liquid phase R contained in the suspension removed from the secondary space as the target product X is> 75% by weight or> 80% by weight or> 85% by weight or > 87% by weight or> 90% by weight or> 92% by weight or> 94% by weight or> 95% by weight or 96% by weight or> 98% by weight or> 99% by weight. As a general rule, the above-mentioned target product content X is, however, <99.95% by weight, most of the time <99.9% by weight.
In fact, the process according to the invention is suitable in the case of liquid phases of this type whose target product content X is> 70% by weight or> 75% by weight or> 80% by weight or> 85% by weight. or> 87% by weight or> 90% by weight or 92% by weight or> 94% by weight or> 95% by weight or 96% by weight or> 98% by weight or> 99% by weight. As a general rule, the above-mentioned content of the liquid phase P conveyed in the process according to the invention to the secondary space of the heat exchanger in target product X is, however, <99.995% by weight, most of the time < 99.99% by weight.
The temperature at which, in the process according to the invention, the at least one fluid coolant is fed to the at least one primary space of the heat exchanger (TKein) is necessarily below the temperature at which, simultaneously, the liquid phase P is conveyed to the secondary space of the heat exchanger. Moreover, the temperature Τκβιη is necessarily below the crystallization onset temperature.
As the target product X for the suspension crystallization carried out in cooling crystallization according to the invention, mention may be made, for example, of saturated or unsaturated carboxylic acids, such as acetic acid, propionic acid, acrylic acid and methacrylic acid, or substituted aromatics (with, for example, halogens, methyl, carboxyl, hydroxyl and / or nitrogen groups (eg, -NH 2) as substituents), such as p-xylene, cresol and chlorobenzene, or multi-ring aromatic compounds, such as naphthalene and bisphenol A, or isocyanates such as TDI and MDI, or vinyl compounds, such as N-vinylpyrrolidone, or formaldehyde oligomers such as trioxane, or inorganic salts, such as Na or K salts (eg, sulfates, chlorides, bromides and iodides).
In particular, the process according to the invention is suitable in the case of acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone as target product X, since a significant fraction of the by-products formed in the their manufacture has a lower molecular weight than the respective target product X itself.
The process according to the invention is particularly suitable in the case of acrylic acid as target product X and a crude acrylic acid as liquid phase P, which has, for example, the following contents:> 70% by weight Acrylic acid, up to 15% by weight Acetic acid, up to 5% by weight Propionic acid, up to 5% by weight Aldehydes of low molecular weight, up to 3% by weight Polymerization inhibitors, 0 to 5 % by weight Diacrylic acid (Michael's adduct), and up to 25% by weight Water; or> 80% by weight acrylic acid,> 100 ppm by weight to <15% by weight of acetic acid, weight> 10 ppm by weight to <5% by weight of propionic acid, weight of up to 5% by weight Aldehydes of low molecular weight up to 3% by weight of polymerization inhibitors, and 0 to 5% by weight of acrylic acid (adduct of
Michael), and up to 15% by weight water; or> 85% by weight acrylic acid,> 100 ppm by weight to <10% Acetic acid, by weight> 10 ppm by weight to <5% propionic acid, weight up to 5% by weight Aldehydes of low molecular weight, up to 3% by weight Polymerization inhibitors, 0 to 5% by weight Acrylic acid (Michael's adduct), and up to 10% by weight Water; or> 90% by weight Acrylic acid,> 100 ppm by weight to <5% Acetic acid, weight> 10 ppm by weight to <2% Propionic acid, weight up to 2% by weight Aldehydes of low molecular weight, up to 2% by weight Polymerization inhibitors, 0 to 3% by weight Acrylic acid (Michael's adduct), and up to 9% by weight Water; or> 95% by weight Acrylic acid,> 100 ppm by weight to <3% Acetic acid, weight> 10 ppm by weight to <2% Propionic acid, weight up to 2% by weight Aldehydes of low molecular weight, up to 2% by weight Polymerization inhibitors, 0 to 2% by weight Acrylic acid (Adduct of
Michael), and up to 4.9% by weight water; or 93 to 98% by weight Acrylic acid, 1 to 5% by weight Water, 0.001 to 3% by weight Acrolein, 0 to 3% by weight Methacrolein,> 0 to 3% by weight Methacrylic acid, 0.1 to 3 % by weight Acetic acid, 0.01 to 3% by weight Propionic acid, 0.001 to 3% by weight Formaldehyde, 0.001 to 3% by weight Aldehydes other than formaldehyde, 0.01 to 3% by weight Maleic acid, and> 0 at 3% by weight Protoanemonin.
Crude acrylic acids are obtained, for example, according to the methods known from the state of the art (see, for example, WO 01/77056, DE-A 103 32 758, DE-A 102 43 625, to the German application for file number 10 2006 057 631.4, the German application file number 10 2006 062 258.8, the German application file number 10 2007 004 960.0, the document WO 2004/035514, the German application of file number 2006 049 939.5, DE-A 10 2005 029 629, WO 03/041832 and DE-A 10 2005 015 639 as well as the state of the art cited in these documents).
In general, these are crude acrylic acids which are obtained from the gaseous product mixture of heterogeneously catalyzed partial oxidation of at least one C3 precursor compound of acrylic acid (e.g. propane, propylene, glycerol, acrolein, propionic acid, propanol and / or propionaldehyde) (we will come back to these).
In this case, for the process according to the invention, particular account will be taken of the liquid phase P, in particular of this crude acrylic acid, which has been produced from the mixture of gaseous products of a heterogeneous catalytic partial gas phase oxidation. at least one C3 precursor compound using at least one imprecise separation method. This is particularly the case when the acrylic acid crystallizate contained in suspension in the suspension thus formed S is then separated from the liquid residual phase R in the residual liquid phase R during the application of the process according to the invention to such crude acrylic acid as liquid phase P and the remaining residual phase R is recycled at least partly in at least one imprecise separation process applied to the production of crude acrylic acid from the mixture of gaseous products of oxidation partial gas phase.
The basic structure of such a combined application of the imprecise separation method and the precise separation method for crystallization is taught, for example, in DE-A 196 06 877, EP-A 792 867 as well as in the documents EP-A 1 484 308, EP-A 1 116 709 and in particular EP-A 1 015 410.
In the general case, the at least one imprecise separation process applied to the production of the liquid phase P to be treated according to the invention from the mixture of gaseous products of a heterogeneous catalyst partial gas phase oxidation of at least a C3 precursor compound of acrylic acid will be a distillation, rectification, absorption, adsorption, extraction, desorption, stripping, destraction, (partial) condensation, fractional condensation, separation process membrane and a pervaporation / permeation with water vapor or a combination of these methods.
In the simplest case, the crude acrylic acid to be used as the liquid phase P in the process according to the invention can be the absorbate and / or the partial condensate and / or obtained by fractionation of an absorption separation and / or or condensing acrylic acid from a gaseous product mixture of a heterogeneously catalyzed partial gas phase oxidation of at least one C3 precursor detailed herein. A recycling of the liquid residual phase R separated from the suspension S (mother liquor) is then suitably done during absorption and / or condensation.
Suitably, a combination to be applied as described by imprecise separation and precise (crystallization) separation of the acrylic acid from the gaseous product mixture of the partial gas phase oxidation has at least one outlet for the different secondary components acrylic acid and having boiling points at normal pressure (1 bar) higher than acrylic acid. In terms of application technique, this output is advantageously on the side of the imprecise separation process. As a general rule, for this outlet, the crankcase liquid is used for a separation column, from which the liquid phase P (the crude acrylic acid to be used as such) itself or the current is separated from the separation column. of material to be subsequently transformed into the liquid phase P (crude acrylic acid to be used as such) is removed, for example, by lateral sampling and / or sampling at the top. It goes without saying that this outlet can also be on the side of the crystallization separation according to the invention. In this case, the outlet consists of a residual liquid phase R (mother liquor). Usually, an outlet for secondary components having a lower normal pressure boiling point than acrylic acid is also on the side of the imprecise separation process.
Advantageously, the acrylic acid to be used as liquid phase P in the process according to the invention is recycled to a mixture of gaseous products of partial oxidation, which contains:
The acrylic acid contained as target product X in the liquid phase P is advantageously recycled to a gaseous product mixture which is subjected to partial oxidation, which contains: 1 to 30% by volume of acrylic acid, 0 to optionally 0.005 to 10% by weight. % by volume of propylene, 0 0 or 0.001 to 2% by volume of acrolein, ^ 0 or 0.001 to 2% by volume of methacrolein, ^ 0 or 0.001 to 2% by volume of methacrylic acid, 0 0 or 0.005 to 10% by volume of molecular oxygen,> 0 or 0.005 to 3% by volume of acetic acid, 0 0 or 0.001 to 2% by volume of propionic acid, 0 0 or 0.001 to 2% by volume of formaldehyde,> 0 or 0.001 to 2% by volume of other aldehydes, and 10 to 98 or 50 to 98% by volume of diluent gas (inert).
The dilution gases may contain, for example:> 0 or 0.005 to 90% by volume of saturated hydrocarbons in CrC6 (in particular propane, methane and / or ethane),> 0 or 0.05 to 30% by weight volume of water vapor, 0 0 or 0.05 to 15% by volume of carbon oxides (CO and / or CO2), and 0 0 or 1 to 90% by volume of molecular nitrogen.
In this case, the mixture of gaseous partial oxidation products can be reduced in particular to a partial oxidation, as described in documents EP-A 1,818,324, DE-A 10 2004 032 129 and their foreign protection rights. equivalent, DE-A 102 45 585, WO 03/076370, WO 01/96271, EP-A 117 146, WO 03/011804, US-A 3 161 670, DE-A 33 13 573, DE-A 103 16 039 and the like. and WO 01/96270 from propylene and / or propane, and the propylene source optionally has a hydrogenation of propane and / or a hydrogenation of propane oxide (optionally heterogeneously catalyzed) as a reaction stage arranged upstream.
Advantageously, the crude acrylic acid desired for the liquid phase P to be treated according to the invention will be produced from the aforementioned gas product mixtures by partial oxidation of C 3 acrylic acid precursors so that the acrylic acid originating from the mixture of gaseous products of the partial oxidation is condensed. The condensate formed in this way advantageously forms a liquid phase P to be treated directly according to the invention. Advantageously, the condensation of acrylic acid is made from the mixture of gaseous products (optionally cooled beforehand) in the form of a fractional condensation (optionally additionally superimposing an absorption with water and / or a solution aqueous solution (it generally contains an amount greater than or equal to 90% by weight, frequently greater than or equal to 95% by weight of water), to reduce the losses of acrylic acid, refer, for example, to the EP document -A 1 818 324), as described in detail in EP-A 1015 410, WO 2004/035514, DE-A 102 43 625, EP-A 1 015 411, DE-A 102 35 847, EP-A 1 159 249, EP-A 1 163 201, EP-A 1 066 239 and EP-A 920 408.
In this case, the mixture of gaseous products is suitably condensed by fractionation, optionally after a direct and / or indirect cooling carried out beforehand (for example with a quenching liquid according to EP-A 1 065 239 or according to EP-A 1,163,201) in a separation column having effective built-in elements for the separation by adding side-by-side crude acrylic acid (which preferably forms the liquid phase P to be treated according to the invention; optionally, the crude acrylic acid is further processed by rectification and / or distillation to produce the liquid phase P).
From the liquid phase P produced in this way by condensation (possibly also by rectification), it is now possible to separate, according to the invention, a finely divided acrylic acid crystallizate. The mother liquor (residual phase R) subsequently separated from the suspension thus obtained S is recycled, according to the preamble, for example from document EP-A 920408 or WO 2004/035514, at least in part, preferably completely, in the condensation of the acrylic acid formed from the mixture of gaseous products. The high boiling point compound output is set below the side draw off of the crude acrylic acid. In this way, by partial or total condensation and / or absorption superimposed with water or an aqueous solution as well as possibly by post-treatment by rectification, the liquid phase to be treated according to the invention P (crude acrylic acid) is obtained. may contain:> 85 to 99.5% by weight of acrylic acid,> 0, in general from 0.1 to 40% by weight of water,> 0, in general from 0.001 to 5% by weight of acrolein,> 0, in part from 0.001 to 10% by weight of methacrolein,> 0, in part from 0.001 to 10% by weight of methacrylic acid,> 0, in general from 0.01 to 10 or 5% by weight of acetic acid, > 0, in general 0.01 to 5% by weight of propionic acid,> 0, in general from 0.001 to 5% by weight of formaldehyde,> 0, in general from 0.001 to 5% by weight of aldehydes other than formaldehyde ( by aldehyde),> 0, in general from 0.01 to 5% by weight of maleic acid,> 0, in general from 0.01 to 10% by weight of benzaldehyde and / or benzoic acid, and> 0 to3% by weight of protoanemonin.
In order to separate the suspension S from the crystallizate contained therein and from the residual liquid phase R (mother liquor), all the methods detailed in the documents WO 01/77856, WO 02/055469 and WO 03/078378 for separating a crystallizate are considered. suspension and mother liquor (for example a mechanical process such as centrifugation). Preferably, the separation is in a washing column. This is advantageously a wash column with a forced transport of the separated acrylic acid crystals. In this case, the volume fraction of crystallizate in the crystallizate bed generally reaches values greater than 0.5. In the normal case, the washing column is operated with values from 0.6 to 0.75. As the washing liquid, the melt of acrylic acid crystals previously purified (separated) in the washing column is advantageously used. The washing is normally done against the current. In this way, the process according to the invention comprises in particular processes which comprise the following treatment steps (these processes can also be used in the case of target products other than acrylic acid): a) crystallization separation according to the invention; invention of acrylic acid from a liquid phase P (e.g., liquid acrylic acid) by forming (withdrawing) a suspension S, b) separating the suspension S into crystallizate of acrylic acid and mother liquor (liquid residual phase R), c) melting at least part of the separated acrylic acid crystallizate, and d) recycling at least a part of the molten acrylic acid crystallizate in state b) and / or in state a).
Preferably, step b) in this case is carried out by backwashing with previously separated molten acrylic acid crystallizate recycled in step b). Advantageously, steps b), c) and d) are carried out in a washing column.
According to the invention, the liquid phase P (in the case of acrylic acid as target product X) advantageously contains water during the application of the process according to the invention, since crystallization of acrylic acid in The presence of water conditions, according to the teaching of WO 01/77056 and WO 03/078378, a crystalline form particularly favorable for the subsequent separation of the crystallizate of the remaining mother liquor. This applies in particular when the separation of the subsequent mother liquor from the suspension S is carried out in a washing column and even more so when the already purified acrylic acid crystallizate melt (separated by purification) is used as washing liquid. ) of the washing column.
In fact, the process according to the invention comprises, in particular, processes in which crude acrylic acid is transferred as liquid phase P according to the invention to a suspension S consisting of crystallizate of acrylic acid and residual liquid phase R. (mother liquor), a portion of the remaining mother liquor is mechanically separated from the slurry S and the crystallizate of acrylic acid is released from the remaining mother liquor in a washing column to such extent that: a) the liquid phase P (crude acrylic acid) contains in relation to the acrylic acid contained therein 0.20 to 30, frequently up to 20, more frequently up to 10% by weight of water and b) is used as washing liquid the melt of the purified acrylic acid crystallizate (separated by purification) from the wash column.
In particular, the process according to the invention comprises remarkable processes, in which the liquid phase P has a content> 70% by weight of acrylic acid or> 75% by weight of acrylic acid or> 80% by weight of acrylic acid or> 85% by weight of acrylic acid or> 90% by weight of acrylic acid or> 95% by weight of acrylic acid.
Furthermore, it is advantageous according to the invention for the water content of the liquid phase P (crude acrylic acid) to be in the treatment modes described above (or quite generally during the application of the process according to the invention), with acrylic acid as the target product X, with respect to the acrylic acid contained in the liquid phase P, 0.2 or 0.4 to 8, or up to 10, or up to 20, or up to 30% by weight or 0.6 to 5% by weight or 0.60 to 30% by weight.
It goes without saying that the process of the invention can also be applied to all the crude acrylic acids of WO 98/01414 as well as to all the crude p-xylenes of EP-A 097405.
As a rule, the temperature Tsaus is, when using crude acrylic acid as liquid phase P in the process according to the invention (where acrylic acid is the target product X according to the invention) in the range from -25 ° C to 14 ° C, especially in the range of -5 ° C to + 12 ° C and most preferably in the range of 4 or 6 to 9 ° C.
All that has been said above is especially worthwhile when the washing column is a column of washing with forced transport of the acrylic acid crystals and this, especially when it is about a column of hydraulic washing or mechanical according to WO 01/77056 and that it is exploited as it is mentioned therein.
All that has been said above applies especially when the washing column is carried out and operated according to the teachings of WO 03/041832 as well as WO 03/041833 and WO 2006/111565.
The method according to the invention thus allows with the sequence "partial oxidation of at least one C3 precursor compound, condensation of the fractionated acrylic acid and / or absorption (for example aqueous) of the gaseous mixture of the partial oxidation crystallization separation according to the invention of acrylic acid from the acrylic acid condensate removed from the acrylic acid condensation as a liquid phase while removing a suspension of acrylic acid crystallizate S from the secondary space of the heat exchanger, and separating the slurry S in the remaining mother liquor and acrylic acid crystallizate in a washing column while applying a melt of acrylic acid crystallizate separated previously as washing liquid "most effectively the manufacture of superabsorbent acrylic acid adapted to the respective market demand.
It goes without saying that all the steps of the process, in which acrylic acid is involved, are carried out so as to prevent the polymerization. In this case, one can proceed as described in the state of the art. A decisive position in the context of the total quantity of available acrylic acid process stabilizers is adopted here by the radicals dibenzo-1,4-thiazine (PTZ), 4-hydroxy-2,2,6,6 tetramethylpiperidine-1-oxyl (4-OH-tempo) and p-methoyphenol (MEHQ), which can be per se or in a mixture of three, components of the liquid phase P (crude acrylic acid) . Usually, its total amount is 0.01 to 2% by weight relative to the acrylic acid contained in the liquid phase P.
Correspondingly, as seen for example for acrylic acid, the method according to the invention can also be integrated into the process of manufacturing other target products X.
In fact, the present application comprises in particular a process, in which the process according to the invention is connected to a process for the continuous separation of the finely divided crystallizate of the target product X contained in the suspension S, in which process: the suspension S is conveyed to a washing column, which has a washing column wall, which encloses a treatment space, - maintaining the crystallizate contained in the suspension S and forming a crystallizate bed in the treatment space from the suspension S conveyed to the treatment space through filtration devices, the mother liquor (residual liquid phase R) is delivered out of the treatment space, the crystallized bed is conveyed into the treatment space, in the treatment space in the conveying direction of the crystallizate bed a force different from the gravitation which carries the crystallizate bed into the treatment space, in the countercurrent treatment space with the crystallized bed of crystallized melt and crystallizate previously separated after this separation process in a washing column is conveyed and formed in the crystallizate bed a washing front, which divides the crystallizate bed into a mother liquor zone and a pure melting zone, and at the end of the washing column opposite to the suspension of the suspension S, is extracted continuously crystallizate which has been washed in the wash column in solid and / or melted form.
What has been mentioned above applies especially when, in the process according to the invention, the target product X is acrylic acid (in particular, when the liquid phase P is a crude acrylic acid according to the present application). As a general rule, in this case, after separation of the finely divided acrylic acid crystallizate, another process is connected, in which the separated and molten acrylic acid crystallizate is then subjected to polymerisation (preferably a radical polymerization). ) with itself or at least with monoethylenically unsaturated compounds (eg solution polymerization, emulsion polymerization, suspension polymerization, gas phase polymerization or substantial polymerization). Such a process can also be connected when the separation of crystallizate and the mother liquor is carried out in another way than with a washing column.
In this case, the aforementioned washing column is a hydraulic or mechanical washing column. Corresponding washing columns are described, for example, in WO 2006/111565, DE-A 10 2007 032 633, WO 03/041832, WO 03/041833, DE-A 2005 015 639 and WO 01/77056 and in the state of the art cited in these documents.
In the present document, the term "heat flow" of crystallization developed by calculation as a function of the desired degree of crystallization Y in the secondary space of the heat exchanger (cooler) the flow per unit time in the secondary space for the crystallization of the target product X in total the heat of crystallization (enthalpy of crystallization) which would emerge freely at each moment in the secondary space of the heat exchanger if the mass current currently conveyed to it in the liquid phase P was a stationary current, which would convert inside the secondary space into a suspension of stationary crystallizate S and be removed from the secondary space as such in the form of a mass current ms ~ m, with the degree of stationary crystallization Y.
Kr-Y forms, in the control structure according to the invention, the guiding quantity, which is delivered (routed) to the control circuit at each moment from the outside.
For this purpose, is calculated as follows: QKr. v =% · Y · cKr mi 'is in this case the mass current respectively currently conveyed to the secondary space of the heat exchanger (frequently also referred to as the intensity of the mass current) on the liquid phase P.
m / 'can be for example determined continuously using a Coriolis mass flow measurement device. In this case, it is in principle, for example, a metal tube, which may have, for example, the shape of an arc and which is traversed by the liquid phase P in the direction of direct flow . For example, using a magnet, the elbow is moved in vibration. Input side and output side, is mounted on the magnet oscillation system, which induce a voltage proportional to the displacement in a coil which is respectively adjacent thereto.
The signals thus produced are sinusoidal. Without mass flow, the two signals have an identical phase. In the case of a mass flow, because of the Coriolis force acting on the flying mass due to the oscillation applied, the phase shift of the two aforementioned phase being a measurement of the mass current (or the intensity of the mass current). Since the resonance frequency of the entire oscillating system, besides the properties of the measuring tube, depends on the mass density of the contents of the measuring tube, the oscillation frequency correlates, in a mass flow, directly with the mass density of the mass flow flowing through the measuring tube, so that with a Coriolis mass flow measurement device, it is possible simultaneously with the determination of the mass flow to determine the mass density of the mass flow. which flows there. Both determinations are possible even when the mass current is polyphase, that is to say for example with a suspension of crystallizate.
Alternatively, the current mass current mp can also be determined using a swirling flow measurement device. In this measurement method, a parasitic body is incorporated in the flow channel of the mass flow. On the parasitic body traversed by the mass current is formed, on two sides, alternately, vortices which are dispersed by the flow and driven with it and form in the direction of flow, behind the parasitic body, a Swirling alley of Benard-Karman. The vortex resolution frequency is correlated (independently of mass density and mass flow viscosity) directly with the flow velocity obtained for the mass current (this is usually a direct proportionality). The local pressure variations that are caused by the vortex resolution are detected by a piezoelectric sensor and are converted into electrical pulses as a function of vortex frequency. By including the mass density of the liquid phase P as well as the flow section, the result of the measuring device is a direct measurement for the mass flow.
Another possibility to access the mass current m '' is offered by magneto-inductive flow meters. These are precision measuring instruments for measuring the volume flow of liquids, which exhibit electrical conductivity, for example, when the acrylic acid is delivered as the liquid phase P. The measuring principle exerts action of a force on loads displaced in a magnetic field (input: Hall effect).
The liquid phase to be measured P flows through a tube made of a non-magnetic material. Load carriers contained therein (positive-negative) are deflected by a magnetic field which is perpendicular to the direction of flow and produce electrical voltages in the millivolt range in the tube wall. In this case, a coupling as much galvanic as capacitive can be done. Since the magnetic induction B (the intensity of the magnetic field) and the spacing of the electrodes have constant values, the measurement voltage is proportional to the flow velocity. By multiplication by the surface of the cross-section of the flow measuring device as well as by the mass density of the mass flow, the desired mass current (or the desired mass current intensity) is obtained.
In most of the processes for the production of liquid phases P to be treated according to the invention, the mass density of the liquid phase P, with respect to the window, inside which the composition of the liquid phase P fluctuates. possibly over the operating period, is relatively robust. In fact, with respect to composition fluctuations, the mass density can, in these cases, be delivered in the context of the control structure according to the invention in the form of a constant. With respect to the temperature, at which the liquid phase P is conveyed to the secondary space of the heat exchanger (TPein), this is frequently no longer correct. Since the temperature TPe, n is relatively easily accessible by means of thermoelements or resistance thermometers for continuous determination, there may be cases where this is true and cases where the stored temperature dependence (obtained by experimental way for this purpose) in the computer of the mass density of the liquid phase concerned P to the actual mass density of the liquid phase P made in the secondary space of the heat exchanger, from which we obtain the necessary mass flow for equation 1 using the volumetric currents to be determined described above.
Alternatively, the mass density of the liquid phase P conveyed to the secondary space of the heat exchanger can be determined using a bending resonator, but also continuously. This is used in these cases in addition to one of the measuring devices described above for the liquid phase flow P P routed to the secondary space bypass with the mass current itself. In a bending resonator, the determination of the density of liquids is returned to an electronic measurement of the duration of the oscillation (for example, the oscillation frequency), which, as has already been done in connection with the device mass flow measurement of Coriolis, is directly correlated with this density.
When a sample to be analyzed is actually incorporated into an oscillating structure, its frequency is influenced by the mass of the embedded sample. Preferably, the oscillating structure is a U-shaped bent hollow bending resonator, for example made of glass or metal, which is excited by electronic means to oscillate without damping. The two branches of the U-shaped oscillating tube form in this case the elastic elements of the resonator (the "tuning fork"). The direction of the oscillations is normal in the plane of the two branches. The natural frequency of the resonator is influenced only by the part of the sample that actually participates in the oscillation. This volume participating in the oscillation is limited by the stationary oscillation nodes at the resonator voltage points. If the resonator is filled with the sample at least to the point of tension, it always adopts exactly the same volume defined precisely on the oscillation and the mass of the sample can be proportional to its density. Resonator overload at voltage points is of no importance for the measurement. For this reason, with the resonator, it is also possible to measure medium densities, which pass through the resonator (continuous measurement).
Other methods suitable for the process according to the invention for the measurement of flow are, for example, in "Technische Durchflussmessung", Publisher: K.W. Bonfig, 3rd edition, 2002, Vulkan Verlag Essen.
These other flow measurement methods also include the floating body flow measurement. A floating body flow measuring apparatus is constituted by a tube, for example, extending vertically and flaring upwards, formed, for example, of glass or a non-magnetic metal, which is traversed from bottom to top by the fluid. In the tube, for example glass, is a mobile floating body. It has a flow resistance in the flowing fluid, that is to say that a force F in the direction of flow is exerted thereon which depends on the flow rate. Against this direction, the force of gravity FG acts on the floating body.
The height of the floating body in the floating body flow measuring device depends on the volume flow. As the volumic current increases, the resistance to flow increases. The floating body rises and the surface between the floating body and the glass tube becomes larger. In this case, the resistance to flow back down until it is equal to the force of gravity of the floating body and the body floats. The floating height of the floating body in the glass tube is a direct measure of the respective flow rate of the fluid. For example, using a small magnet incorporated in the floating body, which can interact with a second magnet mounted movably in the environment of the glass tube, the height of the floating body is communicated to the outside and it s' then an electromagnetic signal.
Sensors operating according to the measurement principles described in the present application can be acquired commercially.
The degree of crystallization is predetermined by the operator according to the wishes (depending on the model) and C "r is in essence a characteristic material property for the target product X, which is independent of it in the area of the applied working pressures usually to the process according to the invention (normally not more than 5 bars, more preferably not more than 3 bars, even better not more than 2 bars and generally smaller than or equal to 1.5 bar and greater than or equal to 1 bar, for reasons, for example, monomer suction, the working pressure can also be below atmospheric pressure). The same is normally true for the temperature dependence of this, especially taking into account the situation that makes the differences> 50 K> for the process of the invention rather unusual. The different components of the target product X and contained in the liquid phase P normally influence 0 "Γ only slightly.
But if one then tries to find the desired absolute value of Y as accurately as possible (in many cases, however, in the first instance, a relative constancy of Y is sought over the operating life of the process according to In the invention, so that limited deviations of the ideal absolute value envisaged for Y can be considered), CKr (J / g) for crystallization separation of the product - target X from the liquid phase P can be determined by corresponding caloric measurement. in experimental mode and then, with this value of Οκη one can calculate the heat flow> instead of using for this calculation the material value to be drawn from the literature for CKr (in this way, one takes into account a tiny influence of possible secondary components contained in the liquid phase P). CKr is the calorific quantity that is released when a gram of target product X is obtained by crystallization.
The heat flow QK has removed from the secondary space at a given operating time on the fluid coolant flowing through the at least one primary space (usually a coolant) through the two separate spaces. one of the other at least by a material separating wall, is given with a very good approximation by the following equation:
In this case, is the mass current (or the intensity of the mass current itself), with which the coolant is conveyed to at least one primary space and with which, according to the law of maintenance of the mass , is necessarily "also extracted from it. m * may, by applying one of the measurement methods performed with respect to mi> in the present application, be determined experimentally continuously (it can be tracked online).
CKP is the mass specific heat capacity (enthalpy) (J / (gK)) relative to heating at constant pressure, which the coolant (coolant) has at the temperature (TKaus + TKein) / 2, where Kaus is the temperature at which the coolant is extracted from at least one primary space and TKein is the temperature (in both cases in degrees Kelvin (as for the other temperature measurements and temperature considerations of the present application as far as nothing else is mentioned or explained explicitly)), to which the coolant is introduced into the at least one primary space.
TKaus and TKein can, as explained later, be determined online experimentally.
Ckp can be determined experimentally for the coolant respectively used as a function of temperature by corresponding caloric measurement (at the working pressure envisaged in the primary space) and stored in the computer as a function of temperature.
In many cases, particularly when using coolants, the temperature dependence of CKP in the relevant temperature range of the invention (TKaus-TKein differences greater than 50 K are rather unusual for the method according to the invention) is however insignificant, so that the calculation of QK aus is further simplified (one can then store a constant CKP in the computer at a temperature representative of the process). The pressure dependence of CKP is insignificant for the problems according to the invention.
It is not completely problematic that one can find on the side facing the secondary space the at least one separating wall respectively separating the primary space from the secondary space to form crystallization layers remaining glued to the wall separator, which layers reduce the passage of heat through the separating wall.
For this reason, the side facing the secondary space of these partition walls is operated in many cases by scraping. In fact, using a scraping device (for example, similar to the scraping windshield of an automobile) operated in the secondary space, the crystals remaining glued to the corresponding side of the dividing wall of the target product X are scraped continuously and suspended in the suspension S. Simultaneously, the scraper device generally provides a mixture of the crystallizate suspension S in the secondary space.
In many cases, however, there remain surface elements of the divider wall that can not be scraped off or only with difficulty. This is, for example, the case where the primary space and the internal space of a circular cooling disk, which is, for example, immersed in a simple manner in the liquid phase flowing in the secondary space. While the front and rear sides of the cooling disc can be scanned in a relatively simple manner, this is no longer valid normally on the envelope surface of the cooling disc. These surface elements are therefore generally subject to an accompanying heating, which must remove its crystallization deposit. Such deposits are ultimately not desired at all, as they eventually dissolve spontaneously when a defined level is exceeded and can disrupt the crystallization separation process in the form of larger crystalline fragments resulting therefrom.
A heat flow Q "em is conveyed to the secondary space by the accompanying heating in terms of the technical balance (the fraction of heat flow due to the accompanying heating flows directly into the at least one primary space, although that it can be treated according to the technical balance in the context of the present invention as if it flowed in the primary space via the secondary space).
In the case of an electric resistance heating element, this can be calculated from the intensity of the electric current J and the electrical resistance R QH ein = I2 · R. It goes without saying that such accompanying heating can however be achieved by indirect heat exchange. For example, in the case of using the aforementioned cooling discs -circular, one can apply on the surface of their envelope (on the front side of the unexpanded disk wall), for example, a tube hollow heating apparatus (or other hollow section), in which a fluid heating agent is continuously supplied at the temperature of THem and is re-evacuated therefrom, the same fluid heating agent is reevacated at the temperature of THaus <Thein. Preferably, the fluid heating agent is also a liquid. In particular, the heating agent (heating agent) is the same substance that is simultaneously fed at a different temperature than the coolant through the primary space.
In this case, an accompanying heat by indirect heat exchange, there is complete analogy with the equation 2 for Qh ein according to the following equation 3:
► m "is the mass current (or the intensity of this mass current), with which the heating agent is conveyed to the heating tube and with which it is re-evacuated according to the law of the maintenance of mass as necessary. m "can, by applying a method of measurement detailed with respect to m> * in the present application, be determined continuously by experiment (online monitoring).
CHp is the mass-specific heat capacity (enthalpy) (j / (g.K)) relative to heating at constant pressure, which the heating agent has at the temperature (THein + Haus) / 2. In fact, it is the amount of heat that is necessary to heat 1 gram of the heating agent, which has the above-mentioned temperature, at a constant pressure of 1 K. Moreover, Chp can be experimentally accessible in a corresponding manner and can be taken into account in equation 3, just like GKp in equation 2. "
The online determination of the corresponding temperatures THein, THaus, TKaus, TKein is possible in a simple manner, for example using resistance thermometers. A resistance thermometer is a thermometer, in which temperature is determined not by the change in length or volume of a substance, but by the temperature dependence of the electrical resistance of materials. Pure metals have stronger strength variations than alloys and have a relatively constant temperature coefficient of electrical resistance. For the process according to the invention, it is preferable to use fine metals (for example, preferably platinum), since these have particularly little aging and the resistance thermometers can be manufactured with low tolerances, allows particularly accurate temperature measurements. But the resistance can in principle be made of ceramic (sintered metal oxides) or semiconductors, so that even higher sensitivities can be obtained. These resistors are designated by thermistors, in which the thermal conductors (NTC resistor) and the refrigerant conductors (PTC resistor) are differentiated. Particularly precise temperature detections are possible insofar as the resistance thermometer respectively used is calibrated prior to its use again particularly according to the envisaged range of temperatures used. As a rule, the metal at the base of the resistance thermometer is not routed as such, but in a corresponding measuring socket in the medium to be measured.
Now, instead of converting only the signal of each resistance thermometer applied in the feed stream or in the output stream of a soaking agent, respectively, by means of a measuring converter assigned respectively to this one. ci in a standardized output signal (we will use a total of two different measurement converters), which is redirected to the computer (a sensor for online detection of a physical quantity to be measured is constituted as a rule of a sensor element, which converts the measured variable into an electrical signal (for example, the resistance thermometer) and a signal converter (measurement converter), which strengthens the input electrical signal at first normally and then converts it into a standardized output electrical signal, which can be understood and converted by the computer or the process control system as the output quantity. measured measurement), can with an individual temperature difference converter not only convert each of the two signals from the two resistance thermometers individually to an output signal corresponding to the respective temperatures THem or THaus and be rerouted to the computer . The temperature difference measurement conversion device may rather also form the difference of two output signals and forward them as a temperature difference (for example THein-THaus) as a signal corresponding to the computer. This is all the more advantageous when a systematic error occurring during the conversion of the individual signal falls during the formation of the difference, so that the temperature difference will be captured in a particularly precise manner (it is thus possible to obtain precision less than or equal to ± 0.05 K when detecting the difference in temperature). According to the present invention, a field-bus measuring transformer is preferred for the temperature difference measuring transformer. It is a transformer, which guarantees an exclusively (totally) digital signal transfer from the temperature difference to the computer, which also allows a transfer without loss of multiple conversion accuracy. In other measuring transformers, the measurement signal detected by the sensor (analog signal) in the sensor element (contains a small "computer") is first digitized and then again converted to an analog standard output signal. and, as such, routed to the computer. This multiple conversion * may to some extent affect the conversion errors.
Instead of resistance thermometers, the in-line temperature measurements required for the process according to the invention could in principle also be carried out using thermoelements. A thermoelement is a component made up of two different metals and connected to each other at one end (point of connection). At the free ends of the two conductors connected to one another, in case of temperature difference along the conductors due to the Seebeck effect, an electrical voltage can be produced. The connection point and the free ends must therefore have different temperatures for this purpose. A thermoelement application for the process according to the invention therefore assumes a stable comparative temperature in the environment of the free ends of the respective thermoelement, so that their use is less preferred according to the invention compared to a use of resistance thermometers.
As a possibility to extend the comparative temperature constant, the aforementioned comparison point may be located, for example, in a bath with hot water (0 ° C) or also in a thermostat (for example at 50 ° C). As a variant, the connection of the measuring apparatus can be used as a comparison point and the optionally variable temperature can be sensed with a transistor or a resistance thermometer to numerically correct the measured thermal voltage.
Similarly, integrated switching circuits for this correction may be used, which not only serve as an amplifier for the measured voltage, but also directly compensate the temperature of the point of comparison, provided that they have the same temperature as the point of comparison. .
If the point of connection is brought to the point of entry of a balancing medium and the free ends to the point of exit of the balancing medium, the thermal tension that appears will be a direct measure of the difference between Tin and Taus. - »
Another element to be taken into account in the heat balance exposed according to the invention is the difference between the palpable heat current conveyed to the secondary space by conveying the mass current having a TPein inlet temperature and the heat flow. palpable extracted from the secondary space by the extraction of the mass current having the output temperature Tsaus formed in the secondary space (crystallization).
This difference is for example given with a sufficiently good approximation in the method according to the invention the equation:
"* Mp is in this case identical to because of the mass hold necessary.
Tpein and Tsaus can be picked up online using sensors made as already mentioned and Cpp is the mass-specific heat capacity referred to heating at constant pressure (frequently also simplified by "mass-specific heat" in J / gK) , which the liquid phase P presents. They can be obtained experimentally with respect to the inlet temperature Tpein and with respect to the inlet pressure of the liquid phase P at the inlet into the secondary space and are then adopted as independent of pressure and temperature in the context of the method according to the invention and are stored as such in the computer. Cpp can also be considered sufficiently robust compared to the limited fluctuations in the composition of the liquid phase P.
The accuracy of the determination of QPjljn can be further increased if necessary, for example, by following (as already described) the mass density of the suspension S extracted from the secondary space of the in-line heat exchanger. As this mass density is correlated with the degree of crystallization Y of the suspension S, Y is accessible online.
Instead of using Cpp in equation 4, it can also be calculated with (cp + c '') / 2 in a better approximation, Csp being the heat capacity of the mass-specific suspension S referred to pressure heating. constant.
Csp is in this case obtained with a good approximation by the equation
CKrp is in this case the heat capacity of the mass-specific crystallizate relative to heating at constant pressure.
CKrp is accessible under the framework conditions of the process according to the invention by caloric measurement and may be considered further within the scope of the invention as being independent of temperature and pressure.
In general, Cpp and Csp are broadly similar, so that only one calculation of Cpp is sufficiently accurate. In a very general way, the degree of precision to be applied to the establishment of the thermal balance required according to the invention is fixed with respect to the respective separation problem. In this case, for example, in the above equation, it must be taken into account that, when Y is high,
Qicr.Y is also particularly large (so that an approximation "c> eC " In QP ein will not be particularly noticeable) and that, when Y is small, the approximation "C '· Ä cr" is particularly good because the crystallizate fraction and hence the CKrp-weighted contribution thereof is low. For large heat flows, the fraction used should be more accurate than in the case of small heat fluxes. ^ - -
There is thus still finally the consideration of diffuse thermal heat flow occurring during the realization of a method according to the invention, which condition by their sum a total heat flow which can be, depending on the framework conditions used for the realization the method according to the invention in terms of the technical balance, a heat flow flowing in the secondary space of the heat exchanger or a heat flow flowing out of it.
This heat flow is normally relatively small compared to other heat flows that occur. This is due in part to the fact that the heat exchanger, in which crystallization separation takes place, is operated thermally insulated from the environment by heat-insulating materials applied from the outside to the heat exchanger. of heat (materials having a low coefficient of thermal conductivity λ (W / mK), such as wood, wood wool, fiber mats made from ramie fibers, Poroton, mineral wool (for example, wool of glass), foam glass, polystyrene-based heat-insulating substances and Styropor®, Styrodur® and Neopor® expanded polystyrenes (contain finely divided graphite particles in addition), polyurethane insulating substances, such as hard polyurethane foam, carbon dioxide-PUR, C-iso-pentane-PUR, pyrogenic silicic acid (eg formed from individual pressed plates), vacuum PUR and silicic acid under vacuum). An air intake of the environment into the heat exchanger is normally largely excluded.
In addition, as a general rule, a water vapor barrier layer (for example, a composite aluminum foil according to EP-A 1 090 969 or DE 29 917 320 U1) which holds the water vapor contained in the ambient air and thus avoids a condensation of this water vapor on the heat exchanger possibly having a low external temperature.
In this case, thermal insulation is suitably provided so that the dew point temperature level is between the water vapor barrier and the surface of the heat exchanger. Frequently, the heat exchanger operated according to the invention is also in a closed chamber and the air is between the enclosure and the heat exchanger heat insulated and has a water vapor barrier is maintained by intervention of a thermostat at a favorable temperature. As a material for the accessible enclosure, wood can be used in the simplest case. Other materials such as plastic, lead, masonry or concrete are also possible. Frequently, the temperature difference between the air temperature in the enclosure and Tsaus is less than 25 K.
Thermal fluxes possibly introduced into the fluid content of the secondary space by scraping and / or stirring devices possibly moving in the secondary space are normally also low heat flows (small). In sufficiently precise approximation for the process according to the invention, it is therefore possible to determine δ with a "water course".
In fact, the heat exchanger is filled, for example, with a liquid (for example water, but one could generally also use any other substance, which occurs under the marginal conditions corresponding to the state of liquid aggregate), whose temperature reaches (Tpein + Tsaus) / 2, where Tpem and Tsaus are the values envisaged for the regular exploitation of the crystallizer. Then, moving parts such as, for example, scraping devices and / or stirring devices in the secondary space will be used and the temperature of the water in the secondary space will be monitored as a function of time. .
According to the equation Qn ~ (cr * ΔΤ) / At, where ΔΤ is the temperature difference occurring in the time interval A of the liquid in the secondary space of the heat exchanger and here is the capacity corresponding absolute heat capacity relative to a constant pressure (absolute heat, enthalpy) of the heat exchanger filled with liquid at temperature (Tpein + Tsaus) / 2. Cflp is determined in advance in a separate "water course" in which a specified (defined) amount of heat is supplied to a heat exchanger filled with the liquid (for example with an immersion heater connected over a defined period of time and immersed in the liquid) and the resulting variation in temperature is observed. In an even simpler way, is accessible in the context of a water course by conveying through the secondary space of the heat exchanger operated without accompanying heat as liquid phase P, for example, a mass flow of stationary water whose Twein temperature at the entrance to the secondary space corresponds to the temperature Tpein during the operation according to the invention of the heat exchanger. At the same time, a coolant is passed through the at least one primary space of the heat exchanger so that the stream of water leaves the secondary space of the heat exchanger stationarily at a temperature Twaus, which corresponds to the temperature Tsaus during the operation according to the invention of the heat exchanger.
The equation:
provides simple access to the total heat flux diffuse. Cwp is here the mass-specific heat capacity related to a constant pressure of the water used for the water course or the liquid used for this water course (at the temperature T = (Twaus + Twein) / 2.
The δ /> thus determined is stored in the computer as a constant.
As a result, the total heat balance is obtained as follows:
(Normally, δo in equation 5 is obtained with a positive sign, but in principle it can also be obtained with a negative sign in equation 5. For the sign, this is the result of water course describes who decides, the case of a positive sign corresponds to a flow of water flowing in the secondary space).
On the basis of the standard output signals provided by the sensors used continuously at the computer, the computer can calculate the values of both sides of the equation 5 continuously. If these values are equal, there is no need to introduce regulatory measures.
But if the values calculated for the two sides of equation 5 are different from each other, there is a need for regulation to guarantee the degree of crystallization Y. The computer controls from the difference in magnitudes The result of the results obtained for both sides, the variation of which causes the variable heat fluxes to be influenced on the right side of equation 5 "(δ 0 is a constant) so that the value of the right side of the equation 5 is again derived successively from the value of the guiding quantity. During this alignment operation, there is a permanent alignment of the values currently calculated for both sides of the equation 5 and this results in a continuous adaptation of the influence on the adjustment variable. According to the invention, it is preferred in this case to control the control variables which have influence on QK 'aus. It is particularly preferred to control the control variables which have an influence on TKein.
If we introduce equations 1 to 4 in equation 5, we obtain the following total heat balance, for example:
(equation 6)
In this case, the underlined terms in bold form the terms that can be tracked experimentally online by means of the illustrated sensor elements and can be transmitted to the computer via the related measuring transformers without time delay, while the terms not underlined in bold are stored in the computer (these are components of the software).
It can be seen at this stage that, by tests carried out prior to the actual crystallization separation of the invention to increase the accuracy of the process of the invention, an adaptation of the terms stored in the computer will normally again be introduced. that is to say, those not followed online, on the results obtained for Y in the tests (fine tuning). In fact, one determines (one adjusts) stationary operating states different from each other from the separation by crystallization, which generally have also different degrees of crystallization Y and one obtains, by the quality of the alignment performed by calculation for these states on both sides of equation 6, adaptations of the memorizations improving the quality of the alignment.
At this point, it will be furthermore established that, in the case where the secondary space of the heat exchanger is in contact with several spatially separated primary spaces (in a scraped plate heat exchanger, the internal space of each individual cooling disc forms, for example, such a primary space) and that each individual primary space is operated with a materially different refrigerant, for example, refrigerants carried in the other primary spaces independently, Equation 6 remains maintained, but on the right side there is for example a sum of expressions "mK · Cp (TKaus - TKem)", each element of the sum representing a primary space. Otherwise, one can proceed in a manner completely equivalent to that which follows, taking the example of the application of only a refrigerant substance.
It is preferred according to the invention, in the case where the secondary space comes into contact with several primary spaces, that all the primary spaces are traversed by one and the same refrigeration substance (the delivery of this refrigerant substance can possibly be done through partial amounts of the primary spaces independently (separately) from the flow of one or more other partial quantities).
Directly behind (or directly in front of) the coolant outlet of the respective primary space, it is possible, in this case, to purify the various streams of coolant which respectively come out in a technically appropriate manner to form only one. a single total stream of refrigerant, whose mixed temperature forms the relevant temperature T "aus (and followed in line according to the invention) for equation 6. This total stream of refrigerant is then brought back to the relevant TKein temperature for Equation 6 and then, as needed, on the various primary spaces or their partial quantities. As in the case where several primary spaces traversed by a refrigerant, it is possible to proceed correspondingly if more than one indirect heating is applied by indirect heat exchange in the context of the process according to the invention:
Moreover, in the computer (often referred to as a process pilot system (PLS), that is to say a computer network), these are computers, which are characterized by the following parameters: input signals come exclusively from sensors; the output signals are exclusively delivered via actors; the data processing is done in real time; programming is done only through operator intervention; the actors are the counterpart of the sensors referred to the conversion and form the adjustment element of a regulation structure; they convert control signals from the computer most of the time into mechanical work, that is to say movements, for example a valve that opens or closes; that is to say that the actors constitute, observed technically, the switching of a power converter with a power adjustment element; the power control element connects the derived energy (usually electrical energy) to the control signal; a modulated energy is obtained, which is converted by the converter into the energy type of the control variable (mostly mechanical energy) and continuously compares the left side of equation 6 (or 5) with the right side of equation 6 (or 5).
When both sides have the same size, there is no need for regulation to guarantee the degree of crystallization Y. If the heat fluxes of the two sides are different from each other, there is a difference of adjustment to the theoretical value "0" for the difference on both sides. If, for example, the left side is larger than the right side, preference will be given so that the value of the expression mK · Cp (TKaus -TKein) increases (otherwise, Y would decrease by undesired manner as a result of the adjustment deviation). For this purpose, control variables that are controlled by the computer and influence their modification n, K and / or TKein will normally be used. With a corresponding increase of niK and / or a reduction of Τκβιη, the adjustment difference can be compensated. For reasons of flow technique, the adjustment sets are usually relatively limited with respect to an adaptation of}, K. In front of this background, it is thus preferred most of the time to compensate a difference of adjustment only with a variation of TKein.
Advantageously, a deviation of adjustment will therefore be detected directly by an alignment with respect to TKein.
For this purpose, in the computer, equation 6 is appropriately solved as follows in terms of the application technique:
(equation 7)
The right side is continuously determined in the computer and is aligned with T "®1", which is accessible for online determination, for example if the right side is larger than the left side setting will be compensated so that Τκβιη increases.
For this purpose, one can proceed as follows for example. From the coolant stream leaving the heat exchanger, while a residual current remains, only a partial flow of a tank equipped with a coolant thermostat is conveyed and in principle to the tank via indirect heat exchange, it is cooled to the relatively low temperature in the tank equipped with the thermostat (this temperature can be up to 10 K or more below the stationary temperature TKein. fed to the tank is simultaneously aligned so that a corresponding larger partial stream is withdrawn from the tank, mixed with the residual stream, and then the mixture thus obtained is again conveyed to the heat exchanger. The level of the two partial currents is in this case adjusted, for example, via drawers or corresponding valves controlled by the computer with the aid of These are controlled as adjustment variables so that the mixture has the value respectively necessary for T ein. If, as a consequence of a deviation, for example, the temperature TKe, n has to be increased, the partial current is reduced by control of the computer. If, as a consequence, a deviation of adjustment Τκβιπ must be reduced, the partial current is raised by control of the computer.
By increasing or decreasing TKem, the computer routes its value on both sides of Equation 7 so that equality is reached again. In the application technique, suitably, the return of the partial stream of coolant stream leaving the heat exchanger and returning to the coolant tank equipped with the thermostat can be achieved as follows by simultaneously removing the coolant stream. a corresponding partial flow of the reservoir.
As a coolant tank, a refrigerant transfer circuit will be used, which is conveyed, for example, on the brine side by the indirect evaporator to an ammonia compression cooling plant. A make-up temperature of the coolant transfer stream for the amount of ammonia corresponding to the indirect evaporator is liquefied beforehand and vaporized by the vaporizer which receives the coolant stream which passes therethrough cooling it to the expected temperature of the thermostat (the evaporating temperature of ammonia is in this case regulated by the suction pressure of the compressor (this treatment mode is also designated by suction pressure regulation)).
The recycling of the partial flow to be returned to the thermostatic tank of the refrigerant stream leaving the heat exchanger is now carried out by a flow valve controlling the amount of partial flow in the brine-side supply stream for the indirect evaporator. the ammonia compression cooling system and the corresponding simultaneous partial-flow recirculation of the tank is via a corresponding withdrawal valve controlling the partial flow amount of the brine-side stream leaving the indirect evaporator of the cooling plant. ammonia compression. The valve openings are in this case again controlled according to the setting of the amount of partial current required by the computer at the respective temperature TKein.
Alternatively, it is also possible to adjust only the coolant stream supplied from the coolant tank to the heat exchanger via a valve. The coolant stream returning from the heat exchanger to the coolant tank is automatic. In this case, only this valve opening is controlled by the computer.
This method of treatment for TKein adjustment will be referred to herein as an ammonia compression process.
Corresponding circuit guides allow, if necessary, a modification of TKein. In this case, a thermostat heating agent tank at a high temperature is incorporated.
According to the invention, it is even more convenient to report a deviation directly to the temperature difference TKein-
T aus I K
For this purpose, one can solve the equation 6 advantageously as follows in the computer: T ^ mH * cP T - ΤΓ) + ™ € · ΡΡ {ΤΓ-Ts ~) + Qo + ™ P-Y-c r
(K *} mK · CpK
(equation 8)
The advantage is that, as already explained in the present application, the temperature difference TKaus-TKein can be guided by using resistance thermometers corresponding to the inlet and the outlet of the respective primary space of the heat exchanger and applying a fieldbus temperature difference measuring converter without systematic conversion error and directly digitized form by an input signal. In the computer, the alignment is then done on the right-hand side of equation 8 and, when establishing a control deviation, the corresponding actor for the control variable to be influenced can be controlled, because of this difference, either in digitized form (requires another fieldbus for the actor), or in analog form (for example with a normalized signal of 4 up to 20 milliamps) directly. The application of the fieldbus (refer to DIN 19245 as well as IEC-61158-2) thus enables general digital information to be exchanged between the sensor and the actor (for example, with a PROFIBUS- PA or a foundation groundbus), which allows for particularly high adjustment accuracy. If the left side, for example, is smaller than the right side, there is a need for regulation. To counteract this regulatory deviation, the temperature Τκβιη, as already described above, will preferably be increased to the corresponding extent as needed until the values on both sides of equation 8 correspond again.
The control system according to the invention implies, on the one hand, that it reacts relatively quickly on the disturbances relevant to the degree of crystallization Y and, on the other hand, that it behaves in a relatively robust manner with respect to disturbances rather irrelevant vis-à-vis the degree of crystallization Y. It also has a high stability as well as a very high static accuracy and a small inclination to overshoot.
In principle, to carry out the process of the invention, it is possible to take into account all types of indirect heat exchangers (they have, according to the definition, the primary space / secondary space structure required by the invention) (see for example, Kristallisation, Grundlage und Technik, Gunther Metz, Springer-Verlag, Berlin 1969, pp. 214 and following, and at Ullmanns Encyclopedia of Technische Chemie, Verfahrenstechnik I, Verlag Chemie Weinheim, 4th edition, 1972, pages 672 to 682, as well as to the state of the art cited in these standard works).
The problem of the formation of deposits on the side facing the secondary space of the separating wall (heat exchange wall) between the primary space and the secondary space has already been discussed. As already mentioned, this can be countered by, for example, continuous scraping of the heat-transferring surface by means of appropriate scraping devices. These heat exchangers (coolers) are also referred to as scraper coolers. Alternatively, mobile primary space elements (e.g. removable cooling disks) may also be used and exchanged from time to time.
The direct displacement of the fluid phase in the secondary space through it is in many cases already sufficient to condition a suspension of the separated crystallizate in the secondary space. But, as a rule, the secondary space has in addition one or more mixing devices. It can be in the simplest case a splash with an auxiliary gas (for example air), one or more agitators, scraping device and / or pumping in circulation. The direct transport of the mass flow fed to the secondary space through it is normally carried out so that the liquid phase P is compressed in the secondary space by means of pumps. The removal of the (crystallizate) suspension S from the secondary space is usually done by overflow adjustment (but it can also be done by level adjustment via a submerged tube). For this purpose, a height-adjustable overflow weir is advantageously used in the application technique.
As an example of choice, the following apparatus can be used for the process according to the invention: rotary tube crystallizers (the secondary space is the internal space of the tube, the cladding of the tube is a double envelope, in which the refrigerant is conveyed inside the tube in the same direction or in countercurrent with the mass flow, preferably the inside of the tube is slightly inclined with respect to the horizontal, the crystallizing deposits which form on the inner wall of the tube can be released continuously (for example with chains) and / or scraped (for example with radial scrapers), the liquid phase P is introduced continuously into the first end of the tube, the suspension S is evacuated continuously at the other end of the tube; - a container with suspended cooling elements (cooling elements (for example cooling discs) are suspended in an unstirred container, the liquid phase P is for example introduced to the left below the container and is discharged from the container to the right above the suspension S by adjusting the overflow; elements with deposits are replaced by new cooling elements); stirring containers (for example, containers which are surrounded by a cooling jacket and / or equipped with cooling elements (cooling coils, cooling discs), in addition stirring, which continuously mixes by agitating the contents of the internal space which is not occupied by the cooling elements, the liquid phase P is pumped and the suspension S is discharged by overflow; (agitated tube cooled by a liner, the wall of which is scraped by scraping blades pressed by springs, the liquid phase P is introduced by pumping at one end, the suspension S is evacuated at the other end); trays crystallizers (trough-shaped container with horizontally mounted shaft, on which, at regular distances, hollow trays (hollow disks) are mounted, which are traversed by the ref agent. generally countercurrently with the liquid phase to crystallize P and which have sector-shaped sections for the passage of the liquid phase P or the crystallizate suspension; slow stirring of the crystallizate suspension by the trays and the refrigerant lines which connect them; the liquid phase P is introduced by a first side by pumping into the tray crystallizer and is discharged from the tray crystallizer on the opposite side by overflow adjustment); - forced circulation crystallizers from Swensson or Meso Chemie Technik.
For the process according to the invention, particularly suitable crystallizers (in particular in the case of acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone as target product X) are crystallizers. with cooling discs (the cooling discs in the secondary space contain the primary spaces), for example those described in Research Disclosure Database Number 496005 (published August 2005) and in Research Disclosure Database Number 479008 ( published in March 2004).
As the fluid coolant (or auxiliary agent), both gases and liquids can be used.
It is preferred according to the invention to use liquid refrigerants (or heating agents). As such liquid refrigerants (or heating agents), mention may be made, for example, of heat-transfer oils, water, salt solutions in water, mono- or multivalent organic alcohols, such as methanol or ethanol. propanol, glycol and / or glycerol, but also mixtures of one or more of the above-mentioned refrigerants, for example mixtures of water and methanol or mixtures of water and glycol (e.g. with 10 to 60% by weight of glycol).
The temperature T ein is set, in a cooling crystallization according to the invention, typically at 0 to 20 K, frequently at 1 to 15 K and most often at 2 to 15 K below Tsaus. The temperature THein is suitably selected in a range greater than Tsaus, for example, in the range 0 to 20 K, frequently 0.5 to 10 K and most 1 to 5 K above it. .
The crystals of the suspension crystallizer formed in the course of carrying out the process according to the invention typically have a longitudinal extension (the longest direct straight connecting line of two of the points on the surface of the crystals) in the range of 1 at 10,000 pm, frequently from 10 to 1000 pm, more frequently from 100 to 800 pm and very frequently from 300 to 600 pm.
Moreover, the separation by crystallization can be carried out as for the suspension crystallizations carried out in the state of the art.
The suspension S (crystallizate) extracted from a separation according to the invention is normally not conveyed directly after separation into crystallizate and residual phase R (mother liquor). Instead, it is buffered in a tank, for example, stirred and / or pumped and withdrawn continuously from it and, for example, fed to a separation in a washing column.
If there are several (for example two or three) crystallizers (heat exchangers), for example, of the same structure which are operated in parallel in the manner of the invention (each of the crystallizers operated in parallel preferably has a control According to the invention (independent of the other crystallizers) the degree of crystallization Y obtained therein, the feed of the respective circuits of coolant and optionally of the heating agent is advantageously in the plane of the application technique from a coolant tank or a heating agent tank with a thermostat common to all the crystallizers) and all the suspensions S respectively removed from the various crystallizers are appropriately conveyed to the plane of the Application technique firstly to a common buffer tank and are mixed by stirring per se. This buffer tank feeds the separation devices for the mother liquor / crystallization separation (for example hydraulic washing columns, the number of which corresponds advantageously to each of the crystallizers operated in parallel (but, in principle, this number may also be larger or smaller). less important) and are also operated in parallel and usually also have an identical structure). The pure melt product removed, for example, from the melting circuit of the respective scrubbing column is fed to a common storage tank, into which the incoming streams of pure product are mixed with each other.
The pure target product X (possibly inhibited in terms of polymerization) is conveyed from the storage tank to the respective user. As far as the application technique is concerned, it is conveniently carried out on the way between the buffer tank and the mother liquor / crystallizate separation by means of a Coriolis mass flow rate measuring device. the degree of crystallization of the crystallizate suspension by determining its mass density.
Accordingly, the present invention particularly comprises the following embodiments: 1. A method for the continuous separation of a target product X in the form of a finely divided crystallizate of the target product X from a liquid phase P containing the target product X as well as different components of the target product X by means of a heat exchanger having a secondary space and at least one primary space, in which the secondary space and the at least one primary space are separated spatially from one another by at least one partition wall which serves as a surface for the transfer of heat from the secondary space into the at least one primary space, into which a liquid phase P is continuously introduced into the secondary space of the heat exchanger, while the at least one primary space is traversed simultaneously by at least one fluid refrigerant so that it is formed in the space this secondary, while leaving a residual liquid phase R from the liquid phase P, a finely divided crystallizate of the target product X, which is suspended in the residual liquid phase R, which contains, in comparison with the liquid phase P the different components of the target product X in the enriched state and whose target product content X reaches at least 70% by weight, while retaining a suspension S, having a degree of crystallization Y, of finely divided crystallizate of the target product X in the residual liquid phase R and the suspension S is removed from the secondary space of the heat exchanger continuously, characterized in that, to adjust the desired degree of crystallization Y of the suspension S withdrawn from the secondary space of the heat exchanger, use is made of the difference obtained at the respective operating point by means of a computer between the QKrY heat transfer flux. corresponding to the degree of crystallization Y and developing calculatedly in the secondary space and the difference formed between the heat flow Qaut otherwise removed in total from the secondary space of the heat exchanger and the heat flow Qein conveyed in total in the secondary space of the heat exchanger.
2. Process according to embodiment 1, characterized in that the content of the liquid residual phase R in target product X is greater than or equal to 80% by weight.
3. Process according to embodiment 1, characterized in that the content of the residual liquid phase R in target product X is greater than or equal to 90% by weight.
4. Process according to any one of embodiments 1 to 3, characterized in that the target product X is acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone.
5. Process according to any one of embodiments 1 to 4, characterized in that the liquid phase P contains at least two different components of the target product X.
6. Process according to any one of embodiments 1 to 5, characterized in that the liquid phase P is a crude acrylic acid, which has the following contents:> 85% by weight of acrylic acid,> 100 ppm in weight at <10% by weight of acetic acid,> 10 ppm by weight at <5% by weight of propionic acid, up to 5% by weight of low molecular weight aldehydes, up to 3% by weight of polymerization inhibitors, 0 to 5% by weight of diacrylic acid, up to 10% by weight of water.
7. Process according to any one of embodiments 1 to 6, characterized in that it comprises in addition to the process step according to embodiment 1 the following process steps: b) separation of the suspension S removed from the secondary space of the heat exchanger in crystallization of the target product X and in the residual liquid phase R, c) melting at least part of the crystallizate separated from the target product X, and d) recycling at least part of the crystallizate melting of the target product X in step b) and / or in the step of the continuous separation process of the target product X according to any embodiment.
8. Process according to any one of the embodiments 1 to 6, characterized in that a process of continuous separation of the finely divided crystalline product concentrate X contained in the suspension S is connected, in which: the suspension S is conveyed to a washing column, which has a washing column wall, which encloses a treatment space, - by maintaining the crystallizate contained in the suspension S and forming a crystallizate bed in the treatment space, it is delivered from the suspension S conveyed to the treatment space through filtering devices a residual liquid phase R coming from the treatment space, - the crystallizate bed is conveyed into the treatment space, - in the treatment space in the direction of advancement of the crystallizate bed acts at least one force different from the gravitation, which advances the crystallizate bed into the treatment space, - da In the counter-current treatment space with the crystallizer bed, a pure melt consisting of crystallized melt crystallized previously separated after this washing-column process is conveyed so that a crystalline bed is formed in the crystallizing bed. washing, which divides the crystallizate bed into a mother liquor zone and a pure melt zone, and at the end of the washing column opposite the introduction of the suspension S is continuously extracted a crystallizer which has developed in the wash column in a solid and / or melted form.
9. A process according to claim 8, characterized in that the target product is acrylic acid and is connected to another process in which the crystallized and separated acrylic acid crystallizate is subjected to polymerization with itself or with other compounds having at least one monoethylenic unsaturation.
10. Process according to any one of embodiments 1 to 9, characterized in that the liquid phase P is introduced into the secondary space of the heat exchanger with the mass current intensity and the method comprises the determining the intensity of the mass current m and / or the volume flow intensity belonging to the process according to embodiment 10, characterized in that the determination of the mass current using a Coriolis Mass Flow Meter, or a Swirl Flow Meter or a Magneto-Inductive Flow Meter or Flow Meter floating body.
12. Process according to any one of embodiments 1 to 10, characterized in that the liquid phase P is introduced at a Tpein temperature in the secondary space and the suspension S is removed from the secondary space at a temperature Tsaus and the method comprises determining Tpein, Tsaus and Tpe difference 13. Process according to Embodiment 12, characterized in that the determination of Tpein and Tsaus is carried out with a thermometer respectively. resistance.
14. Process according to embodiment 13, characterized in that the resistance thermometer is a platinum resistance thermometer.
15. Process according to any one of embodiments 1 to 14, characterized in that the fluid refrigerant traveling at least one primary space is introduced at a temperature TKein in the at least one primary space and is evacuated at least a primary space at the temperature T "aus θί the method comprises the determination of Τκβιη, T" aus and the difference Tk3US-TV "1.
16. Process according to embodiment 15, characterized in that the determination of Tkem and Tk3us is carried out respectively with a resistance thermometer.
17. A method according to embodiment 16, characterized in that the resistance thermometer is a platinum resistance thermometer.
18. Process according to embodiment 15, characterized in that the determination of the difference TKaus-TKein is carried out with two resistance thermometers and only one transformation device for measuring the temperature difference.
19. The method according to embodiment 18, characterized in that the temperature difference measuring transformation device is a fieldbus measuring transformer.
20. Process according to any one of embodiments 1 to 19, characterized in that the fluid refrigerant flowing through the at least one primary space is introduced into the at least one primary space at the mass current intensity mK and the method comprises determining the mass current intensity mK and / or the volume flow intensity belonging to mK.
21. The method according to embodiment 20, characterized in that the determination of the mass intensity mK is done using a Coriolis mass flow measurement device or a swirling flow measurement device or a magneto-inductive flow measurement device or a floating-body flow measurement device.
22. Process according to any one of embodiments 1 to 21, characterized in that the coolant passing through the at least one primary space is introduced into the at least one primary space at the temperature TKe, n and, in the case where the difference between QKr and the difference Qaus -Qein is not infinitely small, the temperature TKein is modified.
23. A process according to any one of embodiments 1 to 22, characterized in that the target product X is acrylic acid, which has been produced by a heterogeneously catalyzed partial gas phase oxidation.
24. Process according to any one of embodiments 1 to 23, characterized in that the target product X is acrylic acid and the liquid phase P returns to a fractional condensation and / or absorption of the gaseous product mixture. heterogeneous catalytic partial gas phase oxidation for the production of acrylic acid.
25. Process according to any one of embodiments 1 to 24, characterized in that the heat exchanger is a cooling disc crystallizer.
26. Process according to any one of the embodiments 1 to 25, characterized in that a mixture of water and methanol or a mixture of water and glycol is used as the cooling agent.
27. A method according to any one of embodiments 1 to 26, characterized in that is connected to the method a determination of the mass density of the suspension S with a Coriolis mass flow measurement device.
28. Process according to any one of the embodiments 1 to 27, characterized in that Y has a value of 0.10 to 0.50.
29. The method of any one of embodiments 1 to 27, characterized in that Y is 0.20 to 0.40 or 0.25 to 0.35 or 0.30.
30. A method of manufacturing a target product X, characterized in that it comprises a method according to any one of embodiments 1 to 8 or according to any one of embodiments 10 to 29.
The principle of formation of a heat balance which is the basis of the setting according to the invention of the degree of crystallization Y during separation by continuous crystallization can also be used in the case of separation by discontinuous crystallization or semi -keep on going. Instead, on the basis of the introduced and evacuated heat flows, the thermal balance is carried out, but on the basis of quantities of heat introduced and evacuated. For their calculation, the initial and final temperatures replace the inlet and outlet temperatures and, instead of the mass currents, the summed masses are used as a function of time (integral).
EXAMPLES
Two agitated and scraped cooling disk crystallizers with the same structure of the type of construction described in Research Disclosure Database number 496005 (published in August 2005) are operated in parallel (alternatively, respectively, three of these crystallizers can be used in parallel with two of the wash columns or with three wash columns). It is a trough, in which 24 scraped circular cooling plates are arranged suspended one behind the other at equidistant intervals of 30 ± cm. The diameter of the plates is 3.3 m. The thickness of the plates is 5.2 cm.
As the cooling agent, a mixture of 70% by weight of water and 30% by weight of glycol is used for each of the two crystallizers. The refrigerant is fed into the respective crystallizer countercurrently with the liquid phase P delivered to the crystallizer therethrough and is further enriched by passing from a cooling disc to a subsequent upper cooling disc. In fact, the coolant is fed into each of the two crystallizers divided into two parallel streams of the same size over the cooling plates of the respective crystallizer. Half of the current passes through the digitally aligned cooling plates, while the other half of the current passes through the digitally non-aligned cooling plates (the cooling discs are coded in the direction of flow of the refrigerant starting with 1). The cooling surfaces are made of thin steel (material DIN 1.4541). The wall thickness of the stainless steel cooling surfaces is 4 mm. The rotation of the blades reaches 6 revolutions / minute. The squeegee axis is centered through the cooling discs and sealed by water-rinsed packing glands (Teflon packing cord, flush quantity equal to a few liters per hour up to 10 liters per hour). hour and seal). On the circumference of each cooling disc, where there can be no scraping, a hollow profile (a welded tube (material: high-grade steel material DIN 1.4541), wall thickness = 3.5 mm) is applied. The hollow section of the individual cooling discs of a crystallizer is covered, for purposes of accompanying heating, by a liquid heating agent, which is also composed of 70% by weight of water and 30% by weight of glycol .
The scrapers are segmented in the radial direction (4 segments).
The specific squeegee pressing force is in the embedded state perpendicular to the cooling surface at about 4 N / cm of active squeegee length. As scraping material, Multilene® PE1000 is used. In addition to the squeegees, the shaft drives pallets (between two cooling discs and in front of the first and last cooling disc, respectively in symmetrical arrangement), which ensure better mixing. In the rear part of the respective crystallizer in the conveying direction of the crystallizate suspension (behind the last cooling disc), the (crystallizate) suspension formed in the individual crystallizer S flows respectively onto an overflow weir in a buffer tank agitated by a propeller stirrer (made of stainless steel, material DIN 1.4541 or 1.4571), with the aid of a low accompanying heating thereof, it is possible, if necessary, to suppress an existing supersaturation of the suspension S), device by which, from two hydraulic washing and melting columns of the same structure, a suspension S withdrawn from the buffer tank in two partial mass flows of more or less identical size (after separation of the mass flow of suspension S removed from the buffer tank on the two washing columns, respectively performs, before entering the respective washing column, the passing through a device Coriolis mass flow measurement to determine the degree of crystallization Y via the mass density of the respective partial mass flow) to separate it in the residual phase R and crystallized. The separation in the washing columns of the melt is as described in EP-A-1 272 453, WO 2006/111565, EP-A 1 448 283, WO 03/041833, EP-A 1 305 097, DE -A 101 56 016, DE-A 2005 018702, DE-A 102 23 058. The internal diameter of the individual washing column is 1.4 m. The loading of the washing columns by the crystallizate suspension S is carried out respectively by means of a centrifugal pump (Kanalrad type), in which the quantity control is done via a regulation of the number of revolutions of the pumps.
The slurry (crystallizate) flow stream S fed to the respective scrubbing column corresponds substantially to the mass flow of an individual crystallizer in the slurry buffer tank S. The stationary filling content of the slurry buffer tank S is 16 m3.
Each of the two crystallizers has a roof (thin steel (material DIN 1.4541)) and is protected against entry of ambient air. Both the washing columns, also made of stainless steel (material DIN 1.4541, wall thickness 10 mm), the crystallizers and the buffer tank are protected against water vapor (see, for example, DE-A 10 2007 032 633) and insulated with an alubutyl sheet from the company Vego System Baustoff, subsidiary VT 1 at 67014 Ludwigshaffen / Rhein stuck on Styropor applied to its stainless steel sheathing.
The washing columns, the buffer tank and the crystallizers are housed in a common enclosure. The temperature of the air in the common enclosure is between 25 and 28 ° C. The material transport of the crystallizers in and from the buffer tank in the washing column is also protected from the surrounding air and is also insulated and sealed with water vapor.
The degree of crystallization Y is regulated according to the invention independently for each of the two crystallizers operated in parallel. The value determined for Y in both crystallizers for this purpose is unitarily 0.28. The adjustment of this degree of crystallization is done for each of the two crystallizers on the basis of equation 8 independently of that of the other crystallizer. In this case, a deviation is compensated for in each case by an increase or an individual reduction of the respective temperature T "®" 1. The adjustment of the respective temperature TKein is carried out for each of the two crystallizers after the compression process. to ammonia, but here a common refrigerant reservoir is used.
The heating agent delivery stream fed to the respective crystallizer is divided, upon entry into the respective crystallizer, into a number of parallel streams corresponding to the number of cooling discs in the crystallizer, which streams are combined into a stream of water. discharging the heating agent after each passage of the hollow profile welded to the respective cooling disk before the crystallizer outlet to again form a heating agent discharge stream. The inlet temperature THein of the respective heating agent flow is maintained for both crystallizers over the entire operating time unitarily at a constant value of 12 ° C. To adjust the temperature THein, all of the heating agent discharge streams are assembled to form a total heating agent discharge stream.
A suitable partial stream of this total heating agent discharge stream (set via a computer-controlled control valve) is supplied to a heating agent tank, the temperature of which is maintained at a value of 20 to 50 ° C, and a corresponding partial stream is withdrawn from the tank simultaneously, which is mixed with the remaining residual stream to form a new total heating agent delivery stream having the required temperature Th®1 ". The heating agent transport stream fed to the respective crystallizer is also kept constant in its intensity with respect to the duration of the heating agent flow and is again conveyed to the respective crystallizer. total exploitation.
In order to apply a thermal balance control according to the autonomous invention of its degree of crystallization Y, each crystallizer and the related autonomous refrigerant circuit have, alongside an autonomous process management, the following sensors and actors: TKein, TKaus and T "aus - TKein - a 3144P type temperature difference transformer with PLS digital data transfer via fieldbus type" foundation field bus "and - two type Pt100 resistance thermometers MEW in the protection tube; (All of the elements mentioned by Rosemont / Emerson Process Management, 8200 Market Boulevard Chanhassen, MN 55317, USA); b) for> ηκ - a magneto-inductive flow measurement device of the IFM 42K type from the company Krohne, DE-47058, Duisburg, data transfer to the PLS by a normative (analog) signal of 4 to 20 mA (the 4 mA corresponds to the start of the measurement zone, the 20 mA at the end of the measurement zone); the mass density of the refrigerant is stored with the value of 1055 g / dm3 as a constant in the measuring apparatus; c) for THein and THaus - two MEW type Pt100 resistance thermometers in the protection tube; - for each resistance thermometer a type 248 temperature measuring transformer, PLS data transfer with a normative signal of 80 mA; (all items come from Rosemont / Emerson); d) for mu - a Krohne type H250 floating body flow meter, data transfer to the PLS with a normative signal of 80 mA; the mass density of the refrigerant is stored at the value of 1055 g / dm3 as a constant in the measuring apparatus; (e) for Tin and Tsaus - two Pt100 MEW resistance thermometers in the protective tube; - for each resistance thermometer a type 248 temperature measuring transformer, PLS data transfer with a normative signal of 4 to 20 mA; (all of the above are from Rosemont / Emerson); f) for m,> - a swirling flow measuring device of the ProWirl 72 type from Endress + Hauser, D-79576, Weil am Rhein; transfer of data to the PLS with a normative signal of 80 mA; the mass density of the liquid phase P is stored at a value of 1060 g / dm3 as a constant in the computer; (g) to adjust the flow to and from the refrigerant tank at the same time: - two control valves with Flowserve Flow Top DN100 nominal values, D-45141 Essen, ····. · PLS data transfer with a normative signal of 80 mA.
Behind the division of the mass flow removed from the buffer tank in suspension of crystallizate S in the two washing columns, but also before the entry of the respective partial mass flow into the respective washing column, there is respectively a device for measuring the mass flow rate. Coriolis of the MFM 7051K type from Krohne, which comprises a sensor element of the Optima 7000 type and a measurement transformation device of the type 051 K. In this way, it is determined as an additional safety measure that the mass flow current of the suspension of crystallized material conveyed to the washing columns as their mass density (which, for their part, is a measure of the actual degree of crystallization Y of the crystallizate suspension removed from the buffer tank).
The transfer of data to the PLS is done by a normative (analog) signal of 80 mA.
For Cxr, CpP, Cpk, CpH and δo (determined by water course), the following constant values are stored in all computers: CKr = 178J / g;
Cpp = 1.97 J / (g · K);
Cpk = 3.55 J / (g · K);
CpH = 3.55 J / (g · K); Q "= 72 MJ / h.
We start from a stationary state of operation of the two crystallizers, which is characterized by the following framework conditions:
Target product X = acrylic acid
The crystallizers are supplied to the liquid phase P, which is crude acrylic acid, which comes from a fractional condensation of a mixture of gaseous products of a two-stage, heterogeneously catalyzed partial gas phase oxidation of chemical-grade propylene. In acrylic acid, the following contents were present: 94.44% by weight of acrylic acid, 1.0105% by weight of acetic acid, 3.64% by weight of water, 0.0304% by weight of acid formic acid, 0.0346% by weight of formaldehyde, 0.0209% by weight of acrolein, 0.0945% by weight of propionic acid, 0.1061% by weight of furfural, 0.0027% by weight of acrylate allyl, 0.0017% by weight of allyl formate, 0.0194% by weight of benzaldehyde, 0.1038% by weight of maleic anhydride, 0.4337% by weight of diacrylic acid, 0.0055% by weight of phenothiazine, 0.0192% by weight of MEHQ and 0.0003% by weight of molecular oxygen.
Operating state of the crystallizer 1 TKein = 2.30 ° C; T "aus - TKein = 2.55 K; TKaus = 4.85 ° C; mK = 210.0 t / h; THein = 12.03 ° C; THA-THein = -1.67 K; THaus = 10.36 ° C; m = 42.5 t / h; TPein = 14.06 ° C;
Tsaus-Tpeln = -7.0 K;
Tsaus = 7.06 ° C; m / - = 26.05 t / h;
Operating state of the crystallizer 2 TKein = 1.90 ° C; TKaus - TKein = 2.7 K; TKaus = 4.60 ° C; = 206.8 t / h; THein = 12.03 ° C; THA-THein = -1.67 K; THaus = 10.36 ° C; MH = 44.0 t / h; TPein = 14.06 ° C;
Tsaus - TPein = -7.27 K;
Tsaus = 6.79 ° C; rnr = 26.75 t / h.
The mass density p of the crystallizer slurry S conveyed from the buffer vessel to the wash columns is 1122.4 to 1122.7 g / cm3. This corresponds to a real degree of crystallization Y of 0.291.
The content of the mother liquor (residual liquid phase R) in acrylic acid in the suspension S is 92.34% by weight.
Starting from this stationary operating state, we increase mr as shown in FIG. 1 for both crystallizers on the basis of curves 1 and 2, so that they correspond to a greater demand of the market.
Modifying the process conditions the manufacture (inter alia, by the addition of oxygen to reduce the tendency to deposits) or the maintenance of the cooling power); corrosive water is an aqueous solution produced as a rule in connection with the transfer of acrylic acid from the mixture of gaseous products from the partial oxidation to the condensed phase, which solution normally contains at least 60% by weight of water and at least 3% by weight of acrylic acid as well as secondary components (see for example WO 2004/035514, DE-A 102 43 625, EP-A 1818324, DE-A 103 23 758 and at the request German Patent No. 10 2007 004 960.0): 93.73% by weight of acrylic acid, 0.9792% by weight of acetic acid, 4.43% by weight of water, 0.0284% by weight of formic acid, 0.0305% by weight of formaldehyde, 0.0210% by weight of acrolein, 0.0904% by weight of propionic acid, 0.0965% by weight of furfural, 0.0025% by weight of acrylate. allyl, 0.0015% by weight of allyl formate, 0.0178% by weight of benzaldehyde, 0.0972% by weight of maleic anhydride, 0.4048% by weight of diacrylic acid, 0, 0071% in stock ds of phenothiazine, 0.0179 wt% MEHQ, and 0.0003 wt% molecular oxygen.
Fig. 1 also represents the time course of Τκθιπ (curves 3 and 4) resulting from the modification of m> 'as well as the progress of the mass density of the suspension S (measured in front of the washing columns, curves 5 and 6) in time until reaching the new stationary operating state.
In this case, the abscissa of FIG. 1 gives the time (8 parts of scale correspond to 1 hour and a half) and the ordinates represent in t / h (curves 1 and 2), TKein in ° C (curves 3 and 4) as well as p in g / dm3 ( curves 5 and 6). The point of intersection of the ordinates with the abscissa corresponds in this case to the following conditions: 15 t / h for (m> '); -3 ° C (for TKein); and 1090 g / dm3 (for p).
The end point of the ordinates corresponds in this case to the following conditions: 35 t / h for (nt> '); +7 ° C (for TKein); and 1, 140 g / dm3 (for p).
The intermediate values on the ordinates must be interpolated linearly between the two aforementioned points.
The values of the ordinates at mid-length of the ordinates are thus: 25 t / h for ("" '); 2 ° C (for TKein); and 1115 g / dm3 (for p).
The large constancy of p as a function of time reflects the remarkable stability of Y despite a considerable and abrupt change in m> A overshoot of Y does not occur.
The purity of the pure acrylic acid separated in the washing columns reaches, over the total operating time, a value greater than 99.7% by weight, although the increase of m 'in the respective washing column reproduced in part.
The content of the mother liquor (the residual liquid phase R) in acrylic acid in the suspension S is 91.34% by weight after the increase in
US Provisional Patent Application Serial No. 60/971969, filed September 13, 2007, is appended to this application as indicated in the literature. With respect to the above teaching, many modifications and many derivations of the present invention are possible. It can therefore be assumed that the invention, within the scope of the appended claims, also described differently than the specific description, can be realized.

权利要求:
Claims (30)
[1]
A process for the continuous separation of a target product X in the form of a finely divided crystallizate of the target product X from a liquid phase P containing the target product X as well as different components of the target product X to using a heat exchanger having a secondary space and at least one primary space, wherein the secondary space and the at least one primary space are spatially separated from each other by at least one material separating wall which serves as a surface for the transfer of heat from the secondary space into the at least one primary space, into which a liquid phase P is introduced continuously into the secondary space of the heat exchanger, while the at least one space at least one fluid coolant so that it is formed in the secondary space while leaving a residual liquid phase R remaining liquid phase P, a finely divided crystallizate of the target product X, which is suspended in the residual liquid residual phase R, which contains, in comparison with the liquid phase P, the different components of the target product X in the enriched state and whose the target product content X reaches at least 70% by weight, while retaining a suspension S, having a degree of crystallization Y, of finely divided crystallizate of the target product X in the residual liquid phase R and withdrawn from the secondary space of the heat exchanger continuously the suspension S, characterized in that, to adjust the desired degree of crystallization Y of the suspension S withdrawn from the secondary space of the heat exchanger, the difference obtained from FIG. respective operating point using a computer between the ¥ QKrY heat transfer flux corresponding to the degree of crystallization Y and developing in a manner re calculated in the secondary space and the difference formed between the heat flow Qam otherwise removed in total from the secondary space of the heat exchanger and the heat flow Qein routed in total in the secondary space of the heat exchanger .
[2]
2. Method according to claim 1, characterized in that the content of the liquid residual phase R in target product X is greater than or equal to 80% by weight.
[3]
3. Method according to claim 1, characterized in that the content of the residual liquid phase R of target product X is greater than or equal to 90% by weight.
[4]
4. Method according to any one of claims 1 to 3, characterized in that the target product X is acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone.
[5]
5. Method according to any one of claims 1 to 4, characterized in that the liquid phase P contains at least two different components of the target product X.
[6]
6. Process according to any one of claims 1 to 5, characterized in that the liquid phase P is a crude acrylic acid, which has the following contents: 85 85% by weight of acrylic acid, 100 100 ppm by weight at <10% by weight of acetic acid, -10 ppm by weight to 5% by weight of propionic acid, up to 5% by weight of low molecular weight aldehydes, up to 3% by weight of polymerization inhibitors, 0 to 5% by weight of diacrylic acid, up to 10% by weight of water.
[7]
7. Method according to any one of claims 1 to 6, characterized in that it comprises in addition to the method step according to claim 1 the following process steps: b) separation of the suspension S removed from the secondary space of the heat exchanger in crystallization of the target product X and in the residual liquid phase R, c) melting at least part of the separated crystallizate of the target product X, and d) recycling at least part of the molten crystallite of the target product X in step b) and / or in the step of the continuous separation process of the target product X according to any claim.
[8]
8. Method according to any one of claims 1 to 6, characterized in that a connection is connected to a continuous separation process of the finely divided target product crystallizate X contained in the suspension S, wherein: the suspension S is conveyed to a washing column, which has a washing column wall, which encloses a treatment space, - by maintaining the crystallizate contained in the suspension S and forming a crystallizate bed in the treatment space, it delivers from from the suspension S conveyed to the treatment space through filtering devices a residual liquid phase R coming from the treatment space, - the crystallizate bed is conveyed into the treatment space, - in the space of treatment in the direction of advancement of the crystallizate bed acts at least a different force of the gravitation, which advances the crystallizate bed in the treatment space, - in the counter-current treatment space with the crystallizer bed, a pure melt is conveyed consisting of crystallized crystallized and separated previously after this washing column process so that it forms in the bed of crystallizing a front of washing, which divides the crystallizate bed into a mother liquor zone and a pure melt zone, and at the end of the washing column opposite the introduction of the suspension S is continuously extracted a crystallizate which developed in the wash column in a solid and / or melted form. ''
[9]
9. A process according to claim 8, characterized in that the target product is acrylic acid and is connected to another process in which the crystallized and separated acrylic acid crystallizate is subjected to polymerization with itself or with other compounds having at least one monoethylenic unsaturation.
[10]
10. Process according to any one of claims 1 to 9, characterized in that the liquid phase P is introduced into the secondary space of the heat exchanger with the mass current intensity mp and the method comprises the determination of the intensity of the mass current njp and / or the intensity of the volumic current belonging to mp.
[11]
11. The method of claim 10, characterized in that the determination of the mass current intensity mp is done using a Coriolis mass flow measurement device, or a swirling flow measurement device. or a magneto-inductive flow measurement device or a floating-body flow measurement device.
[12]
12. Method according to any one of claims 1 to 10, characterized in that the liquid phase P is introduced at a Tpein temperature in the secondary space and the suspension S is removed from the secondary space at a temperature Tsaus and the The method comprises the determination of Tpein, Tsaus and the difference Tpein-r aus * s
[13]
13. The method of claim 12, characterized in that the determination of Tpem and Tsaus is carried out respectively with a resistance thermometer.
[14]
14. The method of claim 13, characterized in that the resistance thermometer is a platinum resistance thermometer.
[15]
15. Method according to any one of claims 1 to 14, characterized in that the fluid refrigerant componentconcentrating at least one primary space is introduced at a temperature Ti <ein in the at least one primary space and is removed from the at least a primary space at the temperature Tk3us and the method comprises the determination of Τκβιπ, TKaus and the difference TKaus-TKein.
[16]
16. The method of claim 15, characterized in that the determination of TKein and TKaus is carried out respectively with a resistance thermometer.
[17]
17. The method of claim 16, characterized in that the resistance thermometer is a platinum resistance thermometer.
[18]
18. The method of claim 15, characterized in that the determination of the difference TKaus-TKein is carried out with two resistance thermometers and only a transformation device for measuring the temperature difference.
[19]
19. The method of claim 18, characterized in that the temperature difference measuring transformation device is a fieldbus measuring transformer.
[20]
20. Process according to any one of claims 1 to 19, characterized in that the fluid refrigerant flowing through the at least one primary space is introduced into the at least one primary space at the mass current intensity mK and the process includes determining the mass current intensity mK and / or the volume flow intensity belonging to mK.
[21]
Method according to claim 20, characterized in that the determination of the mass intensity mK is carried out using a Coriolis mass flow measurement device or a swirling flow measurement device or a magneto-inductive flow measurement device or a floating-body flow measurement device.
[22]
22. Process according to any one of claims 1 to 21, characterized in that the coolant passing through the at least one primary space is introduced into the at least one primary space at the temperature Τκθιη and, in the case where the difference between QKr and the difference Qaus -Qem is not infinitely small, the temperature TKein is changed.
[23]
23. Process according to any one of claims 1 to 22, characterized in that the target product X is acrylic acid, which has been produced by a heterogeneous catalytic partial gas phase oxidation.
[24]
24. Process according to any one of claims 1 to 23, characterized in that the target product X is acrylic acid and the liquid phase P returns to a fractional condensation and / or absorption of the gaseous product mixture. a heterogeneous catalytic partial gas phase oxidation for the manufacture of acrylic acid.
[25]
25. Process according to any one of claims 1 to 24, characterized in that the heat exchanger is a cooling disc crystallizer.
[26]
26. Process according to any one of claims 1 to 25, characterized in that a mixture of water and methanol or a mixture of water and glycol is used as the cooling agent.
[27]
27. A method according to any one of claims 1 to 26, characterized in that is connected to the method a determination of the mass density of the suspension S with a Coriolis mass flow measurement device.
[28]
28. Process according to any one of claims 1 to 27, characterized in that Y has a value of 0.10 to 0.50.
[29]
29. Process according to any one of claims 1 to 27, characterized in that Y is 0.20 to 0.40 or 0.25 to 0.35 or 0.30.
[30]
30. A method of manufacturing a target product X, characterized in that it comprises a method according to any one of claims 1 to 8 or according to any one of claims 10 to 29.

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法律状态:

优先权:

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申请号 | 申请日 | 专利标题

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US97202307P| true| 2007-09-13|2007-09-13|

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US97196907P| true| 2007-09-13|2007-09-13|

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US97202307|2007-09-13|

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DE102007043758A|DE102007043758A1|2007-09-13|2007-09-13|Target product continuous separating operation in form of fine crystals from liquid phase, includes heat exchanger having secondary space and primary space|

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DE102007043759A|DE102007043759A1|2007-09-13|2007-09-13|Procedure for continuous separation of target product in the form of fine particle of crystallisate, comprises indirectly operating a heat exchanger having primary and secondary areas, which are spatially separated with one another|

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DE102007043748A|DE102007043748A1|2007-09-13|2007-09-13|Method for separating target product i.e. acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone in form of fine crystallized product, involves utilizing heat exchanger, where heat flow is gathered from heat exchanger|

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DE102007043748|2007-09-13|

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DE102007043759|2007-09-13|

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DE102007043758|2007-09-13|

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US97196907|2007-09-13|

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