PROCESS FOR THE IMPLEMENTATION OF A CONTINUOUS SEPARATION OF TARGET PRODUCT X IN THE FORM OF A CRYST

专利摘要:
Process for carrying out a continuous separation of a target product X in the form of a finely distributed crystalline product from a liquid phase P containing the target product X and constituents different from the target product X by virtue of a product crystallization in suspension by cooling in the secondary space, against which the liquid phase P flows continuously, of an indirect heat exchanger with simultaneous continuous crossing of the primary space of the indirect heat exchanger by a refrigerant as well as continuously withdrawing a suspension of crystallization product S having a degree of product crystallization Y from the secondary space in two operating states I and II, the temperature of the refrigerant in the state operating state I, being lower than it is in the operating state I, the mass flow intensity of the liquid phase P being greater than it is in the operating state I and the molar share of the different constituents of the target product X in the liquid phase P being greater than it is in the operating state.
公开号:BE1018538A3
申请号:E2008/0501
申请日:2008-09-11
公开日:2011-03-01
发明作者:Joerg Heilek；Ulrich Hammon；Klaus Joachim Muller-Engel
申请人:Basf Se；
IPC主号:

专利说明:

PROCESS FOR THE IMPLEMENTATION OF A CONTINUOUS SEPARATION OF TARGET PRODUCT X IN THE FORM OF A CRYSTALLIZED PRODUCT FINELY DISTRIBUTED FROM THE TARGET PRODUCT X
The present invention relates to a method for carrying out a continuous separation of a target product X in the form of a finely distributed crystalline product of the target product X from a liquid phase P consisting of the target product X and as different constituents Bi of the target product X, whose total molar fraction in component Bi has the. MBges value, 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 respectively by at least one material partition, which serves as a surface for the heat transfer of the secondary space at least one primary space, in which a liquid phase current P, and a mass flow mx of target product X as constituent of that it is introduced into the secondary space of the heat exchanger, while the at least one primary space is traversed simultaneously by at least one fluid cooling medium, which is fed to the at least one primary space at the temperature TKein , so that in the secondary space is formed from the liquid phase P, with subsistence of a liquid residual phase R, the finely distributed crystalline product of the target product X, which is suspended in the residual liquid phase R remaining, which contains, in comparison with the liquid phase P, enriched the constituents different from the target product X and whose target product content X is at least 70%, with obtaining a suspension S having a degree of product crystallization Y, of the finely distributed crystalline product of the target product X in the residual liquid phase R, a stream of the suspension S is withdrawn continuously from the secondary space of the heat exchanger, in states I and II different from each other, wherein in the operating state I, the at least one fluid cooling medium TKein temperature (I) is fed to the at least one primary space and the current of liquid phase P having a mass flow mx (I), contained in this same current, of target product X is brought to the secondary space, and in the operating state II, the at least one cooling medium, fluid of TKein temperature (II) is fed to the at least one primary space and the liquid flow current P of mass flow mx (II), contained in the same stream, of target product X being fed to the secondary space, provided that mx, ( II)> mx (I) and TKein (II) <TKein (I).
Methods for the continuous separation of a target product X in the form of a finely distributed crystalline product composed of a liquid phase P containing the target product X as well as constituents Bj different from the target product X using an indirect heat exchanger having a secondary space and at least one primary space (cooler or crystallizer) are known (see for example the documents DE-A 10 332 758, WO 2004/035 514, "Research Disclosure Database" Numbers 496005 and 479008 and the German application with the reference 10 2007 004 960.0).
By transferring heat from the liquid phase P, fed to the secondary space through the partition (the heat transfer surface) separating the secondary space and the at least one primary space from each other, to in the cooling medium flowing in the at least one primary space, the liquid phase P cools until the saturation limit of the liquid phase P with target product X is exceeded and the supersaturation is compensated by formation of a crystallized product of the target product X.
The term "degree of crystallization Y" of the suspension of crystallized product S suspended from the crystallized product of the target product finely distributed in the residual liquid phase R means in this document the mass fraction but also the mass fraction of the finely divided crystallized product. contained in the suspension S on the total mass of the suspension S. The degree of crystallization Y is thus calculated in the form of a fraction consisting of the mass of crystalline product mKr, Y contained in the suspension S for the degree of crystallization Y divided by the total mass ms of the suspension:
The degree of crystallization Y of the suspension S is thus necessarily between 0 and 1. The value "0" corresponds to an exclusively liquid phase and the value "1" corresponds to an exclusively solid phase (ie say, that in both cases no suspension is no longer present).
If a constituent Bi is contained in the liquid phase P in the molar quantity and the molar quantity n is calculated here from the mass, in which the component Bi is contained in the liquid phase P, divided by the molar mass of component Bi) and if the target product X is contained in the liquid phase P in the molar quantity nx (the molar quantity nx is calculated here from the mass, in which the target product X is contained in the liquid phase P, divided by the molar mass of the target product X), then the molar fraction Mb1 of the constituent Bi contained in the liquid phase P is understood to be the quotient of the molar number ni, divided by the sum formed from the molar number nx and the molar numbers respective constituents, different from the target product X, contained in the liquid phase P. That is,
assuming that the liquid phase P contains in total I of target product X and of constituents Bi different from each other.
By total molar fraction MBges of the different Bif constituents of the target product X, contained in the liquid phase P, this document comprises the sum of all the individual values Mb1 calculated for the respective constituents Bi.
Correspondingly, the molar fraction Mx, in which the target product X is contained in the liquid phase P, is defined by Π y
Mx = - ^ - nX + Σ ni i = l
We admit the relation Mx + MBges = 1.
A crystallization separation of a target product X from a liquid phase P containing the target product X as well as the different constituents of the target product X is used in particular to separate the target product X from the by-products formed in the context of his preparation. The preparation of the target product X can also be carried out immediately immediately by chemical reaction in the liquid phase. Naturally, the preparation of the target product X can also be carried out for example in the gaseous phase, from which the target product X can then be transferred into the liquid phase, as a rule by means of condensation and / or absorption, normally in common with some secondary components accompanying the target product X in the gas phase.
The crystallization separation of the target product X can then take place in the form of a "fine" thermal separation process essentially directly from the liquid phase occurring as part of the preparation of the target product X and containing the target product X and the secondary components s.
Prior to the use of a crystallization separation of the target product X, however, the liquid phase mentioned above is initially frequently subjected to at least one "diffuse" thermal separation process in order to separate a partial amount of the secondary components mentioned. above, of the target product X.
A diffuse separation process is here defined as a separation process, in which, from a thermodynamic point of view, the composition of the phase, enrichedly containing target product X and forming during the use of the process is strongly thermodynamically dependent on the composition of the mixture to be subjected to the separation process (see for example the Mc-Cabe-Thiele diagram). Simple distillation, rectification, absorption, fractional condensation, desorption, extraction, stripping, azeotropic rectification, etc. belong for example to diffuse thermal separation processes.
In contrast to this, crystallization separation is a fine thermal separation process in that the composition of crystals forming is thermodynamically largely independent of the composition of the initial liquid mixture (see also the documents DE-A 2005 009 890 and DE-A 10 300 816).
The advantage of sharp diffuse separation methods is generally that they can be implemented with high space-time yields. The disadvantage of diffuse separation methods is however that the separation efficiency achieved by them is comparatively limited.
The disadvantage of the fine separation processes is their usually comparatively limited space-time yield, for a separating action however the highest in normal operation.
Therefore, the two principles of separation are also used, in the prior art mentioned above, frequently in the following combination.
For the product mixture occurring as part of the preparation of the target product X, initially at least one diffuse thermal separation process is used and the liquid phase P is produced, which already contains enriched, compared to its weight share in the product mixture, the target product X. 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 crystallization isolation of the target product X, and the residual liquid phase R remaining (which is also frequently called mother liquor), which contains comparatively enriched secondary components, is at least partially recycled in at least one previously used diffuse thermal separation process. In this way, the advantages of the two principles of separation can be simultaneously highlighted.
This is why a liquid phase P to be subjected to a crystallization separation of the target product X and having a target product X (and this also concerns the liquid phases P falling within this application) contains in many cases at least two, most at least three or four times, frequently at least five or six and often at least seven or eight, or at least nine or ten different secondary components of the target product X (secondary components of this type are therefore contained in the liquid phase P within the meaning of this application, when they can be demonstrated for example by gas chromatography, liquid chromatography or in another way (for example as water by Karl Fischer titration) as a component of this. this.
In addition to secondary products characteristic of the conditions of preparation of the target product X, the liquid phase P containing the target product X may additionally contain solvents or a mixture of solvents and / or adjuvants co-used for the separation of the target product. X from a mixture of reaction products in the context of the production of the liquid phase P (for example absorption agent, extraction agent, etc.). That is, the liquid residual phase R can be, for example, fusions of the target product X and impurities as well as solutions composed of target product X and solvents (or mixtures of solvents) as well as as a rule, impurities.
To a method, as described in the preamble, of continuous crystallization separation of a target product X from a liquid phase P containing the target product X as well as secondary components (constituents) different from the target product X, usually connects a continuous process for separating the crystallized product from the target product X suspended in the suspension (of crystalline product) S in the residual liquid phase R with the residual liquid phase R ("water mother").
Such separation can be undertaken for example by filtration, by sieving centrifugation and / or in washing columns, as described for example in WO 01/77 056 and the prior art cited. Normally, such separation also involves washing the separated crystalline product to remove the adherent mother water from the crystalline surface. Such washing may take place for example with the melting of the crystallized product previously separated and washed.
It is furthermore essential for effective continuous separation (as well as separation action and space-time yield) of the crystallized product in suspension from the remaining mother liquor (liquid residual phase R), that the device The separation ratio used for the separation is adapted in its design (in its model) to the degree of crystallization Y of the suspension (of crystallized product) S and that Y remains stable within certain limits during the continuous operation.
The degree of crystallization Y of the suspension S thus influences, for example, all the technical flow properties of the suspension S. However, it also influences, for example, the internal structure of the crystallized product cake to be washed or the bed of crystallized product to be washed and co-determines through this also the washing action as well as the pressures prevailing during washing. The latter can in particular increase abruptly (eg exponentially) in unfavorable cases for example for wash columns with constrained transport in the form of a specified separation device in the case of an undesired increase in the degree of crystallization Y for otherwise identical mass flow rates, and cause a safety shutdown or damage to the separation device. However, the degree of crystallization Y also influences the permeability of the crystallized product cake or the crystallized product bed for the residual liquid phase R (the mother liquor remaining during the separation by crystallization). In addition, in the case of low degrees of crystallization Y when using pusher centrifuges for crystalline product separation, there may be an overflow of the crystallized product slurry. In hydraulic wash columns, too low degrees of crystallization Y may result in the loss of stable crystallized product bed.
Depending on the respective separation problem (including the separation device used) as well as the type and size of crystals constituting the crystallized product, the ideal degree of crystallization Y is frequently in the range of 0.10 to 0.50. with a higher frequency in the range of 0.20 to 0.40, and is particularly frequently 0.25 to 0.35 or 0.30.
For a continuous separation, as described in the preamble, of a target product X in the form of a finely distributed crystalline product of the target product X from a liquid phase P containing the target product X as well as the different constituents of the product X, using a crystallization method described in the preamble of this document, it is therefore desirable that the degree of crystallization Y at the base of the design of the device is kept constant within certain limits (which are specific to the respective separation problem as well as to the separation system respectively used) over the duration of implementation of the separation process.
Advantageously, the product of the degree of crystallization Y by the number 100 must not deviate, over the duration of implementation of the separation process of more than ± 30%, at best not more than ± 20%, preferably not more than ± 10%, more preferably not more than ± 5%, preferably not more than ± 4%, more preferably not more than ± 3% and most preferably not more than more than ± 2% or not more than ± 1% of the corresponding product of the desired setpoint for Y or the stationary value (as a reference base) of Y.
For a liquid phase stream P unmodifiedly fed to the secondary space of the heat exchanger over the duration of operation, as well as for the stream of fluid cooling medium having passed through unmodified the at least one a primary space, the degree of crystallization Y of the suspension (of crystallized product) S discharged continuously from the secondary space is in particular determined by the temperature Tkein, to which the fluid cooling medium is brought to the at least one primary space .
In most cases, the market demand is for example a target product X
(For example to an organic target compound such as acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone) but does not represent a stable value, and fluctuates on the contrary over long periods. For example, it can increase inconstantly. Instead of reacting with an additional production facility to a market need having increased in such a way, one can also react to it with an increase in the space-time yield of the target product X in production facilities already built up. . Conversely, the space-time yield of the target product X in these same production facilities must therefore be lowered again in the case of falling demand from the market.
Such a transition from a stationary operating state to another stationary operating state is possible in the case of crystallization separation of the target product X from the liquid phase containing it, as described in the preamble to this document, for example by increasing or stopping the liquid phase flow P to bring to the secondary space of the heat exchanger according to a demand of the target product market X increasing or decreasing , and TKein is simultaneously adjusted so that a stream of crystallized product increased or decreased according to the change in market demand can be output as a constituent of the suspension stream S.
If the liquid phase current P to be supplied to the secondary space of the heat exchanger is increased, TKein is normally decreased and if the liquid phase current P to be supplied to the secondary space of the heat exchanger is decreased. , TKe; Ln is generally increased again.
It has proved disadvantageous, when using a method as described above, that the tendency to form crystallization incrustations on the wall facing the secondary space of the at least one partition respectively separating the at least one primary space of the secondary space also increases with the increase of TKein, as the ability of the incrustation to remain stuck on the partition. With the formation of layers of crystallized product remaining stuck on the wall, however, there is a slow decrease in the heat transfer through the wall, which goes against the objective of crystallization separation of the target product X. For the reason mentioned above, the side facing the secondary space of this type of partition works in most cases being wiped. That is to say that crystals of the target product X continuing to adhere to the relevant face of the partition are wiped off continuously (scraped or scraped continuously) by means of a wiper device driven into the secondary space (For example similar to windshield wipers of an automobile), and suspended in the suspension S. As a rule, the wiper simultaneously causes a stirring of the suspension of crystalline product S in the secondary space.
However, a tendency towards incrustation by crystallization, increasing with the decrease of TKein, proves to be a disadvantage, also in the case of wiped partitions, increased wear of the comparatively expensive wiping devices occurring each time. Moreover, the wiping intensity to be added increases and, in an extreme case, the wiper device is no longer able to cope with the wiping task to be filled, so that stubborn incrustations can form in which the brooms remain. possibly stuck. Crystallization incrustations of this type can additionally optionally spontaneously detach in the form of comparatively large individual pieces when they reach a defined size and cause a variety of subsequent damage.
They may for example cause damage to the pump used for transporting the suspension of crystallized product S output from the secondary space (for example a centrifugal pump).
In the most serious case, the crystallization process must be interrupted and the crystallized product inlay formed must be melted. The wiper device may possibly be damaged in the context of an incrustation formation.
In this context, the object of the present invention is to provide a method as described in the preamble of this document, which has the damaging consequences presented above with a reduced amplitude as possible.
Accordingly, there is provided a method for carrying out a continuous separation of a target product X in the form of a finely distributed crystalline product of the target product X from a liquid phase P consisting of the target product X as well as than of constituents Bi different from the target product X, whose total molar fraction of component Bi has the value MBges, by means of an indirect heat exchanger having a secondary space and at least one primary space, in which the space secondary and the at least one primary space are spatially separated from each other respectively by at least one material partition, which serves as a surface for the heat transfer of the secondary space at least one primary space, wherein a current of liquid phase P, and a mass flow mx of target product X as a constituent thereof, is introduced into the secondary space of
the heat exchanger, while the at least one primary space is traversed simultaneously by at least one fluid cooling medium, which is fed to the at least one primary space at the temperature TKein, so that in the secondary space is formed from the liquid phase P, with the support of a liquid residual phase R, of the finely divided crystalline product of the target product X, which is suspended in the residual liquid phase R
subsistent, which contains, in comparison with the liquid phase P, enriched the different constituents of the target product X and the content of the target product X is at least 70%, with obtaining a suspension S having a degree of product crystallization Y, of the finely distributed crystalline product of the target product X in the residual liquid phase R, a stream of the suspension S is withdrawn continuously from the secondary space of the heat exchanger, in operating states I and II different from each other, wherein in the operating state I, the at least one fluid cooling medium TKe; Ln (I) is fed to the at least one primary space and the liquid phase stream P having a mass flow rate rhx (I), contained in this same stream, of target product X is fed to the secondary space, and in operating state II, the at least one fluid cooling medium of temperature TKein (II ) is brought to the at least one primary space and the liquid flow current P of mass flow mx (II), contained in the same stream, of target product X being fed to the secondary space, provided that mx (II)> mx (I) and TKein ( II) <TKein (I), characterized in that the total molar fraction MBges of different constituents of the target product X in the liquid phase P brought to the secondary space is greater in the operating state I than it is in the operating state II.
That is to say, the solution provided by the present invention to combat the tendency to incrustation increased on the side facing the secondary space of the at least one partition respectively separating the at least one primary space of the secondary space, which slowly sets in place with the decrease of TKein for a mx simultaneously increased under otherwise unmodified operating conditions, is to increase in a targeted way the total molar fraction of the constituents Bi (that is to say MBges) different from the target product X in the liquid phase P brought to the secondary space.
Finally, this solution formulation is to be reduced to the fact that the temperature of a liquid phase P containing the target products X, for which the formation of the crystallized product of the target product X dissolved in the inside takes place from this liquid phase (the possibility of occurrence of supersaturation events being neglected) is all the lower as MB9es is large in the liquid phase P. This phenomenon is also referred to in the literature as a "point depression". crystallization "molar.
The link with the trend towards increasing / decreasing incrustation is likely to grow as follows.
The at least one partition between the secondary space and the at least one primary space normally has, in an indirect heat exchanger, a comparatively high thermal conductivity, so that the temperature on the side facing the secondary space of a This partition is not very far from the temperature of the fluid cooling medium passing through the primary space. Simultaneously, a boundary layer consisting of the target product X and the liquid phase containing different constituents Bi of the target product X is normally on the side facing the secondary space of such a partition.
If a crystallized product formation ("layer crystallization") occurs in this boundary layer, the crystallites from the individual crystallization seeds increase additionally on each other until the total mole fraction of the constituents Bi contained in the mother water remaining liquid in the boundary layer is so large that the temperature in the boundary layer can no longer condition any settling solids.
If the total mole fraction present in the boundary layer prior to crystalline product formation, B + constituents contained in the boundary layer is already comparatively higher, the growth of crystallized product terminates for temperature conditions identical to a moment where the weight share of the mother liquor remaining liquid in the boundary layer is comparatively greater than the level of the boundary layer. These parts remaining liquid however disturb the anchoring between the different crystallites and their adhesion to the side facing the secondary space of the partition wall between the secondary space and the at least one primary space. Both of the above mentioned activities reduce the formation of incrustations of crystallized product on the side facing the secondary space of the separation surface mentioned above. (If the total molar fraction, contained in the boundary layer prior to the formation of crystalline product, of constituents Bi is on the contrary lower, the growth of crystallized product ends, for identical temperature conditions, first at a time where the weight share of liquid mother water remaining is still lower, which promotes the tendency to incrustation). In other words, a total molar fraction increased to different constituents Bi of the target product X, contained in the liquid phase P, also guarantees, for a comparatively low TKein, guarantees the permanence of a traceable proportion of liquid mother liquor. in the boundary layer, and thus decreases the tendency to incrustation identified.
Surprisingly and according to the present invention, it is essential here that an increase of MBges in the liquid phase P conditions a further drop in the temperature at which crystalline product formation is used in the liquid phase P, and that the trend This low crystalline product formation temperature is, however, less pronounced than for the lower crystalline product formation temperature belonging to MBges. Among other things, this behavior is likely to be related to the fact that, in the case of MBges increased in the liquid phase P, the formation of crystallized product is associated with the formation of an increased number of seeds of crystallized product.
The difference between mx (I) and mx (II) may, relative to the arithmetic mean of the two mass flow rates, be for the process according to the present invention at least 5%, or at least 10%, or at least 15%, or at least 20%, or at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least minus 7 0%, or at least 80%, or at least 90%, or at least 100% or more. As a general rule, the difference reported in the same way, however, is not more than 190%, most of the time not greater than 180% and frequently not more than 170%.
The difference between TKein (II) and TKein (I) is normally designed so that for constant current currents of the coolant stream flowing through the at least one primary space, the degree of crystallization Y (II) ) the suspension of crystallized product S taken from operating state II from the secondary space and the degree of crystalline product Y (I) of the suspension of crystalline product S taken from operating state I from the secondary space is differentiated from the other, by the mean of the arithmetic mean of Y (I) and Y (II) by not more than 20%, advantageously not more than 10%, preferably not more than 5%, particularly preferably not more than 3% and particularly preferably not more than 1%.
In many cases, the difference between TKein (II) and TKein (I) is up to 30 K or more. The difference between TKein (II) and TKein (I) is also frequently only up to 25 K, or up to 20 K, or up to 15 K, or up to 10 K, or until to 5 K. But the process according to the present invention naturally also suits, when the difference between TKein (II) and TKein (I) is only 0.1 to 5 K, or only 0.2 to 4 K K, or only 0.3 to 3 K, or only 0.4 or 0.5 to 2 K, or 0.7 to 2 K, or 0.9 or 1 to 2 K. The difference between TKein (II) and TKein (I) is often at least 0.1 K or at least 0.2 K, or at least 0.3 K.
For the increase of the total molar fraction MBges up to the desired value in the operating state II, the liquid phase P containing the target product X can theoretically be added to each of the constituents (types of constituent) Bi contained within in a manner conditioned by the preparation. But such constituents, which were not contained in a manner conditioned by the preparation in the liquid phase P, can also be added theoretically for the increase of the total molar fraction MB9es up to the desired value in the state of operation II. But two of the above-mentioned types of different constituents of the target product X can also naturally be added for the increase of MBges in the liquid phase P.
Advantageously according to the present invention, the total molar number, contained in the operating state II in the liquid phase P brought to the secondary space (the liquid phase P (II)), of constituents Bi, different from the target product X, contained in the liquid phase P (II) whose molecular weight is less than three times (preferably less than twice) the molecular weight of the target product X (preferably less than the molecular weight of the target product X), is greater than the number total molar, contained in the operating state I in the liquid phase P (the liquid phase P (I)) supplied to the secondary space, of constituents Bi, different from the target product X, contained in the liquid phase P (I ), whose molecular weight is less than three times (preferably less than twice) the molecular weight of the target product X (preferably less than the molecular weight of the target product X). The total molar number is here the sum of all the molar numbers Ni of the constituents Bi contained respectively in the liquid phase P, provided that the molecular weight of the constituents Bi taken into account for the calculation of the sum is less than the triple of (or at least twice the or the molecular weight of the target product X.
That is to say, advantageously according to the present invention, such constituents Bi, whose molecular weight is less than twice the molecular weight of the target product X and preferably less than the molecular weight of the target product X (conditions 1) are co-used (or exclusively used) for increasing the total molar fraction MBges to its value in operating state II (also referred to as MBges (II) in this document), from its value in the operating state I (also referred to as MBges (I) in this document Normally, both the target product X and the constituents Bi, different from the target product X, from the liquid phase P are dissolved in the liquid phase P.
In a preferred manner according to the present invention, constituents Bi, whose depletion coefficient BB1, in the context of the continuous crystallization separation (according to the present invention) of the target product X, is at least> 5, in particular preferred> 10 and more preferably> 15 (conditions 2) are further co-used (or exclusively used) for increasing the total molar fraction MBges to its value in the operating state II (to from its value in the operating state I). By depletion coefficient AB1, the concentration ratio of the concentration, remaining in the mother liquor, of the component Bi on the concentration, remaining in the crystallized product, of the constituent Bi (expressed respectively as percent by weight relative to the total amount of mother liquor (or residual liquid phase R) remaining or the total amount of crystalline product formed). A separation of crystalline product / mother liquor up to more than 90% by weight, preferably up to more than 95% by weight, or 97, or 98, or 99% by weight of the total amount In general, the presence of mother liquor is sufficient for the determination of AB1 (the influence of the residual moisture on the crystallized product is generally negligible). The values mentioned above for ABi preferably relate to the combination, used in the preparation of the target product X, of suspension crystallization and subsequent separation of the crystallized suspension product formed from the suspension. S. suspension
Particularly preferably according to the present invention, Bi constituents which satisfy both a condition 1 and a condition 2 are co-used (or exclusively used) for increasing the total molar fraction MBges to its value in operating state II (from its value in operating state I).
Very particularly preferably according to the present invention, Bi constituents which satisfy both a preferred condition 1 and a preferred condition 2 are co-used (or exclusively used) for increasing the total molar fraction MB9 to to its value in operating state II (from its value in operating state I).
There is a particular advantage that the constituents Bi mentioned above are those whose preparation is conditioned by their type in the liquid phase P as well as those contained therein.
As a general rule, the increase of MBges up to its value for the operating state II occurs only to the extent that this is required by the technique of use for reasons of decreasing the incrustation, because an increased separation expense is associated with the increase of MBges in the liquid phase P brought to the secondary space during the separation of the target product X from the liquid phase P.
As a rule, the increase of MBges
(I) up to MBges (II) during the process according to the present invention takes place at least in an order of magnitude where the use temperature of the crystalline product formation of the liquid phase P
(II) is at least 0.1 K, often at least 0.2 K and frequently at least 0.3 K below the crystallization product use temperature of the liquid phase P (I). Crystallized product formation temperature of a liquid phase P is understood here to mean the temperature which is present in the liquid phase P at the moment when heat is supplied, with constant stirring (in the ideal case) to this suspension of crystalline product S, from a suspension of crystalline product S produced with the liquid phase P by cooling thereof, to melt the crystals contained in the suspension of crystalline product S, and where the last crystallized product is already melted. It is also partially referred to in the literature as the dissolution temperature.
In the process according to the present invention, the increase of MBges (I) to MBges (II) frequently takes place in an order of magnitude where the use temperature of the crystalline product formation of the liquid phase P (II) ) is up to 30 K (or up to 20 K, or up to 15 K, or up to 10 K, or up to 5 K, or up to 4 K, or up to 3 K, or up to 2 K, or up to 1 K, or up to 0.5 K) below the use temperature of crystalline product formation of the liquid phase P (I).
In a manner appropriate for the use technique, the increase of MBges (I) to MBges (II) can be undertaken in the liquid phase P in a simple manner, so that the (incorporated) additional constituents Βχ envisaged for a liquid phase P produced separately prior to its arrival in the secondary space of the indirect heat exchanger in the desired order of magnitude. Such a procedure is advantageous, inter alia, insofar as one omits (or decreases, when the new operating state (I) is a state other than the original operating state (II)) the additional quantities of constituents Βχ again in a simple way when changing from an operating state (II) to an operating state (I). When switching from an operating state I to an operating state II, the operation of the operating state I is preferably maintained initially, so that only MB9es are increased in an order of magnitude desired. TKein will then be lowered to essentially maintain Y, as the crystallization temperature declines in the mixture of substances in the secondary space. As a result, mx is increased from mx (I) to mx (II) (by correspondingly increasing the current intensity of the liquid phase P brought to the secondary space) and by continuously lowering TKein associated for purposes of maintaining extended Y. During the transition from an operating state II to an operating state I, it can proceed in essentially the opposite way.
That is, we will initially lower mx (II) again to mx (I) and thus increase again in a TKein-like manner, to essentially maintain Y. As a result, we lower MBges (II) up to MBges (I) and after that, one increases TKein in an order of magnitude in which the crystallization temperature increases in the mixture of substances in the secondary space, until the desired operating state (I) is reached.
That is, when changing from an operating state I to an operating state II, the increase of MBges (I) to MBges (II) advantageously takes place prior to the increase from mx (I) to mx (II). The lowering of mx (II) to mx (I) during the transition from an operating state II to an operating state I instead has preceded the lowering of MBges (II) to MBges ( I).
When changing from an operating state II to an operating state I, a lowering of MBges (II) to MBges (I) is also advantageous insofar as, for MBges (II) lower, the crystallized product , separated according to the present invention, the target product X has a coarser particle size composition, which normally facilitates the subsequent separation of the crystallized product and the residual liquid phase R remaining. A lower value of MBges is also advantageous in the case of a separation of the crystallized product and the residual liquid phase R remaining using a pure fusion washing column comprising a forced transport of crystallized product through that it lowers the temperature difference between the liquid phase R and the pure melting (melting of the crystallized product previously separated from the target product X), which limits the recrystallization of the target product X from the pure melting used for washing of the crystallized product bed, and thus guarantees a measured permeability of the crystallized product bed for the liquid phase ("washing melting").
A low value of MBges is also advantageous if it is considered that the residual liquid phase R, separated from the crystallized product, still containing target product X, is normally recycled in a diffuse process co-used several times as part of the preparation. the liquid phase P to avoid losses of target product X (see for example Figure 5 of WO 01/77 056). If the liquid residual phase R thus recycled contains a smaller proportion of different constituents of the target product X, this reduces the separation expense in the diffuse separation step.
Naturally, the modification of MB9es in the liquid phase P can also be carried out in an integrated manner directly within the framework of the process for preparing the liquid phase P. This can for example take place by appropriately varying the number of stages of theoretical separation during the obtaining of the liquid phase P. This can for example take place in a simple manner through a variation of the reflux ratio in a separator column.
The operating state II or the operating state I can theoretically be the operating state situated temporally before, in the method according to the present invention.
The method according to the present invention is therefore suitable when the content of the residual liquid phase R (mother liquor), contained in the suspension S extracted from the secondary space, in target product X is> 70% by weight in the two states of the invention. operation I, II. But it is also suitable when the above-mentioned target product content X in the residual liquid phase R in the two operating states I, II 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 in the two operating states I, II is however <99.95% by weight, most of the time <99.9% by weight.
That is, the process according to the present invention is suitable in the case of liquid phases P, whose target product content X in the two operating states I, II is> 70% by weight, or> 75% by weight, or> 80% by weight, or> 85% by weight,> 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 aforesaid content of the liquid phase P introduced in the process according to the present invention to the secondary space of the heat exchanger into target product X in the two operating states I, II is however <99.995 % by weight, most of the time <99.99% by weight.
The temperature at which, in the process according to the present invention, the at least one fluid cooling medium is fed to the at least one primary space of the heat exchanger (TKein), is conveniently below the temperature at which the liquid phase P is fed simultaneously to the secondary space of the heat exchanger. TKein is also advantageously below the crystallization utilization temperature.
As the target product X, for the suspension crystallization carried out according to the present invention as cooling crystallization, for example saturated or unsaturated carboxylic acids such as acetic acid, propionic acid, propylene acrylic acid and methacrylic acid, or substituted aromatic substances (eg, halogens, methyl, carboxyl, hydroxyl and / or nitrogen (eg -NH2) 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 sodium or potassium salts (for example sulphates, chlorides, bromides and iodides).
The process according to the present invention is particularly suitable in the case of acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone as the target product X, since a significant proportion of the by-products occurring in the of their preparation has a lower molecular weight than the respective target product X.
If acrylic acid is the target product X, then water, diacrylic acid (Michael adduct), methacrylic acid, benzoic acid, formic acid, acetic acid and propionic acid Form Bi appropriate components according to the present invention, which can be added in a targeted manner to the liquid phase P containing the target product X (in this case acrylic acid), to increase their MBges.
In the case of acrylic acid as target product X, it is particularly advantageously used according to the present invention for the variation of MBges in the liquid phase P, so-called corrosive water (often referred to as also as "acidic water") (if necessary added to the liquid phase P), as it normally appears in the context of a separation of acrylic acid from the production gas mixture of an oxygenation in heterogeneously catalyzed partial gas phase of a C3 precursor compound of acrylic acid (for example propane, propylene, acrolein, propionic acid, propanol, glycerin and / or propionaldehyde) ( for example, WO 2004/035 514, German Application No. 10 2007 004 960.0, DE-A 10 243 625 and DE-A 10 323 758). In general, the corrosive water contains at least 60% by weight (frequently at least 70% by weight, most of the time at least 75% by weight, often at least 80% by weight) of water and at least 3% by weight. % by weight (frequently at least 5% by weight, more often at least 7% by weight, more often at least 9% by weight or at least 11% by weight) of acrylic acid.
The acidic water also contains, in small amounts, other secondary carboxylic acids occurring in the context of the heterogeneously catalyzed partial gas phase oxidation of the C3 precursor compound to obtain acrylic acid, such as acetic acid, propionic acid and formic acid. A use of corrosive water for a regulation according to the present invention of MB9es in the liquid phase P is thus particularly advantageous when using a wiring such as in FIG. 5 of the document WO 01/77 056 in the context of the preparation of acrylic acid (German Application No. 10 2007 004 960.0 also discloses suitable cabling). Through the use of corrosive water ("water containing acrylic acid from the process of preparation of acrylic acid" (or aqueous solution), this type of corrosive water can always be taken from a process of acrylic acid preparation, comprising a heterogeneously catalyzed partial gas phase oxidation of a C3 precursor compound of acrylic acid and a subsequent separation of acrylic acid from the phase oxidation production gas mixture gaseous, because water is an inevitable by-product of the heterogeneously catalyzed partial oxidation of the gas phase, the water content of this type of aqueous solution may be at least 60% by weight, or from at least 70% by weight, or at least 75% by weight, or at least 80% by weight), it is possible to minimize the total losses of acrylic acid occurring in the process for the preparation of acrylic acid. The corrosive water may also have already been co-used for the adjustment of MBges in the liquid phase P brought into the operating state I at the secondary space.
If methacrylic acid is the target product X, then water, acrylic acid and acetic acid form, for example, appropriate Bi components according to the present invention, which can be added in a targeted manner to the liquid phase P containing the target product X (in this case methacrylic acid), to increase its MB9es.
If p-xylene is the target product X, then water as well as n-xylene and o-xylene form, for example, suitable Bi components according to the present invention, which can be added in a targeted manner to the liquid phase. P containing the target product X (in this case p-xylene), to increase its MBges.
If N-vinylpyrrolidone (and also 1-vinyl-2-pyrrolidone) is the target product X, then water and 2-pyrrolidone form, for example, suitable Bi components according to the present invention, which may be added in a targeted manner to the liquid phase P containing the target product X (in this case N-vinylpyrrolidone), to increase its MBges.
The process according to the present 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 in the two operating states I, II for example compositions of 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 low molecular weight aldehydes, up to 3% by weight polymerization inhibitor weights, 0 to 5% by weight diacrylic acid (adduct of
Michael), and up to 25% by weight water; or> 80% by weight acrylic acid> 100 ppm by weight acetic acid up to <15% by weight> 10 ppm by weight propionic acid up to <5% by weight up to 5% by weight low molecular weight aldehydes , up to 3% by weight polymerization inhibitors, and 0 to 5% by weight diacrylic acid (adduct of
Michael), and up to 15% by weight water; or> 85% by weight acrylic acid> 100 ppm by weight acetic acid up to <10% by weight> 10 ppm by weight propionic acid up to <5% by weight up to 5% by weight low molecular weight aldehydes up to 3% by weight polymerization inhibitors, 0 to 5% by weight diacrylic acid (adduct of
Michael), and up to 10% by weight water; or> 90% by weight acrylic acid> 100 ppm by weight acetic acid up to <5% by weight> 10 ppm by weight propionic acid up to <2% by weight up to 2% by weight low molecular weight aldehydes up to 2% by weight polymerization inhibitors, 0 to 3% by weight diacrylic acid (adduct of
Michael), and up to 9% by weight water; or> 95% by weight acrylic acid> 100 ppm by weight up to <3% by weight acetic acid> 10 ppm by weight up to <2% by weight propionic acid up to 2% by weight low molecular weight aldehydes , up to 2% by weight polymerization inhibitors, and 0 to 2% by weight diacrylic 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 to 3% by weight protoanemonin
Crude acrylic acids can be obtained for example by methods known from the prior art (see, for example, WO 01/77 056, DE-A 10 332 758, DE-A 10 243 625, the German application with the reference 10 2006 057 631.4, the German application with the reference 10 2006 062 258.8, the German application with the reference 10 2007 004 960.0, WO 2004/035 514, the German application with the reference 10 2006 049 939.5, DE-A 10 2005 029 629, WO 03/041 832 and DE-A 2005 015 639 as well as the prior art cited herein).
These are generally crude acrylic acids which are obtained from the heterogeneously catalyzed partial oxidation production gas mixture of at least one C3 precursor compound of acrylic acid (e.g. propane, propylene, glycerine, acrolein, propionic acid, propanol and / or propionaldehyde).
For the process according to the present invention for producing the liquid phase P in the two operating states I, II, particular consideration is given here to a crude acrylic acid which has been produced from the production gas mixture of a heterogeneously catalyzed partial gas phase oxidation of at least one C3 precursor compound using at least one diffuse separation process. This is especially the case when the crystalline product of acrylic acid suspended in the liquid residual phase R in the suspension S occurring during the application of the process according to the present invention is separated from the residual liquid phase R at a constant temperature. such liquid phase P, and when the remaining residual phase R is recycled at least partially in at least one of the diffuse separation processes used for the preparation of the crude acrylic acid at. from the production gas mixture of the partial oxidation in the gas phase.
As already mentioned, corrosive water is in these cases the preferred additive for the adjustment according to the present invention of MBges in the liquid phase P.
The basic structure of such a combined use of a diffuse separation process and of the fine crystallization separation process is taught to us for example by the documents DE-A 19 606 877, EP-A 792 867 as well as EP-A A 1,484,308, EP-A 1,116,709 and in particular EP-A 1 015 410.
In the normal case, the diffuse separation process used for the co-production of the liquid phase P to be handled according to the present invention from the heterogeneously catalyzed gas phase partial oxidation production gas mixture of at least one C3 precursor compound of acrylic acid is a distillation, rectification, absorption, adsorption, extraction, desorption, stripping, destraction, (partial) condensation, fractional condensation, membrane separation process such as pervaporation / vapor permeation or a combination of such methods.
In the simplest case, the crude acrylic acid to be used for obtaining the liquid phase P can be the absorbed product and / or the partial condensed product and / or fractionally obtained by an absorption separation and / or or by condensation of the acrylic acid from the heterogeneous catalyzed gas phase oxidation production gas mixture of at least one C3 precursor presented herein. Recycling of the residual liquid phase R (mother liquor) separated from the suspension S is suitably carried out in the absorption and / or condensation (see, for example, EP-A 1818324).
Suitably, a combination, to be used in the described manner, of a diffuse and fine (crystallization) separation of acrylic acid from the gas phase partial oxidation production gas mixture has at least one output for secondary components, different from acrylic acid, having a boiling point under normal pressure (1 bar) higher than acrylic acid. This is advantageously from the point of view of the technique of use on the side of the diffuse separation process. As a general rule, for this outlet, the bottom liquid of a separating column will be used, from which the liquid phase P (the crude acrylic acid to be used as such) in itself is taken, or the substance stream to transform into the liquid phase thereafter, for example by means of lateral withdrawals and / or via a head withdrawal. Naturally, such an outlet may also be on the crystallization separation side according to the present invention. In this case, the outlet may consist of the residual liquid phase R (mother liquor). An outlet for secondary components having a boiling point at normal pressure lower than acrylic acid is usually additional to the diffuse separation process.
Advantageously, the acrylic acid contained as the target product X in the liquid phase P relates to a partial oxidation production gas mixture, which contains: 1 to 30% by volume of acrylic acid,> 0 or 0.005 to 10% by volume of propylene,> 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 or 0.005 to 10% by volume of molecular oxygen,> 0 or 0.005 to 3% by volume of acetic acid,> 0 or 0.001 to 2% by volume of propionic acid,> 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 diluent gases may contain, for example: 0 0 or 0.005 to 90% by volume of saturated C1 to C6 hydrocarbons (especially propane, methane and / or ethane),> 0 or 0.005 to 30% in volume of water vapor,> 0 or 0.005 to 15% by volume of carbon oxides (CO and / or CO2), and> 0 or 1 to 90% by volume of molecular nitrogen.
The partial oxidation production gas mixture can furthermore be derived in particular from a partial oxidation, as described from propylene and / or propane in EP-A 1,818,324, DE-A 2004 032 129 and their equivalent equivalent protection rights abroad, DE-A 10 245 585, WO 03/076 370, WO 01/96 271, EP-A 117 146, WO 03/011 804, US-A 3 161 670, DE-A 3,313,573, DE-A 10,316,039 and WO 01/96 270, and which has as propylene source optionally a dehydrogenation of propane and / or a hydrogenation of propane oxide (optionally catalyzed heterogeneously) as a series reaction step.
Advantageously, the crude acrylic acid desired for obtaining the liquid phase P to be treated according to the present invention is produced from the aforementioned mixtures of production gases of the partial oxidation of C3 acrylic acid precursor, condensing the acrylic acid from the partial oxidation production gas mixture. The condensed product which appears as such or after additional addition of Bi constituents for the desired MBges adjustment advantageously forms the liquid phase P to be treated according to the present invention in one of the two operating states I, II. The condensation of the acrylic acid from the production gas mixture (optionally previously cooled) advantageously takes the form of a fractional condensation (optionally additionally superimposed on absorption with water and / or an aqueous solution, to reduce the losses of acrylic acid - see for example EP-A 1818324), as described in detail for example in document EP-A 1 015 410, WO 2004/035 514 , DE-A 10 243 625, EP-A 1 015 411, DE-A 10 235 847, German Application No. 10 2007 004 960.0, EP-A 1 159 249, EP-A 1 163 201, EP-A 1 066,239 and EP-A 920,408.
The production gas mixture is hereby condensed in an appropriate fractionation and upflow manner, optionally after direct and / or indirect cooling (for example with a quenching liquid according to EP-A-1 066 239, or in accordance with EP -A 1,163,201) in a separator column having separating action packings with lateral withdrawal of a crude acrylic acid (which can form, as such, the liquid phase P to be treated according to the present invention; optionally further treated by rectification and / or distillation to produce the liquid phase P or mixed with constituents Bj.).
From such a liquid phase P produced by condensation (and possibly additionally by rectification as well as possibly after additions of constituents Bi (preferably corrosive water)), a crystallized product of finely divided acrylic acid according to the present invention can be separated. From the mother liquor (residual phase R) separated consecutively from the suspension S obtained here, at least partially, preferably completely, is recycled in the condensation of the acrylic acid from the production gas mixture, in accordance with for example the model of EP-A 920 408 or WO 2004/035 514. The output of high boilers is installed below the side draw off of the crude acrylic acid.
Such a liquid phase P to be treated according to the present invention, produced by partial or total condensation and / or superimposed absorption with water or an aqueous solution (which contains as a rule> 90%, frequently> 95% water; see EP-A 1 818 324) and optionally a reprocessing by rectification and optionally an addition of Bi constituents (for example corrosive water); may contain:> 85 to 99.5% by weight of acrylic acid> 0, as a rule 0.1 to 40% by weight of water,> 0, as a rule 0.001 to 5% by weight of acrolein> 0, partially 0.001 to 10% by weight of methacrolein,> 0, partially from 0.001 to 10% by weight of methacrylic acid,> 0, as a rule from 0.01 to 10% by weight up to 7% by weight of acetic acid,> 0, as a rule 0.01 to 5% by weight of propionic acid,> 0, as a rule 0.001 to 5% by weight of formaldehyde,> 0, as a rule 0.001 to 5% by weight of aldehydes other than formaldehyde (each aldehyde),> 0, as a rule from 0.01 to 5% by weight of maleic acid,> 0, as a rule from 0.01 to 10% by weight of benzaldehyde and / or benzoic acid, as well as> 0 to 3% by weight of protoanemonin.
For the separation of the suspension S into a crystallized product contained in and into a residual liquid phase R (mother liquor), all the methods present in the documents WO 01/77 856, WO 02/055 469 and WO 03/078 378 for the separation of a suspended crystalline product and mother liquor (e.g. mechanical separation processes such as centrifugation) are generally taken into consideration following a process according to the present invention. The separation is preferably carried out in a washing column. This is advantageously a washing column with forced transport of the separated crystals (for example acrylic acid crystals). In general, the mass fraction of crystallized product in the crystallized product bed reaches values> 0.5. In the normal case, the wash column operates for values from 0.6 to 0.75. As a washing liquid, advantageously the melting of crystals (eg acrylic acid crystals) purified (separated) previously in the washing column. The washing takes place normally against the current. The process according to the present invention thus comprises, in particular, processes which comprise the following process steps (these processes can be used thus also in the case of target products other than acrylic acid): a) (in the two operating states I, II) separation according to the present invention by crystallization of acrylic acid (as a target product) from a liquid phase P (for example from liquid crude acrylic acid) with formation (sampling) of a suspension S, b) separation of the suspension S into a crystallized product of acrylic acid and a mother liquor (residual liquid phase R), c) at least partial melting of the crystallized product of separated acrylic acid and d) recycling at least partial crystallized product of acrylic acid melted in step b) and / or in step a).
Step b) is preferably carried out by backwashing with crystallized acrylic acid product previously separated and recycled in step b). Steps b), c) and d) advantageously take place in a washing column.
That is, the process according to the present invention also includes processes in which the liquid phase P containing acrylic acid is transferred as a target product according to the present invention into a suspension S consisting of a product crystallized with acrylic acid and a residual liquid phase R (mother liquor), a portion of the residual mother liquor (residual liquid phase R) is mechanically separated from the suspension S and the crystallized product is freed from acrylic acid remaining mother liquor in a washing column, provided that: (a) the liquid phase P in the two operating steps I, II, with respect to the acrylic acid contained therein, contains from 0.20 to 30 frequently up to 20, often up to 10% by weight of water, and b) melting the crystallized product of purified acrylic acid (purifying separated) in the wash column is used as LAVAG e.
The process according to the present invention comprises in particular the above processes, the liquid phase P having amounts of acrylic acid> 70% by weight, or> 75% by weight, or> 80% by weight, or> 85% by weight, or> 90% by weight, or> 95% by weight.
It is furthermore advantageous according to the present invention that the water content of the liquid phase P containing acrylic acid as the target product X in the processes described above (or generally when using the process according to the present invention), with respect to the acrylic acid contained in the liquid phase P, at least in the operating state II of 0.2 or 0.4 up to 8, or up to 10, or up to 20, or up to 30% by weight, or from 0.60 to 5% by weight, or from 0.60 to 3% by weight.
The process according to the present invention can naturally also be adapted to all the crude acrylic acids of WO 98/01 414 as well as to all the crude p-xylenes of EP-A 097 405 as liquid phase P.
As a general rule, the temperature of the suspension of crystalline product S during its removal from the secondary space (Tsaus) during a use of liquid phase P containing crude acrylic acid as target product X in the process according to the present invention is, in the two operating states I, II, in the range of -25 ° C to + 14 ° C, in particular in the range of -5 ° C to + 12 ° C and particularly preferably in the range of 4 or 6 to 9 ° C.
All that has been mentioned above is particularly worthwhile when the washing column is a column of washing with forced transport of the crystals of acrylic acid, and this especially when it is about a column of hydraulic washing or a column of mechanical washing according to WO 01/77 056 and that it functions as shown above.
All that has been mentioned above is particularly applicable when the washing column is carried out and operates according to the information of German Application No. 10 2007 004 960.0, and WO 03/041 832 as well as WO 03/041 833 and WO 2006/111 565.
With the sequence "partial oxidation of at least one C3 precursor compound, fractional condensation of acrylic acid from the production gas mixture of the partial oxidation, separation according to the present invention by crystallization of acrylic acid from the condensates of acrylic acid taken from the condensation of acrylic acid as a liquid phase P (optionally after addition of constituents Bi to adjust MBges with outward guidance of a suspension of crystalline product of acrylic acid S from the secondary space of the heat exchanger, and separating the suspension S into a remaining mother liquor and a pure crystalline product of acrylic acid into a washing column using a pure crystalline product melt of acid acrylic previously separated as a washing liquid ", the method according to the present invention allows the most effective way a preparation of acrylic acid. suitable for superabsorbents, adapted to the respective demands of the market.
Of course, all process steps in which acrylic acid is involved are carried out with inhibition of the polymerization. Here it is possible to proceed as described by the prior art. Dibenzo-1,4-thiazine (PTZ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-loxyl (4-OH-TEMPO) and p-methoxyphenol (MEHQ), which may be a component of the liquid phase P (for example crude acrylic acid) are in themselves, in pairs or in the form of a mixture of three, occupy an excellent position, less than the total amounts of the stabilizing agents of the process; acrylic acid available. Their total amount relative to the acrylic acid contained in the liquid phase P is usually from 0.001 to 2% by weight.
In a manner corresponding to that presented by way of example for acrylic acid, the process according to the present invention can also be integrated in the process for the preparation of other target products X.
That is, the present application comprises in particular a process in which a continuous separation process of the finely distributed crystallized product contained in the suspension S of the target product X follows the process according to the present invention, the suspension S is fed to a washing column, which has a washing column wall, which surrounds a process space, mother water (liquid residual phase R) from the process space is emitted through devices filtration, with retention of the crystallized product contained in the suspension S and with formation of a crystallized product bed in the process space from the suspension S brought into the process space, the bed of crystallized product is transported in the process space, at least one force different from gravitation, which transports the crystallized product bed into the process space, acts in the process space in the direction of the process space. When the crystallized product bed is transported, a pure melting consisting of the molten crystallized product previously separated by this washing column process is brought countercurrently to the crystallized product bed in the process space, so that a washing front is formed in the crystallized product bed, which divides the crystallized product bed into a mother water zone and a pure melt zone, and crystallized product continuously washed in the wash column is evacuated under a solid form and / or melted at the end, opposite the arrival of the suspension S, the washing column.
What has been mentioned below is particularly applicable when the target product X is, in the process according to the present invention, acrylic acid (in particular when the liquid phase P in at least one of the two operating states I, II , is a crude acrylic acid according to the present document). As a general rule, another method, in which crystallized product of separated acrylic acid is melted and then subjected to polymerization (preferably radical polymerization) with itself or with other compounds at least once ethylenically unsaturated (eg solution polymerization, emulsion polymerization, suspension polymerization, gas phase polymerization, or substance polymerization), in this case following the separation of the crystalline product of finely divided acrylic acid. Such a process can also be followed when the separation of the crystallized product and the mother liquor (residual liquid phase R) is undertaken otherwise than with a washing column.
The above-mentioned washing column is advantageously a hydraulic washing column or a mechanical washing column. Corresponding washing columns are for example described in the documents WO 2006/110565, DE-A 10 2007 032 633, WO 03/041 832, WO 03/041 833, DE-A 2005 015 639 and WO 01 / 77,056 and by the prior art cited in these documents.
For the adjustment of the desired degree of crystallization Y of the suspension S output from the secondary space of the heat exchanger, it is possible to approach, in the process according to the present invention, for example the difference, determined for each operating moment. using a process calculator, between the crystallization heat stream Οκγ, υ developing in a justified manner in the secondary space, and corresponding to the degree of crystallization Y, and the difference, formed between the heat flow Qaus also guided completely out of the secondary space of the heat exchanger and the Qein heat flow also introduced completely into the secondary space of the heat exchanger. As a setting value, TKein can be used here as appropriate to the technique of use.
For the implementation of the method according to the present invention, all types of indirect heat exchangers are considered theoretically (they have, by definition, the primary space / secondary space structure required according to the present invention (see, for example, Kristallization, Grundlage und Technik, Günther Metz, Springer-Verlag, Berlin 1969, pages 214 and following as well as Ullmanns Encyclopedie der technischen Chemie, Verfahrenstechnik I, Verlag Chemie Weinheim, 4th edition, 1972, pages 672 to 682, as well as the prior art mentioned in these reference works).
As an indirect heat exchanger, a heat exchanger is preferably used according to the present invention in which the side facing the secondary space of the at least one partition wall respectively separating the at least one primary space of the The secondary space operates by being wiped off (continuous scraping of the heat transfer surfaces concerned with appropriate wipers). These types of indirect heat exchangers (crystallizers, coolers) are also frequently referred to as scraper coolers. The at least one primary space can be placed in the indirect heat exchanger immovably or movably (eg extractable cooling discs). In the latter case, the mobile primary space elements can be exchanged from time to time.
The transport movement of the fluid phase in the secondary space through it is in many cases already sufficient to condition a suspension of the separated crystallized product in the secondary space. In general, however, the secondary space additionally has one or more mixing devices. In the simplest case, it may be a drip with an adjuvant gas (for example air), one or more agitators, the wiper and / or a transfer to the pump. Transport of the mass flow rate fed to the secondary space through this same secondary space is normally achieved by pushing the liquid phase P by means of pumps into the secondary space. The removal of the (crystallized product) suspension S from the secondary space usually takes place with overflow control (but it can also take place with a level adjustment by means of a submerged tube).
To this end, a height-adjustable overflow barrier is advantageously used for the technique of use.
As a selection given by way of example, it is possible to use for the process according to the present invention: rotary tube crystallizers (the secondary space is the internal tube space; a double jacket in which the coolant is conducted in a flow parallel to or against the flow of mass flow into the tube interior, the tube interior is preferably slightly inclined with respect to the horizontal; inner wall of the tube, drops of crystalline product possibly forming can be detached continuously by shocks (for example with chains) and / or scraped (for example with radial brushes), the liquid phase P is fed continuously in the first end of the tube, the suspension S is continuously output at the other end of the tube); a container with hinged cooling elements (cooling elements (for example cooling discs) are hooked in a non-agitated container, the liquid phase P is for example introduced from the bottom left into the container and the suspension S is removed from the container with overflow regulation from the top right, cooling elements possibly with inlays being replaced by intact cooling elements); - stirred containers (eg containers which are surrounded by a cooling jacket and / or are equipped with cooling elements (cooling coil, cooling disk), they additionally have an agitator which continuously stirring the contents of the interior space not covered by the cooling elements, the liquid phase P is fed through pumps and the suspension S is output by overflow); a votator (tube at rest, cooled by the casing, the wall of which is scraped by plane scraping sheets pressed by springs, the liquid phase P is pumped inside at one end, the suspension S flows outward at the other end); - Traycrystallizer (bowl-shaped container having a horizontally mounted shaft, on which hollow trays (hollow disks) are arranged at regular intervals, which are traversed by the cooling medium as a rule against the flow of the phase liquid P crystallizing, and which have sector-shaped cutouts for the passage of the liquid phase P or the suspension of crystallized product; gentle stirring of the suspension of crystallized product through the trays and the axial cooling ducts which connect the liquid phase P is introduced into the tray crystallizer by the first side through pumps and is discharged from the tray crystallizer by the opposite side through a regulation of the overflow); - forced recirculation crystallizer from Swenson or Messo Chemietechnik.
Crystallizers particularly suitable for the process according to the present invention (in particular in the case of acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone as the target product X) are crystallizers with cooling disc (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 March 2004).
As the fluid cooling agent (or adjuvant), both gases and liquids can be used.
Liquid coolants (or heating agents) are preferably used according to the present invention. Examples of liquid cooling agents (or heating agents) are heat transfer oils, water, salt solutions in water and monovalent or multivalent organic alcohols, such as methanol. ethanol, propanol, glycol and / or glycerine, but also mixtures consisting of one or more of the aforementioned cooling agents, for example water-methanol mixtures or water-glycol mixtures (for example with 10 to 60% by weight of glycol).
The temperature TKein is adjusted, typically for cooling crystallization according to the present invention, from 0 to 20 K, often from 1 to 15 K and most of the time from 2 to 10 K under Tsaus (the temperature at which the suspension S is taken from the secondary space).
In many cases, however, there remain wall surface elements that can not be wiped or only with difficulty. This is for example the case when the primary space is the internal space of a circular cooling disk, which is for example simply immersed in the liquid phase flowing in the secondary space. While the front face and the rear face of the cooling disc are relatively easily accessible to wiping, it no longer normally applies to the envelope surface of the cooling disc. Surface elements of this type are therefore generally subject to tracing, which must eliminate their incrustation comprising crystallized product. Such a tracing can be for example a tracing by resistance. Of course, such tracing can however also be achieved through indirect heat exchange.
In the case of use of the circular cooling discs claimed above, a hollow heating pipe (or other hollow profile) may for example be applied to their envelope surfaces (on the front face of a non-circular wall). wiped), in which a fluid heating medium is continuously fed to the temperature ΤΗβιη and out of which is evacuated the same fluid heating medium at the temperature THaus <THein. The fluid heating medium is preferably also a liquid. The heating agent (heating medium) is particularly preferably the same substance which is fed simultaneously as a heating agent through the primary space at another temperature. The temperature THein is suitably chosen in a range greater than Tsaus, for example in the range of 0 to 20 K, often 0.5 to 10 K and most of the time 1 to 5 K.
Bi components are normally in the present invention molecular compounds. For the case where it is ionic or highly polar compounds, the degree of dissociation of these compounds in the liquid phase P is to be reported again optionally in known manner to the molar number or relevant according to the present invention.
The crystals of the crystallized suspension product formed during an implementation of the process according to the present invention typically have a longitudinal dimension (the longest straight forward connecting line between two points on the crystal surface) in the range from 1 to 10,000 μm, often from 10 to 1000 μm, frequently from 100 to 800 μm and very often from 300 to 600 μm.
The separation by crystallization can, moreover, be carried out as the suspension crystallizations carried out in the prior art.
The suspension (of crystallized product) S from a separation according to the present invention is not normally brought immediately to its separation of crystallized product and residual phase R (mother liquor). It is rather retamped in a tank for example agitated and / or repompé and taken continuously from it and for example brought to a separation washing column. If several (for example two or three) crystallizers (heat exchangers) for example of identical construction operate in parallel according to the present invention, all the suspensions S respectively outputs of different crystallizers (which have essentially all the same degree of crystallization Y) are initially fed appropriately for the technique of use to a buffer tank I and mixed in the same tank by stirring. From this buffer tank I, the separation devices for the mother liquor / crystallized product separation (for example hydraulic washing columns, the number of which corresponds advantageously to that of the crystallizers operating in parallel (but which may, however, be lower or higher to these) which also operate in parallel (and are usually also of the same design) are then fed in. The pure melted product taken for example from the melting circuit of the respective washing column is fed to a storage tank. In this case, the pure product streams arriving are mixed with each other and from the storage tank the pure target product X (possibly with inhibition of polymerization) can then be fed to the respective user. of the mother liquor (liquid residual phase R), at least a partial amount is frequently recycled in a process diffuse separation used for the preparation of the liquid phase P (cf. Figure 5 of WO 01/77 056 or German Application No. 10 2007 004 960.0). This recycling generally does not take place immediately from the device used for the separation of the mother liquor and the crystallized product.
The separated mother liquor (the separated residual liquid phase R) is rather initially fed to a common buffer vessel II, in which the residual phases R arriving from the different separation devices (for example washing columns) are mixed with one another. . Any overflow of the buffer tank I containing the suspension S is also brought to this buffer vessel II. From this buffer vessel II, the recycling in a diffuse separation process mentioned above can then take place (for example in the case of acrylic acid as the target product X according to FIG. 5 of the document WO 01 / 77,056 or in accordance with German Application No. 10 2007 004 960.0 in the fractional condensation of the production gas mixture of the heterogeneously catalyzed partial gas phase oxidation of a precursor compound C3 of acrylic acid). . If there exists in the context of such an acrylic acid preparation for example a need for a hot rinsing acrylic acid, for example to rinse crystallized product encrusted filters in the hydraulic washing columns used for product separation. crystallized and liquid residual phase, it is appropriately taken also in the buffer vessel II.
An increase of mx is possible in a simple manner in the process according to the present invention by increasing the flow (mass), brought to the secondary space, of liquid phase P containing target product X (by increasing the flow intensity of this product). arrival flow). For this purpose, the space-time yield is normally increased in existing production facilities for the preparation of the liquid phase P. This is possible in the case of a heterogeneously catalyzed partial gas phase oxidation for the preparation of the liquid phase. target product X (for example acrylic acid or methacrylic acid), for example in a simple manner by increasing with the production gas mixture the charge of the fixed bed of catalyst with a reaction gas mixture and the charging of the devices following the partial oxidation for the separation of the target product X from the partial oxidation production gas mixture (see for example DE-A 10 337 788 and the prior art mentioned herein).
The working pressures usually used in the process according to the present invention are normally not higher than 5 bar, most of the time not higher than 3 bars, frequently not higher than 2 bars and generally <1.5 bar and> 1 bar. For reasons of eg evacuation of monomers by suction, the working pressure can be also below atmospheric pressure.
The present invention thus comprises in particular the following embodiments: 1.- A method for carrying out a continuous separation of a target product X in the form of a finely divided crystalline product of the target product X from a liquid phase P consisting of the target product X as well as constituents Bi different from the target product X, whose total molar fraction of component Bi has the MBges value, with the aid of 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 respectively by at least one material partition, which serves as a surface for heat transfer from the space at least one primary space, in which a liquid phase stream P, and a mass flow mx of target product X as a constituent thereof, is introduced into the secondary space of the exchanger heat, while the at least one primary space is traversed simultaneously by at least one fluid cooling medium, which is fed to the at least one primary space at the temperature TKein, so that in the secondary space is formed from of the liquid phase E, with subsistence of a liquid residual phase R, of the finely divided crystalline product of the target product X, which is suspended in the residual liquid phase R which contains, in comparison with the liquid phase P, in an enriched manner the different constituents of the target product X and the content of the target product X is at least 70%, obtaining a suspension S having a degree of product crystallization Y, the crystallized product finely distributed of the target product X in the residual liquid phase R, a stream of the suspension S is withdrawn continuously from the secondary space of the heat exchanger, in different operating states I and II of the other, where, in the operating state I, the at least one fluid cooling medium TKein temperature (I) is fed to the at least one primary space and the liquid phase stream P having a flow rate mx (I), contained in this same current, of target product X is brought to the secondary space, and in the operating state II, the at least one fluid cooling medium of temperature TKein (II) is brought at least one primary space and the liquid flow current P of mass flow mx (II), contained in the same stream, of target product X being fed to the secondary space, provided that mx (II)> mx (I ) and TKein (II) <TKein (I), characterized in that the total molar fraction MBges of different constituents of the target product X in the liquid phase P brought to the secondary space in the operating state I is greater than that it is in the operating state II.
2. A process according to embodiment 1, characterized in that the degree of product crystallization Y in the operating state I and in the operating state II is 0.10 to 0.50.
3. - Process according to embodiment 1, characterized in that the degree of product crystallization Y in the operating state I and in the operating state II is 0.20 to 0.40.
4. - Process according to embodiment 1, characterized in that the degree of product crystallization Y in the operating state I and in the operating state II is 0.25 to 0.35.
5. - Method according to any one of embodiments 1 to 4, characterized in that the difference between mx (I) and mx (II) is at least 5%, relative to the arithmetic mean of ihx ( I) and mx (II).
6. Process according to any one of embodiments 1 to 4, characterized in that the difference between mx (I) and rhx (II) is at least 20%, relative to the arithmetic mean of m × ( I) and mx (II).
7. - Method according to any one of embodiments 1 to 4, characterized in that the difference between mx (I) and rhx (II) is at least • 50%, relative to the arithmetic mean of mx (I) and mx (II).
8. - Process according to any one of embodiments 1 to 7, characterized in that the degree of product crystallization Y in the operating state I, Y (I), and the degree of product crystallization Y in the operating state II, Y (II) does not deviate by more than 20% from each other, with respect to the arithmetic mean of Y (I) and Y (II).
9. - Process according to any one of embodiments 1 to 8, characterized in that the difference between TKein (II) and TKein (I) is from 0.1 to 30 K.
10. - Process according to any one of embodiments 1 to 8, characterized in that the difference between TKein (II) and TKein (I) is at least 0.3 K.
11. - Method according to any one of embodiments 1 to 8, characterized in that the difference between TKein (II) and TKein (I) is at least 0.5 K.
12. - Process according to any one of embodiments 1 to 11, characterized in that the target product content X of the residual liquid phase R contained in the suspension S taken from the secondary space is> 80% by weight in the two operating states I, II.
13. Process according to any one of embodiments 1 to 11, characterized in that the target product content X of the residual liquid phase R contained in the suspension S taken from the secondary space is> 90% by weight. weight in the two operating states I, II.
14. - Process according to any one of embodiments 1 to 13, characterized in that the target product X is acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone.
15. Process according to any one of embodiments 1 to 14, characterized in that, in operating state II, the total molar number, contained in the liquid phase P brought to the secondary space, of constituents Bi whose molecular weight is less than three times the molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P, is greater than the total molar number contained in the liquid phase P brought to the secondary space in operating state I, of constituents Bi whose molecular weight is less than three times the molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P.
16. - Process according to any one of embodiments 1 to 14, characterized in that, in the operating state II, the total molar number, contained in the liquid phase P brought to the secondary space, of the constituents Bi in the state whose molecular weight is less than twice the molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P, is greater than the total molar number contained in the phase liquid P brought to the secondary space in operating state I, Bi components whose molecular weight is less than twice the molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same phase liquid P.
17. - Method according to any one of embodiments 1 to 14, characterized in that, in the operating state II, the total molar number, contained in the liquid phase P brought to the secondary space, constituents Bi, whose molecular weight is less than the simple molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P, is greater than the total molar number contained in the liquid phase P brought to the secondary space in operating state I, of constituents Bi whose molecular weight is less than the simple molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P.
18. - Process according to any one of embodiments 1 to 14, characterized in that, in the operating state II, the mole fraction of H2O contained in the liquid phase P brought to the secondary space is greater than the molar fraction of H 2 O contained in the liquid phase P brought into the operating state I at the secondary space.
19. - Process according to any one of embodiments 1 to 18, characterized in that the target product X is acrylic acid, which comes from a process for the preparation of acrylic acid which comprises a process of heterogeneously catalyzed partial gas phase oxidation of a C3 precursor compound to give a production gas mixture containing acrylic acid and subsequent isolation of acrylic acid from said production gas mixture, and co-used for the adjustment of MBges in the liquid phase P brought to the secondary space, resulting, in the operating state II, of the aqueous solution containing acrylic acid, taken from the preparation process of acrylic acid, the water content of which is at least 60% by weight.
20. - Process according to any one of embodiments 1 to 19, characterized in that the target product X is acrylic acid, which comes from a process for the preparation of acrylic acid which comprises a process of heterogeneously catalyzed partial gas phase oxidation of a C3 precursor compound to give a production gas mixture containing acrylic acid and subsequent separation of acrylic acid from said production gas mixture, and co-used for the adjustment of MBges, in the liquid phase P brought to the secondary space, resulting, the operating state I, of the aqueous solution containing acrylic acid taken from the preparation process of acrylic acid removed, the water content of which is at least 80% by weight.
21. - Process according to any one of embodiments 1 to 20, characterized in that the target product X is acrylic acid, which comes from a process for the preparation of acrylic acid which comprises a process of heterogeneously catalyzed partial gas phase oxidation of a C3 precursor compound to give a production gas mixture containing acrylic acid and a separation of acrylic acid from this production gas mixture by absorption and / or fractional condensation.
22. - Method according to embodiment 21, characterized in that a method of separating the suspension S into a crystallized product, contained therein, of the target product X and a residual liquid phase R, contained therein, follows. and at least a partial amount of the residual liquid phase R is recycled to the absorption and / or fractional condensation.
23. - Process according to any one of embodiments 1 to 22, characterized in that the target product X is acrylic acid and the liquid phase P in the two operating states I, II has the contents below. below:> 70% by weight acrylic acid, up to 15% by weight acetic acid, up to 5% by weight propionic acid, up to 5% by weight low molecular weight aldehydes, up to 3% by weight polymerization inhibitors 0 to 5% by weight diacrylic acid, and up to 20% by weight water.
24. - Method according to any one of embodiments 1 to 23, characterized in that the operating state I is temporally before the operating state II and the increase of MBges (I) to MBges (II) takes place before the increase of mx (I) and mx (II), during the transition from the operating state I to the operating state II.
25. - Method according to any one of embodiments 1 to 23, characterized in that the operating state II is located temporally before the operating state I and the fall of mx (II) to mx ( I) takes place before the decrease of mBges (II) to mBges (I), during the transition from operating state II to operating state I.
26. - Process according to any one of embodiments 1 to 25, characterized in that it further comprises in the method step according to claim 1, the process steps below, consisting of: b) separating the suspension S removed from the secondary space of the heat exchanger into a crystallized product of the target product X and a residual liquid phase R, c) at least partially melt the crystallized product of the separated product product X and ) at least partially recycling the molten crystallized product of the target product X to step b) and / or to the continuous separation process step of the target product X according to claim 1.
27. - Process according to any one of embodiments 1 to 26, characterized in that the heat exchanger is a cooling disk crystallizer.
28. - Process according to any one of embodiments 1 to 27, characterized in that the heat exchanger is a scraped heat exchanger.
29. - Process according to any one of embodiments 1 to 28, characterized in that a continuous separation process of the finely divided crystallized product, contained in the suspension S, of the target product X follows, in which the suspension S is fed to a washing column, which has a washing column wall, which surrounds a process space, a residual liquid phase R from the process space is emitted by filtration devices, with retention of the crystallized product contained in the suspension S and forming a bed of crystallized product in the process space from the suspension S brought into the process space, the bed of crystallized product is transported into the space of method, at least one force different from the gravitation acts in the process space in the transport direction of the crystallized product bed, which transports the bed of crystallized product into the process space. In this case, a pure melting consisting of the molten crystallized product, previously separated by this washing column process, is brought countercurrent to the crystallized product bed in the process space, so that a washing front is formed in the process space. the crystallized product bed, which divides the crystallized product bed into a mother water zone and a pure melt zone, and the crystallized product continuously washed in the wash column is discharged in a solid and / or melted form at the end, opposite the arrival of the suspension S, the washing column.
30. - Method according to embodiment 29, characterized in that the target product X is acrylic acid and another process ensues, in which crystallized product of acrylic acid separated and melted is subjected to polymerization with itself or with other compounds at least once ethylenically unsaturated.
31. - Process for preparing a target product X, characterized in that it includes a process according to any one of claims 1 to 29. Example and Comparison Example I. Two crystallizers are operated in parallel with disks stirred and wetted coolers of a similar design, of the type described in Research Dislosure Database No. 496,005 (published August 2005). This is a bowl, in which 24 wiped circular cooling plates (cooling discs) are arranged by hanging at an interval of 30 + 1 cm equidistant one behind the other. The plate diameter is 3.3 m. The plate thickness is around 5.2 cm.
For each of the two crystallizers, a mixture consisting of 60% by weight of water and 30% by weight of glycol is used as the cooling agent. The coolant is passed through the crystallizer into the respective crystallizer in countercurrent to the liquid phase P supplied to the crystallizer and is further passed from a cooling disc to the cooling disc after the next. That is, the coolant is supplied for each of the two crystallizers in a shared manner as two parallel streams of the same size on the cooling plates of the respective crystallizer. One-half of the partial flow is passed through the even-numbered cooling plates, the other half of the partial flow is conducted through the odd-numbered cooling plates (encryption of the cooling discs starting with 1 in the flow direction of the coolant). The cooling surfaces are made of stainless steel material DIN 1.4541). The wall thickness of the stainless steel cooling surfaces is 4 mm. The speed of rotation of the brushes is 5 to 6 rotations per minute. The shaft driving the brushes, guided centrally by the cooling disc, is sealed by packing glands with flushing water (Teflon packaging cord, amount of flush = a few liters per hour to 10 1 / h for each joint). On the circumference of each cooling disc, where it is not possible to wipe, is installed a hollow profile (a welded pipe, • (material: stainless steel material DIN 1.4541), wall thickness = 3.6 mm). The hollow profile of the individual cooling discs of a crystallizer is traversed, for the purpose of tracing thereof, in parallel manner by a liquid heating agent, which is also composed of 70% by weight of water and 30% by weight of water. % by weight of glycol.
The brushes are segmented radially (4 segments).
The specific pressing force of the brushes is, in the assembled state, perpendicular to the cooling surface with about 4 N per centimeter of active edge length of brushes. As a brush material, Multilene® PE 1000 is used. In addition to the brushes, the shaft drives pallets (between two cooling discs and before the first and last cooling discs, respectively in a symmetrical arrangement) which causes improved brewing In the rear part, in the transport direction of the crystallized product suspension, of the respective crystallizer (behind the last cooling disk) the suspension (of crystallized product) S formed in the individual crystallizer sinks respectively over an overflow dam in a buffer tank (made of stainless steel, DIN material 1.4541 or 1.4571) agitated by a helical stirrer, from which two hydraulic washing columns of the same design are fed in parallel with a suspension S taken from the buffer tank (after separation the mass flow, taken from the buffer tank, of suspension S between the two washing columns is followed, respectively before entering the respective washing column, by the passage of a Coriolis flow meter for the purpose of determining the degree of of crystallization Y by means of the mass density of the partial mass flow rate f) to separate them into a residual phase R and a crystallized product. The separation in the melt washing column takes place as described in EP-A-1 272 453, EP-A-1 448 283, WO 2006/111 565, WO 03/041 833, EP-A 1 305 097, DE -A 10 156 016, DE-A 10 2005 018 702, EP-A 10 223 058 and the German application with the reference 10 2007 004 960.0. The inside diameter of the individual washing columns is 1.4 m. The feeding of the washing columns with the suspension of crystallized product is carried out respectively by means of a centrifugal pump (of the unobstructed type), the quantity control taking place by means of a regulation of the speed of rotation of the pumps. The residual liquid phase R separated in the washing columns is recycled via a buffer vessel, as described in FIG. 5 of the document WO 01/77 056 or as described in the German application No. 10 2007 004 960.0, in the fractional condensation co-used for the preparation of the liquid phase P containing the acrylic acid as the target product.
The stationary filling capacity of the suspension tank of crystallized product S is 16 m3.
Each of the two crystallizers has a roof covering (stainless steel (material DIN 1.4541)) and is closed to counteract a surrounding air supply. The washing columns, also made of stainless steel (material DIN 1.4541, wall thickness 10 mm), as well as the crystallizers and the buffer tank, are thermally separated and sealed against water vapor (see, for example, DE-A 10 2007 032 633) using alu-butyl sheets, glued on their styrofoam installed so as to wrap the stainless steel, the company WeGo Systembaustoffe, Niederlassung VTI Ludwigshafen / Rhein 67014.
The washing columns, the buffer tank and the crystallizers are sheltered in a common enclosure. The temperature of the air in the common enclosure is between 25 ° C and 28 ° C. The transport of substance from the crystallizers into and out of the buffer tank into the washing column also takes place by closing it to the surrounding air, isolating it from the heat and making it waterproof to water vapor. The degree of crystallization Y is independently adjusted to 0.28 for each of two crystallizers operating in parallel. In both cases, one opposes a deviation of adjustment by an increase or a decrease of the respective TKein.
An operating state I of the two crystallizers is considered as acquired, which is characterized by the following conditions:
Target Product X = Acrylic Acid A P (I) phase delivered to the crystallizer corresponds to a crude acrylic acid, which results from a fractional condensation of a heterogeneous catalyzed gas phase partial oxidation production gas mixture. two stages of chemical grade propylene to give acrylic acid. Its acrylic acid content is 94.44% by weight. MBges (I) is 0, 1483.
The inlet temperature TKein (I) of the coolant in the primary space sector of the respective crystallizer is about 2.1 ° C.
The outlet temperature TKaus (I) of the coolant from the primary space sector of the respective crystallizer is about 4.7 ° C.
The mass flow rate mK (I) of cooling medium fed to the primary space of the respective crystallizer is about 208 t / h.
The inlet temperature THein (I) of the heating agent in the respective hollow section of the cooling discs of the respective crystallizer is about 12 ° C.
The outlet temperature THaus (I) of the heating agent from the respective hollow section of the cooling discs of the respective crystallizer is about 10.4 ° C.
The total mass flow mH (I) of heating agent fed to the hollow sections of the cooling discs of the respective crystallizer is about 43 t / h.
The inlet temperature TPein (I) of the liquid phase P (I) in the respective secondary space is about 14 ° C.
The temperature of the suspension S (I) when withdrawn from the respective secondary space, Tsaus (I), is about 7.0 ° C.
The acrylic acid content of the residual liquid phase R in the suspension S (I) taken from the secondary space is 92.34% by weight.
The intensity of the mass flow rate of mp (I), with which the liquid phase P (I) is fed to the secondary space of the respective crystallizer and the suspension S is removed from the secondary space of the respective crystallizer, is about 26.4 t / h. This results in an m × (I) of about 24.9 t / h for each secondary space.
The brushes are able to preserve the cooling disc surfaces of the respective cooling disk crystallizer from the crystallized product without effort in the operating state I over an operating time of 15 hours.
II. In the operating state (II), an increased mass flow rate mp (II) is fed to the secondary space of the respective crystallizer. Thanks to the addition of corrosive water taken from the fractional condensation (it contains 10.8% by weight of acrylic acid, 79.5% by weight of water, 6.4% by weight of acetic acid and 2 , 47% by weight of formaldehyde) to the liquid phase P, MBges in the operating state II is increased to the value of MBges (II) = 0.1724. The acrylic acid content of the liquid phase P (II) is thus 93.73% by weight. The mass flow rate mp (II), at which the liquid phase P (II) is fed to the secondary space of the respective crystallizer is about 33 t / h. This results in an mx (II) of about 31 t / h for each secondary space.
To maintain the degree of crystallization Y of the suspension S taken from the respective secondary space at 0.28, TKein should be lowered to the TKein (II) value of about -0.3 ° C in both crystallizers, without changing the cooling. TKaus (II) is at about 3.0 ° C. The tracing is maintained unmodified with THein (II) at about 12 ° C. THaus (II) is about 10 ° C. The acrylic acid content of the residual liquid phase R in the suspension S (II) taken from the secondary space is about 91.34% by weight.
The brushes are able to preserve the surfaces of the cooling disks of the respective cooling disk crystallizer from the crystallized product without effort in the operating state II over an operating period of 15 hours.
III. In the comparison operating state (V), a mass flow intensity mp (V) of about
32.5 t / h of a liquid phase P
essentially identical to the operating state I is fed to the secondary space of the respective crystallizer.
mx (V) is thus about 30.7 t / h for each secondary space.
To maintain the degree of crystallization Y of the suspension S taken from the respective secondary space at 0.28, TKein must be adjusted in both crystallizers without modification of the cooling at the TKein (V) value of approximately 0.6 ° C. . TKaus (V) is at about 3.8 ° C. The tracing is maintained without modification with a THein (V) of 12 ° C. THaus (V) is about 10 ° C. The acrylic acid content of the residual liquid phase R in the suspension S (V) taken from the secondary space is 92.3% by weight.
After an operating time of 15 hours in the comparative operating state (V), several cooling discs of the two crystallizers are covered with an incrustation of tough crystalline product about 1 to 2 cm thick, which can no longer be eliminated by the brooms.
US Provisional Patent Application No. 60 / 972,023, filed September 13, 2007, is added to this application as information on the existing literature. In view of the information mentioned above, multiple modifications and variations of the present invention are possible. That is why; it can be assumed that the present invention, within the scope of the appended claims, may be carried out in a manner different from that specifically described herein.

权利要求:
Claims (31)
[1]
1. A process for carrying out a continuous separation of a target product X in the form of a finely distributed crystalline product of the target product X from a liquid phase P consisting of the target product X and of different constituents Bi of the target product X, whose total molar fraction of constituent Bi has the value MB9es, with the aid 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 is spatially separated from each other respectively by at least one material partition, which serves as a surface for the heat transfer of the secondary space at least one primary space, in which a phase current liquid P, and a mass flow mx of target product X as a constituent thereof, is introduced into the secondary space of the heat exchanger, while the at least one primary space is traversed simultaneously by at least one fluid cooling medium, which is fed to the at least one primary space at the temperature TKein, so that in the secondary space is formed from the liquid phase P, with the subsistence of a residual liquid phase R, finely distributed crystalline product of the target product X, which is suspended in the residual liquid phase R remaining, which contains, in comparison with the liquid phase P, enriched the different constituents of the target product X and whose product content target X is at least 70%, to obtain a suspension S having a degree of crystallization product Y, of the finely distributed crystalline product of the target product X in the residual liquid phase R, a stream of the suspension S is withdrawn in continuous of the secondary space of the heat exchanger, in operating states I and II different from each other, where, in the operating state I, the at least one cooling medium The temperature fluid TKein (I) is fed to the at least one primary space and the liquid phase stream P having a mass flow mx (I), contained in this same stream, of target product X is fed to the secondary space. and in the operating state II, the at least one TKein (II) fluid cooling medium is supplied to the at least one primary space and the mx (II) mass flow liquid phase P, contained in the same current, of target product X being brought to the secondary space, provided that mx (II)> mx (I) and TKein (II) <TKein (I), characterized in that the total molar fraction MBges of different constituents of the target product X in the liquid phase P brought to the secondary space in the operating state I is greater than it is in the operating state II.
[2]
2. A process according to claim 1, characterized in that the degree of product crystallization Y in the operating state I and in the operating state II is 0.10 to 0.50.
[3]
3. Method according to claim 1, characterized in that the degree of product crystallization Y in the operating state I and in the operating state II is 0.20 to 0.40.
[4]
4. Method according to claim 1, characterized in that the degree of product crystallization Y in the operating state I and in the operating state II is 0.25 to 0.35.
[5]
5. Method according to any one of claims 1 to 4, characterized in that the difference between mx (I) and mx (II) is at least 5%, relative to the arithmetic mean of mx (I) and of mx (II).
[6]
6. Method according to any one of claims 1 to 4, characterized in that the difference between mx (I) and mx (II) is at least 20%, relative to the arithmetic mean of ihx (I) and mx (II).
[7]
7. Method according to any one of claims 1 to 4, characterized in that the difference between mx (I) and mx (II) is at least 50%, relative to the arithmetic mean of mx (I) and mx (II).
[8]
8. Process according to any one of claims 1 to 7, characterized in that the degree of product crystallization Y in the operating state I, Y (I), and the degree of product crystallization Y in the operating state II, Y (II) does not deviate more than 20% from each other, relative to the arithmetic mean of Y (I) and Y (II) ·
[9]
9. Method according to any one of claims 1 to 8, characterized in that the difference between TKein (II) and Τκειη (I) is from 0.1 to 30 K.
[10]
10. Process according to any one of claims 1 to 8, characterized in that the difference between TKein (II) and TKein (I) is at least 0.3 K.
[11]
11. Method according to any one of claims 1 to 8, characterized in that the difference between TKein (II) and TKein (I) is at least 0.5 K.
[12]
12. Method according to any one of claims 1 to 11, characterized in that the target product content X of the residual liquid phase R contained in the suspension S taken from the secondary space is> 80% by weight in both operating states I, II.
[13]
13. Method according to any one of claims 1 to 11, characterized in that the target product content X of the residual liquid phase R contained in the suspension S taken from the secondary space is> 90% by weight in both operating states I, II.
[14]
14. Process according to any one of claims 1 to 13, characterized in that the target product X is acrylic acid, methacrylic acid, p-xylene or N-vinylpyrrolidone.
[15]
15. Method according to any one of claims 1 to 14, characterized in that, in the operating state II, the total molar number, contained in the liquid phase P brought to the secondary space, Bi constituents whose molecular weight is less than three times the molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P, is greater than the total molar number contained in the liquid phase P brought to space secondary in the operating state I, of constituents Bi whose molecular weight is less than three times the molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P.
[16]
16. Process according to any one of claims 1 to 14, characterized in that, in the operating state II, the total molar number, contained in the liquid phase P brought to the secondary space, of the constituents Bi in the a state whose molecular weight is less than twice the molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P, is greater than the total molar number contained in the liquid phase P fed in the secondary space in operating state I, components Bi whose molecular weight is less than twice the molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P.
[17]
17. Process according to any one of claims 1 to 14, characterized in that, in the operating state II, the total molar number, contained in the liquid phase P brought to the secondary space, of the constituents Bi, whose the molecular weight is less than the simple molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P is greater than the total molar number, contained in the liquid phase P brought to space secondary in the operating state I, of constituents Bi whose molecular weight is less than the simple molecular weight of the target product X, divided by the total molar number of all the constituents contained in this same liquid phase P.
[18]
18. Method according to any one of claims 1 to 14, characterized in that, in the operating state II, the molar fraction of H2O contained in the liquid phase P brought to the secondary space is greater than the molar fraction. H20 contained in the liquid phase P brought into the operating state I to the secondary space.
[19]
19. A method according to any one of claims 1 to 18, characterized in that the target product X is acrylic acid, which comes from a process for preparing acrylic acid which comprises a partial oxidation process. heterogeneously catalyzed gas phase of a C3 precursor compound to provide a production gas mixture containing acrylic acid and subsequent isolation of acrylic acid from said production gas mixture, and is co-used for the adjustment of MB9es in the liquid phase P fed to the secondary space, resulting, in the operating state II, from the aqueous solution containing acrylic acid, taken from the process for the preparation of acrylic acid, whose water content is at least 60% by weight.
[20]
20. Process according to any one of claims 1 to 19, characterized in that the target product X is acrylic acid, which comes from a process for the preparation of acrylic acid which comprises a partial oxidation process. heterogeneously catalyzed gas phase of a C3 precursor compound to provide a production gas mixture containing acrylic acid and subsequent separation of acrylic acid from said production gas mixture, and is co-used for the adjustment of MBges, in the liquid phase P brought to the secondary space, resulting, the operating state I, of the aqueous solution containing acrylic acid taken from the acrylic acid preparation process taken, whose water content is at least 80% by weight.
[21]
21. Method according to any one of claims 1 to 20, characterized in that the target product X is acrylic acid, which comes from a process for preparing acrylic acid which comprises a partial oxidation process. heterogeneously catalyzed gas phase of a C3 precursor compound to give a production gas mixture containing acrylic acid and a separation of acrylic acid from this production gas mixture by absorption and / or condensation fractionating.
[22]
22. Process according to claim 21, characterized in that a process for separating the suspension S into a crystallized product, contained therein, of the target product X and a residual liquid phase R contained therein, follows, and less a partial amount of the residual liquid phase R is recycled in the absorption and / or fractional condensation.
[23]
23. Process according to any one of claims 1 to 22, characterized in that the target product X is acrylic acid and the liquid phase P in the two operating states I, II has the contents below: 70% by weight acrylic acid, up to 15% by weight acetic acid, up to 5% by weight propionic acid, up to 5% by weight low molecular weight aldehydes, up to 3% by weight polymerization 0 to 5% by weight diacrylic acid, and up to 20% by weight water.
[24]
24. A method according to any one of claims 1 to 23, characterized in that the operating state I is temporally before the operating state II and the increase of MB9es (I) to MBges (II) takes place before the increase of mx (I) and rhx (II), during the transition from the operating state I to the operating state II.
[25]
25. A method according to any one of claims 1 to 23, characterized in that the operating state II is located temporally before the operating state I and the fall of mx (II) up to mx (I) a instead of the decrease of mBges (II) to mBges (I), during the transition from operating state II to operating state I.
[26]
26. Process according to any one of claims 1 to 25, characterized in that it further comprises in the process step according to claim 1, the process steps below, consisting of: b) separating the suspension S withdrawn from the secondary space of the heat exchanger into a crystallized product of the target product X and into a residual liquid phase R, c) at least partially melting the crystallized product of the separated target product X and d) recycling at at least partially the molten crystalline product of the target product X to step b) and / or the step of continuous separation process of the target product X according to claim 1.
[27]
27. Method according to any one of claims 1 to 26, characterized in that the heat exchanger is a cooling disk crystallizer.
[28]
28. Process according to any one of claims 1 to 27, characterized in that the heat exchanger is a scraped heat exchanger.
[29]
29. Process according to any one of claims 1 to 28, characterized in that a continuous separation process of the finely distributed crystallized product contained in the suspension S, of the target product X follows, in which the suspension S is fed to a washing column, which has a washing column wall, which surrounds a process space, a liquid residual phase R from the process space is emitted by means of filtration devices, with retention of the crystallized product contained in the suspension S and with formation of a bed of crystallized product in the process space from the suspension S brought into the process space, the bed of crystallized product is conveyed into the process space at minus a force different from the gravitation acts in the process space in the transport direction of the crystallized product bed, which transports the crystallized product bed into the process space, a pure melting consisting of the molten crystallized product and previously separated by this washing column process is brought countercurrent to the crystallized product bed in the process space, so that a washing front is formed in the bed of crystallized product, which divides the crystallized product bed into a mother liquor zone and a pure melt zone, and crystallized product continuously washed in the wash column is evacuated in a solid and / or melted form. end, opposite the arrival of the suspension S, the washing column.
[30]
30. The process according to claim 29, characterized in that the target product X is acrylic acid and another process follows, in which crystallized product of separated and molten acrylic acid is subjected to a polymerization with it. same or with other compounds at least once ethylenically unsaturated.
[31]
31. Process for preparing a target product X, characterized in that it includes a process according to any one of claims 1 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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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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DE102007043758|2007-09-13|

---