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    • 专利摘要:
    Process for the separation with purification of crystals of acrylic acid, methacrylic acid, N-vinylpyrrolidone, or p-xylene from their suspension in a mother liquor by means of a washing column with forced transport , of which the envelope of the process space is a metal wall, the washing column being, in addition, enveloped by a thermal insulation material having a barrier to water vapor and a specific heat flux> 0.1 Wm2 and <10 Wm2 entering the process space via the metal wall of the wash column.
    公开号:BE1018534A3
    申请号:E2008/0380
    申请日:2008-07-09
    公开日:2011-03-01
    发明作者:Ulrich Hammon；Dieter Baumann；Joerg Heilek；Klaus Joachim Muller-Engel
    申请人:Basf Se；
    IPC主号:
    专利说明:

    Process for the separation with purification of crystals of acrylic acid, methacrylic acid, N-vinylpyrrolidone or p-xylene from their suspension in a mother liquor
    Description
    The present invention relates to a process for the separation with purification of crystals of acrylic acid, methacrylic acid, N * vinylpyrrolidone or p-xylene from their suspension in a mother liquor, wherein the suspension is fed into a wash column that has a metal wall that surrounds a process space, the mother liquor is removed from the guided suspension into the process space of the process space with crystal retention and crystal bed formation in the process space, the crystal bed is conveyed into the process space, at least one force different from the gravitational force acts in the process space, in the direction of progression of the crystal bed, which conveys the crystal bed in the process space, a pure melt consisting of melted and separated crystals with purification according to the claimed process is guided into the countercurrent process space with respect to the crystal bed such that a washing front is formed in the crystal bed which distributes the crystal bed to a mother liquor zone and a pure melt zone, and a heat flow Specifically between, flowing through the metal wall of the wash column (from the outside), into the process space of the wash column.
    The concept of mother liquor must be understood in this document in that it comprises melts of the compound to be crystallized and impurities and / or solutions of the compound to be crystallized and of solvents (or mixtures of solvents) as well as impurities.
    Numerical references in this document always refer to the figures appended to this document.
    The method according to the preamble of this document is known (see for example WO 03/041832 as well as WO 03/041833).
    It generally follows a suspension crystallization, which forms a very active and economically favorable process for obtaining a high purity of a desired chemical compound. It is exploited here that during the growth of crystals in a liquid, the impurities are largely removed from the crystal lattice and remain in the mother liquor. In a one-step crystallization process, thus, crystals of high purity of the desired compound are already obtained. If necessary, the suspension crystallization can be carried out in several steps.
    A decisive step which predominantly influences the purity of the crystallized target product is the separation of the high purity crystals from their mother liquor, which contains the impurities in enriched form and the non-crystalline proportions of the target product, by a solid separation process. /liquid. This separation process can take place in several stages, where at least in the last stage is often used what is called a washing column. The washing column can however also form the single separation step. Its essential role lies in the separation of the relatively pure crystalline phase from the relatively contaminated mother liquor.
    The washing columns are also known from the prior art. They include a generally cylindrical wall that delimits a process space. The process space is often preceded by a distribution space in which is supplied the crystal suspension to be separated in the washing column. On its way from the distribution space in the process space, the crystal suspension is distributed to a large extent regularly over the section of the process space. In the process space a denser crystal bed is produced by the withdrawal of the mother liquor and this bed is conveyed into the process space (this can be done from top to bottom or from bottom to top). A melt of the molten crystals themselves is countercurrently guided as a wash liquid in the crystal bed.
    For the formation of a crystal bed, various methods are in principle considered. In the case of gravitation washing columns, the crystal suspension is introduced from the top into the column, the crystal bed is formed in a sedimentation process and its progress in the direction of progression occurs only under the effect of gravity.
    The use of these columns is excluded from the process according to the invention, because it does not generally form a defined washing front. This last point is particularly the case when they are provided on part of their height of a stirring device (see Figure 1).
    The process according to the invention is therefore limited to processes in washing columns with a forced progression of the crystal bed (a detailed description of the different types of washing columns is found among others in Chem.-Ing.-Techn. 57 (1985) Nr., 291-102, in Chemical Engineering Science Volume 50, No. 17, pages 2712-2729, 1995, Elsevier Science Ltd., in Applied Thermal Engineering Volume 17, No. 8-10, pages 879. -888, 1997, Verlag Elsevier Science Ltd. and in the above extracts from the literature as well as in DE-A 102 45 164, DE-A102 11 686, DE-A 101 49 353, WO 03/041832 and WO 03 / 041,833).
    The washing columns with a forced transport (or progression) of the bed of crystals are characterized in that a force with a progressive effect, different from gravitation, acts in the direction of progression (or direction of transport) of the bed. of crystals.
    In principle, the columns of pressure (also called hydraulic washing columns or hydraulic columns) and the mechanical columns are distinguished from the washing columns with forced transport of the crystal bed. In the pressurized columns, the crystal suspension is conveyed into a pressure washing column (for example by pumps and / or a hydrostatic head). The flow of the liquid marked by the pressure of the feed column then ensures compaction of the crystals in a bed of crystals (see Figure 2) and its progression (the hydraulic pressure is usually 0.1 to 10 bar, often 1 to 5 bars). The mother liquor generally flows through a filter out of the wash column (on either side of the filter can be a normal pressure, a vacuum or a pressure above atmospheric pressure). The recycling of a part of the mother liquor allows the adjustment of the transport force (control flow).
    On the other hand, the mechanical washing columns contain a mechanical device for forced progression for the crystals. It may be, in the simplest case, a semi-permeable piston, which is permeable to the mother liquor but impervious to the crystals in the fed suspension (see Fig. 3) and the pressure for the compaction and progression of the crystal bed is produced by the displacement of said piston.
    Compaction into a crystal bed and its progression can however also be achieved by separating the mother liquor via a filter and mechanical transport of the crystals from the filter to the crystal bed by a rotating progress element (for example, screws stirrers, propellers or spirals) (see Fig. 4) .The filters can also be integrated into the rotary progress elements. On either side of the outlet of the mother liquor can again reign, here, a normal pressure, a depression or a pressure higher than the atmospheric pressure.
    The crystal bed has, in the case of the washing columns to be used according to the invention, with a forced transport of the bed of crystals, what is called an elaboration front, at which the crystals of the suspension of crystals introduced accumulate continuously. The preparation front therefore designates the transition of the suspension into a bed of crystals and is characterized by a relatively abrupt increase in the level of creep content in the suspension. In the hydraulic washing columns, this preparation edge is also called the filtration front.
    At the opposite end to the crystal bed developing edge is generally disposed a type of rotary knife (eg a rotary knife disc, slotted) or a slab which continuously removes crystals from the crystal bed. By the continuous accumulation of crystals on the front of elaboration on the one hand and the continuous evacuation of crystals at the end opposite to the front of elaboration of the bed of crystals on the other hand, one defines the direction of transport of the bed of crystals (which can go from top to bottom as well as from bottom to top). Crystals removed from the crystal bed, optionally after resuspension in a pure melt, are melted by heat transfer. Part of the melt is discharged as a pure product stream and another portion of the pure melt is recycled to the process space as a wash liquid against the direction of crystal bed transport at its opposite end to the front of the melt. development. Usually, the washing liquid has the temperature of the melting point.
    The melting of a part of the crystals can, however, also be carried out directly in the washing column (for example via correspondingly integrated devices for heating at the end opposite to the front of the generating space. process).
    Only a portion of the melt produced is then removed from the column. The other part rises as a washing melt.
    By the progression of the pure melt opposite to the direction of progression of the crystal bed, the bed of crystals impregnated with mother liquor is practically pushed into the pure melt and, in the bed of crystals, the mother liquor is effectively repulsed. to some extent by the pure melt.
    In the stationary state, as a result of this process, a defined height of the crystal bed is obtained, a washing front, which is defined as the site of the process space in the washing column where the gradient exists. of the highest temperature and concentration (i.e., in the wash front, the temperature is, for example, skipped, above and below the wash front there are essentially constant temperatures). In the washing front, it can be roughly said that the melt and the mother liquor are next to one another. The area from the wash front to the working edge is referred to as the mother liquor zone and the wash front zone to the opposite end to the crystal bed elbow is called the mass zone. pure fondue. The position of the washing front can be regulated by regulating the mass flow of crystals transported and the pure flow of pure melt guided in the opposite direction. It is often considered that the wash effect is improved as the length of the pure melt zone increases. Normally, the washing front has a longitudinal extent (perpendicular to the section of the wash column) of 100 mm, typically 60 mm and often 40 mm. These latter longitudinal stretches are particularly valid when the crystal bed is absolutely not agitated, contrary to EP-A 098 637. The section of the process space of the washing column may be circular, oval or polygonal (for example example a regular polygon).
    As the material for the wall delimiting the process space of the washing column, WO 03/041832 recommends the use of metal. As metals, metals of different types can be used depending on the surface to be purified. It may be pure metals, but also alloys, for example carbon steels, iron-based alloys (noble steel, for example with an addition of Cr / Ni) or alloys based on nickel (eg Hastelloy grades). When it comes to the crystals to be separated with purification, acrylic acid crystals (when acrylic acid is the target product), is preferred as the material for the wall of the washing column of noble steel , in particular noble steel made of material according to the standards DI N 1.4571 or 1.4541, or a noble steel similar to these noble steels with regard to the alloying elements. The thickness of the metal wall delimiting the process space is suitably from 3 to 30 mm, often from 4 to 20 mm and most often from 5 to 15 mm. This is especially true in the case of noble steel.
    The disadvantage of the use of metal as a material for the wall delimiting the process space of the washing column, however, lies in the high thermal conductivity of the metals (at 300 K, the thermal conductivity of unalloyed steel is, for example of 50 W / m * K, that of the noble steel is 21 W / m * K and that of the aluminum is 237 W / πνΚ, whereas the corresponding thermal conductivity of the glass is only 1, 0 W / m "K).
    The above is disadvantageous in that the melting point of a pure substance is at a temperature higher than the melting point of the same substance, but containing impurities (key word: lowering of the freezing point). The consequence of this fact is that the temperature in the mother liquor is normally below the temperature in the pure melt zone. Depending on the impurity content of the mother liquor, this temperature difference can be up to 15 ° C and higher, often from 4 to 10 ° C, and only at a low impurity content of the mother liquor, from 2 to 4 ° C.
    Due to the high conductivity of the metals, it follows that heat from the pure melt zone at a higher temperature is discharged into the zone of the mother liquor at a lower temperature by the temperature. metal wall surrounding the process space. In fact, undesired formation of crystals may occur along the length of the pure melt zone along the face of the metal wall facing the process space, which decreases the flow rate in the column of washing due to higher friction losses which increases the loss of charge.
    As a solution, the document WO 03/041832 recommends the introduction, at least over the length of the zone of the pure melt, of a specific controlled thermal flux from the outside via the metal wall in the space of washing column process, specific heat fluxes of 10 to 50 W / m2 being very particularly preferred.
    As a particularly favorable embodiment of a technical point of view of using such an introduction of a heat flux, the document WO 03/041832 recommends to dress the washing column itself and to maintain the air lying in it. between the cladding (which is permeable to ambient air) and the metal wall by heating to a temperature which is higher than the melting point temperature of the pure melt taken from the wash column. The difference between the two temperatures can be up to 20 ° C or more.
    In the case of crystals of acrylic acid, methacrylic acid, N-vinylpyrrolidone or p-xylene, however, such a procedure has proved disadvantageous, since according to D'ANS * LAX, Taschenbuch für Chemiker und Physiker, Springer-Verlag, Berlin 1964, Volume II, Organische Verbindungen, the melting points of the aforementioned compounds in the form of pure substance are in the range of 12 to 16 ° C.
    That is, the temperature of the slurry, in which the crystals of the above mentioned compounds normally occur during the corresponding slurry crystallization (and thus the temperature of the mother liquor zone in the column). washing) is generally 110 ° C and the ambient air temperature in the casing is usually 17 ° C.
    This is disadvantageous in that, for example, the dew point of the air having a temperature of 18 ° C. and a relative humidity of 85% is 15.4 ° C. (even at a relative humidity of the hot air at 18 ° C.). Above-mentioned C temperature of only 65%, the dew point of 11.3 ° C is still higher than 10 ° C). At a relative humidity of 95% of the air exhibiting 18 ° C, its dew point is 17.2 ° C. At an air temperature of 15 ° C and a relative humidity of 95% (75%) its dew point is still at 14.2 ° C (10.6 ° C).
    The relative humidity of the air indicates the percentage of the maximum possible water vapor content at the temperature in question that the air contains. The dew point temperature (dew point) is defined as the temperature at which the actual water vapor content in the air is the maximum content (100% relative humidity). That is, passing under the dew point temperature (the dew point), a partial amount of the water vapor contained in the air separates by condensation.
    When following the recommendation described in WO 03/041832, water vapor generally separates by condensation of the ambient air on the outer metal surface of the washing column, at least at the level of the the mother liquor. Such formation of a condensate is disadvantageous for various reasons. On the one hand, the condensate flowing in drops of the wash column could undesirably simulate leakage from the wash column. On the other hand, the aqueous condensate can lead, undesirably, to corrosion phenomena (for example with regard to the rotary knife drive device for the continuous removal of the crystal bed) and, finally, the condensation heat released during condensation can compromise the regularity of operation of the wash column.
    The problem of the present invention resides therefore in the improvement of the procedure recommended in the state of the art.
    Accordingly, there is provided a method for the separation with purification of crystals of acrylic acid, methacrylic acid, N-vinylpyrrolidone or p-xylene from their suspension in a mother liquor, wherein the suspension is fed into a wash column that has a metal wall that surrounds a process space, the mother liquor is removed from the guided suspension into the process space of the process space with retention of crystals and formation of a a crystal bed in the process space, the crystal bed is conveyed into the process space, at least one force different from the gravitational force acts in the process space, in the direction of progression of the crystal bed, which conveys the crystal bed into the process space, a pure melt consisting of fused crystals and separated with purification according to the claimed process is guided in the process space against -current relative to the crystal bed so that a washing front is formed in the crystal bed which distributes the crystal bed to a mother liquor zone and a pure melt zone, and a flow of crystals. specific heat between, flowing through the metal wall of the wash column (from the outside), into the process space of the wash column.
    characterized in that the metal wall surrounding the process space of the washing column is in turn surrounded by an envelope of thermal insulation material, provided that the thermal insulation material casing has a thermal insulation material. a water vapor barrier whose chamber opposite to the process space is permeable to ambient air and whose surface opposite to the process space has a temperature which is greater than the dew point (greater than the dew point temperature) of the ambient air, and the specific heat flux entering the process space of the wash column via its metal wall is> 0.1 W / m2 and <10 W / m2.
    According to the invention, the specific heat flux entering the process space of the washing column via its metal wall is preferably> 1 (or 2 2) to 9 9 W / m 2, advantageously from 3 3 to 8 8 W / m2 and very particularly preferably S: 4 to <7W / m2.
    Surprisingly, the thermal fluxes of the aforementioned levels are sufficient to oppose in a sufficient measure the undesired formation of crystals discussed in WO 03/041832 on the face oriented towards the process space of the metal wall. along the area of the melt.
    This is particularly relevant when the temperature difference between the zone of the mother liquor and the zone of the melt is 3 to 12 ° C, or 4 to 10 ° C or even 3 to 8 ° C.
    The metals that are considered for the wall surrounding the process space are all the metals already mentioned in this document as well as all the metals mentioned in WO 03/041832, including the wall thicknesses recommended therein.
    The thermal insulation materials that come into consideration are basically all materials whose thermal conductivity Λ (W / nvK) is lower than that of the metal chosen for the metal wall surrounding the process space (often, Λ is also called coefficient thermal conductivity, thermal conductivity index or specific thermal conductivity).
    Advantageously, according to the invention, it is preferable for the casing of the washing column to use materials whose thermal conductivity Λ (W / nvK) is 0.3 W / m · K, preferably 0.1 W nvK, particularly preferably 0.08 W / m 2 K and very particularly preferably <0.06 and often even 0.04 or 0.02, or 0.01 W / rmK (at each times at a temperature of 300 K). Generally, the thermal conductivity of thermal insulation materials to be used according to the invention is, however, at 300 ° C., values of 0.001 W / m * K, often even values of 0.002 W / m * K .
    Thermal insulation materials that come into consideration, for example, are: wood, wood wool, Chinese reed fiber mats, Poroton, mineral wool (eg glass wool), foamed glass, polystyrene insulation, such as Styropor® expanded polystyrene, Styrodur® and Neopor® (also contains finely divided graphite particles), polyurethane insulation such as polyurethane hard foam, carbon dioxide-PUR , c-iso-pentane-PUR, pyrogenic silica (for example compressed plates made of this material), degassed PUR and degassed silica.
    From a technical point of view of use, particularly easily, the thermal insulation material can be applied directly to the metal wall of the washing column (for example Styropor in a thickness of 40 to 80 mm). The envelope can be made by different pieces of thermal insulation material assembled in an overall envelope (for example pieces of Styropor). The fixing on the metal surface of the washing column is preferably carried out mechanically (from a technical point of view of use, fixing with the aid of a wire (for example noble steel) or with the use of steel clamping bands is particularly appropriate).
    Instead of applying the thermal insulation material directly to the metal surface of the washing column, it is possible to leave between the metal surface and the thermal insulation material per se, for example, an air cushion consciously. In this case, the overall thermal insulation material which envelopes the washing column consists of two layers. An inner air layer, oriented towards the metal surface of the wash column (the process space of the wash column) and an outer layer, of thermal insulation material per se. Basically, thermal insulation materials that are considered for the process according to the invention are also composite insulation materials consisting of a series of successive layers of materials different from each other.
    An integral constituent of the surrounding thermal insulation material (surrounding) the washing column is obligatorily according to the invention a barrier against water vapor (often also called barrier against the diffusion of water vapor). This concept defines, in this document, according to the ISO 9229 standard, a layer which suppresses the continuous diffusion of water vapor contained in the ambient air towards the surface of the metal wall of the washing column opposite to the process space of the wash column.
    Basically, the water vapor barrier may be a relatively thin layer of substantially water vapor impermeable material, which may simply be applied to the surface opposite to the process space (outer surface) of the material thermal insulation per se (for example glued). In this way a composite thermal insulating material is formed again, from which the envelope according to the invention of the washing column is formed.
    The materials that come into consideration here are in particular those which have a high index of resistance to the diffusion of water vapor μ. It is a dimensionless material characteristic that indicates which factor the material concerned is more vapor-tight than a layer of resting air of the same thickness. Its determination is made based on the standards DI N EN ISO 7783 (1-2) and DIN EN ISO 12572.
    For the production of a layer forming a barrier against water vapor, the materials which are considered in particular for the process according to the invention are those whose resistance index to the diffusion of water vapor is 5000, preferably 10,000, and most preferably 15,000, more preferably 50,000, or 100,000, or 1,000,000 or 10,000,000.
    These materials allow, especially at a relatively small layer thickness, a barrier effect against water vapor completely satisfactory in the direction according to the invention. As a measure for the water vapor barrier effect, the product sd = μ-x is usually used, where x is the thickness of the layer in "meters". The product sd is also called air layer thickness equivalent to water vapor diffusion. It indicates the thickness of the layer of air, in meters, which offers a resistance identical to the diffusion of the steam that a layer of air at rest of thickness sd in "meters".
    According to the invention, layers forming a barrier against water vapor having a value of 500 m, preferably 1000 m, and particularly preferably 1500 m, or even more preferably 30 000 m, are preferred. m.
    Often the water vapor barrier layers to be used according to the intention are made of polyolefins (eg polyethylene). The μ value of polyethylene sheet is typically 500,000. That is, a 2 mm thick polyethylene coating has a sd value of 1000 m.
    Preferably, however, for the process according to the invention, the layers forming a barrier against water vapor of metal foils are used. Their μ values are generally greater than 10,000,000 (eg Al, μ = 30,000,000). That is to say that layer thicknesses of less than 1 mm (in the case of AI for example 0.05 mm) are generally sufficient to reach a sd value of 1500 m which has, according to DIN 4108 a "impervious to water vapor". Particularly preferred water vapor barrier layers are aluminum foils.
    The disadvantage of metal foils, however, lies in their low tear strength. In practice, it is therefore advantageous to use metal composite sheets as layers forming a barrier against water vapor. It is in this case sheets in the core of which is always a metal sheet, in particular an aluminum sheet. The thickness of the metal foil is typically 0.02 to 0.1 mm, in particular 0.05 mm according to the invention. EP-A 1090 969 and DE 299 17 320 U1 disclose composite sheets particularly suitable as water vapor barrier layers for the process according to the invention.
    On the outer side of the metal foil (e.g. aluminum foil) is normally applied a layer of a base polymer. This base polymer provides protection for the fragile metal sheet and represents the transition to the environment. This base material protects the metal foil (e.g., aluminum foil) against mechanical degradation, increases its tear strength (e.g., tear propagation resistance) and further protects the foil against corrosion. In exceptional cases, the metal foil (for example aluminum foil) can be protected on both sides by a polymer layer. The polymers which come into consideration in this case are in particular polyesters, polypropylene and polyamide. In the case of aluminum foils, poly (ethylene terephthalate) is a preferred base polymer. Usually, the base polymer is adhered to the metal foil by means of a laminating adhesive (for example a polyurethane dispersion). Characteristic layer thicknesses for the base polymers are from 0.01 to 0.02 mm.
    On the side not protected by the base polymer of the metal foil (for example an aluminum foil) is generally applied a self-adhesive sensitive to pressure based on natural rubber, synthetic rubber or polyacrylate, which allows to stick the composite metal sheet on the thermal insulation material per se. These amounts of typical adhesives are about 40 g / m 2.
    So that the metal sheet can be wound on one hand to save storage space and on the other hand be adhered, with a covering, on the substrate to be equipped with a layer forming a barrier against the vapor of water, the base polymer has, on its side opposite to the aluminum foil, advantageously a silicone coating of the "Controlled Release" type, which ensures that by applying take-off forces in the range of 1 N / cm to 3 N / cm, the wound metal composite sheet can be unrolled again without being damaged (see DIN EN 1939 and FINAT 10).
    A composite sheet of synthetic-aluminum material which is remarkably suitable for the purpose according to the invention is for example "Terostat-Alu-Fixband" from Teroson (Henkel). It has a water vapor diffusion resistance index μ of 600,000 and a sd value of 900 m. For the purpose according to the invention, the "Alu-butyl-Madness" sheet of the company WeGO Systembaustoffe, Niederlassung VTI in 67014 Ludwigshafen is also suitable.
    The latter contains an aluminum foil having a thickness of 0.038 mm. The base polymer is poly (ethylene terephthalate) with a thickness of 0.012 mm. It is laminated with an aqueous adhesive dispersion based on polyurethane on the aluminum foil. As a pressure-sensitive adhesive, a synthetic butyl rubber is applied to the back of the aluminum foil (0.6 mm layer thickness). The self-adhesive layer in the case of this composite sheet is covered with a sheet of silicone polyethylene on one side, which allows a winding without causing without bonding of the composite sheet, but which must be removed before application as a barrier against the vapor of water.
    The aforementioned Alu-butyl-Madness foil can be purchased in standard sizes 50mm x 10m, 500mm x 10m and 1000mm x 10m. Preferably, the standard measurement 500 mm x 10 m is used. Basically, it would also be possible to stick only a metal foil (for example an aluminum foil) with the corresponding self-adhesive on the substrate to be primed with the layer forming a barrier against water vapor.
    Of course, water vapor barrier sheets suitable according to the invention may also be barriers consisting solely of several polymer layers. By an appropriate combination of these different polymers, synergistic barrier potentials can be obtained.
    Instead of applying a vapor barrier layer to the thermal insulation material per se, the water vapor barrier layer may also be incorporated into the thermal insulation material. This is for example the case when using closed-pore thermal insulation materials.
    When a layer forming a barrier against water vapor (for example an aluminum composite sheet on polystyrene) is applied to the thermal insulation material per se, it is of course possible to apply to the layer forming a barrier against water vapor is another thermal insulation material, so that a new global thermal insulation material is formed.
    It is essential for the barrier against water vapor or for the layer forming a barrier against water vapor to be positioned, when carrying out the process according to the invention, in such a way that its surface opposite to the process space has a temperature that is greater than the dew point (greater than the dew point temperature) of the ambient air, to which the chamber opposite the process space of the vapor barrier of water is permeable.
    Generally, the thickness of the water vapor barrier layers in the process according to the invention is in the range of 0.01 to 2 mm, often in the range of 0.025 to 1 mm. Their water vapor barrier effect must be suitably achieved according to the invention in that its permeability to water vapor is 0.5 g / m 2 / day (for example a sheet of polyethylene of a thickness 0.2 mm), preferably 0.4 g / m 2 / day, particularly preferably 0.1 g / m 2 / day (for example composite aluminum sheets with an aluminum core with a thickness of 0.05 mm). Since the water vapor permeabilities depend directly on the external atmosphere, the above-mentioned values refer to a test atmosphere of 20 ° C with a relative humidity of 85%. The test is carried out gravimetrically according to DIN 53122-1 / DIN53122-A or ASTME-96 with respect to air in which a desiccator has been added.
    In principle, the test can also be carried out according to ISO 2528: 1995, or DIN N 53312-1 / DIN 5312-A or DIN 53122-2 / DIN 53122-2-A (the latter is an electrolysis process with a particularly low detection limit). The different test methods are essentially distinguished by their sensitivity limits.
    The wrapped washing column according to the invention of a thermal insulation material having a barrier against water vapor (a layer forming a barrier against water vapor) can now be dressed as such permeable to the ambient air and the air between the casing and the wrapped scrubbing column according to the invention (ambient air) can be maintained by heating to a temperature which ensures the necessary heat flow according to the invention via the metal wall from the washing column to its process space. Usually, for the process according to the invention, a temperature difference between the temperature of the zone of pure mass and the temperature of the ambient air in the coating of 2 de or 5 ° C to 20 ° C. or at 30 ° C is sufficient (ambient air with the highest temperature). The thermal insulation and the water vapor barrier are in this case carried out in such a way that the plane of the dew point temperature for the ambient air is, coming in the opposite direction from the space process of the washing column, behind the barrier against water vapor (behind the layer forming a barrier against water vapor).
    The plane of the dew point temperature is the plane (for example cylindrical or having another curvature) in the jacket (the casing) of the wash column (or the metal wall of its process space) in which the temperature corresponds to the temperature of the dew point of the ambient air. Ambient air naturally has a limited water vapor content.
    As a material for the dressing of the washing column, it is possible to use, in the simplest case, wood. Other materials such as synthetic materials, sheet metal, masonry and concrete are also possible.
    The present invention therefore also particularly includes a process for the separation with purification of crystals of acrylic acid, methacrylic acid, N-vinylpyrrolidone or p-xylene from their suspension in a mother liquor, in which the suspension is fed into a washing column which has a metal wall surrounding a process space, the mother liquor is removed from the guided suspension into the process space of the process space with retention of crystals and formation of a crystal bed in the process space, the crystal bed is conveyed into the process space, at least one force different from the gravitational force acts in the process space, in the direction of the progression of the bed of crystals, which conveys the crystal bed into the process space, a pure melt consisting of fused and separated crystals with purification according to the claimed process is guided by the process chamber countercurrent to the crystal bed so that a wash front is formed in the crystal bed which distributes the crystal bed to a mother liquor zone and a pure melt, and a specific heat flow between, flowing through the metal wall of the washing column, into the process space of the washing column, which is characterized in that the metal wall surrounding the The process space of the washing column is in turn surrounded by a casing made of a thermal insulation material, provided that the thermal insulation material casing has a barrier against water vapor (a layer forming a barrier against water vapor), the washing column wrapped (surrounded) by the thermal insulation material is housed in a covering filled with ambient air (containing water vapor) and permeable to the ambient air, the air temperature am the binder in the cabinet is adjusted (to a value) such that a specific heat flow of> 0.1 W / m2 and <10 W / m2 flows into the process space via the wall metal of the washing column, and the plane of the dew point temperature for the ambient air is, coming in the opposite direction from the process space of the washing column, behind the vapor barrier of water (behind the layer forming a barrier against water vapor).
    Preferably, the above-mentioned specific heat flux is 21 (or 2 2) at 9 W / m2, preferably 23 and 8 W / m2 and most preferably at 7 W / m2.
    Normally, the aforementioned specific heat flux is greater along (at) the area of the mother liquor than the long (at the level) of the pure melt zone.
    The thermal insulation material of the envelope is preferably constituted by a core thermal insulation material (whose thermal conductivity 1 (W / nvK) is 0.3 W / rrvK, preferably 0.1 W m / K, particularly preferably 0.08 W / m * K, very particularly preferably 0.06 and often even 0.04 or 0.02 or 0.01 W / nrK, generally however, 2 0.001 W / m * K, often even 0.002 W / nrK) and a layer forming a barrier against the water vapor applied thereto (the thickness of which is generally 0.01 to 2 mm) . As core heat insulating material, all the materials mentioned in this document whose λ value corresponds to the above-mentioned requirements profile, are suitable.
    The materials which are particularly relevant for the water vapor barrier layer are those (especially all materials mentioned herein) whose μ-index is 2,500, preferably 2,000, and so Especially preferred is 15,000, even more preferably 2,50,000, or 2,100,000, or 2,000,000 or 2,10,000,000.
    The sd value of the water vapor barrier layer is favorably> 500 m, preferably 1000 m, particularly preferably 1500 m, and most preferably> 30 000 m.
    Polyethylene foils as well as metal composite foils (for example of aluminum) are particularly suitable as a barrier layer against water vapor. In particular those of EP-A 1 090 969 and DE 299 17 320 U1 and those which are indicated in the state of the art according to the above documents are considered for the process according to the invention.
    To protect the washing column wrapped with a heat-insulating material having a water vapor barrier, in addition, against mechanical influences that could damage the barrier against water vapor (the layer forming a barrier against the water vapor barrier effect could be suppressed), it is also appropriate according to the invention to coat the washing column wrapped with a thermal insulation material having a barrier against water vapor in addition to a metal sheet. Suitable for this purpose are, for example, steel sheets (for example noble steel sheets), which may for example have a thickness of 0.1 to 2 mm, preferably 0.5 mm to 1 mm.
    Suitably, from a technical point of view, the steel sheet has, on both sides, as protection against corrosion, an Al-zinc coating (for example in an amount of 175 g / m 2 per side). Corresponding steel sheets can be obtained commercially. Metal sheets which are particularly suitable for this purpose according fihvenlfön are Galvalume® sheets of the company Thyssen Krupp. In particular the sheet which is marketed under the name DX51D + AZ185A.
    Galvalume sheets are melt-immersed steel sheets, with a double-sided aluminum-zinc alloy coating, which contains approximately 55% by weight of aluminum, approximately 43.4% by weight of zinc, and about 1.6% by weight of silicon. In this case, the steel sheets may for example be a DIN material No. 1.0226 or 1.215. Preferably, it is, for the steel sheet of a cold-rolled steel sheet.
    The sheet metal liner of the steam vapor-wrapped wash column is normally located at a distance of about 10 mm from the outer surface of the vapor barrier envelope. The intermediate space is normally occupied by ambient air, with respect to which the sheet metal coating is not airtightly closed. From a technical point of view of use, the various sheet metal elements of the sheet metal coating are conveniently assembled to one another by means of self-tapping screws. On the side facing the washing column of the sheet metal lining, self-tapping screws conveniently terminate in a Styropor protection strip.
    According to the invention, washing columns are preferably used with a cylindrical process space. Their diameter is usually 2: 25 cm, most often £ 50 cm. Usually, the diameter will not exceed 3 m. From a technical point of view, diameters from 1 m to 2 m are appropriate.
    According to the invention, the remainder is preferably used hydraulic washing columns as described in DE-A101 56 016, DE-A 100 17 903, DE-A 100 36 880 and DE-A 100 36,881.
    The method according to the invention is, inter alia, favorable in the case of washing columns whose separation power is 0.5 T / h, or 1 T / h. Generally, the separation power will not be greater than 30 T / h. Characteristic values are 2 to 20 T / h.
    In Figures 1 to 4 of this document, reference numerals have the following meanings: 1: Suspension 2: Residual melt (mother liquor) 3: Product (pure molten crystals) 4: Contaminated residual melt 5: Lit moving crystals 6: (Molten mass of) washing liquid 7: Washing column 8: Suspension pump 9: Heat exchanger for the melting of the crystals 10: Adjusting valve to adjust the proportions of quantities (melting mass of ) Washing liquid / product 11: Circulation pump of the melt circuit 12: Melt circuit 13: Agitator 14: Filtration tube 15: Filter 16: Rotary knife for resuspending the washed crystals 17: Oscillating piston with filtering face and residual melt discharge 18: Tilted sheet rotor for transporting the crystal bed 19: Cylindrical pusher
    According to the invention, it is also possible to use pulsed washing columns or the washing columns can be operated with pulsed flows, as described in the document EP-A 097 405.
    The process according to the invention is particularly suitable for the separation with purification of crystals of acrylic acid, methacrylic acid, N-vinylpyrrolidone or p-xylene as target product crystals from their suspension in mother liquor. , which may for example be obtained by slurry crystallization of crude melts containing impurities of the target product in question, which contain 70% by weight, or 80% by weight, or 90% by weight, or 95% by weight. % by weight, or 98% by weight of each target product (acrylic acid, methacrylic acid, N-vinylpyrrolidone or p-xylene).
    The process according to the invention is particularly favorable for the separation with purification of acrylic acid crystals from their suspension in contaminated acrylic acid melts, as described in WO 01/77056.
    These are suspensions which can for example be obtained by suspension crystallization of crude acrylic acids which contain, for example, 70% by weight of acrylic acid up to 15% by weight of acetic acid, up to 5% by weight. % by weight of propionic acid up to 5% by weight of low molecular weight aldehydes, up to 3% by weight of polymerization inhibitors, and up to 5% by weight of acrylic acid oligomers (Michaël's addition products); (Often these crude acrylic acids additionally contain up to 20% by weight of water) or 90% by weight of acrylic acid> 100 ppm by weight to <5% by weight of acetic acid, 10 ppm by weight at 2% by weight of propionic acid up to 2% by weight of aldehydes of low molecular weight, up to 2% by weight of polymerization inhibitors, and 0 to 3% by weight of oligomers of acrylic acid (Michael adducts); (often, these crude acrylic acids additionally contain up to 9.5% by weight of water)
    However, the process according to the invention is also suitable in the case of p-xylene crystal suspensions of EP-A 097 405.
    Figure 5 appended hereto schematically shows the construction of a hydraulic wash column typically suitable for the method according to the invention. It is explained in the following with the aid of the example of a separation with purification of acrylic acid crystals.
    The suspension (1), withdrawn from the crystallizer of a suspension, of acrylic acid crystals in a mother liquor is fed by means of a pump (8) and / or via a hydrostatic head at a pressure greater than the pressure atmospheric in the washing column (7). In the upper part of the washing column is a fluid register, which serves two functions. Via passage openings (24) from the upper part of the column to the lower part of the column, the suspension is distributed over the section of the washing column. The coherent internal space of the fluid register (23) serves as a collector for the discharged liquids (mother liquor and washing liquid (2)). Below the fluid register, drainage tubes (14) have been arranged (they have a constant section in the concentration zone, and from the point of view of feeding the suspension, this is the zone up to to the first filter) which are connected to the interior space (23). The drainage tubes are provided, at a defined height, with at least one usual filter (15), through which the mother liquor (4) is discharged from the washing column (the mother liquor can in this case be at normal pressure, at a pressure above atmospheric pressure or at a lower pressure than this). A compact crystal bed (5) is formed. The crystal bed is forcibly transported as a result of the hydraulic head loss of the mother liquor flow through the filters in the washing zone under the filter. The recycling of a portion of the mother liquor into the column by means of the control flow pump (13) allows the adjustment of this transport force. Variations in the crystal content in the fed suspension or changes in the crystal size distribution, which essentially influences the pressure drop of the flow, can thus be compensated. These variations can be detected by changing the position of the filter front (17), which can be determined by optical position detectors (18).
    At the lower end of the wash column, the crystals are removed from the crystal bed by means of a rotary knife (16) and suspended in the melt of pure product, which can be overinhibited with p-methoxyphenol (MEHQ) as a polymerization inhibitor. This suspension is guided in a melt circuit (12) via a heat exchanger (9), via which the heat required for the melting of the crystals is introduced indirectly. About 70 to 80% by weight, in favorable cases (for example in the case of a marked recrystallization) even> 80 to 100% by weight of the molten crystals are discharged as pure product (3) out of the mass circuit molten. The setting of the quantity of pure product is carried out via the product control valve (10). The residual portion of the melt of pure product flows as a washing agent (6) against the direction of transport of the crystal bed to the filters (15), whereupon there occurs in the washing zone a wash at countercurrent crystals. The purification of the crystals is essentially based on the repression and the dilution of the mother liquor in the corners of the bed of crystals by the washing liquid. The dilution effect here is based on the mixing in the wedges crossed between the crystals and the diffusion in the contact sites not traversed by the flow, or in the boundary layer near the surface of the crystals.
    In the case of stationary operation, the washing front (19) is set at a defined height in the washing zone. At the level of the wash front there is a concentration transition from the concentration in the mother liquor (above the wash front) to the concentration of the pure melt (under the wash front). The washing front (19) must be positioned to achieve a proper cleaning effect at a minimum height above the rotary cutter (16). The position (19) is set as dynamic equilibrium from the mass flow of crystals (5) transported and the flow of washing agent (6) guided in the opposite direction and is located under the filter. The amount of washing agent results from the amount of pure product removed.
    In the case of a relatively good purity of the crude acrylic acid, the crystallization temperature in the crystallizer of a suspension is less than 1 to 4 ° C at the melting point of the pure product. At the washing front, when balancing the temperatures of the cold crystals and the washing melt, there is only a slight recrystallization in the washing melt. This limits the recovery of melt by recrystallization as well as the reduction of the porosity of the crystals under the washing front by recrystallization. Such low porosity of the crystal bed would reduce the expense of the scrubbing agent in the same manner as recrystallization recovery.
    In the case of a good purity of the crude acrylic acid, it is also appropriate to already introduce into the molten circuit (12) of the washing column the methoxyphenol storage stabilizer (MEHQ). For this purpose, the MEHQ dissolved in pure product is introduced with a metering pump (22) into the melt circuit at melting temperature for stabilization thereof.
    To ensure stable operation of the hydraulic washing column in the sense of a defined space-time efficiency and a good constant cleaning effect, the balancing of external disturbing elements, such as variations in the amount of suspension, the modification of the crystal content in the suspension, - the variation in the distribution of the crystal size and - the concentration variations in the feed and / or the mother liquor is appropriate via the regulation a) of the filtration front (Fig. 5, reference number 17), b) the specific amount of washing agent (Fig. 5, reference number 6) and c) the heat of the melt (Fig. 5, reference number 9).
    For the rest, the reference numerals in FIG. 5 have the following meaning: 1 = supply of the crystal suspension 2 = removal of the mother liquor 3 = acrylic acid, pure product 4 = internal flow of mother liquor 5 = moving crystal bed 6 = washing melt 7 = washing column 8 = suspending pump 9 = heat exchanger for melting crystals 10 = regulating valve for adjusting the mixing ratio washing melt / extraction of acrylic acid, pure product 11 = circulation pump of the melt circuit 12 = melt circuit 13 = control flow pump 14 = drainage tube for the mother liquor and the washing liquid 15 = filter 16 = rotary knife for resuspending the washed crystals 17 = filtration front (upper limit of the crystal bed) 18 = detection of the filtration front (4 optical remission probes) 19 = washing front (concentration transition) pure-contaminated liquid phase) 20 = detection of the washing front (4 optical remission probes) 21 = inhibitor solution (MEHQ in pure acrylic acid product) 22 = dosing pump for the inhibitor solution 23 = register for fluids: bottom of collection for the mother liquor and the washing liquid 24 = register for fluids: bottom of distribution for the suspension of the crystals 25 = detection of the front of washing (4 probes of temperature)
    For the rest, it is possible to proceed as in WO 03/041833.
    Example
    Fractional condensation of a two-stage, heterogeneously catalyzed, gas-phase product gas-phase oxidation mixture of propylene is withdrawn into a side discharge of a fractionation-condensing column through hour, 1.5 T of a crude acrylic acid having the following contents in the composition:
    Acrylic acid 96.1% by weight
    Acrolein 446 ppm by weight
    Allyl acrylate 20 ppm by weight Di (acrylic acid) 3764 ppm by weight Acetic acid 7460 ppm by weight Furfural 6719 ppm by weight
    Benzaldehyde 7131 ppm by weight Propionic acid 751 ppm by weight Phenothiazine 91 ppm by weight MEHQ 247 ppm by weight
    Water 0.83% by weight
    By a continuous addition of 22.5 kg / h of water with crude acrylic acid, its water content is increased to 2.3% by weight, then it is introduced at a temperature of 20 ° C in a crystallizer of suspension. As a crystallizer, a cooling disc crystallizer (manufacturer: GMF company, the Netherlands) with 7 cooling disks having a diameter of 1.25 m and a nominal capacity of about 2500 l is used. passes a water / glycol mixture (70/30% by volume) into the cooling discs. The melt is cooled, during the passage in the crystallizer, at 8 ° C, with formation of about 24% by weight of crystals relative to the total mass of the suspension.
    A portion of this suspension is continuously guided via a rotary piston pump (adjusted according to the number of revolutions) on a hydraulic washing column. This washing column has a cylindrical process space having an internal diameter of 263 mm and a metal wall delimiting the 1.4571 noble steel process space with a wall thickness of 5 mm. For the withdrawal of the liquid, a centrally mounted filter tube (made of the same noble steel) with an outer diameter of 48 mm (wall thickness = 2 mm) is used in the washing column. The length of the process chamber is 1230 mm. The length of the filtration tube is 1225 mm. The length of the filter is 60 mm. The filter is mounted after a tube length of 970 mm (measured from the top). The evacuation of the crystals at the lower end of the washing column is carried out with a rotary knife (60 t / min). The direction of transport is from top to bottom.
    The evolved crystals are resuspended in a melt circuit which is operated at 14 ° C (melting point of the separated crystals with purification). As polymerization inhibitors, MEHQ and air (bubbled) were introduced into the circulating guided suspension (278 ppm by weight of MEHQ). Via a heat exchanger, indirect heat is introduced into the suspension guided in the circuit, to melt to a large extent the crystals which are suspended therein. As a pump in the melt circuit, a centrifugal pump with horizontal axis (1500 rpm) with double function sealing ring is used. As a stop liquid, a water / glycol mixture (85/15% by volume) is used which is cooled indirectly with cooling water. To obtain a better exchange of acrylic acid at the sealing ring of this pump, a flushing line is drawn from the pressure side of the pump to the product space surrounding the sealing ring and is continuously open. during operation. The position of the washing front in the column is monitored by several temperature measurements mounted at several heights, axially different in the washing column and adjusted by adjusting the amount of pure product withdrawn from the melt circuit. Control of the height of the crystal bed is achieved via four optical sensors, arranged axially at different heights of the wall of the washing column and adjusting the amount of control flow. As a control flow pump, a rotary piston pump (governed by the number of revolutions) is also used, but a horizontal axis centrifugal pump with a control valve could also have been used.
    On the metal outer wall of the washing column, a cylindrical Styropor wrap with a layer thickness of 50 mm is applied using steel clamping strips.
    On the thermal insulation layer Styropor is then glued, with a lap gluing mode, an "Alu-butyl-Madness" sheet from the company WeGo Systembaus-toffe Niederlassung VTI 67014 Ludwigshafen.
    The washing column thus wrapped is placed in a covering made of wood sheets and permeable to the surrounding air, the (surrounding) air being between the wrapped washing column and the wooden wall being heated to a temperature such that the air temperature in the entire cladding is in the range of 23 ° C to 26 ° C (measured at ten representative test points). The relative humidity of the ambient air at these temperatures is about 85%.
    The wash column is packed with a suspension amount of 1400 kg / hr from the cooling disk crystallizer. The temperature of the suspension is 8 ° C. An overpressure with respect to the atmosphere at the top of the wash column is set at 2.0 to 2.2 bar, which varies closely around the center value of 2.05 bar. The overpressure at the lower end of the column is 1.8 to 2.0 bar. Via a control flow pump, a quantity of control flow of 1400 kg / h is recycled to the washing column to adjust the height of the crystal bed.
    The flow of purified pure acrylic acid product withdrawn from the melt circuit is -310 to 340 kg / h (i.e., average = 325 kg / h). This corresponds to a yield of 96.7% by weight relative to the mass flow of crystals fed with the suspension in the washing column. The pure product has the following contents in the composition:
    Acrylic acid 99.75% by weight
    Undetectable acrolein
    Non detectable allyl acrylate
    Acetic acid 1457 ppm by weight
    Furfural 3 ppm by weight
    Benzaldehyde 2 ppm by weight
    Propionic acid 209 ppm by weight
    Non-detectable phenothiazine MEHQ 278 ppm by weight
    Water <0.05% by weight
    The wash front exhibits satisfactory stability throughout the test.
    Both for the stationary state of operation described and for the subsequent lapse of 14 days, no formation of condensate was observed. The specific heat flux flowing in the process space of the wash column is 5 to 6 W / m2 along the pure melt zone and about 8 W / m2 along the laundry zone. -mother.
    Comparative example
    We proceed as in the example. The envelope according to the invention of the washing column is however omitted. Already before reaching a stationary operating state (ie about 30 minutes after commissioning) condensate formation can be detected on the noble steel outer wall of the wash column.
    US Provisional Patent Application No. 60/949056, filed July 11, 2007, is hereby incorporated by reference of literature.
    In view of the above-mentioned teachings, a large number of modifications and deviations of the present invention are possible. It should be understood that the invention, within the scope of the appended claims, may be carried out in another manner than that described herein.
    权利要求:
    Claims (11)
    [1]
    A process for the separation with purification of crystals of acrylic acid, methacrylic acid, N-vinylpyrrolidone or p-xylene from their suspension in a mother liquor, wherein the suspension is fed into a column of washing that has a metal wall that surrounds a process space, the mother liquor is discharged from the guided suspension into the process space of the process space with retention of crystals and formation of a bed of crystals in the process space, the crystal bed is conveyed into the process space, at least one force different from the gravitational force acts in the process space, in the direction of the progression of the crystal bed, which conveys the bed of crystals in the process space, a pure melt consisting of fused and separated crystals with purification according to the claimed process is guided in the countercurrent process space with respect to the crystalline bed. in such a way that a washing front is formed in the crystal bed which distributes the crystal bed to a mother liquor zone and a pure melt zone, and a specific heat flow between, in flowing through the metal wall of the washing column into the process space of the washing column, characterized in that the metal wall surrounding the process space of the washing column is in turn surrounded by an envelope of a thermal insulation material, provided that the envelope of thermal insulation material has a dam against the water vapor whose chamber opposite to the process space is permeable to the ambient air and whose surface opposite to the process space has a temperature which is higher than the dew point of the ambient air, and - the specific heat flow entering the process space of the washing column via its metal wall is> 0, 1 W / m1 and <10 W / m1. A process for the separation with purification of crystals of acrylic acid, methacrylic acid, N-vinylpyrrolidone or p-xylene from their suspension in a mother liquor, wherein the suspension is fed into a washing column which has a metal wall that surrounds a process space, the mother liquor is removed from the guided suspension into the process space of the process space with retention of crystals and formation of a bed of crystals in the space of process, the crystal bed is conveyed into the process space, at least one force different from the gravitational force acts in the process space, in the direction of the crystal bed progression, which conveys the crystal bed into In the process space, a pure melt consisting of fused and separated crystals with purification according to the claimed process is guided in the countercurrent process space with respect to the crystallization bed. x such that a wash front is formed in the crystal bed which distributes the crystal bed to a mother liquor zone and a pure melt zone, and a specific heat flow between, in s' flowing through the metal wall of the washing column into the process space of the washing column, characterized in that the metal wall surrounding the process space of the washing column is in turn surrounded by an envelope in a thermal insulation material, provided that the envelope of thermal insulation material has a barrier against water vapor, the washing column wrapped by the thermal insulation material is housed in a covering filled with ambient air and permeable to ambient air, the temperature of the ambient air in the cladding is adjusted in such a way that a specific heat flux of> 0.1 W / m2 and <10 W / m2 flows in the process space via the wall of the washing column, and the plane of the dew point temperature for the ambient air is, coming in the opposite direction from the process space of the washing column, behind the vapor barrier of water.
    [2]
    3. Method according to claim 1 or 2, characterized in that the specific heat flux is 1 to 9 W / m2. Process according to Claim 1 or 2, characterized in that the specific heat flux is 2 to <8 W / m2.
    [3]
    5. Method according to any one of claims 1 to 4, characterized in that the thermal conductivity of the thermal insulation material is 0.001 W / ητΚ and <0.3 W / m-K.
    [4]
    6. Method according to any one of claims 1 to 4, characterized in that the thermal conductivity of the thermal insulation material is 0.002 W / m »K and 0.1 W / nvK.
    [5]
    7. Method according to any one of claims 1 to 6, characterized in that the barrier against water vapor consists of a material whose resistance index to the diffusion of water vapor is 15,000 .
    [6]
    8. Method according to any one of claims 1 to 6, characterized in that the barrier against water vapor consists of a material whose resistance index to the diffusion of water vapor is £ 100,000 .
    [7]
    9. Method according to any one of claims 1 to 8, characterized in that the barrier to the water value comprises a metal sheet.
    [8]
    10. Process according to any one of claims 1 to 9, characterized in that the barrier to the water value comprises an aluminum foil.
    [9]
    11. Process according to any one of claims 1 to 10, characterized in that Styropor is used as thermal insulation material with a composite aluminum foil applied to Styropor as a barrier against water vapor.
    [10]
    12. Process according to any one of claims 1 to 11, characterized in that the temperature difference between the zone of the mother liquor and the zone of the melt is 3 to 12 ° C.
    [11]
    13. Process according to any one of claims 1 to 12, characterized in that the washing column wrapped by the thermal insulation material is, in addition, coated with a metal sheet which is not closed with respect to Ambiant air.
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    同族专利:
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    申请号 | 申请日 | 专利标题
    US94905607P| true| 2007-07-11|2007-07-11|
    DE102007032633|2007-07-11|
    US94905607|2007-07-11|
    DE102007032633|2007-07-11|
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