DE102016119938A1 - Purification and concentration of carboxylic acids from fermentation processes - Google Patents

Abstract

The present invention relates to a process for the purification of carboxylic acids from fermentation processes, wherein a biomass-free acidified carboxylic acid-containing fermentation mixture is first subjected to a simulated moving bed chromatography step and then a two-stage nanofiltration, wherein the second nanofiltration has a lower separation limit compared to the first nanofiltration , By this purification sequence, fermentation residues such as, in particular, salts and sugar residues can be removed with high efficiency, so that costly and circuit-complex treatments with ion exchangers and / or activated carbon can be dispensed with in the course of the further purification. The present invention also relates to a device which is designed to carry out a corresponding method. The invention relates to both liquid carboxylic acids such as lactic acid and crystallizable carboxylic acid such as succinic acid.

Description

The present invention relates to a process for the purification of carboxylic acids from fermentation processes, wherein a biomass-free acidified carboxylic acid-containing fermentation mixture is first subjected to a simulated moving bed chromatography step and then a two-stage nanofiltration, wherein the second nanofiltration has a lower separation limit compared to the first nanofiltration , A further aspect of the present invention relates to a device which is designed for carrying out a corresponding method and in particular has two nanofiltration stages, of which the second nanofiltration stage has a lower separation limit than the first nanofiltration stage.

State of the art

Decisive for the industrial use of carboxylic acids which are produced by fermentation of carbohydrate-containing substrates by means of various microorganisms, is the efficiency and efficiency of the separation and purification of carboxylic acids from aqueous fermentation solutions, as these enter into a significant proportion in the price of fermented carboxylic acids. In addition to the carboxylic acid or the carboxylic acids, the fermentation broths also contain other organic acids, other by-products of the fermentation, the microorganisms and their constituents as well as residues of the substrates, such as sugar. These impurities interfere with the subsequent further processing of the carboxylic acids produced and must therefore be separated from the carboxylic acids. This problem arises in particular with lactic acid, which is intended for further processing to polylactic acid to obtain a biodegradable plastic, since even small amounts of impurity significantly affect the achievable molecular weight and thus the chemical properties of polylactic acid. In order to ensure a high degree of polymerization of the lactic acid and thus favorable application properties of the polymer, it is therefore necessary to use extremely pure monomer. This has long been known and goes for example J. Dahlmann et al., British Polymer Journal, Vol. 23 (1990), pp. 235-240 ,

The same is known, for example, for succinic acid. A distinction is made here between the qualities of the succinic acid produced by the subdivision into a technical grade with a succinic acid content of at least 97% by mass and a succinic acid (polymer grade) which is suitable for use in particular with a content of at least 99.5% by mass.

In the production of polymer-grade lactic acid, the prior art has hitherto encountered the difficulty that relatively expensive procedures are required for the purification and concentration of lactic acid, in particular ion exchange steps or activated carbon treatment at acid concentrations <40% by weight. , and different evaporation levels. That's how it describes US 8,957,249 Among other things, a process for the purification of dicarboxylic acids from fermentation processes, the simulated moving bed separation (SMB), a fine separation, which can be carried out for example by nanofiltration, subsequent purification by means of ion exchange or activated carbon treatment, and evaporation and crystallization of the product.

The WO 2013/064219 describes, inter alia, a process for the separation and purification of lactic acid in which after separation of the biomass, a purification of the lactic acid by means of a SMB separation, two ion exchange and two evaporations takes place. One of the ion exchange purifications can be combined with nanofiltration.

The WO 2014/106532 A2 describes a process for the separation and purification of carboxylic acids from fermentation processes, wherein initially the biomass contained in the fermentation broth is separated and the resulting carboxylic acid is pre-purified in a first step using an SMB chromatography. Subsequently, according to the WO 2014/106532 a fine cleaning is provided, in which a nanofiltration with relatively low separation limit (about 200 Da) is used, which can be followed by an activated carbon filtration and / or an ion exchange step. According to the WO 2014/106532 the finishing of the carboxylic acid should involve concentration, for example via reverse osmosis, as well as crystallization of the desired carboxylic acid.

A problem in the production of suitable for the polymerization of lactic acid, as mentioned above, is that in particular hydroxyl-containing by-products, especially in the form of sugar residues from the fermentation process, must be removed as completely as possible, since these by-products in the polymerization process suppress the formation of long-chain polylactic acid molecules. A disadvantage of the nanofiltration mentioned in the above prior art documents is thereby in that, with the separation limits specified for nanofiltration, residues of glucose and salts can not be adequately separated. Therefore, a further purification by means of an ion exchanger and / or an activated charcoal treatment is regularly provided in the above prior art, are separated over the not retained in the context of nanofiltration residual glucose and salts. However, the ion exchange process is relatively unfavorable because of the required regeneration of the ion exchange material and the increased water consumption required for the overall process.

Against this background, the present invention proposes a more efficient overall purification process of carboxylic acids and especially of lactic acid, which avoids an ion exchange step for eliminating residual salts and glucose from the carboxylic acid solution obtained via the SMB process.

Description of the invention

1. (i) eine Biomasse-freie, angesäuerte, Carbonsäure-haltige Fermentationsmischung einer Simulated-Moving-Bed-Chromatographiestufe unterzogen wird,
2. (ii) die aus Schritt (i) erhaltene Carbonsäure-haltige Fraktion einer ersten Nanofiltration unterzogen wird, und
3. (iii) die aus Schritt (ii) erhaltene Carbonsäure-haltige Retentat-Fraktion einer zweiten Nanofiltration unterzogen wird, die eine gegenüber der ersten Nanofiltration geringere Trenngrenze aufweist.

According to a first aspect, the present invention therefore relates to a process for the purification of carboxylic acids from fermentation processes, wherein:

1. (i) a biomass-free, acidified, carboxylic acid-containing fermentation mixture is subjected to a Simulated Moving Bed chromatography step,
2. (ii) subjecting the carboxylic acid-containing fraction obtained from step (i) to a first nanofiltration, and
3. (iii) subjecting the carboxylic acid-containing retentate fraction obtained from step (ii) to a second nanofiltration which has a lower cut-off limit than the first nanofiltration.

The present invention is therefore based on the surprising finding that with a two-stage nanofiltration in which a higher separation limit is used in a first stage than in a second stage, a better separation of the impurities, in particular of glucose and salts, can be achieved. so that a subsequent ion exchange step at acid concentrations <40 wt .-% is no longer required. As a result, the disadvantages of higher equipment and circuit complexity and losses due to the regeneration and initial loading of resins and activated carbon are avoided.

The statements "upstream" and "downstream" in the context of the present description designate process steps or stages which are directly or indirectly connected upstream or downstream of the respectively explained process step.

The terms "Simulated Moving Bed Chromatography" and "SMB Chromatography" or "Simulated Moving Bed Chromatography Level" and "SMB Chromatography Level" are interchangeable in the following description, in which case, in the case of the indication "Chromatography Level" also the indication "level" or "step" can be specified.

In the context of the present description, the term "retentate" denotes the portion retained in the respective process step, while the term "permeate" designates the transmitted portion of the feed stream.

When percentages are given in the present specification, these are, unless otherwise indicated, as percentages by weight.

The first nanofiltration is carried out in the context of the inventive method expediently with a lower concentration factor, such as a concentration factor of less than 20, preferably less than 10 and more preferably about 4 to 6, wherein a good quality permeate is obtained and substances such as glucose, amino acids and Salts, in particular sulfates and phosphates, are well retained.

In the first nanofiltration stage, it is further expedient to use pressures below 30 bar and preferably about 25 to 15 bar. It is also preferred in the context of the first nanofiltration if the membrane used for the first nanofiltration has a cut-off of dalton or less, and preferably 400 dalton or less. A particularly useful membrane for the first nanofiltration has as separation limit of about 400 to about 300 daltons. In another embodiment, the membrane has a cut-off of about 500 to about 300 daltons.

Due to the higher separation limit and the possibly lower concentration factor in the first nanofiltration, a larger amount of retentate is obtained as part of this nanofiltration, which is subsequently subjected to a second nanofiltration in the course of step (iii). As mentioned above, in the second nanofiltration, a membrane is used which has a lower separation limit than the membrane used in the first nanofiltration. The separation limit for the second nanofiltration is suitably 300 daltons or less, preferably 250 daltons or less, and more preferably in the range of about 250 to 200 daltons. In addition, it is preferred if the second nanofiltration is carried out at pressures of more than 25 bar and in particular at from 30 to about 40 bar. Alternatively or additionally, a concentration factor of, ideally, about 65 to 90, more preferably 65 to 80, and most preferably about 75 is set.

To avoid losses during the second nanofiltration, diafiltration can be carried out in the last stage. The retentate obtained after diafiltration, which substantially contains the aqueous carboxylic acid in a lower concentration, can in this case be discharged as waste water. The distillates from the product distillation and / or from the membrane distillation can be used as water for this diafiltration.

Since the carboxylic acid-containing permeate fractions obtained from the first and second nanofiltration contain a comparable composition with water and carboxylic acid as essential constituents, it makes sense to combine the permeate fractions for further purification. In a preferred embodiment, the permeate fractions obtained from the first and second nanofiltration are therefore mixed together before further processing.

By the method described above, which includes a downstream nanofiltration SMB chromatography stage, wherein the first nanofiltration has a higher cut-off as compared to the second nanofiltration, better separation of solids, such as glucose, can be achieved in the process of the present invention. Amino acids and salts and in particular of glucose and salts, yielding a product having similar proportions of these impurities, such as a product obtained after simple nanofiltration and subsequent ion exchange / charcoal treatment.

In the context of the present invention, the carboxylic acid is expediently a hydroxycarboxylic acid or dicarboxylic acid, which is preferably selected from the group comprising malic acid, glycolic acid, isocitric acid, mandelic acid, lactic acid, tatronic acid, tartaric acid, citric acid, beta-aminohydroxybutyric acid, mephalonic acid, salicylic acid , Oxalic, maleic, succinic, glutaric, adipic, pimelic, suberic, fumaric and itaconic acids.

Most preferably, the carboxylic acid is a hydroxycarboxylic acid, and most preferably the carboxylic acid is lactic acid.

The concentration of the carboxylic acid-containing fraction to be used for the nanofiltration in steps (ii) and (iii) is suitably in the range from about 5 to about 15% by weight of carboxylic acid, based on the total weight of the carboxylic acid-containing fraction, more preferably about 7 to 12 wt .-% and most preferably about 9 wt .-%.

In the context of the present invention, the retentate obtained from the second nanofiltration, if it has not been subjected to diafiltration, usually still contains residual carboxylic acid content in a concentration in the range of 80-120 g / l. It is therefore expedient to supply this retentate to a material recycling. A particularly suitable further utilization is a reaction of the carboxylic acid with an alcohol, such as methanol, ethanol or propanol, under esterification conditions. Since in particular for ethyl lactate a broad market, e.g. As a component of paints, detergents and in chip production, esterification with ethanol is particularly preferred in the context of the present invention.

The process described above may be conveniently further developed by subjecting the carboxylic acid-containing permeate fractions obtained from steps (ii) and (iii) to reverse osmosis following the two-fold nanofiltration to increase the concentration of the carboxylic acid solution. In this reverse osmosis, the carboxylic acid concentration in the carboxylic acid-containing fraction can be increased to about 25 to 40%. Thus, e.g. By using a high pressure reverse osmosis concentrations of about 35% carboxylic acid can be obtained.

The reverse osmosis is moreover advantageously carried out at a temperature in the range of below 40 ° C, in particular in the range of about 25 to 35 ° C.

The reverse osmosis can be carried out in particular as a two-stage process, in which case the still carboxylic acid-containing permeate is concentrated again in a second stage. The resulting concentrate or retentate can be combined with the retentate of the first stage. The permeate obtained from the second reverse osmosis can be suitably used as eluent in the SMB stage. This leads to a reduction in the RO water requirement (RO = reverse osmosis) for the SMB.

The permeate obtained as part of a reverse osmosis can also be used with advantage over a process water recycling in other process steps, for example, for the approach of nutrient solutions for fermentation.

Subsequent to the reverse osmosis, the resulting carboxylic acid-containing retentate fraction may conveniently be subjected to membrane distillation to achieve further concentration of the carboxylic acid solution. Thus, the pre-concentrated in the reverse osmosis product stream can be further concentrated in a downstream membrane distillation to a carboxylic acid concentration of more than 40 wt .-% and in particular about 50 to 55%. Conveniently, this membrane distillation can be carried out at temperatures of about 70 to about 80 ° C.

To prepare for the process according to the invention, it is furthermore expedient for the carboxylic acid-containing fermentation mixture, prior to addition to the Simulated Moving Bed chromatography step in step (i), to be subjected to a pre-purification comprising removal of biomass residues and acidification of the resulting crude product to form the biomass-free acidified carboxylic acid-containing fermentation mixture. For the pre-cleaning are essentially the known from the prior art process measures into consideration. Thus, for example, the separation of the biomass from the fermentation broth by a precoat and / or separation / centrifugation and / or microfiltration and / or ultrafiltration and the separated biomass can be recycled back into the fermenter. In this case, the temperature and pH correspond to the values of the fermentation, since it was found that by inactivating the biomass by increasing the temperature and lowering the pH by adding acid, autolysis of the biomass is accelerated and more lysis products are released into the fermentation broth. This is unfavorable due to the then required separation of the lysis products for the overall process. Also, the time between completion of the fermentation and separation of the biomass should be as short as possible and suitably not more than 2 hours, preferably less than 1-2 hours. The biomass concentration in the filtrate should not exceed 1 g / l. This process management positively influences the end product quality.

The filtrate from the precoat or microfiltration or the clarification of the separation / centrifugation is optionally fed to a single- or multi-stage ultrafiltration in which residual biomass fractions, insoluble solids and relatively high molecular weight compounds are separated off. Membranes with a cut-off of ≤ 50 kDa were found to be the optimum between product quality and flux rates of the membrane, preferably the cut-off limit is about 5 to 50 kDa and more preferably about 10 to 20 kDa. In a very particularly preferred embodiment, a conventional ultrafiltration with wound modules is first carried out up to a concentration factor of about 15 to 30. The permeate of this first ultrafiltration step is then fed directly to the acidification.

The concentrate or retentate of the first ultrafiltration step is expediently further concentrated in a second ultrafiltration unit to a concentration factor of 95 to 100. The second ultrafiltration stage can be operated with hollow fiber modules and / or tubular modules and in continuous filtration operation as well as in batch operation, with batch operation being preferred. The permeate of this second ultrafiltration stage may also be fed to the acidification while the retentate is being introduced into the effluent.

For the acidification of the obtained crude product it is expedient to use a mineral acid and in particular sulfuric acid. Acidification takes place, depending on the pKa of the carboxylic acid, such that at least 90%, more preferably at least 99% and most preferably at least 99.9% of the carboxylic acid is in the form of the fully protonated carboxylic acid. For lactic acid, a suitable pH range of 1.8 to 3.0, and preferably about 1.9 can be given here.

Since the process according to the invention is of particular advantage for the purification of non-crystalline carboxylic acids, of which lactic acid is the most important representative, in a preferred embodiment the process according to the invention does not involve any step of crystallization. Alternatively or additionally, the inventive method preferably for the purification of the carboxylic acid to a concentration of about 40% does not include a step of treating the carboxylic acid with activated carbon and / or an ion exchanger. It is particularly preferred if the method according to the invention does not include a step of crystallizing and for the purification of the carboxylic acid up to a concentration of about 40% any step of treating the carboxylic acid with activated carbon and / or an ion exchanger.

In an alternative preferred embodiment, the present invention relates to a process involving a crystallization step, preferably a cooling crystallization, of crystal-forming carboxylic acids. As the starting material for the crystallization, it is preferable to use a carboxylic acid having a concentration in the range of about 10 to 20%.

In the context of the process according to the two preceding variants, it is expedient if the saline by-product obtained from the Simulated Moving Bed chromatography step is subjected to concentration, since the recovery of this by-product is of great importance for economical operation of the process. For concentration, in the context of the present invention in particular a membrane distillation has been found to be particularly suitable. Membrane distillation has the advantage of lower overall and operating costs (for example, for the required steam and electric energy) over conventional multistage evaporation of the solvent used in the prior art. The membrane distillation is suitably preceded by a reverse osmosis with which the saline by-product for membrane distillation is preconcentrated to a concentration of up to 15 wt .-%.

The distillate obtained from the membrane distillation of the salt from the saline by-product can e.g. be used as eluent for the Simulated Moving Bed Chromatography stage, which is associated with the advantage of almost complete replacement of the previously required RO water (RO = reverse osmosis) as eluent for SMB chromatography. The above-described procedure also has the advantage that when using neutralizing agents in the fermentation which are different from ammonium hydroxide, e.g. NaOH or KOH, and the aqueous solutions of these salts formed during the salination and after successful SMB chromatography can be concentrated by reverse osmosis and membrane distillation.

For the membrane distillation of the carboxylic acid, which is connected downstream of the reverse osmosis, it is also advantageous if the vapor condensate from the evaporation of the saline by-product is used. This is primarily a purely thermal use into consideration, in which the still hot vapor condensate from the evaporation of the saline by-product is used to the carboxylic acid-containing fraction in the context of membrane distillation indirectly, i. e.g. via a heat exchanger, to heat.

Following the concentration steps of reverse osmosis and membrane distillation described above, it is expedient to subject the approximately 50% crude product to further nanofiltration, which will be referred to below as third nanofiltration. This third nanofiltration is suitable to carry out at pressures in the range of 30 to 40 bar. As a particularly favorable separation limit for the third nanofiltration, a separation limit of 300 daltons and in particular in the range of about 150 to 250 daltons can be specified.

For this nanofiltration of about 50% lactic acid, a pH in the range of about 1.3 to 1.5 can be given.

Depending on the preferred technology, the third nanofiltration retentate may be subjected to diafiltration, and then recycled back to the nanofiltration input stream in step (iii) or step (i) depending on the composition to avoid losses in the process.

Depending on the desired process procedure, it may also be advantageous to perform no diafiltration, but to esterify the retentate with a relatively high lactic acid content of about 60% together with the retentate of the second nanofiltration with an alcohol. Also in this case, a somewhat lower concentration factor is advantageous for a high quantity of the permeate of the third nanofiltration.

Subsequent to the third nanofiltration, the resulting carboxylic acid-containing fraction may be subjected to a polishing step in which the carboxylic acid is used to produce a high-grade carboxylic acid suitable for the polymerization, in particular in the form of lactic acid, via an ion exchanger, for example in the form of an anion and / or cation exchanger, and / or is cleaned via an activated carbon cleaning. Due to the already relatively high purity of the carboxylic acid and its relatively high concentration (about 50%) before polishing, much lower expenses for the regeneration and initial loading of the resins and / or the activated carbon are required than with corresponding purification steps with carboxylic acid fractions with concentrations below 20% and at an earlier stage of the cleaning process.

Since the product after the third nanofiltration, in particular when it is lactic acid, has a still insufficient for the polymerization, it is appropriate to increase the concentration, wherein the carboxylic acid-containing fraction is subjected to distillation. It is advantageous if the residue obtained in the distillation is mixed with water and then fed before step (iii) or step (i) as indicated above. With the help of distillation, the concentration of lactic acid can be increased to nearly 100%. When carrying out a distillation to produce the quality polymer grade can be dispensed with an upstream ion exchange and / or activated carbon treatment, when the yield of the distillation is economical and the required quality can be produced.

In the context of the investigations underlying the invention, it was surprisingly found that the carboxylic acid solution can be preconcentrated to a concentration of about 80% with a membrane distillation. For this membrane distillation, it is possible with advantage to use a system consisting essentially of plastic components, which may be e.g. under the trade name Memsys of Memsys Clearwater Pte. Ltd. is available. This system is a multi-stage vacuum multi-effect membrane distillation.

As is known, e.g. Lactic acid in the concentration range of 50 to 80% is very corrosive, especially at higher temperatures, so that in conventional distillation equipment only very high quality stainless steel, e.g. must be used in the form of Hastelloy. The use of a plastics-based membrane distillation system can reduce the cost of the concentrator. In addition, due to the lower temperature level required for membrane distillation, it is possible to remove waste heat streams from the treatment system, e.g. of the saline product stream obtained from the SMB chromatography step, via a heat exchanger in the membrane distillation system to use.

In order to achieve a concentration of the carboxylic acid of 100%, a distillation is required in the last concentration and purification step. The resulting vapors (i.e., gaseous distillation by-products that do not condense with the carboxylic acid as part of the condensation) typically still contain a portion of carboxylic acid. To avoid losses, these vapors are therefore returned to the process, for example, before the nanofiltration in step (iii) is returned to the process.

In addition, it has been found that the bottom product resulting from the distillation contains a proportion of carboxylic acid oligomers, e.g. of lactic acid. It is therefore useful in the context of the present invention for the bottom product obtained in the distillation to be admixed with water and then to be subjected to the purification before step (iii) or (i) as described above. For this purpose, it may be useful if the bottom product is first transferred to a container in which it is mixed with water and treated at a suitable temperature for a period of time, that the monomers form from the carboxylic acid oligomers by hydrolysis. For lactic acid, a temperature of about 50 ° C may be given as a suitable temperature and a period of about 2 hours as a suitable period.

It is possible to combine the recirculation of the vapor condensates with the recycle of the hydrolyzed carboxylic oligomers by passing the vapor condensates into the vessel in which the hydrolysis of the carboxylic acid oligomers occurs.

Alternatively, it is possible to use the by-products obtained in the distillation, such as the vapors and the bottom product after mixing with water for the preparation of derivatives of carboxylic acids, for example in the form of esters and in particular ethyl esters. It may therefore be appropriate if the Mixture of vapor condensates and the hydrolyzed carboxylic acid oligomers from the bottom product of a derivatization and in particular an esterification is subjected.

Depending on the nature of the carboxylic acid, if no direct further processing into polymers is possible, it may be expedient to dilute the 100% carboxylic acid obtained for storage with demineralized water. This is the case, for example, with lactic acid, since 80 to 90% lactic acid compared to 100% lactic acid has a much better storage stability.

As an alternative to the procedure described above after the third nanofiltration, crystallization, and preferably cooling crystallization, can also be carried out following this step if the carboxylic acid to be purified is crystallizable. Suitable methods and apparatus for carrying out a cooling crystallization are, for example, in DE 10 2014 213 637 A1 described.

In a second aspect, the present invention relates to an apparatus for purifying carboxylic acids from fermentation processes comprising a simulated moving bed chromatography stage 5, which is in flow communication with a first nanofiltration stage 6, and a second nanofiltration stage 60 in fluid communication with the retentate side of the first nanofiltration step 6 wherein the second nanofiltration step 60 a membrane with one compared to the membrane of the first nanofiltration stage 6 has lower separation limit. With regard to the specific embodiments of the membrane to be used in the nanofiltration stages, the statements made in this regard in the above statements on the process according to the invention apply analogously.

If, with the aid of the device according to the invention, in addition to the purified carboxylic acid, a carboxylic acid derivative, for example in the form of a carboxylic acid ester, is to be prepared, it is expedient for the device according to the invention to have a transfer 64 provided with the retentate side of nanofiltration 60 connected, and with the retentate from nanofiltration 60 in a device for derivatization 160 the carboxylic acid contained in the retentate can be converted.

The simulated moving bed chromatography step provides, in addition to the desired carboxylic acid product, a salt by-product in the form of a saline solution which can be recovered to improve the overall economics of the process. For this reason, the device according to the invention is useful with a derivative 51 equipped in fluid communication with the SMB chromatographic stage and a concentration stage 150 stands. In addition, it is useful if that in the Konzentrierstufe 150 distillate obtained via a feed line 153 to the SMB chromatography stage 5 is recycled as eluent, as can be reduced by this structure required for this process step amount of demineralized water. As mentioned above, it is advantageous if the evaporation stage 150 is carried out as membrane distillation. In this case, it is expedient for the evaporation stage to be preceded by a reverse osmosis stage / high-pressure reverse osmosis with which the salt solution for membrane distillation can be preconcentrated.

In a preferred embodiment, the device according to the invention has a reverse osmosis stage 7 which is in fluid communication with the first and second nanofiltration step (6, 60). Moreover, it is preferred if the device according to the invention further comprises a membrane distillation stage 8th which is in fluid communication with the reverse osmosis stage 7 stands.

The distillate of membrane distillation consists of sufficiently pure water and can therefore be used in the previous process stages as a replacement of demineralized water. In a preferred embodiment, therefore, the present invention has a feed line 80 on, with the recovered from the membrane distillation water as the eluent of the SMB chromatography stage 5 is supplied.

The at the evaporation stage 150 generated vapors can be used with advantage during the cleaning and concentration process thermally, are heated in the process streams in other process steps via heat exchange. For this reason, it is preferable for the device according to the invention, if they make a transition 153 identifies with which the vapors from the evaporation stage 150 be transferred to a heat exchanger, with which the process streams in the membrane distillation 8th can be heated.

Downstream of the membrane distillation is expediently a further nanofiltration stage 9 , with which from the membrane distillation 8th obtained concentrated product is further purified. Since the obtained in this purification retentate usually has a certain proportion of product carboxylic acid, it is associated with the advantage of a better product yield, if the nanofiltration with a derivative 92 Mistake is, with which the retentate from nanofiltration 9 as feed stream into the nanofiltration 60 can be returned. If, in addition to the carboxylic acid as product, a carboxylic acid derivative is also to be produced with the specified device, the device according to the invention can be used instead of the derivative 92 , or in addition, also a derivative 95 over that at the nanofiltration stage 9 generated retentate of a device for derivatization, in particular for the esterification of the carboxylic acid, can be supplied.

Upstream of the described device according to the invention are expedient conventional devices for the fermentative production of carboxylic acids, devices for the separation of fermentation residues from the fermentation broth and devices for acidification of the carboxylic acid. In other words, the present invention thus also relates to a device comprising the above-described process steps in combination with an upstream device for the fermentative production of carboxylic acids, one or more devices for separating fermentation residues from the fermentation broth and an apparatus for acidifying the carboxylic acid. The technical background for the acidification device is that in the fermentative production of the carboxylic acid from non-acidic precursors such as glucose, the pH increases systemically. Since the production efficiency of the microorganisms normally used for fermentation processes decreases significantly at strongly acidic pH values, the pH is kept substantially constant during the course of the fermentation by addition of a base, such as, in particular, ammonium hydroxide, but with the result that as a product not the carboxylic acid itself, but its salt is obtained. It is particularly preferred if the device according to the invention is a fermentation device 1 , a separation device 2 in which the biomass from the fermentation is separated from the fermentation broth, and an acidification device 4 , in which the carboxylic acid product is converted by the addition of an acid from the carboxylic acid salt in the corresponding carboxylic acid, is connected upstream.

The permeate obtained from the reverse osmosis can still contain small amounts of carbon-based compounds such as in particular carboxylic acids. The device according to the invention can therefore be advantageously further configured by the one line 71 with which the obtained from the reverse osmosis permeate the fermentation device 1 can be forwarded. Before the supply of permeate in fermentation device 1 In addition, a mixing device may be present in which the composition of the permeate can be adapted by adding further substances to that of a sewing medium which is optimal for the fermentation.

The separation device 2 is useful as a two-stage separation device with a separation stage 2 taking advantage of gravity and an ultrafiltration stage 3 executed. The ultrafiltration stage can be carried out in one or more stages, wherein preferably initially a conventional ultrafiltration stage with wound modules is present, from which the permeate via a derivative 31 directly into the acidification device 4 can be transferred, and from which the retentate is transferred to a further ultrafiltration stage, which is preferably equipped with hollow fiber modules and / or tube modules. This ultrafiltration stage expediently has a feed line 33 on, with the generated in this ultrafiltration step permeate in the acidification device 4 can be transferred.

To that from the Nanofiltrationsstufe 9 The product according to the invention can be concentrated further with a distillation apparatus 11 be fitted downstream to the membrane distillation stage 8th is positioned. This distillation device 11 is preferably designed so that a concentration of the carboxylic acid to about 80% is possible.

As explained above, it makes sense to use the carboxylic acid-containing permeate of the nanofiltration stage 9 subject to a polish. This is particularly useful if you want to dispense with a distillation. It is therefore preferred for the device according to the invention, if this one of the nanofiltration 9 in the flow direction downstream polishing device, which is expediently equipped with a cation exchanger and / or anion exchanger and / or an activated carbon cleaning. For the production of lactic acid in the quality grades technical quality and / or food-grade can be dispensed with the ion exchange and / or the activated carbon treatment.

Furthermore, it has already been mentioned above that there is a favorable Vorkonzentrierung the on the distillation apparatus 11 final carboxylic acid to be concentrated via one of the distillation apparatus 11 achieves upstream membrane distillation. For the device according to the invention it is therefore preferred when the distillation device 11 a membrane distillation device 10 upstream in the flow direction. Also for these, the waste heat of the condensation of the vapors from the evaporation 150 be used thermally, so that the membrane distillation device 10 preferably with a transfer 152 is provided, with which the vapors from the evaporation device 150 be transferred to a heat exchanger, with which the process streams in the membrane distillation 10 can be heated.

In order to reduce the loss of product contents in by-products of the cleaning and concentration apparatus according to the present invention, the apparatus according to the invention, when using a distillation apparatus 11 has, preferably one or more transitions 111 / 112 on, on the residues resulting from the distillation with water and upstream to the distillation apparatus 11 , preferably before and in particular directly before the second nanofiltration stage 60 can be returned to the device. So has the distillation device 11 appropriate a transfer 111 on, with the vapors from the distillation device 11 in a mixing container 110 can be converted, in which the vapors or condensates thereof can be mixed with water. In addition, the distillation device 11 appropriate a transfer 112 on, with the bottom product from the distillation apparatus 11 in the mixing container 110 can be transferred. The mixing vessel in this case is preferably equipped with stirring and heating devices with which the mixed product can be heated and subjected to hydrolysis. The mixing container is also useful with a transfer 120 equipped with the optionally hydrolyzed product in front of the nanofiltration device 60 and in particular directly in front of the nanofiltration device 60 , can be returned to the device according to the invention.

Alternatively or additionally, it is possible that the mixing container 110 with a transition 114 equipped with the optionally hydrolyzed product in a device for dervation of the carboxylic acid 160 can be transferred. Preferably, both devices are concerned 160 to a device for the esterification of the carboxylic acid.

In another embodiment, this may be from the nanofiltration step 9 obtained product are fed to a crystallization apparatus when the carboxylic acid to be purified is crystallizable. Preferably, this crystallization device is designed as a cooling crystallization, as described for example in the DE 10 2014 213 637 is described.

In the following, the present invention will be explained in more detail with reference to the figures, without these being considered to be relevant to the scope of the present invention.

In 1 a process diagram of an embodiment of the present invention is shown, in which a return of product streams is provided, without that in addition to concentrated carboxylic acid still other products are generated. 1 is explained with reference to lactic acid as the carboxylic acid as follows.

In the fermentation unit 1 a fermenter broth is produced, which preferably contains lactic acid in the form of ammonium lactate in aqueous solution, as well as biomass and residual nutrients / metabolites of the microorganisms. In the subsequent separation process stage 2 the biomass and remaining particles are in the form of biomass suspension 21 separated from the fermenter broth. In the separation, using gravity, a solid free clear is obtained, which is then used for further purification of an ultrafiltration 3 is supplied. The permeate of the ultrafiltration becomes the acidification 4 fed during the retentate into the wastewater 130 is initiated.

In the acidification 4 is made with the help of concentrated sulfuric acid, which is via the supply line 140 is fed, the permeate of the ultrafiltration acidified to a pH of about 1.9. The purified and acidified fermentation solution is then subjected to SMB chromatography 5 in aqueous lactic acid solution and ammonium sulfate solution 51 separated. The ammonium sulfate solution is used in the subsequent process stage 150 further processed to ammonium sulfate crystals.

For separation into carboxylic acid and saline in the SMB, an eluent is needed. In conventional design, this is RO water 52 used. In 1 In order to reduce the demand for RO water, the distillate produced from the membrane distillation upstream in the course of the process 81 , as well as vapor condensate 153 fed to the conventional evaporation.

The extract of the SMB chromatography is further purified in the nanofiltration process stage. Nanofiltration is also carried out in two stages. In nanofiltration 6 Concentration is based on the concentration factor 3 - 5 using membranes with a cut-off of 300-500 Da. The permeate 61 the nanofiltration 6 is led directly to the concentration stage reverse osmosis, while the retentate 62 as starting material for the second stage nanofiltration 60 is used. In this Cleaning step, a concentration on the factor 65 - 80 with membranes of cut-off 200-250 Da. The permeate 63 also flows to the reverse osmosis.

The resulting retentate 64 gets into the sewage stream 65 initiated.

To avoid losses during nanofiltration 60 In the last step a diafiltration is carried out. As diafiltration water 82 is distillate from the upstream membrane distillation 8th used. To avoid losses in the upstream processing steps is carried out a return of retentate 93 from nanofiltration 9 and product from the recycle of the reverse oligomerization 120 ,

In the next process step, reverse osmosis 7 Concentration of the purified solution, whereby conventional reverse osmosis (up to 70 bar) lactic acid concentrations of 20-25% can be achieved. When using high-pressure reverse osmosis (up to 140 bar), concentrations of up to approx. 35% lactic acid can be obtained. The permeate of reverse osmosis 71 contains still small amounts of lactic acid and can be used as starting water for the carbon source of the fermentation or of nutrient solutions in the dissolution station of the fermentation 100 be used.

The preconcentrated in the reverse osmosis product stream is in the subsequent membrane distillation 8th be concentrated to a lactic acid concentration of 50-55%. Membrane distillation occurs at temperatures of 70 to about 80 ° C. To heat the feed stream is the vapor condensate 151 used for the evaporation of the ammonium sulfate solution (only thermal utilization of the heat content of the vapors, the vapors are used materially in the SMB). For the distillation 10 it is necessary to use cooling water 180/181.

The distillate 80 Membrane distillation is used as eluent for the SMB and as water for nanofiltration diafiltration as previously described. After membrane distillation 8th the concentrate is in the form of an approximately 50% lactic acid solution of a repeated nanofiltration 9 subjected. Diafiltration water also becomes in this filtration stage 83 used in the form of distillate from the membrane distillation. To prevent product loss, the retentate 92 the nanofiltration 9 in the nanofiltration 60 recycled.

To remove further pollutants, in particular for the production of a high-quality lactic acid for the polymerization, the permeate 91 the nanofiltration 9 in the polishing unit 90 further cleaned. Periodically, a partial stream of nanofiltration retentate 94 directed into the sewage.

2 shows the further processing of the permeate from nanofiltration 9 to 100% lactic acid, for better storage with demineralized water over the supply line 53 diluted to 90% lactic acid. For this purpose, the permeate from the nanofiltration is first in a polishing unit 90 which may consist of the following parts: cation exchanger and / or anion exchanger and / or activated carbon cleaning. The regeneration solutions obtained in the regeneration of the exchange resins are at higher content of lactic acid via the supply line 192 the re-polymerization in the container 110 fed, or are at low lactic acid concentration on the derivative 191 discharged into the sewage.

The now purified again concentrated lactic acid becomes a final membrane concentration in the form of a membrane distillation 10 subjected.

The feed stream for membrane distillation 10 becomes analogous to membrane distillation 8th by regenerative heat exchange with expiring product and by using the heat content of the vapors 152 from the ammonium sulfate evaporation to about 80 ° C warmed. On the distillate side cooling also takes place with cooling water 180/181. The distillate 101 the membrane distillation 10 is also used for nutrient uptake in fermentation.

The past purification and concentration of the lactic acid solution by a membrane process is gentle on the product and produces a concentrated lactic acid of very good quality, i. obtained polymerizable.

The last concentration and purification step is a distillation 11 carried out. The lactic acid is concentrated to 100%. The outgoing in the distillation overhead vapors still have a high lactic acid content and are therefore to avoid losses via the supply line 111 in the mixing device 110 recycled. The same applies to the bottom product of the distillation, via the supply line 112 into the mixing device 110 to be led.

By the mixture of waste products from the distillation 11 with the regeneration waters from the polishing 90 There is a re-polymerization of higher lactic acid polymers to the monomer. This repolymerization takes place in the stirred tank 110 instead of. To avoid losses, this solution becomes 120 for cleaning the nanofiltration 60 fed. Alternatively, the solution 120 the product stream before the SMB chromatography step 5 be fed into the process. The impurities contained are thereby with the retentate 64 into the sewage 65 discharged from the system.

Periodically, a portion of the bottoms product is in the wastewater 113 discharged. After the production of 100% lactic acid in the distillation is by adding deionized water through the feed line 53 a storage stable 80 to 90% lactic acid as the final product 12 produced.

In 3 is a process diagram of another embodiment of the present invention is shown, is used in the lactic acid-containing by-products of the process for the production of a product other than lactic acid, for example in the form of lactic acid ethyl ester. The basic structure of this process diagram corresponds to that 1 but instead of recycling the lactic acid-containing process by-pass stream from nanofiltration 9 a supply line 95 is provided, with the lactic acid-containing fraction of an esterification device 160 is supplied. Another difference of the process diagram is that the nanofiltration 60 is not carried out as a diafiltration, but that produced by a regular nanofiltration retentate also an esterification device 160 is supplied.

4 shows a process diagram for the further processing of the permeate from nanofiltration 9 analogous 2 , where from the distillation 11 about the derivatives 111 and 112 derived lactic acid-containing by-product after passing through the mixing device 110 an esterification device 160 is supplied.

5 shows a process diagram for working up of crystal-forming carboxylic acids.

The process of succinic acid explains this process in more detail below. The permeates of the first and second nanofiltration 61 and 62 will be in the following reverse osmosis 7 concentrated to a concentration of about 12% by mass. The concentrate of this succinic acid solution is also in the third nanofiltration 9 further purified, the retentate 95 an esterification 160 is supplied.

The permeate of the third nanofiltration 9 is then a cooling crystallization 170 fed. This cooling crystallization may be as in DE 10 2014 213 637 be executed described. The first stage of the cooling crystallization is done with cooling water 183 / 184 and the 2nd stage to increase the crystal yield with brine 185 / 186 operated. The final product of the cooling crystallization are the purified and dried succinic acid crystals 171 receive.

In the prior art, a concentrated salt solution, referred to as a mother liquor, is produced in the cooling crystallization. To avoid product losses, this mother liquor may be recycled to the process, or it may be a leak from the process 173 , preferably with a feed into an esterification 160 respectively.

The mother liquor 173 is useful in the context of a return of the third nanofiltration 9 fed. But it is also technologically possible a return / partial return 174 / 175 in the first nanofiltration 6 , or before the SMB chromatography 5 make.

In the following, the application will be explained in more detail with reference to some examples, which, however, are not to be regarded as authoritative for the assessment of the scope of protection of the present application.

Examples:

Example 1:

2-stage nanofiltration, comparison of conventional nanofiltration with a 2-stage nanofiltration and different separation limit.

In a nanofiltration plant of a large-scale experimental plant for the production of organic acids, an experiment for the filtration of aqueous lactic acid solution was carried out. This nanofiltration system consists of two filtration loops, each with a pressure tube and a loop pump. Each pressure tube was fitted with 3 NF polymer winding elements of size 8038 with a total membrane area of 103.5 m ² . Filtration batches of about 75 m ³ were always filtered.

The key data for this two-stage nanofiltration are given below: Feed product: permeate of nanofiltration with separation limit 450 Da Feed current: 3.5 m ³ / h Temperature: 40 ° C Operating pressure: 12-25 bar, increasing for constant flux rate Flux Rate Loop1: 15-20 l / m ² h Flux Rate Loop2: 10-12 l / m ² h Concentration factor: 70 x diafiltration: 5 % of the feed stream

A mixed permeate with the following quality was produced: Sulfate content: 240 mg / l Ammonium content: 750 mg / l Phosphate content: 50 mg / l APHA value: 150

In a subsequent trial period was in the 2nd Filtration loop 3 Pieces of NF winding modules with a lower separation limit of 200-300 Da installed. This corresponds to the specifications for the second nanofiltration according to the invention. As in the other experimental period, about 75 m ³ each were filtered in a batch.

The following parameters were set or determined during the experiment: Feed current: 3.5 m ³ / h Temperature: 40 ° C Operating pressure: 10-18 bar, increasing for constant flux rate Flux Rate Loop1: 20-23 l / m ² h Flux Rate Loop2: 10-15 l / m ² h Concentration factor: 60 x diafiltration: 7 % of the feed stream

A mixed permeate with the following quality was produced: Sulfate content: 90 mg / l Ammonium content: 450 mg / l Phosphate content: 20 mg / l APHA value: 45

A comparison between the conventional nanofiltration and the separation into first and second nanofiltration with different separation limit is given in Table 1 below: TABLE 1 parameter Conventional nanofiltration Nanofiltration according to the invention Improvement of permeate quality Cut off Loop 1 (Da) 400-450 400-450 Cut off Loop II (Da) 400-450 200-300 Sulfate concentration (mg / l) 240 90 62.5% Phosphate concentration (mg / l) 50 20 60% Ammonium content (mg / l) 750 450 40% APHA value 150 45 70%

Example 2:

Third Nanofiltration: Nanofiltration of a 50% lactic acid solution

In a small scale filtration experimental plant, an attempt was made to nanofilter 50% lactic acid. For this purpose, a polymer winding element with a filter area of 0.23 m ^{2 was} used. The separation limit was 200-300 Da. 200 l of a 50% strength lactic acid from the first evaporation stage of a large-scale pilot plant was used as feed product.

The following parameters could be determined in the filtration test. permeate: 192 l retentate: about 8 l Concentration factor: 20 x Filtration Yield: 95 % Filtration pressure: 33 bar flux rate: about 20 l / m ² h pH value feed solution: 1.25 APHA value feed: 145 APHA value permeate: 25 Reduction of APHA value: 83 %

In comparison to the concentration in the feed product, a reduction was determined in the permeate pool obtained from the following substance groups: Glucose: 70% Ammonium: 75% Sulfate: 95%

The permeability of the membrane with respect to lactic acid was found to be 96%, which means that despite the low pH only a small part of the lactic acid is preferentially enriched in the retentate. This experiment shows that even a 50% lactic acid can be purified with a narrow nanofiltration membrane.

Example 3:

Third Nanofiltration: Nanofiltration of a 50% lactic acid

In a technical test facility, the following results were determined using a size 2540 NF polymer winding module. Concentration factor: about 7 x Filtration Yield: 88 % Filtration pressure: 20 bar flux rate: about 9 l / m ² h pH value feed solution: 1.1 APHA value feed: 290 APHA value permeate: 42 Reduction of APHA value: 85.5 % Amino Acids Feed: 258 mg / l Amino Acids Permeate: 104 mg / l Reduction of amino acids: 60 %

Example 4:

In a reverse osmosis plant of a large-scale experimental plant for the production of organic acids, an attempt was made to concentrate aqueous lactic acid solution. The reverse osmosis system consisted of two membrane stages, wherein in the 1st stage 6 Piece of 4040 polymer wound modules with a filter area of 94.7 m ² and in the second stage 3 Piece winding elements with a membrane area of 47.3 m ^{3 were} installed. The experiment was successfully carried out over a period of 72 h, with the following parameters being determined: Feed product: permeate of nanofiltration with separation limit 450 Da Feed current: 3.5 m ³ / h Temperature: 38 ° C Operating pressure: 75 bar Permeate stream 1st bank: 1.77 m ³ / h Permeate stream 2nd bank: 0.45 m ³ / h Concentrate stream: 1.3 m ³ / h Volume concentration rate: 2.7 x LA concentration feed stream: 86 g / l LA concentration concentrate stream: 230 g / l

Example 5:

In a 1-stage technical pilot plant a high-pressure reverse osmosis test was carried out with a size 2540 polymer winding module.

The following parameters were determined in this experiment: Operating pressure: 120 bar Temperature: 24.5 ° C flux rate: 15.2 l / m ² h Volume concentration rate: 2.8 x LA concentration feed stream: 117 g / kg LA concentration concentrate stream: 328 g / kg

Example 6:

In a pilot plant with a multi-stage vacuum multi-effect membrane distillation (manufacturer of the membrane modules: Messrs. Memsys) and a membrane area of 6.4 m ² , the following parameters were determined: Feed current: 130 l / h recirculation: 95 l / h Distillate flow: 35 l / h flux rate: 5.5 l / m ² h Distillation temperature: 70-74 ° C Distillate outlet temperature: about 37 ° C Volume concentration rate: 6.5 x LA concentration feed stream: 110.5 g / kg LA concentration concentrate stream: 714.6 g / kg Lactic acid retention: 99.6 %

LIST OF REFERENCE NUMBERS

1

fermentation

2

separation

3

ultrafiltration

4

acidification

5

SMB chromatography

6

Nanofiltration I

7

reverse osmosis

8th

Membrane distillation I

9

Nanofiltration III

10

Membrane distillation II

11

distillation

12

Final product 90% lactic acid

21

biomass suspension

30

Ultrafiltration high concentration

31

Permeate ultrafiltration

32

Retentate ultrafiltration, feed high concentration

33

Permeate Ultrafiltration High Concentration

51

SMB raffinate

52

DI water eluent SMB

53

DI water, dilution 100% lactic acid

60

Nanofiltration II

61

Permeate Nanofiltration I

62

Retentate Nanofiltration I, Feed Nanofiltration II

63

Permeate nanofiltration II

64

Retentate nanofiltration II

65

sewage

71

Permeate reverse osmosis

80

Distillate membrane distillation I

81

Distillate membrane distillation I, eluent SMB

82

Water Diafiltration Nanofiltration II

83

Water Diafiltration Nanofiltration III

90

Polishing unit

91

Permeate Nanofiltration III

92

Retentate Nanofiltration III

93

Retentate recycling Nanofiltration III

94

Retentate nanofiltration III, wastewater

95

Retentate Nanofiltration III

100

Media approach fermentation

101

Distillate Membrane Distillation II

110

Mixing, re-oligomerization

111

Vapor distillation

112

Recycling bottom product distillation

113

Bottom product distillation wastewater

114

Mixed product Rückoligomerisierung for esterification

120

Recycling to nanofiltration II

121

Feedback to SMB chromatography

130

Retentate ultrafiltration high-concentration wastewater

140

concentrated sulfuric acid

150

Evaporation SMB raffinate

151

Vapors evaporation SMB raffinate for thermal utilization in MD I

152

Vapors evaporation SMB raffinate for thermal utilization in MD II

153

Vapors evaporation SMB raffinate as eluent SMB

160

esterification

170

cooling crystallization

171

Succinic acid crystals

172

Mother liquor recycling nanofiltration III

173

Mother liquor for esterification

174

Mother liquor recycling Nanofiltration I

175

Mother liquor recycling SMB chromatography

181

Cooling water flow Membrane distillation

182

Cooling water return membrane distillation

183

Cooling water flow cooling crystallization

184

Cooling water return cooling crystallization

185

Cooling brine flow cooling crystallization

186

Cooling brine return cooling crystallization

191

Wastewater Polishing

192

Recycling rinse water polishing

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 8957249 [0004]
• WO 2013/064219 [0005]
• WO 2014/106532 A2 [0006]
• WO 2014/106532 [0006]
• DE 102014213637 A1 [0052]
• DE 102014213637 [0068, 0092]

Cited non-patent literature

• Dahlman, J., et al., British Polymer Journal, 23: 235-240, 1990 [0002]

Claims (17)

Process for the purification of carboxylic acids from fermentation processes, in which: (i) subjecting a biomass-free, acidified, carboxylic acid-containing fermentation mixture to a Simulated Moving-Bed chromosome stage, (ii) subjecting the carboxylic acid-containing fraction obtained from step (i) to a first nanofiltration, and (iii) subjecting the carboxylic acid-containing retentate fraction obtained from step (ii) to a second nanofiltration which has a lower cut-off limit than the first nanofiltration. Method according to Claim 1 , characterized in that the carboxylic acid is in the form of a hydroxycarboxylic acid and preferably in the form of lactic acid. Method according to Claim 1 or 2 , characterized in that the obtained from step (ii) carboxylic acid-containing fraction is subjected to a reverse osmosis. Method according to Claim 3 , characterized in that the obtained from the reverse osmosis carboxylic acid-containing fraction is subjected to a membrane distillation. Method according to one of Claims 1 to 4 characterized in that a carboxylic acid-containing fermentation mixture, prior to being added to the simulated Moving-bed chromamography step in step (i), is subjected to a pre-purification comprising separation of biomass residues and acidification of the resulting crude product, preferably with sulfuric acid to form the biomass-free, acidified, carboxylic acid-containing fermentation mixture. A method according to any one of the preceding claims, characterized in that the membrane used for the first nanofiltration has a cut-off of 500 daltons or less, preferably 400 daltons or less, and more preferably about 400 to 300 daltons. Method according to one of the preceding claims, characterized in that the membrane used for the second nanofiltration has a cut-off of 300 daltons or less, preferably 250 daltons or less, and more preferably about 200 daltons. A method according to any one of the preceding claims, characterized in that the method does not involve a step of crystallizing and for the purification of the carboxylic acid to a concentration of about 40%, no step of treating the carboxylic acid with activated carbon and / or ion exchanger. Method according to Claim 4 or any claim depending thereon, characterized in that the salt-containing by-product obtained from the simulated moving-bed chromatography step is subjected to evaporation, and that the waste heat obtained from this evaporation is used for membrane distillation. Method according to one of the preceding claims, characterized in that the salt-containing by-product obtained from the simulated moving-bed chromatography step is subjected to evaporation and the distillate of the simulated moving-bed chromatography step (i) released during the evaporation is used as eluent is fed again. Method according to Claim 4 or a claim dependent thereon, characterized in that the carbonic acid-containing fraction obtained from the membrane distillation is subjected to a third nanofiltration, which is preferably carried out at a pH of at least 3 and in particular about 1.5, and preferably a separation limit in the range of about 150 to 250 daltons. A process according to any one of the preceding claims, characterized in that the carbonic acid-containing fraction obtained by the process steps according to the preceding claims is subjected to distillation, water preferably being added to the residue obtained in the distillation, followed by purification prior to step (iii). according to Claim 1 is supplied. Method according to Claim 11 , characterized in that the process after the third nanofiltration involves crystallization and that the carboxylic acid is a carboxylic acid forming crystals. Method according to Claim 13 , characterized in that the crystallization is carried out as a cooling crystallization, wherein the resulting mother liquor is recycled to upstream stages of the process. An apparatus for purifying carboxylic acids from fermentation processes comprising a simulated moving bed chromosome stage (4) in fluid communication with a first nanofiltration stage (6) and a second nanofiltration stage (60) in fluid communication with the retentate side of the first nanofiltration stage , wherein the second nanofiltration stage has a membrane with a lower separation limit compared to the membrane of the first filtration stage. Device according to Claim 15 characterized in that it further comprises a reverse osmosis stage (7) which is in flow communication with the second nanofiltration stage (60) and preferably additionally comprises a membrane distillation stage (8) in fluid communication with the reverse osmosis stage (7). Device according to Claim 16 , characterized in that it has one of the membrane distillation stage (8) in the flow direction downstream distillation apparatus (11) having one or more cross-overs, with which formed in the distillation residues with water and recycled before the second Nanofiltrationstufe (60) in the device can be.

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