A PROCESS FOR THE RECOVERY OF DICARBOXYLIC ACID

Abstract: The invention provides a process for the recovery of a dicarboxylic acid from an aqueous feed solution containing at least one salt of the acid, comprising the steps of: (a) reacting the feed solution with CO2 and with an anion exchanger, the anion exchanger being water immiscible in both free base and salt form, whereby the dicarboxylic acid forms an adduct with the anion exchanger and a carbonate of the salt's cation is formed in the resulting aqueous solution; (b) separating the dicarboxylic acid-anion exchanger adduct from the resulting aqueous solution; and (c) recovering the dicarboxylic acid from the adduct by methods known per se.

Description: A Process for the Recovery of Dicarboxylic Acid The present invention relates to a process for the recovery of a dicarboxylic acid from a feed aqueous solution containing salts thereof. Dicarboxylic acids such as fumaric acid, malic acid and succinic acid can be produced by fermentation of carbohydrates such as dextrose, pure sucrose dissolved in an aqueous solution and sucrose in molasses. The fermentation is conducted at about neutral pH and a neutralizing agent is added for pH adjustment. Both pKa's of the dicarboxylic acids are below 7 and typically below 6. As a result, at the pH of fermentation, both carboxytic groups are neutralized. Thus, their recovery, in an acid form, from the fermentation liquor requires chemical conversion. Several processes were developed for such conversion. The conversion could liberate the dicarboxylic acid in solution, e.g. by displacement with a strong, usually mineral, acid. Thus, when caicium bases are used as the neutralizing agents in the fermentation of fumaric acid, calcium fumarate is formed. Reacting the calcium fumarate containing fermentation liquor with sulfuric acid results in precipitation of gypsum and liberation of fumaric acid. By-products that are preferred over gypsum could be formed. Thus, in those cases where ammonia was used as the neutralizing agent and sulfuric acid is the displacing acid, ammonium sulfate is the by-product salt. It can be used as a low grade fertilizer. The latter, however, does not pay for the ammonia and sulfuric acid consumed. Another difficulty is that of separating the liberated acid. Some of the dicarboxylic acids are of low water solubility and precipitate out of the solution due to the acidulation. Additional purification steps are required to remove impurities resulting from the broth. In some cases the by-product salt may coprecipitate as well. For soluble dicarboxylic acids one may consider distillation as such, distillation of their esters or extraction. As the acid is liberated, the extractant could be a relatively weak one and would allow the recovery of the product acid at a r elatively high concentration by back-extraction. The known (and food approved) weak extractants to be considered are amine-based ones or solvating extractants (one may consider esters, ethers, ketones, etc., however alkanols are preferable). Out of these two groups, the amine-based ones are more attractive for several reasons: (i) they are more selective and would therefore provide for higher product purity, (ii) their extraction capacity is higher and therefore the extractant flow will be lower, and (iii) the amine-based extractants provide for temperature sensitive distribution and therefore provide for the "uphill pumping" through back-extraction at a temperature that is higher than that of the extraction. These preferred amine-based extractants would not work where the strong displacing acid is added to the fermentation liquor to form a soluble by-product salt since amine-based extractants prefer the stronger acid in a mixture and wouid therefore reverse the reaction (remove the added acid). Acidulating neutral fermentation liquors by the addition of strong acids usually results in the formation of by-product salts such as gypsum, ammonium and sodium sulfate. Reagents are consumed and disposal of undesired by-products is required. Efforts have recently been made to recover acids from fermentation liquors without formation of such by-products In some recently published patents liquid-liquid extraction (LLE) is applied for salt splitting Thus, e.g., in King's US Patent 5,132,456, a strongly basic extractant extracts part of the acid from the neutral solution, which results in an acid-loaded extractant and a basic solution. This basic solution that still contains most of the acid values could be recycled as a neutralizing medium to the fermentation. Recovery of the extracted acid, in acid form, from such strong extractants is difficult as they are strongly bound thereto. US 5,132,456 suggests a way to solve this problem it comprises back-extraction with an aqueous solution of ammonia or low molecular weight alkyl amine, especially tπmethyl amine (TMA). The resultant aqueous ammonium or alkylammomum carboxylate solution can be concentrated, if necessary, and the carboxylate can be thermally decomposed to yield the product carboxylic acid and ammonia or amine, which can be condensed and recycled. The main problem with this process is the strong binding between the acid and the rather strongly basic ammonia or TMA (pKa's of 9-11). Energy consumption is high and undesired reactions take piace. Another difficulty results from the fact that TMA is highly soluble in aqueous solution and highly undesired in food products. Its complete removal could be problematic. King's process is, therefore, costly and complex. Urbas proposes , in his US patent 4,444,881 , a process for the recovery of an organic acid selected from the group consisting of propionic acid, butyric actd, lactic acid and citric acid, from an aqueous solution of its calcium salt, which comprises the steps of: (a) adding a molar equivalent of a water soluble tertiary amine carbonate to the calcium salt solution to form a trialkylammonium salt of the acid in solution and a precipitate of calcium carbonate; (b) concentrating the trialkylammonium salt solution; and (c) heating the concentrated trialkylammonium salt solution to obtain the acid and the tertiary amine. Urbas' process reaches higher yields than that of King due to the fact that most of the acid could be bound to the amine, whiie the pH in the solution remains relatively low. The liberated base does not accumulate in the aqueous solution as calcium carbonate forms and precipitates. Yet, the reaction does take place in the basic pH range and, in order to form the trialkylammonium salt of the organic acid, the tertiary amine should be a strong one. That is why Urbas selects water soluble amines. Separating the organic acid from the tertiary amine is therefore as problematic as in King's process. With this state of the art in mind, it has now been found according to the present invention that reacting an aqueous solution that comprises a salt of a dicarboxylic acid with a moderately strong anion exchanger in the presence of C0 2 results in significant binding of the carboxylic acid to the anion exchanger. In a multi-stage counter current contact most of the acid values in the solution can be transferred to the anion exchanger. Thus, according to the present invention, there is now provided a process for the recovery of a dicarboxylic acid from an aqueous feed solution containing at least one salt of said acid, comprising the steps of: (a) reacting said feed solution with C0 2 and with an anion exchanger, said anion exchanger being water immiscible in both free base and salt form, whereby said dicarboxylic acid forms an adduct with said anion exchanger and a carbonate of said salt's cation is formed in the resulting aqueous solution; (b) separating said dicarboxylic aαd-anion exchanger adduct from the resulting aqueous solution, and (c) recovering said dicarboxylic acid from said adduct by methods known per se. In the process of the present invention said salts of said dicarboxylic acid contained in said aqueous feed solution can be mono- salts, di- salts and mixtures thereof and said formed carbonate can be a carbonate or a bicarbonate Said recovery of said dicarboxylic acid can be effected by various methods including distillation, neutralization and displacement by another acid. In a first preferred embodiment of the present invention said recovery in step (c) ts effected by contacting said adduct with an aqueous medium to effect the back extraction and recovery of said acid. In a further preferred embodiment of the present invention said recovery in step (c) is effected by reacting said adduct with known reagents to form a compound of said acid. In yet another preferred embodiment of the present invention said recovery in step (c) is effected by contacting said adduct with another acid, whereby said dicarboxylic acid is displaced by said acid. Israeli Patent 33,552, assigned to Israel Mining Industries - Institute for Research and Development (hereinafter IMI) and of which the inventor of the present invention was a co-inventor, claims a process for the manufacture of alkali metal bicarbonates, wherein a saturated aqueous brine is reacted with CO 2 in the presence of a solvent containing a water insoluble amine, separating the solvent phase and treating the separated organic phase with a slurry of a magnesium base in order to decompose the amine hydrochloπde, regenerating thereby the solvent As far as one can conclude from the IMI patent and from a later publication by one of the inventors (R Blumberg et. al. in Proceedings of the International Solvent Extraction Conference 1974, Vol. 3 pp. 2789-2802), this process is not applicable to the recovery of dicarboxylic acids from their salts According to the teaching there, the aqueous feed to the reaction should be saturated and should stay nearly saturated throughout the reaction. For the present case that would mean that the salt of the dicarboxylic acid would first have to be crystallized from the fermentation liquor and that the crystalline salt would have to be added to the reaction medium. This costly operation may still work in the case where the salt can be crystallized in a rather pure form In the case of a fermentation liquor the crystallized salt would contain impurities that would accumulate in the solution. In addition, a nearly complete recovery of the salt from the solution is not feasible. That is not a problem in the case of a low cost salt as in the case of the IMI patent, but is not acceptable for a dicarboxylic acid salt. Another problem is indicated by the method of recovering the acid and regenerating the solvent. The hydrochloric acid carrying solvent is reacted with a rather strong mineral base such as magnesium oxide or hydroxide. The mineral base is stronger than the active component of the ion exchange solvent, the amine, and displaces it from the amine hydrochloride formed on the reaction. The solvent is thereby regenerated. The magnesium chloride formed is decomposed at high temperature to the magnesium base and to HCI Similar separation of the bound acid and regeneration of the anion exchanger would be very difficult to implement in the case of the dicarboxylic acids, which have high boiling points and are sensitive to thermal decomposition Yates, in US patent 4,282,323 claims a process for recovering a carboxylic acid containing from 1 to 20 carbon atoms from an aqueous source solution of an alkali metal, alkaline earth metal or ammonium salt of said carboxylic acid, comprising contacting said aqueous solution in the presence of a liquid polar organic solvent having a boiling point of from -30C to 90C, with carbon dioxide under pressure, to convert at least part of said salt to the corresponding acid, whereby said acid is dissolved in said solvent, and recovering said acid therefrom Yates' process applies only for weak acids (and is specifically described mainly for acetic acid) The reason for that is that the claimed conversion is, in fact, displacement of the separated acid from its salt by carbonic actd, which is a very weak one Even for acetic acid, pKa of 4 75, the yields found by Yates are quite low Reaching a significant conversion yield in the case of stronger acids, such as fumaric acid, is inconceivable Thus, in the patents of King and Urbas the extractant/adsorbent needed was too strong for the needs of the present process. In the case of Yates the extractant is a weak base, but the process applies only for weak acids The IMI process uses an extractant that falls under the definition of the anion exchanger in the present invention, but involves an acid separation/regeneration means, and low yields, which are not acceptable for dicarboxylic acids A recent patent by the present inventor and others (USP 5,510,526) seems prima facie more relevant. It claims a process for the recovery of lactic acid from a lactate feed solution comprising the extraction step of combining said lactate feed solution with an extractant comprising at least one water immiscible trialkyl amine having a total of at least 18 carbon atoms in the presence of carbon dioxide at a partial pressure of at least 50 psig to form an aqueous phase and an organic phase containing extracted lactic acid and said extractant and separating lactic acid from said organic phase. While the extractant used in said patent falls under the definition of the anion exchanger in the present invention, said patent does not teach or suggest the application of said process to the recovery of dicarboxylic acids and at the time of the drafting of said patent it was not obvious to the present inventor that the process described and claimed therein would be applicable to the recovery of dicarboxylic acid, or that it could be modified to render it applicable to the recovery of dicarboxylic acids. Furthermore, in contacting a basic anion exchanger carrying an amine group, e.g. R 3 N with a salt of a dicarboxylic acid H 2 A, e.g. Na A, and with C0 2 many reactions may take place. Some of those could be presented as: (4) H2CO3 + R 3 N = R 3 NH 2 C0 3 (5) Na 2 A = 2NaOH + H 2 A (6) NaOH + H2CO3 = NaHC0 3 + H 2 0 (7) H 2 A = H = HA (8) HA = H + A (9) 2H 2 A = (H 2 A) 2 (10) R 3 N + H = R 3 NH (11) 2R 3 NH + A = (R 3 NH) 2 A (12) R 3 NH + HA = R 3 NHHA (13) R 3 NHHA + H 2 A = R 3 NHHA-H 2 A (14) R 3 NHHA + H 2 0 =R 3 NHHA-H 2 0 (15) R 3 NHHA + H 2 C0 3 = R 3 NHHA-H 2 C0 3 (16) R 3 NHHA-HA + H 2 A = R 3 NHHA-(H 2 A) 2 (17) 2R 3 NHHA = (R 3 NHHA) 2 Many of these reactions are unique to dicarboxylic acids and not only are absent in the case of reaction with lactic acid salt as in US patent 5,510,526, but might be expected to interfere with a recovery process based on the reaction used therein For a more detailed discussion, see e.g. 1 "Extraction of Carboxylic Acids with Amine Extractants. 2. "Chemical Interactions and Interpretation of Data" by Tamada and King in Ind. Eng. Chem. Res. 1990, 29, 1327-1333. In addition, there are expected to be complications due to steπc hindrance, particularly in the case of non-saturated dicarboxylic acids such as fumaric and maleic, due to the strong interaction of the free carboxylic group in R 3 NHHA with water in the aqueous solution and due to intermolecular interactions. Therefore, it was surprising, even to the present inventor to discover that the process of the present invention indeed would be effective for the recovery of a dicarboxylic acid from an aqueous feed solution containing salts of said acid. Another reason for the surprise is detailed below. Urbas extracts carboxylic acids by water soluble amines. Those amines are strong ones, having a pKa of 9 to 11. They are stronger bases than the carboxylates of the monocarboxylic acids specified in Urbas' patent and stronger than all three carboxylates of citric acid. These amines neutralize the carboxylic groups in the extracted acids and the formation of calcium carbonate during the extraction is not surprising. The amines used in Israeli patent 33,552 and in US patent 5,510,526 are water immiscible tertiary amines with an apparent basicity equivalent to pKa of about 4. They are much stronger bases than the chloride anion in Israeli 33,552 and of about similar basicity to the lactate anion. The acids in the organic phase are neutralized and the bicarbonate formed in these two inventions is therefore expected to exist. That is not the case in extraction of dicarboxylic acids as shown by the pKa's of these acids. Lactic acid is a monocarboxylic acid with a single pKa of 3.86. Typical dicarboxylic acids of interest (and their pKa values) are: adipic (4.43, 5.41), fumaric (3.03, 4.44), glutaric (4.31, 5.41), itaconic (3.85, 5.45), malic(3.40, 5.11) and succinic (4.16, 5.61 ). One of the carboxylates is a weaker base than the amine and is neutralized by the latter. The second carboxylate of those acids is a stronger base than the amine and would not react with it. Accordingly, one would expect the formation of R 3 NH- OOCRCOOH in the extraction of such dicarboxylic acid. The basicity of the second carboxylate is, however, lower than that of the carbonic acid (first pKa of 6.37). Therefore one would expect it to react with the bicarbonate salt and to liberate C0 2 . Existence of bicarbonate or carbonates in the presence of these amine-dicarboxylic acid adducts, which represent in fact a free monocarboxylic acid, is therefore surprising. While the invention will now be described in connection with certain preferred embodiments in the following examples so that aspects thereof may be more fully understood and appreciated, it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims. Thus, the following examples which include preferred embodiments will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of formulation procedures as well as of the principles and conceptual aspects of the invention. EXAMPLES Example 1 An aqueous solution comprising 19% di sodium fumarate was introduced into a pressure reactor along with an extractant comprising 50% Alamine 336 (a tricaprylyl amine produced by Henkel), 30% octanol and 20% kerosene. The aqueous to organic phase ratio was 4 to 1. A C0 2 pressure of 25 atmospheres was applied and the phases were mixed for 4 hours at a temperature of 25C. The organic phase was then removed from the pressure vessel while still under pressure and analyzed for fumaric acid content. It was about 0.17 mole/Kg. The pressure vessel was opened and solid sodium bicarbonate was found along with the aqueous solution. A sample of the fumaric acid containing phase (extract) was washed with boiling water. Practically all the fumaric acid in the extract was back- extracted to form an aqueous solution thereof. Example 2 An aqueous solution comprising 27% di sodium succinate was introduced into a pressure reactor along with an extractant comprising 50% Alamine 336 (a tricaprylyl amine produced by Henkel), 30% octanol and 20% kerosene. The aqueous to organic phase ratio was 5 to 1. A CO 2 pressure of 25 atmospheres was applied and the phases were mixed for 4 hours at a temperature of 25C. The organic phase was then removed from the pressure vessel while still under pressure and analyzed for succinic acid content. It was about 0.15 mole/Kg. The pressure vessel was opened and solid sodium bicarbonate was found along with the aqueous solution. A sample of the succinic acid containing organic phase (extract) was washed with boiling water. Practically all the succinic acid in the extract was back-extracted to form an aqueous solution thereof. It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims: WHAT IS CLAIMED IS: 1. A process for the recovery of a dicarboxylic acid from an aqueous feed solution containing at least one salt of said acid, comprising the steps of: (a) reacting said feed solution with C0 2 and with an anion exchanger, said anion exchanger being water immiscible in both free base and salt form, whereby said dicarboxylic acid forms an adduct with said anion exchanger and a carbonate of said salt's cation is formed in the resulting aqueous solution; (b) separating said dicarboxylic acid-anion exchanger adduct from the resulting aqueous solution; and (c) recovering said dicarboxylic acid from said adduct by methods known per se. 2. A process according to claim 1 , wherein said salts of said dicarboxylic acid contained in said aqueous feed solution are selected from the group consisting of mono- salts, di- salts and mixtures thereof. 3. A process according to claim 1 , wherein said formed carbonate is a bicarbonate. 4. A process according to claim 1, wherein said recovery in step (c) is effected by contacting said adduct with an aqueous media to effect the back extraction and recovery of said acid. 5. A process according to claim 1 , wherein said recovery in step (c) is effected by reacting said adduct with known reagents to form a compound of said acid. 6. A process according to claim 1 , wherein said recovery in step (c) is effected by contacting said adduct with another acid, whereby said dicarboxylic acid is displaced by said acid. 7. A process according to claim 1 , wherein said dicarboxylic acid is selected from the group consisting of fumaric acid, succinic acid, malic acid, adipic acid and itaconic acid. 8. A process according to claim 1 , wherein said dicarboxylic acid is a fermentation product. 9. A process according to claim 8, wherein said fermentation is conducted at a pH higher than the first pKa of said dicarboxylic acid. 10. A process according to claim 8, wherein said fermentation is conducted at a pH higher than the second pKa of said dicarboxylic acid. 1 . A process according to claim 1 , wherein said anion exchanger has a basicity lower than that corresponding to pKa of 7. 12. A process according to claim 1 , wherein said anion exchanger has a basicity lower than that corresponding to the second pKa of said carboxylic acid. 13. A process according to claim 1 , wherein said anion exchanger is selected from the group consisting of secondary and tertiary amines with a total of at least 18 carbon atoms. 14. A process according to claim 1 , wherein said anion exchanger is a tertiary amine with a total of at least 18 carbon atoms. 15. A process according to claim 13, wherein said amine is dissolved in a suitable solvent to form a water immiscible extractant and wherein said dicarboxylic acid adduct with the anion exchanger is a component in a water immiscible extract. 16. A process according to claim 15, wherein said extractant comprises a polar solvent. 17. A process according to claim 16, wherein said polar solvent is removed from said extract prior to said recovering of said acid in step (c). 18. A process according to claim 1 , wherein said recovery of said acid from said adduct is effected by contacting said adduct with water. 19. A process according to claim 1 , wherein said recovery of said acid from said adduct is effected at a temperature higher than that of said reaction in step (a). 20. A process according to claim 1 , wherein said reaction is conducted at a temperature lower than 100°C. 21. A process according to claim 1 , wherein said reaction is conducted under C0 2 pressure lower than the critical pressure of C0 2 at the reaction temperature. 22. A process according to claim 1 , wherein said at least one salt of said acid is selected from a group consisting of alkali and ammonium salts. 23. A process according to claim 1 , wherein said bicarbonate or carbonate is used in the formation of said feed solution. 24. A process according to claim 6, wherein said carbonate is used as a neutralizing agent in said fermentation. 25 A process according to claim 1 , wherein at least 80% of the dicarboxylic acid present in the feed solution is recovered.

Inventors: BANIEL AVRAHAM, BANIEL, AVRAHAM
Applicants: BANIEL AVRAHAM, INNOVA SA, WHALLEY KEVIN, BANIEL, AVRAHAM, INNOVA S.A., WHALLEY, KEVIN
Application year: 1997
Main classification: C07C51
IPC codes: C07C51