PROCESS FOR PURIFYING POLYCARBOXYLIC ACIDS

Abstract: Polycarboxylic acids are purified by contacting a crude polycarboxylic acid with a solvent to produce a substantially pure polycarboxylic acid. The solvent is chosen so that the impurities are soluble in the solvent and the polycarboxylic acid is insoluble in the solvent.

Description: Process for Purifying Polycarboxylic Acids BACKGROUND OF THE INVENTION This invention relates to a process for purifying a polycarboxylic acid. More specifically, the invention relates to a process for purifying a polycarboxylic acid made by the biological oxidation of a substrate by a microorganism from a fermentation broth. Aliphatic dioic acids are versatile chemical intermediates useful as raw materials for the preparation of perfumes, polymers, adhesives and macrolid antibiotics. The purity of dicarboxylic acids is critical when they are used to make polyesters because of the dependency of the molecular weight of the polyester on the purity of the dicarboxylic acid. It is well known that maximum molecular weight of a polymer produced by polycondensation will be attained under conditions favoring the most efficient reaction of the functional groups. Such conditions are attained when undesirable side reactions are substantially eliminated through, inter alia, the use of high purity bifunctional reagents. While several chemical routes to the synthesis of long-chain alpha, omega dicarboxylic acids are available, the synthesis is not easy and most methods result in mixtures containing shorter chain lengths. As a result, extensive purification steps are necessary. Dicarboxylic acids, especially long-chain dicarboxylic acids can also be produced by microbial transformation of alkanes, fatty acids or esters thereof. Such syntheses result in dicarboxylic acids having monocarboxylic acid impurities. The presence of monocarboxylic acids can substantially affect the molecular weight of any polycondensation polymer made with dicarboxylic acids having monocarboxylic acid impurities. There is, therefore, a need for methods for preparing highly pure dicarboxylic acids. SUMMARY OF THE INVENTION The present invention relates to a process for purifying a polycarboxylic acid. The method comprises contacting a polycarboxylic acid with a solvent to produce a substantially pure polycarboxylic acid. The solvent is chosen so that the impurities are soluble in the solvent and the polycarboxylic acid is insoluble in the solvent. BRIEF DESCRIPTION OF THE DRAWINGS Not applicable. DESCRIPTION OF THE INVENTION Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. It is understood that a carboxylic acid is any compound containing one or more carboxyl groups. A polycarboxylic acid is any compound having two or more carboxyl groups. The present invention relates to a process for purifying a polycarboxylic acid. The method comprises contacting a polycarboxylic acid with a hydrocarbon solvent to produce a substantially pure polycarboxylic acid. The solvent is chosen so that the impurities are soluble in the hydrocarbon solvent and the polycarboxylic acid is insoluble in the solvent. Substantially pure polycarboxylic acids are substantially free of detectable amounts of monocarboxylic acids, mono- and dicarboxylic acid esters, nitrogen-containing materials and, sulfur-containing materials. Typically, substantially pure polycarboxylic acids produced by the process according to the invention contain less than about 2% by weight of detectable amounts of monocarboxylic acids, mono- and dicarboxylic acid esters, nitrogen-containing materials and, sulfur-containing materials. The process according to the invention can be used to purify any polycarboxylic acid, especially those polycarboxylic acids having monocarboxylic acid impurities as the major impurities. The polycarboxylic acids that can be purified by process according to the invention include aliphatic dicarboxylic acids such as oxalic, malonic, adipic, azelaic, sebacic, dodecanedioc, 1 ,18-octadecendioic acid and the like; low molecular weight aliphatic tricarboxylic acids such as citric acid; aromatic dicarboxylic acids such as phthalic, isophthalic and terephthalic acids; aromatic dicarboxylic acids such as, trimellitic acid. The solvent that can be used in the process according to the invention is any aliphatic or aromatic hydrocarbon solvent and/or mixtures thereof in which the monocarboxylic acid impurities present in the crude dicarboxylic acid are soluble and in which the dicarboxylic acid is substantially insoluble. Examples of such aliphatic solvents include, but are not limited to, linear and branched, cyclic and acyclic alkanes such as pentane, hexane, heptane, octane, 2,2,4-trimethylpentane, cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane; alkenes such as pentene, hexene, heptene, cyclopentene, cyclohexene, methylcyclopentene, methylcyclohexene and the like and liquefied hydrocarbons that are normally gases at room temperature and pressure such as liquid propane and liquid butane. Examples of such aromatic solvents include, but are not limited to, benzene, toluene, xylene. Solvent mixtures include, but are not limited to, petroleum distillates such as naphtha and petroleum ether. The crude polycarboxylic acid is contacted by the hydrocarbon solvent for an effective time and in an effective amount sufficient to remove substantially all detectable amounts of monocarboxylic acids, mono- and dicarboxylic acid esters, nitrogen-containing materials and, sulfur-containing materials. The contacting can be carried out in any manner that is effective in removing at least the above impurities such as by stirring a slurry of solid crude polycarboxylic acid, passing the hydrocarbon solvent through a zone of solid crude polycarboxylic acid such as a column or tower of solid crude polycarboxylic acid. Liquid crude polycarboxylic acids can be contacted by heating a solid crude polycarboxylic acid and the hydrocarbon solvent until the polycarboxylic acid melts thereby forming two liquid phases which are then intimately contacted such as by stirring. The method of contacting the solid crude polycarboxylic acid with the hydrocarbon solvent and the time required will depend upon the nature of the polycarboxylic acid, the hydrocarbon solvent and the amount and type of impurities in the solid crude polycarboxylic acid and will be readily determinable by those of ordinary skill in the art. The process according to the invention is particularly useful for purifying long chain aliphatic dicarboxylic acids having long chain monocarboxylic acid impurities. The process is especially useful for the purification of long chain aliphatic dicarboxylic acids produced by fermentation such as by the methods described in U.S. patents 5,254,466 and 5,620,878, the entire contents of each of which are incorporated herein by reference. A particularly preferred embodiment of the process according to the invention is the purification of mixed saturated and unsaturated dicarboxylic acids having primarily oleic acid impurities by contacting the long chain dicarboxylic acids with a hydrocarbon solvent. The following examples are meant to illustrate but not to limit the invention. EXAMPLE 1 About 58.46g of distilled long chain dicarboxylic acids crushed with a mortar and pestle were added to 292 ml of hexane at room temperature. The mixture was allowed to stir for 1.5 hours. The long chain dicarboxylic acids were then removed from the mixture by filtration, washed three times with 100 ml of room temperature hexane and allowed to air dry. The analysis of the starting and final long chain dicarboxylic acids are listed below. EXAMPLE 2 About 50.16g of distilled long chain dicarboxylic acids were added to 250 ml of hexane. The mixture was slowly heated with slow stirring until the long chain dicarboxylic acids melted and two layers formed. The mixture was then stirred vigorously to allow as much contact as possible of the two layers The mixture was then allowed to cool to room temperature Crystals formed The crystals were removed by filtration, washed three times with 100 ml of room temperature hexane and allowed to air dry The analysis of the starting and final long chain dicarboxylic acids are listed below Contacted long Contacted long Starting long chain Chain dicarboxylic chain dicarboxylic Dicarboxylic acids acids solid state acids liquid state Acid Value 332 364 363 Sap Value 350 366 366 Ester Value 5 1 5 — N 2 (ppm) 185 67, 130 55 98 S(ppm) 115 12 14 G C Analysis by ISTD 2-Octanol 2 56 12 19 C16 11 — — C16 1 11 08 08 C18M 10 — — C18 1M 344 39 30 C18 2M 16 — — C20 1 29 — — C14DI 3 01 3 50 3 47 C14 1DI 36 12 14 C15DI 09 31 28 C16D1 5 21 6 49 6 50 C16 1DI 4 69 3 33 2 76 C17DI — 22 20 C17 1DI 98 77 90 C18D1 85 1 06 1 01 C18 1DI 72 75 84 00 83 33 C18 2DI 3 09 1 30 1 73 C20 1DI 1 28 97 73 TOTAL MONOACIDS 4 21 47 38 TOTAL DIACIDS 92 31 102 07 101 05 TOTAL 99 08 102 66 101 62 Ester content is the % of the carboxyl groups that are as esters vs those that are acid and is defined as Ester % = (SAP Value - Acid Value)/SAP Value X 100% EXAMPLE 3 About 50 OOg of distilled long chain dicarboxylic acids were added to 250ml VM&P Naphtha The mixture was slowly heated to 65°C with stirring until all the long chain dicarboxylic acid was dissolved The mix was then allowed to slowly cool to room temperature Crystals formed The crystals were removed by filtration Residual solvent was removed by heat and reduced pressure. The analysis of the starting and final product is listed below. EXAMPLE 4 About 50.00g of distilled long chain dicarboxylic acids were added to 250ml 1-octene. The mixture was slowly heated to 65°C with stirring until all the long chain dicarboxylic acid was dissolved. The mix was then allowed to slowly cool to room temperature. Crystals formed. The crystals were removed by filtration. Residual solvent was removed by heat and reduced pressure. The analysis of the starting and final product is listed below. EXAMPLE 5 About 50.00g of distilled long chain dicarboxylic acids were added to 250ml 1-decene. The mixture was slowly heated to 65°C with stirring until all the long chain dicarboxylic acid was dissolved. The mix was then allowed to slowly cool to room temperature. Crystals formed. The crystals were removed by filtration. Residual solvent was removed by heat and reduced pressure. The analysis of the starting and final product is listed below. Major Components by Starting Long Recrystallized Recrystallized Long Recrystallized Area % Chain Long Cham Chain Dicarboxylic Long Chain G.C Analysis Dicarboxylic Dicarboxylic Acids Acids in 1-octene Dicarboxylic Acids Acid Mixture in VM&P Naptha in 1-decene C16 ono 12 10 10 08 C16 1 Mono 09 11 10 09 C18Mono 32 26 22 20 C18 1 Mono 7 42 5 30 4 73 4 35 C18 2Mono 55 36 33 30 C16Di 3 69 3 91 3 87 3 81 C18Di 2 70 3 62 3 89 347 C18.1Di 78 19 81 19 82 12 82 48 C18 2Dι 4 28 4 04 3 94 3 88 Total Monocarboxylic Acids 8 50 6 13 548 5 02 Total Dicarboxylic Acids 88 86 92 76 93 82 93 64 Total Carboxyhc Acids 97 36 98 89 99 30 98 66

Claims: What is claimed is: 1. A process for purifying a polycarboxylic acid comprising contacting a crude polycarboxylic acid with an effective amount of hydrocarbon solvent for a period of time sufficient to produce a substantially pure polycarboxylic acid. 2. The process of claim 1 wherein the polycarboxylic acid is an aliphatic dicarboxylic acid. 3. The process of claim 3 wherein the aliphatic dicarboxylic acid is 1 ,18- octadecendioic acid. 4. The process of claim 1 wherein the hydrocarbon solvent is hexane. 5. A process for purifying crude 1 ,18-octadecendioic acid comprising contacting the crude 1 ,18-octadecendioic acid with an effective amount of hexane to produce substantially pure 1 ,18-octadecendioic acid. 6. The process of claim 1 wherein the solvent is a petroleum distillate. 7. The process of claim 6 wherein the petroleum distillate is naphtha. 8. A process for purifying a polycarboxylic acid comprising contacting a crude polycarboxylic acid with an effective amount of a petroleum distillate for a period of time sufficient to produce a substantially pure polycarboxylic acid. 9. The process of claim 8 wherein the petroleum distillate is naphtha. 10. The process of claim 9 wherein the polycarboxylic acid is 1 ,18 octadecendioic acid. 1 1. A process for purifying 1 ,18-octadecendioic acid comprising contacting crude 1 ,18-octadecendioic acid with an effective amount of a naphtha or petroleum ether for a period of time sufficient to produce a substantially pure 1 ,18- octadecendioic acid.

Inventors: STALEY MICHAEL D, STALEY, MICHAEL, D.
Applicants: COGNIS CORP, COGNIS CORPORATION
Application year: 2000
Main classification: C07C51
IPC codes: C07C51