Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2001-10-12
2003-02-11
Parsa, Jafar (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S174000, C560S185000, C562S577000, C562S587000, C562S589000
Reexamination Certificate
active
06518454
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to a process for the preparation of esters of carboxylic acids. More particularly, the present invention pertains to a process wherein a solution of a carboxylic acid in a first solvent and an alcohol are fed to a simulated moving bed reactor (SMBR) containing a solid(s) to produce a first stream comprising a solution of an ester of the carboxylic acid and the alcohol and a second stream comprising the first solvent contained in the alcohol. The solid(s) present in the SMBR facilitates the esterification reaction and the separation of the first solvent from the carboxylic acid.
BACKGROUND
Due to their importance as commercial products, numerous esters of carboxylic acids are produced on a large scale in the chemical industry. The reaction of an alcohol and a carboxylic acid to form an ester is accompanied by the formation of a molecule of water. Since esterification reactions are generally reversible reactions under conditions of acid catalysis, the water molecule produced by esterification and the ester reverse react to form the alcohol and the carboxylic acid, thus limiting the equilibrium conversion of the carboxylic acid. If any water is present along with the carboxylic acid, it will further limit the extent of esterification. Homogenous acid catalysts frequently are used to catalyze the esterification. The removal of the acid catalyst at the end of the reaction requires additional processing steps.
The esterification of 2-keto-L-gulonic acid (KLG) in the overall process of manufacturing ascorbic acid is an example of an important commercial esterification process. Known commercial processes for the production of ascorbic acid comprise four major sections: (1) a fermentation section wherein a sugar such as glucose or sorbose is subjected to fermentation to produce 2-keto-L-gulonic acid (KLG); (2) the purification and isolation of anhydrous KLG; (3) the conversion of the isolated KLG to an alkyl KLG ester (AKLG) by esterification with an alcohol, typically methanol, and (4) cyclization of the AKLG using stoichiometric amounts of a base to produce L-ascorbic acid. This process has evolved from the original Reichstein Process (T. Reichstein, A. Grussner,
Helv. Chim. Acta
17, p. 311, 1934). In traditional processes employed for the production of ascorbic acid from fermentation-derived KLG, the KLG is isolated as a solid from the aqueous fermentation broth by crystallization and drying. Since esterification reactions are equilibrium limited, the isolated KLG normally must be free of water to obtain an acceptable yield of the ester of KLG in the subsequent esterification step. Evaporation of water to obtain dry KLG requires substantial energy and the equipment required to evaporate the water increases the capital cost.
If KLG monohydrate is utilized instead of anhydrous KLG, additional steps to remove the water of hydration are required during the esterification, such as described in Published PCT Patent Application WO 99/03853. Furthermore, during crystallization of KLG, a significant amount of KLG present in the mother liquor stream may not be recovered. Apart from any water that is present in the KLG solids utilized to make the ester, water formed during the esterification reaction limits the equilibrium conversion. Any unreacted KLG results in lost yield. If a homogenous acid catalyst, such as sulfuric acid or hydrochloric acid, is used to catalyze the esterification of KLG ester, removal of the acidic catalysts or salts thereof becomes necessary. Thus, the processes presently employed in the manufacture of ascorbic acid have a number of disadvantages such as (1) high energy requirement and high capital and operating costs occasioned by the isolation of dry KLG, (2) yield loss during the purification of KLG, (3) incomplete conversion of KLG to its ester in the presence of water which is formed during esterification and/or present in the KLG as a result of the KLG manufacturing process, and (4) removal of the homogenous acid esterification catalyst.
Numerous improvements to the traditional processes for the manufacture of ascorbic acid are described in the literature. To address the energy and capital costs involved in isolating dry KLG solids, a process to exchange solvents by simultaneously removing water and adding methanol is proposed in U.S. Pat. No. 6,146,534. In the solvent exchange process described in the '534 patent, an aqueous stream of a carboxylic acid is fed to a simulated moving bed (SMB) unit packed with a basic resin. An organic solvent such as methanol is used as the separating agent to produce (1) a product stream containing the carboxylic acid in the solvent and substantially free of water and (2) a waste stream containing water in methanol. A similar solvent exchange process for dewatering KLG is disclosed in U.S. Pat. No. 6,153,791. The aqueous KLG feed stream contains a significant amount of sugar, e.g., sorbose, remaining from the fermentation as impurity, which also is removed along with the aqueous waste stream thus purifying the KLG. In both processes, though a substantial amount of water is removed from the aqueous KLG solution, some water is present in the organic solvent stream containing KLG. Since the processes disclosed in both the '534 and '791 patents accomplish separation only, an additional step to esterify KLG is required. During the esterification step, the residual water from the separation step and the water formed during the reaction limit the equilibrium conversion of KLG to its ester. The removal of the homogenous acid catalyst used for the esterification is still required.
The extent of esterification can be increased by simultaneously removing water or the ester as the reaction proceeds. WO 9903853 discloses that the esterification of KLG may be carried out in a 2-stage process in which the reaction can be driven to completion by crystallization of methyl 2-keto-L-gulonate coupled with efficient removal of water. This process requires multiple crystallization stages and solid liquid separation equipment. German Patent Application DE 199 38 980 A1 discloses a method for producing C
1
-C
10
alkyl KLG esters by the esterification of KLG with a C
1
-C
10
alcohol in the presence of an acid catalyst, wherein the esterification is carried out in a liquid film on a hot surface with simultaneous removal of water. This process is simple to operate but requires significant energy and large volumes of alcohol solvent to act as a carrier for water removal. This process does not provide a means to remove impurities. Other known means to enhance the extent of esterification include membrane reactors for the selective removal of water during esterifications described, for example, by Feng and Huang, Studies of a Membrane Reactor: Esterification Facilitated By Pervaporation, Chemical Engineering Science, Vol. 51, No. 20, pp. 4673-4679, 1996; Jennings et al U.S. Pat. No. 2,956,070; Okomoto et al, Pervaporation-aided Esterification of Oleic Acid, Journal of Chemical Engineering of Japan, Vol. 26, No 5, pages 475-481,1993; Kwon, et al, Removal of Water Produced from Lipase-Catalyzed Esterification in Organic Solvent by Pervaporation, Biotechnology and Bioengineering, Vol. 46, pp. 393-395, 1995; Keurentjes, The Esterification of Tartaric Acid with Ethanol: Kinetics and Shifting the Equilibrium by Means of Pervaporation, “Chemical Engineering Science, Vol. 49, No. 24A, pages 4681-4689,1994; and Xiuyuam, et al, Modified Aromatic Polyimide Membrane Preparation and Pervaporation Results for Esterification System,” Water Treatment, 10, pages 115-120, 1995. Simulated Moving Bed Reactors have been proposed as another alternative to enhance the extent of esterifications. See, for example, Kawase et al., Increased Esterification Conversion By Application Of The Simulated Moving-Bed Reactor, Chemical Engineering Science, Vol. 51, No 11, pages 2971-2976, 1996; Mazzotti et al., Dynamics Of A Chromatographic Reactor: Esterification Catalyzed By Acidic Resins, Ind. Eng. Chem. Res. 1997, 36, 3163-31
Arumugam Bhaskar Krishna
Blair Larry Wayne
Boyd Brendan William
Collins Nick Allen
Larkin David Anthony
Eastman Chemical Company
Graves, Jr. Bernard J.
Parsa Jafar
Tubach Cheryl J.
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