Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
1998-10-30
2002-09-17
Badio, Barbara P. (Department: 1616)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S138000, C560S179000
Reexamination Certificate
active
06452051
ABSTRACT:
The present invention relates to a process for the production of a condensation product of carboxylic acid from a concentrated medium resulting from fermentation containing a salt of said acid. More specifically, the present invention is particularly useful as an important step in the production of a low cost esters especially in the production of lactic acid and in the production of biodegradable polylactic acid.
Carboxylic acids such as citric, lactic, succinic and malic acids can be produced by the continuous or batch fermentation of sugars, or other biomass streams, such as: hydrolyzed starch. Production is product inhibited and slows with pH reduction reaching a point at which said process is no longer practical. Product concentration in these solutions is in most cases very low, below 1%, and the high energy requirements of its concentration make the whole process uneconomical. In order to enhance fermentation, a base is added to maintain the pH at an optimal level, in most cases at about or somewhat higher than the pKa of the acid. More concentrated medium resulting from fermentation is obtained but said medium contains the salt of the acid rather than the free acid. Since in most cases the free form of the acid is the final product of interest, the substantial cost of acidulation is added. In many cases aciduation is performed by adding a strong mineral acid that displaces the carboxylic acid from the salt. Thus a base is consumed in the fermentation, a mineral acid in the acidulation and a salt is formed as an unwanted by-product. Lactic acid production, for example, uses a calcium base (mostly hydroxide) as the neutralizing agent. The medium resulting from fermentation obtained, containing calcium lactate, is treated with sulfuric acid to precipitate calcium sulfate and liberate the lactic acid. The latter is, however, left with most of the impurities present in the medium resulting from fermentation and requires additional operations for purification. Purification is typically performed by esterification in a reaction with an alkanol and distillation of the ester. The purified ester can be used as such or be hydrolysed to recover pure lactic acid and the alkanol.
Lactic acid has long been used as a food additive and in various chemical and pharmaceutical applications. More recently, lactic acid has been used in the making of biodegradable polymers both as a replacement for present plastic materials as well as various new uses in which biodegradability is needed or desired. Accordingly, there is an ever increasing demand for lactic acid. The present invention aims at meeting this demand by providing an efficient and low cost process for producing lactic acid esters or polyesters which avoids the consumption of bases and acids and substantially reduces, if not eliminates, the formation of waste salts.
Production of lactic acid is commonly carried out by fermentation of a strain of the bacterial genus Lactobacillus and more particularly by the species
Lactobacillus delbrueckii
or
LactobacilIus acidophilus
. The fermentation substrate consists of carbohydrates together with suitable mineral and proteinaceous nutrients. Because the lactic acid producing micro-organisms are inhibited in a strongly acidic environment, the pH of the fermentation broth must be kept above 5.0, and preferably within the rage of about 5.0 to 5.5. To maintain this pH level, suitable water-soluble basic substances that are non-toxic to the acid producing micro-organism, such as alkali metal or alkaline earth-metal carbonates, are commonly added to the fermentation broth. This results in the formation of a lactate solution rather than the desired lactic acid product. Acidulation is thus required.
Various sources of lactic acid may be used for production of polylactic acid biodegradable polymer. These sources include, as disclosed in U.S. Pat. No. 5,142,023, lactic acid in solutions with hydroxylic medium such as water or other solvents, such as: low molecular weight alkanols and mixtures thereof. The source of lactic acid could also be an ester of lactic acid with a low molecular weight alkanol. The lactic acid source is first fed to an evaporator in which a portion of the water or solvent or any condensation reaction by-product is removed and optionally re-cycled. The evaporator thus concentrates the lactic acid causing some condensation. Oligomers and low molecular weight polymers start to form. The concentrated lactic acid is next fed to a pre-polymer reactor in which low molecular weight polylactic polymer is formed. The pre-polymer is then converted to the lactide which is purified and fed to a polymerization system in which the product is formed.
The present invention aims at producing lactic acid esters or polyesters (oligomers) suitable for use as lactic acid sources (as they are or after hydrolysis) in such a process.
Acidulation and esterification can be combined to one process as disclosed by Cockrem and Johnson (PCT, WO 93/00440). A fermentation broth containing ammonium lactate or another basic salt of lactic acid is acidified in the presence of an alcohol of 4-5 carbon atoms as a diluent using continuous addition of sulfuric acid or other strong acid and crystallizing to precipitate out some, or all, of the basic salt of the strong acid. This combined process, however, also consumes a base and a strong acid and produces a low value by-product.
The present invention applies CO
2
as a displacing acid which is surprising as CO
2
is about 7 orders of magnitude weaker than sulfuric acid used by Cockrem and also much weaker than carboxylic acids. Thus, in the present invention CO
2
is a reagent and is used in stoichiometric quantities during the esterification process. One aim of the present invention is to produce a condensation product selected from the group consisting of an amide and an ester of a carboxylic acid without the use of a base and a strong acid and to minimize the production of salts as by-products. The term ester as used herein in reference to the present invention, unless specified otherwise, is intended to include diesters, lactones, oligoesters and polyesters.
The present invention provide s a process for the production of a condensation product selected from the group consisting of an amide and an ester of a carboxylic acid from an organic compound selected from the group consisting of organic compounds carrying a hydroxyl group and organic compounds carrying an amine group and from a concentrated medium resulting from fermentation, said medium containing a salt of said acid, said salt being selected from the group consisting of a sodium salt, a calcium salt and mixtures thereof and said medium being at a pH of at least the pKa of said acid, said process comprising:
(a) reacting said medium with said organic compound and with CO
2
, whereby said condensation product and a salt selected from the group consisting of sodium carbonate, sodium bicarbonate, calcium carbonate, calcium bicarbonate and mixtures thereof are formed; and,
(b) separating said condensation product from the reaction mixture formed in step a.
Reacting carboxylic acids with organic compounds carrying a hydroxyl group forms esters according to the equation:
RCOOH+R′OH═RCOOR′+H
2
O
If any of the reagents or both of them are polyfunctional so that a hydroxyl group or a carboxylic group are present on the ester, the latter could further react to form diester and higher esters. In a similar way reacting of a carboxylic acid with organic compounds carrying a primary or a secondary amine group forms amides, dimides or higher amides according to the following equation:
RCOOH+R′NH
2
═RCONHR′+H
2
O
Both ester formation and amide formation are referred to in the general term: condensation reactions; esters and amides are referred to as condensation products. Both reactions of carboxylic acids involve, in most cases, water formation and are enhanced by lowering the water content in the reaction medium as well as by removing the by-product water from the
Badio Barbara P.
Cargill Inc.
Foley & Lardner
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