Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-11-02
2002-12-03
Shah, Mukund J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S608000
Reexamination Certificate
active
06489508
ABSTRACT:
FIELD OF THE INVENTION
Lactic acid or 2-hydroxypropanoic acid is an &agr;-hydroxylated carboxylic acid which can be produced by fermenting a variety of pure (glucose, sucrose, lactose, etc.) or impure (products of the hydrolysis of starch, molasses, milk serum, etc.) carbonaceous substrates using microorganisms such as bacteria of the genera Lactobacillus, Pediococcus, Lactococcus and Streptococcus, or certain fungi such as Rhizopus Oryzae. Other routes for obtaining lactic acid, by way of chemical transformations of reagents derived from petrochemistry, such as the hydrolysis of lactonitrile, which is itself obtained starting from acetaldehyde, the chlorination and hydrolysis of propionic acid, or else via the nitration of propene, are known to the skilled person.
Lactic acid exists in two diastereoisomeric forms: L(+) and D(−) lactic acid, and finds novel applications every day, from the conventional use as a food preservative through to novel developments such as the synthesis of solvents, pesticides, herbicides, biodegradable polymers, etc. However, because of the increasing stringency of the quality criteria demanded and the necessity of achieving production costs which are compatible with the market, it is crucial to develop purification techniques which are efficient and inexpensive.
Lactic acid can be purified by precipitation in the form of metallic lactates, followed by a neutralization reaction using sulphuric acid (Maesato K., Komori A., Taki Chem. Co., JP 6,272,646 (Sep. 25, 1985)), or by esterification with an alcohol, distillation and hydrolysis of the ester which has been formed (Boroda T. A., Polovko V. N., Chistyakova E. A., Pishch.Prom. 1966, 4, 35-8), or by electrodialysis (Jacquement J. C., Rhone-Poulenc, DE 1,957,395 (Nov. 14, 1968)). The first of these processes suffers from the product being of poor quality and there being heavy losses of lactic acid, while the other two suffer from the fact that their cost is prohibitive. A more recent purification process consists in extracting the lactic acid by liquid/liquid extraction using at least one in water non-miscible organic solvent in the presence or absence of at least one Lewis base such as a tertiary amine. In accordance with this process, the lactic acid has to be recovered in a second step by means of carrying out a liquid/liquid back extraction. This step transfers the lactic acid back into the water. (Baniel A. M., Blumberg R., Hadju K., IMI, DE 2,329,480 (Jun. 19, 1972); Baniel A. M., Miles Lab., EP 49,429 (Oct. 06, 1980)). Finally, the lactic acid, in acid form and/or in the form of ammonium lactate or metallic lactate, can be purified by passing it through cationic and/or anionic ion exchange columns (Napierala W., Siminski M., Przem. Ferment. Rolny. 1972, 16(12), 4-10; Shkurino O. V., Dauksha V. E., Khim-Farm.Zh. 1986, 20(10), 1375-77; Maesato K., Komori A., Taki Chem.Co., JP 6,272,646 (Sep. 25, 1985); Obara H., Shimadzu corp., JP 63,188,632 (Jan. 30, 1987); Obara H., Shimadzu Corp, JP 0,191,788 (Sep. 30, 1987); Zeleneva N. A., Ivanova E. V., Karpushina I. A., Gaevskaya M. V., Teoriya I Prakitika Sorbtsionnyki Protsessov, 1982, 67-69).
It is to be noted that all these purification procedures are generally carried out starting from dilute solutions of lactic acid in water. This is justified by the actual structure of lactic acid, which carries a hydroxyl function and a carboxylic acid group at one and the same time. Thus, the bifunctionality of lactic acid is responsible for condensation reactions which generate lactoyllactic, dilactoyllactic, trilactoyllactic, . . . (n-lactoyllactic) units, which are also termed lactic acid oligomers. While these condensation or oligomerization reactions tend towards an equilibrium, the probability of their occurring increases as the concentration of the starting aqueous solution is increased (Holten C. H., “Lactic acid: Properties and chemistry of lactic acid and derivatives”, Verlag Chemie, 1971).
FIG. 1
shows the equilibrium which exists between the monomeric form of lactic acid and the oligomers over the whole range of conceivable concentrations.
The condensation or oligomerization reactions of lactic acid in fact correspond to esterification reactions; they are catalysed by Brönsted and Lewis acids and bases. Consequently, in order to avoid or minimize the occurrence of these reactions, it is imperative to carry out at least one preliminary purification step for removing any traces of impurities which would be capable of catalysing the oligomerization. Furthermore, it is also recognized that temperature accelerates the formation of oligomers (Holten C. H., “Lactic acid: Properties and chemistry of lactic acid and derivatives”, Verlag Chemie, 1971). This explains why lactic acid in aqueous solution has for a long time been regarded as a substance which is not particularly volatile and which cannot be distilled at 100° C. In actual fact, lactic acid condenses to form oligomers whose boiling point under atmospheric pressure is higher than 100° C. More recent studies on the distillation of lactic acid by steam distilling at 160-200° C. show that the substance can be distilled with yields which are of the order of 75 to 85%. However, these drastic conditions are detrimental to the quality of the product; it is impossible to avoid degradation and racemization. Noerdlinger (U.S. Pat. No. 924,494, DE 221,786 and DE 224,664) has proposed a variant of distilling by steam distillation. This technique consists in passing air or warm inert gas at high speed over the surface of a solution of lactic acid which has previously been freed of the water which it contains. However, the energy consumption and the low yields obtained result in the procedure being of low viability from the industrial point of view. For the sake of completeness, we may also point out that there have been reports of other equipment and arrangement profiles which make it possible, with a greater or lesser degree of success, to concentrate and distil lactic acid, which is in dilute solution in water, under reduced pressure in an evaporator which has a vaporization surface which is very large as compared with the volume of liquid involved (Sepitka A., Prumisi Potravin 13, 385 and 605 (1962) and 14, 45 and 82 (1963); Shishkini A. V., Domanskii I. V., U.S.S.R. 709,613 (May 10, 1977)).
The present invention consists of a process for purifying lactic acid in an aqueous solution, as obtained from a fermentation medium or any other source, which has been previously freed of solid compounds and/or biomass. The reader is referred to any method known to the skilled person, such as centrifugation, flocculation, microfiltration, etc., as far as the step of separating solid compounds is concerned. By contrast, the purification process described in this invention is original in the sense that it ensures that a very high quality of lactic acid is obtained, with a particularly high mass yield and a minimum consumption of energy. “Very high quality” is understood as meaning residual concentrations of mineral and organic impurities which are such that the purified lactic acid can be used for pharmaceutical applications in accordance with any of the current Pharmacopoeias. Moreover, the lactic acid which is purified by the process described in the present invention is thermo-stable, that is it remains colourless after a 2-hour heat treatment at 180° C. and retains the optical activity of the lactic acid employed (stereospecific process). “Mass yield” is understood as being the ratio, expressed in per cent, of the mass of purified lactic acid over the mass of lactic acid employed; these masses correspond to lactic acid concentrations of 100%. Applications which require lower purity can, of course, also be met by the technique which is proposed in the present invention. The quantitative and selective aspects of this purification process are ensured by jointly implementing (1) a pretreatment which is designed to remove substances which are capable of catalysing the lactic acid condensation reaction, (2) tempe
Bogaert Jean-Christophe
Malhaize Etienne
Van Gansbeghe Frederic
Van Gansberghe Martin
Wolff Florence
Brussels Biotech
Ladas & Parry
Shah Mukund J.
Tucker Zachary C.
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