Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-05-22
2002-05-07
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S515000, C435S139000
Reexamination Certificate
active
06384276
ABSTRACT:
The present invention relates to a particular process for the preparation of lactic acid from an aqueous solution containing lactic acid, in the form of salt(s) particularly from a fermentation medium.
The present invention also relates to a process for the preparation of lactic acid, the purity of which is such that it may be used not only in sectors such as food applications, the chemical and agrochemical industries, plastics, cosmetics, but above all in pharmaceutical applications.
According to the invention, a “high purity lactic acid” means a grade of lactic acid which satisfies the pharmaceutical standards of purity (thermal stability test of “The United States Pharmacopeia”) and complies with the standards of the “Food Chemicals Codex”.
The preparation of an aqueous solution of lactic acid in the form of salt(s) usually means the fermentation of microorganisms of the Lactobacillus type (such as
L. acidophilus, L. delbrüeckii
or
L. pentosus
), Lactococcus, Enterococcus, Pediococcus, Vagococcus, Tetragenococcus, Aerococcus, Rhizopus, Bacillus (such as
B. coagulans
), Streptococcus, Bifidobacterium . . .
Indeed, it is known that the growth of most of these lactic acid-producing microorganisms, and even the viability thereof, is inhibited by the fall in the pH of the fermentation medium, this strong acidification of the medium being brought about by the production of organic acids, including lactic acid itself.
It is necessary, therefore, to control the pH and it is generally accepted that this must be kept at a value in the range from 4 to 7, preferably higher than 4.5, for example, in the range from 5.5 to 6.5, by adding bases such as alkali metal or alkaline earth metal hydroxides, carbonates or bicarbonates.
Lactic acid is therefore present in these fermentation media in the form of salts (lactates of sodium, potassium, calcium or ammonium, alone or in mixture, depending on the base selected for controlling the pH of the fermentation medium).
Consequently, all the methods for recovering lactic is acid from aqueous solutions containing them, and particularly if this aqueous solution is composed of a fermentation medium, have to overcome the same difficulties, i.e. carrying out the separation of the salt(s) of lactic acid, the microorganisms which produced them and the impurities of the fermentation medium (unconsumed sugars and proteins, and inorganic salts of various kinds) and, moreover, carrying out the conversion of the salts of lactic acid to lactic acid in the free form, which also then requires the removal of the corresponding base produced.
Various methods have been proposed for recovering lactic acid from an aqueous solution, and particularly from a fermentation medium.
All these methods are based on the same principle, i.e. extraction of the lactic acid as such from the fermentation medium.
However, as has been shown before, lactic acid is present in the form of a salt (lactate).
If the control of the pH of the fermentation medium is achieved by carbonates or bicarbonates of calcium, lactic acid in the free form may be recovered, for example, by acidification of the medium with sulphuric acid.
In this case, the reaction gives rise to the formation of calcium sulphates (gypsum) which precipitate and to the release of lactic acid in the free form which may then be adsorbed, for example, on a suitable support and then desorbed.
As described in EP 849.252, in order to obtain high purity lactic acid, multiple crystallisations are generally carried out, firstly of the calcium lactates in order to remove the soluble impurities from the fermentation medium, and then of the calcium sulphates liberated after treatment with sulphuric acid.
These crystallisation steps are followed by numerous complementary extraction steps with ether or by a long chain amine, combined with purification steps by ion exchange chromatography, electrodialysis, and hydrolysis reactions in order to obtain a high purity lactic acid.
The first disadvantage of this method which is, admittedly, effective in terms of yield, is the high sulphuric acid consumption and above all the production of large amounts of gypsum which poses serious problems in terms of waste treatment and biodegradability for the environment.
The second disadvantage is the complexity and the high number of steps required to obtain a high purity lactic acid.
Other methods have, therefore, been proposed, leading to the crystallisation of salts of lactic acid.
For example, U.S. Pat. No. 5,641,406 describes, after the step involving the precipitation of calcium lactates with sulphuric acid and the treatment with ferrocyanide or hexaferrocyanide salts to remove the copper and iron ions, the decolourisation of the “crude” lactic acid thus obtained with activated charcoal, and after the subsequent purification steps to remove all the residual salts, the concentration by evaporation and hence crystallisation of the lactates.
Here again, this process suffers from a large number of purification steps and the handling of toxic chemicals.
A solution to these problems was given in U.S. Pat. No. 5,210,296 by the use of a process consisting of
continuous acidification of an aqueous solution containing ammonium lactate in the presence of an alcohol having 4 to 5 carbon atoms used as a diluent, with sulphuric acid (or any other strong acid),
removal of water from the acidified mixture by distillation of the water/alcohol azeotrope and in a simultaneous or sequential manner, removal of the ammonium sulphate crystals produced (or salts of strong acid produced),
distillation and hydrolysis of the lactic acid ester liberated in order to produce a free lactic acid having a purity of more than 99.5%.
However, the difficulty of this process lies in particular in the need to remove the ammonium sulphates. It is mentioned that it is imperative to use alcohols having 4 to 5 carbon atoms (namely n-butanol in this case) in order to obtain sufficiently coarse ammonium sulphate crystals to facilitate their separation by simple filtration of the reaction medium.
As a result, it is then possible to produce an azeotropic water
-butanol mixture which will be easy to remove by continuous distillation.
It is still necessary, therefore, to proceed via the lactic acid ester, the distillation and hydrolysis thereof in order to obtain a lactic acid of satisfactory purity.
Consequently, the processes of the prior art all still suffer in practice from this succession of numerous and cumbersome steps which make the purification of lactic acid from an aqueous solution containing lactic acid in the form of salt(s) particularly long and tedious.
It is evident from the above that there is an unsatisfied need for a simpler and cheaper process which permits the separation, concentration and purification of a high purity lactic acid with an excellent yield from an aqueous solution containing lactic acid in the form of salt(s).
Anxious to develop a process which will satisfy the practical limitations better than those that already exist, the Applicant company observed that this objective could be achieved by a process which consists in carrying out, on an aqueous solution containing lactic acid in the form of salt(s), an acidification of said aqueous solution and crystallisation under particular conditions of the salts of the strong acid thus produced, which makes it possible to directly obtain a high quality, free lactic acid.
The Applicant company has thus overcome the technical prejudices whereby the use of a crystallisation step in a protocol for the purification of lactic acid from an aqueous solution containing lactic acid in the form of salt(s):
must mean crystallisation of the salt of lactic acid in order to extract it from said medium, and only then the acidification thereof to precipitate the salts of the strong acid and to produce lactic acid in the free form, or,
if it entails crystallisation of the salts of the strong acid, this must necessarily be in an alcoholic medium in order to produce crystals of a sufficient size to allow their removal from said medium w
Dubois Eric
Fouache Catherine
Geist Gary
Henderson & Sturm LLP
Roquette Freres
Tucker Zachary
LandOfFree
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