Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-11-19
2003-12-23
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06667417
ABSTRACT:
The present invention relates to a process for producing lactic acid. More particularly the present invention relates to a process for producing lactic acid and products thereof, from a medium containing an alkaline earth-metal salt of lactic acid, especially when the medium results from a fermentation of at least one carbohydrate.
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 polylactic acid polymers as a replacement for present plastic materials, as well as for 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 environmentally friendly process for producing lactic acid, which avoids the consumption of bases and acids and substantially reduces, if not eliminates, the formation of waste, and/or of by-product salts.
The production of lactic acid is commonly carried out by fermentation of a strain of the bacterial genus Lactobacillus, and more particularly, for example, by the species
Lactobacillus delbrueckii,
or
Lactobacillus acidophilus.
In general, the production of lactic acid by fermentation in a fermentation broth is well known in the art. 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 is usually kept above 4.5, preferably within the range of about 5.0 to 7.0, more preferably within the range of about 5.5 to 6.5, and most preferably within the range of about 6.0 to 6.5., although fermentation in a pH range of about 3.8-4.5 has also been carried out. To maintain this pH level, suitable water-soluble basic substances, or agents, that are non-toxic to the acid-producing microorganism, are commonly added as a neutralizing agent to the fermentation broth in order to neutralize the acid being produced. Preferred bases are those of alkaline earth metals, more preferably those of calcium or magnesium, most preferably calcium bases selected from the group consisting of carbonates, bicarbonates and hydroxides.
In such processes lactate salts are formed rather than lactic acid, even though lactic acid, as such, or derivatives thereof, e.g. lactic acid condensation products are usually the desired product. (In the following, if not specified otherwise, the term lactic acid will refer to both the acid and its non-salt derivatives such derivatives include lactide, lactoyl lactate, low molecular weight oligomers of lactic acid, polylactic acid and lactic acid esters.) Therefore, many processes were developed for the recovery of lactic acid from its salts, particularly calcium lactate, that forms in fermentations using calcium bases as neutralizing agents. In a common industrial practice sulfuric acid is added to fermentation liquors containing Calcium Lactate (CaLa
2
) to form gypsum and to liberate the lactic acid. The latter is purified from impurities present in the broth and concentrated. The main disadvantage of this process is that it irreversibly consumes the calcium base and sulfuric acid and requires the disposal of large volumes of gypsum. Such disposal of large volumes of gypsum is unacceptable, particularly for the production of an environmental-friendly product, such as, the biodegradable polylactic acid.
DE-C-678 428 describes producing water-free lactic acid and anhydride by treating a solution of ammonium or sodium lactate, wherein said solution is obtained by reacting calcium lactate with ammonium or sodium carbonate.
Nakanishi and Tsuda, in JP 46/30176, proposed production of 1-butyl lactate by extraction of an acidified crude fermentation broth with 1-butanol, followed by esterification of the extract phase. BASF (EP 159 285) proposes a similar process with isobutanol, to form isobutyl lactate. The process of WO 93/00440, assigned to DuPont, comprises the steps of: (1) simultaneously mixing a strong acid, an alcohol, and a concentrated fermentation broth, which contains mainly basic salts of lactic acid, which react to form a crystal precipitate comprising basic salts of the strong acid and an impure lactate ester of the alcohol; (2) removing water from the mixture as a water/alcohol azeotrope which can be accomplished either sequentially or substantially simultaneously with step (1); (3) removing the crystal precipitate from the mixture; and (4) distilling the impure lactate ester to remove impurities and recovering the high purity ester.
In these processes, as in the case of gypsum, a strong mineral acid is used as an acidulant and an undesired by-product salt is formed. Many efforts have recently been made to recover lactic acid from its salts formed through fermentation without formation of by-products. In order to achieve this result, the lactate salt is converted to lactic acid, or a derivative thereof, and to a conjugated base or a basic compound of the lactate salt cation. (In the following, if not specified otherwise, such conjugated base or a basic compound of the lactate salt cation or a mixture thereof, formed in such conversion, is referred to as the conjugated base.) Such conversion is referred to in the following as salt splitting. The salt splitting conjugated base is recycled as is or after further conversion and used as a neutralizing agent in the fermentation.
Examples of such salt splitting processes for lactic acid are given in the many patents dealing with water splitting electrodialysis and in others, such as: U.S. Pat. No. 5,132,456 (King); U.S. Pat. Nos. 4,444,881 and 4,405,717 (Urbas); U.S. Pat. No. 5,252,473 (Walkup); Israeli patent Application 117,232 (Eyal) and U.S. Pat. No. 5,510,526 (Baniel).
Splitting of a salt to its acid and conjugated base requires introduction of energy to compensate for the neutralizing energy. If formation of no by-products is aimed at use of chemical energy of strong acid-base neutralization, should be avoided and other energy sources are needed to drive the reaction forward. Electrical energy is the driving force in those processes using water splitting electrodialysis. Bipolar membranes are used. Such membranes are very sensitive to impurities and applying them to fermentation products requires costly purification operations. Thus, in most alternatives, thermal energy is the main driving force for the salt splitting. In the case of salts of a relatively strong carboxylic acid, such as lactic acid (pKa=3.86), the energy needed is high. That is particularly true in those cases in which a free acid is formed in the salt splitting. Thus, splitting of sodium lactate to lactic acid and sodium hydroxide by the use of thermal energy seems impractical. Such splitting is somewhat easier in the case of ammonium lactate in which case the regenerated, conjugated base, ammonia, is a relatively weak one. Another advantage of the use of ammonia is its volatility which makes it easier to remove from the reaction mixture. Yet, the process for salt splitting of ammonium lactate involves very high temperatures (about 170° C.) and pressures (about 100 atm.) as in the Walkup patent, ibid. and/or a relatively low yield in a very complicated process with some uncontrolled reactions as in the King patent, ibid.
A way to reduce the load on the thermal energy for lactate salt splitting is to combine it with the formation of a water immiscible product, i.e. formation of a water immiscible conjugated base. This approach has two main advantages:
(a) it removes the base formed from the reaction mixture and thereby assists in shifting the reaction forward; and,
(b) it uses the crystallization energy of the conjugated base as a driving force, thereby reducing the thermal energy consumption.
It is very difficult to combine into one step thermal energy driven splitting of a lactate salt to lactic acid and a conjugated water immiscible base. The prior art
Eyal Aharon Meir
Fisher Rod
Witzke David
Ladas & Parry
Oh Taylor V.
Rotman Alan L.
Yissum Research Development Company of the Hebrew University of
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