Liquid purification or separation – Processes – Chromatography
Patent
1995-10-10
1997-06-24
Therkorn, Ernest G.
Liquid purification or separation
Processes
Chromatography
210659, 2101982, 435139, 562580, 562589, B01D 1508
Patent
active
056414064
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is directed to a process for the separation and purification of lactic acid from salt-containing and carbohydrate-containing substrates (fermentation solution) from which coarsely dispersed and lipophilic impurities have been removed.
Industrial production of lactic acids, especially where pure L(+)-lactic acid and D(-)-lactic acid are to be extracted, is presently carried out predominantly by biotechnological processes. The production process can be divided into:
1) the actual production of lactic acid by fermentation of a carbohydrate-containing medium; form pure acid.
Industry has adopted a large number of strains of microorganisms for the production of lactic acid. The most important of these are the homofermentative lactic acid bacteria of the genera lactobacillus, streptococcus and pediococcus. However, these genera reach their maximum productivity only within a very narrow pH range.
Therefore, it is necessary during fermentation not only to maintain a constant optimum temperature for the selected organism, but also to maintain the required pH at a constant value. For this reason, neutralizing agents such as alkali hydroxide, calcium carbonate, milk of lime or ammonia water are added to the mash before and/or during fermentation so as to prevent over-acidification and to maintain a constant pH of 5.5 to 6.5.
Thus, the main component contained in the fermentation mash is the salt of lactic acid (e.g., NH.sub.4 lactate or Ca lactate) in addition to a little free acid, as well as unconverted starter materials (e.g., sugar), heavy metals, coloring matter, metabolic by-products (e.g., acetic or ethanoic acid), cells and cell fragments of the microorganisms, and inorganic salts.
Therefore, direct use of the solution coming from fermentation is not possible and further processing steps are required to extract the pure, free lactic acid.
A number of methods are described for the separation and extraction of free lactic acid from the fermentation mash.
The simplest commercial method of purification, and that most often applied by manufacturers, is precipitation of the lactic acid as calcium lactate. In this method, at the end of the fermentation process the mash is first heated to approximately 80.degree.-90.degree. C. and the pH is increased to 10-11. In this step, the microorganisms are destroyed, the proteins are coagulated and the formed calcium lactate is dissolved. After all insoluble components have been separated, the mash is acidified with sulfuric acid to liberate the lactic acid from its salt. In order to remove the iron and copper ions introduced especially as a result of corrosion, as well, sodium hexacyanoferrate (II) or calcium hexacyanoferrate (II) is added and the precipitated ferrocyanide salts, together with the calcium sulfate, are separated by means of a rotary filter or filter press. Coloring components are removed by activated charcoal. The obtained dilute acid is then concentrated to lactic acid of approximately 80% strength, small amounts of resulting volatile acids being removed at the same time.
In improved precipitation processes, the crude lactic acid is first decolorized with activated charcoal and subsequent purification steps can be carried out by means of cation exchangers for complete removal of any remaining salts. The cation-free solution can then be evaporated or crystallized immediately or can be guided through an anion exchanger in order to remove any remaining foreign anions, mainly sulfate ions and chloride ions (DD-PS 6740).
For a further improvement in quality, especially with respect to odor and flavor, an oxidative treatment with hydrogen peroxide or potassium permanganate is frequently also carried out subsequently (CARLOS BELLAPART VILA, 1964, ES 297969).
However, all precipitation methods have grave disadvantages. Apart from the relatively high technical costs, the primary disadvantage consists in a material loss of up to 20% of the lactic acid due to the precipitation and crystallization processes (HEDING, L. G., Biote
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Berghofer Emmerich
Cramer Adalbert
Sarhaddar Schahroch
Scheibl Anton
Feiereisen Henry M.
Therkorn Ernest G.
Vogelbusch Gesellschaft m.b.H.
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