Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1999-10-26
2000-12-12
Lee, Howard C.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
562580, 560179, 564201, 549273, C07C 51487, C07C 51493
Patent
active
06160173&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the recovery of lactic acid. More particularly, the present invention relates to a process for the recovery of lactic acid from an aqueous solution containing lactic acid, lactate salts, or mixtures thereof.
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 where 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 or byproduct salts.
The production of lactic acid is commonly carried out by fermentation of a strain of the bacterial genus Lactobacilus, 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 microorganisms 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, such as alkali metal hydroxides, carbonates, or bicarbonates, or alkaline earth metal hydroxides or carbonates, are commonly added to the fermentation broth to neutralize the acid being produced. This results in the formation of a lactate solution rather than the desired lactic acid product. Such a lactate solution contains the lactate anion and the corresponding cation of the substance used to neutralize the fermentation broth.
Various methods have been proposed for the recovery of lactic acid from a fermentation broth. When the fermentation is carried out in the presence of calcium carbonate, it is possible to recover the lactic acid by acidification with sulfuric acid. This results in the precipitation of calcium sulfate, while free lactic acid remains in the mother liquor. If desired, the mother liquor may be concentrated to up to about 90 wt % lactic acid. Subsequently, lactic acid may be extracted from the mother liquor with a suitable organic extractant, to yield an extract which is back-extracted with water, or the acid may be adsorbed on a suitable adsorbent and later desorbed. The resulting aqueous lactic acid solution may then be concentrated. This method has the disadvantage that it irreversibly consumes calcium carbonate and sulfuric acid and leaves, as waste, large quantities of calcium sulfate which give rise to disposal problems.
U.S. Pat. No. 5,132,456 (King, et al.), describes a process for recovering carboxylic acid from a carboxylic acid-containing aqueous feed stream having a pH close to or above the pK.sub.a level of the acid. The recovery of that process involves what may be described as a cascade-type acid withdrawal operation, in which the basicity of the extractant is increased stepwise. In a first stage of the process, the feed stream is contacted with an adsorbent such as a strongly basic extractant or a solid anion exchanger. In a second stage, the acid-loaded adsorbent is contacted with an aqueous solution of ammonia or a low molecular weight trialkyl amine having a stronger affinity to the carboxylic acid that is being recovered than that of the adsorber used in the first stage. In this way, an aqueous soluti
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Derwent's Abstract of JP 7-258,154 of Oct. 1995.
Eyal Aharon Meir
Gruber Patrick R.
McWilliams Paul
Witzke David R.
Cargill Incorporated
Lee Howard C.
Maier Leigh C.
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