Lactic acid commercial purified

Song et al. [67] prepared PLA/CNT nanocomposites by one step based on in situ polycondensation of the commercially available lactic acid monomer in the presence of purified CNTs. The TEM image (Fig. 11.5) of core/shell nanostructures clearly indicates that the coating of grafted polymer was uniform both on the CNT s sidewall and tip. It was suggested that the incorporation of CNT into PL A will improvement its solubility and biocompatibility as it may promise a good future in biomedical systems and the development of bio-nanomaterials. The researchers also suggested that the current method of PLA/CNT nanocomposites preparation should be favored in industrialization as it takes less steps and cheaper. 

The recovered liquid stream contains crude lactic acid and impurities such as soluble proteins, residual sugars, salts, other acids, and complex color components which must be removed and purified mainly by chromatography, esterification, and/or distillation. Membrane filtration, crystallization, and/or evaporation may also be used to further purify the product stream, or to concentrate it to the desired degree. Typical commercial lactic acid products are sold at concentrations between 80 and 88%, or even 92-93%. At these concentrations some of the lactic acid molecules may be present as dimers and tiimers at room temperature. 

Poly(lactiC acid). Lactic add, CH3CHOHCOOH, occurs naturally in animals and in microorganisms. It can be produced commercially by chemical synthesis, bnt in the United States fermentation is the major route. In bioreactors, microorganisms are fed a carbon source substrate, such as dextrose, with delds of lactic acid greater than 90%. The lactic acid is recovered from the fermentation broth and purified in a multistep process that represents a major part of production costs. Eighty percent of the world s production of lactic acid is from corn sugar. 

The commercial process for chemical synthesis is based on lactonitrile. Hydrogen cyanide is added to acetaldehyde in the presence of a base to produce lactonitrile. This reaction occurs in liquid phase at high atmospheric pressures. The crude lactonitrile is recovered and purified by distillation. It is then hydrolyzed to lactic acid, either by concentrated HCl or by H2SO4 to produce the corresponding ammonium salt and lactic acid. Lactic acid is then esterified with methanol to produce methyl lactate which is then isolated and purified by distillation and hydrolyzed by water under acid catalyst to produce lactic acid and the methanol that is recycled. This process is represented by the following reactions. 

In 1963, synthetic lactic acid production began on a commercial scale. The chemical synthesis route for synthetic lactic acid yields a racemic mixture of Di-isomers. The commercial process is based on lactonitrile (Holten et al. 1971). Lactonitrile is produced by the base-catalyzed addition of hydrogen cyanide to acetaldehyde. Lactonitrile is then hydrolyzed by strong acid to yield lactic acid, which is purified and recovered. Today, synthetic lactic acid is produced mostly in the United States and Japan, and it accounts for about 50 % of total worldwide production. Industrial fermentations also yield about half the world s lactic acid production and thus are very competitive. 

NADH as an end product. This implicates oxidized malic acid, either pyruvic or oxaloacetic acid, as another end product. By adding commercial preparations of L-lactic dehydrogenase or malic dehydrogenase to the reaction mixture, Morenzoni (90) concluded that the end product was pyruvic acid. Attempts were then made to show whether two enzymes—malate carboxy lyase and the classic malic enzyme, malate oxidoreductase (decarboxylating), were involved or if the two activities were on the same enzyme. The preponderance of evidence indicated that only one enzyme is involved. This evidence came from temperature inactivation studies, heavy-metal inhibition studies, and ratio measurements of the two activities of partially purified preparations of Schiitz and Radlers malo-lactic enzyme (76, 90). This is not the first case of a single enzyme having two different activities (91). 

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