Production of lactic acid by continuous fermentation using an inexpensive raw material and a simplified method of lactic acid purification

Claim 1

A process for producing lactic acid from whey comprising the steps of: (a) providing a whey composition at an acidic pH from which a substantial portion of proteins having a molecular weight over 10,000 have been removed; (b) treating said composition with a protease at a temperature in the range of 40° C. to 65° C. for a period sufficient to degrade proteins to smaller peptides and amino acids, said smaller peptides and amino acids characterized as being nonpercipitable when subjected to heat-sterilization, increased salt concentration or contact with organic solvents; (c) fermenting the composition resulting from step (b) with a lactic acid or lactic acid salt-producing microorganism in a fermentation zone; (d) continuously removing a product-containing broth from said zone, removing cells of said microorganism from said broth to form a cell-free product-containing stream and recycling said cells to said zone; (e) contacting said cell-free product-containing stream at an acidic pH with a water-immiscible liquid consisting essentially of trialkyl tertiary amines of at least 24 carbon atoms and a water-immiscible organic solvent for a sufficient time and temperature, whereby lactic acid and lactic acid salt are extracted from said stream into a water-immiscible phase, said liquid characterized by a distribution coefficient in excess of 1.0 for lactic acid and lactic acid salt in said liquid versus water; (f) separating said water-immiscible phase from the mixture formed in step (e); (g) contacting said water-immiscible liquid from step (f) with a material selected from the group consisting of aqueous ammonium hydroxide, solid alkalis, solid alkaline earth compounds, and aqueous non-homogenous suspensions of solid alkalis or solid alkaline earth compounds for a sufficient time and temperature, whereby lactic acid and lactic acid salt are removed from said water-immiscible phase.