Lactic Acid from Glucose (Conventional Fermentation + Solvent Extraction with CO2)

The process under analysis comprises two major sections: (1) Fermentation; and (2) Purification.

Fermentation. The culture media used in fermentation is prepared by mixing process water, invert sugar and corn steep liquor. The fermentation is carried out in continuous mode and under anaerobic process conditions in an agitated, jacketed fermentor. The pH control of the fermentation is made by addition of recycled sodium carbonate. The fermentation mass yield of lactate on glucose ranges from 85 to 95 wt%. The lactate concentration obtained in the fermentation broth is about 10 wt%.

Purification. After fermentation is complete, cell debris and other suspended solids are removed from the fermentation broth by means of ultrafiltration in membrane system. The retentate, mostly biomass and water, is partially recycled to fermentation. The filtered broth is then concentrated in continuous triple-effect evaporation. The overhead stream is condensed and partially reused as process condensate. The sodium lactate solution is twice extracted with carbon dioxide, extractant solvent and hot water. Lactic acid is generated and separated from bicarbonate and lactate. The resultant Lactic Acid stream, with a concentration of 15-20 wt%, is treated with activated carbon in order to remove impurities. The Lactic Acid is then directed to a multiple-effect evaporator, where it is concentrated to 88 wt%, and subsequently purified in ion-exchange beds.