(467d) A Novel Approach for Carboxylic Acid Recovery From Fermentation Broths

Biobased fermentation processes uniformly produce dilute aqueous solutions of the carboxylic acid as the primary products. Many of those fermentation systems yield a mixture of acids and other products, depending on the intended metabolic pathways and conditions within the bioreactor. The recovery and purification of individual species from these fermentor effluents can be expensive, accounting for 50 to 80% of the overall production cost. For succinic acid fermentation, significant amounts of acetic, formic, pyruvic and/or lactic acid can be formed as byproducts and are present in the broth in addition to non-converted sugars, biomass (cell growth), salts, and supplements. Because fermentation is most efficient at intermediate pH (5-7), base (NaOH, Ca(OH)2, ammonia) is used to control pH that naturally declines as the acid accumulates. The carboxylic acids produced are thus typically obtained as salts of the base used. Several alternatives have been proposed to recover succinic acid from the acid salt broths; these can be classified according to the approach as direct precipitation (as salt or acid), extraction (solvents, amines), ion exchange, membrane recovery, or esterification. In the traditional process, the aqueous broth containing succinate salt is acidified with H2SO4 at a pH below the pKa1 of succinic acid (pH < 4). With calcium as the cation, calcium sulfate is precipitated; the sulfate is removed by filtration and the SA is subjected to several crystallization steps. Because succinic esters are useful as platform species to produce a variety of value-added commodity and specialty derivatives, we have developed and present here a novel approach to directly recover succinic acid esters from fermentation. Following partial water removal, the process performs acidification with sulfuric acid in ethanol. Acidification of salts in EtOH releases succinic acid which simultaneously reacts to form mono- and di-ethyl succinate, while inorganic salts (sodium or calcium sulfate) precipitate out of the solvent. Other carboxylic acids removed in traditional processes are also recovered as ethyl esters which can be separated easily than original mixed acids. Experiments performed using pure and mixed succinate and acetate salts and actual fermentation products show high recovery efficiency and rapid conversion rates.