11-23: By-product reduction in fermentative carboxylic acid production processes

In 2004 the DOE listed four-carbon 1,4-dicarboxylic acids as one the 12 top value added chemicals from biomass.  The fermentative production of organic acids often has to be carried out at near neutral pH, which leads to the production of the organic acid salt.  During recovery the salt has to be converted to the free acid, which is accomplished commonly through the use of a strong mineral acid, such as sulfuric, to react with the carboxylate salt to form the free carboxylic acid and a mineral salt, in the case of a calcium base, this leads to the formation of gypsum.  The disposal of the resulting mineral salt has a large environmental impact and affects the economics of the process. 

MBI has developed fermentation processes for the production of fumaric and succinic acid that use a magnesium hydroxide base.  In both fermentation processes the respective organisms favor the use of the magnesium over other cations.  Subsequent acidification of these fermentation products results in the production of magnesium sulfate.  To minimize the amount of waste MBI has developed a procedure for recycling the magnesium hydroxide to address these issues.  A two step process has been established, that separates the fermentation product from the mineral salt and in a second step converts the mineral salt to the base has been demonstrated.  A 92 % recovery of magnesium hydroxide has been achieved.  Details of the conversion will be presented.