3-04: Recovery and chemical upgrading of succinate and other carboxylates integrated with their fermentative production

Succinic acid is an attractive platform chemical. It can be produced from renewable resources by fermentation. The best bacterial succinic acid fermentations consume sugars and carbonate (which is C-source as well as pH controlling agent), while they produce succinate salt. This salt usually needs to be converted back into the acid and purified, prior upgrading into esters and polyesters. Traditional purification and upgrading processes lead to stoichiometric inorganic acid consumption and inorganic salt production.

Our aim was to develop a novel route for succinate recovery and upgrading to dimethyl succinate. This should produce the carbonate required by the fermentation and therefore minimize chemicals consumption and waste production.

Sodium succinate such as produced by fermentation was efficiently captured from an aqueous stream by using an anion-exchange column. Due to the initial carbonate form of the resin, a sodium carbonate effluent was generated for use in the fermentation. After the capture step, the sorbed succinate was transformed into its dimethyl ester, which simultaneously regenerated the resin into its carbonate form, upon a mild reaction with dimethyl carbonate. This is a state of the art green solvent, industrially produced from CO, O₂ and methanol; potentially from CO₂ and methanol. Dimethyl succinate was obtained in almost quantitative yield after 2 h of reaction, without any production of monoester. Purification by distillation will be straightforward.

Thus, after fermentative production of carboxylic acids at neutral pH, esters of carboxylic acids can be obtained without having to isolate the carboxylic acids and without stoichiometric waste production.