Enhanced extraction of butyric acid under high-pressure CO₂ conditions to integrate chemical catalysis for value-added chemicals and biofuels

Background: Extractive fermentation with the removal of carboxylic acid requires low pH conditions because acids are better partitioned into the solvent phase at low pH values. However, this requirement conflicts with the optimal near-neutral pH conditions for microbial growth.

Results: CO₂ pressurization was used, instead of the addition of chemicals, to decrease pH for the extraction of butyric acid, a fermentation product of Clostridium tyrobutyricum, and butyl butyrate was selected as an extractant. CO₂ pressurization (50 bar) improved the extraction efficiency of butyric acid from a solution at pH 6, yielding a distribution coefficient (D) 0.42. In situ removal of butyric acid during fermentation increased the production of butyric acid by up to 4.10 g/L h, an almost twofold increase over control without the use of an extraction process.

Conclusion: In situ extraction of butyric acid using temporal CO₂ pressurization may be applied to an integrated downstream catalytic process for upgrading butyric acid to value-added chemicals in an organic solvent.