Direct Medium-Chain Carboxylic Acid Oil Separation from a Bioreactor by an Electrodialysis/Phase Separation Cell

Abstract

Medium-chain carboxylic acids (MCCAs) are valuable platform chemicals and can be produced from waste biomass sources or syngas fermentation effluent through microbial chain elongation. We have previously demonstrated successful approaches to separate >90% purity oil with different MCCAs (MCCA oil) by integrating the anaerobic bioprocess with membrane-based liquid-liquid extraction (pertraction) and membrane electrolysis. However, two-compartment membrane electrolysis unit without pertraction was not able to separate MCCA oil. Therefore, we developed a five-compartment electrodialysis/phase separation cell (ED/PS). First, we tested an ED/PS cell in series with pertraction and achieved a maximum MCCA-oil flux of 1.7 × 10³ g d^-1 per projected area (m²) (19 mL oil d^-1) and MCCA-oil transfer efficiency [100% × moles MCCA-oil moles electrons^-1] of 74% at 15 A m^-2. This extraction system at 15 A m^-2 demonstrated a ∼10 times lower electric-power consumption (1.1 kWh kg^-1 MCCA oil) than membrane electrolysis in series with pertraction (9.9 kWh kg^-1 MCCA oil). Second, we evaluated our ED/PS as a stand-alone unit when integrated with the anaerobic bioprocess and demonstrated that we can selectively extract and separate MCCA oil directly from chain-elongating bioreactor broth with just an abiotic electrochemical cell. However, the electric-power consumption increased considerably due to the lower MCCA concentrations in the bioreactor broth compared to the pertraction broth.