Bio-electro CO2 recycling platform based on two separated steps

Abstract

The present work assessed the alliance of microbial electrochemical technologies (METs) and fermentation in a two-step process for the electro-bioconversion of carbon dioxide (CO2) into elongated chemical building blocks. The electro bio-reduction of CO2 into acetic acid and ethanol (EtOH:HAc) at a 1-to-1 ratio is linked to a subsequent elongation step to produce C4 and C6 compounds. Key operational conditions of each step were assessed. Key parameters considered in the first step were pH, and both hydrogen and CO2 partial pressures. Concerning the second stage, selected parameters were pH, ethanol to acetate ratio, and hydrogen availability. The aim was to steer each stage's performance and to obtain higher value products. Reached EtOH:HAc proportion was over 1:1 when fed with CO2, with H2 availability and at pH around 5.3. Formed product reinforced the follow-up chain elongation processes. The fermentation step got up to C6 compounds at pH 7.0, when fed with CO2 and H2. Outcomes demonstrated that pH was a crucial factor in the overall process. The overall process carbon conversion efficiency was 38% being the CO2 transformation the limiting step. 1 kg of CO2 fed in the system resulted in the production of 0.38 kg of elongated acids (C4-C6). In other words, 1 m3 of CO2 (normal conditions) captured resulted firstly in the production of 0.90 kg CC2 and then, 0.75 kg CC4-C6 are finally acquired. The presented results pave the ground for improving the selectivity during the production of reduced commodity chemicals from CO2 and electricity