Cascading the Electrochemical Reduction of CO₂ with Bioprocesses for the Production of Reduced-Carbon-Intensity Chemicals

Electrochemical reduction of CO2 (eCO2R) offers a route to one- and two-carbon (C1/C2) intermediates, and these can serve as lower-carbon-intensity feedstocks for the biobased synthesis of C3+ products. We evaluate the energy inputs for ∼1000 cases of the integrated system, considering 9 intermediates and 50+ bioproducts. The most energetically compelling options include aerobic bioconversion of C2 intermediates or methanol to more oxidized products. As an intermediate, ethanol provides the highest overall bioproduction mass yield among candidate substrates, with over 25% of the products having a mass yield greater than one. For fuels, the anaerobic bioconversion of methanol and CO each appear promising, with energy inputs in the range of 40–60 GJ/ton. We find that the recycling of CO2 generated during bioproduction is optimal when CO2 capture costs for eCO2R exceed the separation costs of the bioreactor gas stream. Overall, this analysis points to privileged {intermediate, product} pairings in such integrated systems.