Electrons to Molecules for Catalytic Processes

Every hour, a typical 90 million gallon ethanol plant produces around 27 tons of carbon dioxide (CO₂), a natural byproduct of fermentation. These waste streams of CO₂ are highly concentrated—almost pure CO₂—which makes them a choice feedstock for making electrofuels by bolting electrolyzers to the refinery.

When given an electrical charge, electrolyzers catalyze chemical reactions that split and reconfigure CO₂—a stable molecule—into compounds easier to upgrade biologically and ultimately into energy-dense fuels and chemicals. In this way, electrolyzers can turn CO₂ that would have been released into the atmosphere into valuable chemicals instead. This process may boost the fuel output of existing ethanol production facilities.

This is a project of the CO₂ Reduction and Upgrading for e-Fuels Consortium, funded by the U.S. Department of Energy Bioenergy Technologies Office, to investigate a promising pathway to convert biorefinery CO₂ flue gas into aviation fuel. We are investigating key process integration hurdles associated with biorefinery CO₂ fermenter utilization stream conversion, including the impact of varied gas sources and compositions on electrolyzer efficiency, lifetime, and specificity. Additionally, the project team will divert the flux from CO₂ formation to mevolonic acid as a high-value gas coproduct and evaluate the cost of separation and yield. We iteratively update techno-economic and life cycle analyses as we make progress on key cost drivers to help identify technology gaps and inform process optimization and industrial deployment.

If successful, an average biorefinery outfitted with electrolyzers and bioreactors could produce as much as 41 million more gallons of ethanol every year.

Contact: Michael Resch

Formate/formic acid can be generated by electrocatalytic reduction of carbon dioxide (CO₂) and has been proposed as a soluble intermediate for the storage of carbon and energy. Biological systems capable of assimilating formic acid could enable conversion of formic acid generated from low-cost energy and waste CO₂ to myriad fuels and chemicals while circumventing the safety, solubility, and mass-transfer challenges associated with gaseous feedstocks. To that end, NREL's goal is to develop the natural formatotroph Cupriavidus necator as a robust microbial chassis for efficient conversion of formic acid to value-added products.

To accomplish this, we use adaptive laboratory evolution to improve formic acid conversion and utilize metabolic engineering to engineer microbials strains capable of converting formic acid to fuel, chemical, and materials precursors. We also use bioprocess development to optimize conversion of formic acid to targeted intermediates. A hybrid electro-biocatalytic system for CO₂ conversion could be colocated with CO₂-emitting processes, including existing and future ethanol biorefineries, to eliminate waste CO₂, thereby improving their overall economics.

Contact: Chris Johnson