(630e) Life Cycle Emissions Assessment of a Renewable Fuel Process: Impact of Catalyst Performance on the Net GHG Emissions of Methanol Production By Direct Electrocatalytic Reduction of CO2

The ability to synthesize liquid hydrocarbon fuels from renewable energy and CO2 would provide a stable, energy-dense storage medium for solar energy, and provide a non-fossil, low-emissions route to liquid fuels. Research is now underway to address technical challenges such as reducing the energy cost of CO2 capture and increasing the efficiency of CO2 reduction catalysts. However, the full system-wide emissions balance of such a process has received little attention. Although the CO2 that is incorporated into a product is diverted from emission to the atmosphere, other aspects of the utilization process may produce greenhouse gas (GHG) emissions that negate some or all of this benefit. To determine whether a CO2-to-fuel process would provide a net emissions benefit requires a life cycle assessment (LCA) that extends across the full life cycle of the utilization process. 

We present a GHG LCA for a CO2-to-fuel process to assess the net emissions benefit of such a process, and to evaluate the importance of catalyst performance and other system parameters in achieving net emissions reductions. As an example of a CO2-to-fuel process, we examine the low-temperature, six-electron reduction of CO2 to methanol ("deCO2rr"). We consider a scenario in which CO2 is supplied from a concentrated point source (coal plant flue gas), and process energy for the electrocatalytic reduction is provided by a low-emissions source (wind generated electricity). We evaluate the total GHG emissions from producing both the methanol fuel and the electricity output from the power plant, and compare to the emissions when producing these from conventional processes.

The analysis projects that the deCO2rr pathway could produce methanol and electricity with lower GHG intensity than conventional processes, with a sufficiently efficient CO2 reduction catalyst (e.g. 40% faradaic efficiency, 40% selectivity for methanol). The maximum emissions reduction potential of the deCO2rr pathway, using a near-ideal catalyst, is a 60% reduction relative to the conventional processes for methanol and electricity production. When the faradaic efficiency of the CO2 reduction catalyst is above 30%, further improvements in faradaic efficiency have little impact on the full system emissions of the deCO2rr route. This analysis demonstrates the opportunity for full system LCA to complement fundamental research and guide technology strategy for sustainable outcomes.