Life Cycle Analysis of Electrofuels: Fischer-Tropsch Fuel Production from Hydrogen and Corn Ethanol Byproduct CO2.

Abstract

Electrofuels from renewable H2 and waste CO2 streams are of increasing interest because of their CO2 emissions reduction potentials compared to fossil counterparts. This study evaluated the well-to-wheel (WTW) greenhouse gas (GHG) emissions of Fischer-Tropsch (FT) fuels from various electrolytic H2 pathways and CO2 sources, using various process designs (i.e., with and without H2 recycle) and system boundaries. Two systems with different boundaries were considered: a stand-alone plant (with CO2 from any source) and an integrated plant with corn ethanol production (supplying CO2). The FT fuel synthesis process was modeled using Aspen Plus, which showed that 45% of the carbon in CO2 can be fixed in the FT fuel, with a fuel production energy efficiency of 58%. Using nuclear or solar/wind electricity, the stand-alone FT fuel production from various plant designs can reduce WTW GHG emissions by 90-108%, relative to petroleum fuels. When integrating the FT fuel production process with corn ethanol production, the WTW GHG emissions of FT fuels are 57-65% lower compared to petroleum counterparts. This study highlights the sensitivity of the carbon intensity of FT fuels to the system boundary selection (i.e., stand-alone vs integrated), which has different implications under various GHG emission credit frameworks.