(619f) Life-Cycle Assessment of Biofuels and Chemicals from Unconventional Methane Feedstocks

This is the result of an ongoing collaboration with a team of researchers in an ARPA-E project to investigate the feasibility of utilizing stranded, small-scale sources of natural gas to produce liquid transportation fuels and value added chemicals. In addition to technical and economic considerations, environmental impacts are being studied through a cradle-to-gate life-cycle assessment approach. Here, we present preliminary findings for the fuel life cycle, involving methane procurement, conversion to lipids in a bioreactor, and further downstream processing. We have defined several potential scenarios for using methane derived from stranded gas, associated gas, and landfill gas. The requirements for procuring each gas stream are taken into account, along with fugitive emissions and considerations of alternate usage for each gas stream. Bioreactor input requirements, along with outputs of products and other material streams, were evaluated in consultation with LanzaTech process engineers. Environmental impacts being considered are global warming potential and fossil energy demand. Initial results reveal that major differences emerge between potential gas feedstock scenarios based upon alternate fate of the gas (flaring vs. utility generation, for instance). Estimated fugitive emissions rates also play a large role in determining the embodied global warming potential of feedstock gases and will need to be thoroughly documented in each commercial setting to verify optimal performance. Large improvements to the overall environmental performance of the system are gained when next-generation LanzaTech bioreactor technology is utilized, in comparison to conventional loop or bubble column reactors, due to improved mass transfer properties and lower gas compression requirements to facilitate the methane fermentation reaction inside the bioreactor.