Greenhouse Gas Footprints of Transportation Fuels Manufactured from Natural Gas Liquids Derived from Shale Gas

Authors: 
Chen, Q., The University of Texas at Austin
Dunn, J. B., Northwestern University
Allen, D., The University of Texas at Austin
In the processes being developed by National Science Foundation Engineering Research Center on the Innovative and Strategic Transformation of Alkane Resources (CISTAR), natural gas liquids (NGLs) are separated from shale gas, then undergo dehydrogenation and oligomerization to produce transportation fuels. The sale of such unconventional transportation fuels can be limited by the environmental footprints of the fuels in some market segments. Section 526 of the Energy Independence and Security Act (EISA) of 20071 requires that alternative transportation fuels sold to the federal government must have lower or equal life cycle greenhouse gas (GHG) emissions compared to petroleum-based fuels. The California Low Carbon Fuel Standard2 limits the sale of transportation fuels in California based on life cycle GHG emissions. These limitations motivate the understanding of GHG footprints of CISTAR fuels.

Life cycle (well to tank) GHG footprints are a combination of upstream and fuel production components. Upstream emissions of methane (a potent greenhouse gas) and the GHG emissions caused by energy demand of the CISTAR conversion processes are the major contributions to life cycle GHG emissions. The GHG footprints analysis is highly sensitive to the region of origin of the light alkane feedstocks. The fuel production segment’s contribution to CISTAR fuel life-cycle GHG emissions depends on the details of the conversion scenarios. Preliminary baselines for CISTAR processes show that CISTAR fuel production would be comparable (+/- 10%) to GHG emissions from conventional gasoline production, but more sensitivity analyses in both upstream and fuel production segments need to be done. The results will guide research towards advances that will reduce environmental impacts of CISTAR fuels.