Biomass Pyrolysis Pathways to Produce Low-Carbon Transportation Fuel

Abstract

Sustainable biofuels can serve as an alternative to petroleum-derived transportation fuels. These synfuels can be integrated with conventional gasoline and diesel without altering current infrastructure in the transportation sector. Depending on the conversion process, biofuels can have a low or net negative carbon footprint, providing a means of reducing atmospheric carbon dioxide levels. Pyrolysis is a thermochemical conversion pathway involving the degradation of cellulose, hemicellulose, and lignin components of biomass. Biomass pyrolysis products include non-condensable gases, condensable vapors (both hydrocarbon and aqueous), and solid char. The condensed hydrocarbon liquid, called pyrolysis-oil, is the desired product for transportation fuel production, but high oxygen content (~ 40 wt%) prevents direct use in motor vehicles. Upgrading processes can reduce oxygen levels, but in general cannot produce the high quality fuels required to replace gasoline and diesel. Advanced pyrolysis techniques, which directly integrate traditional upgrading processes into the pyrolysis reactor, on the other hand, can produce high quality transportation fuels. KiOR has recently commercialized one such pathway. Researchers at Gas Technology Institute (GTI) have developed a particularly interesting pilot scale catalytic pyrolysis pathway, which integrates catalytic hydrotreatment with thermal pyrolysis. Process designs based around GTI’s Integrated Hydropyrolysis and Hydroconversion (IH\(^{2}\)) pathway were evaluated to determine technical and economic feasibility of producing liquid transportation fuels. The technoeconomic analyses of configurations that co-process natural gas with and without electricity generation, both yield a levelized cost of fuel of $2.41/gal. Both of these processes have significantly lower lifecycle carbon footprints than corresponding petroleum-derived fuels. Liquid fuel and electricity coproduction achieves net negative lifecycle carbon emissions per MJLHV of liquid fuel. When carbon capture and storage is added to both process designs, carbon footprint is further reduced at a cost ranging from $28-59/tCO\(_{2}\) avoided. Ultimately, processes modeled on GTI’s IH\(^{2}\) system can provide a renewable, low carbon liquid transportation fuel.