(48b) Synergistic Biomass and Natural Gas Process Design for Liquid Fuel Production with Reduced CO2 Emissions

For the past century, petroleum derived liquid hydrocarbons have been the predominant fuel for the transportation sector. However, concerns regarding scarce petroleum reserves and increasing greenhouse gas (GHG) emissions from fossil fuels urge advancements in alternative transportation fuels as well as production of liquid fuels from alternative carbon sources, such as natural gas (NG), coal, and biomass.

Liquid fuels derived from biomass can result in lower lifecycle GHG emissions relative to petroleum-derived fuels [1]. However, the supply of biomass-derived liquid fuel is limited by the sustainably available (SA) biomass feedstock and the relatively low (30-40 %) carbon conversion during standalone liquid fuel production. Biomass carbon conversion to liquid fuel can be increased by using supplemental non-carbon energy. However, such processes have to overcome the intermittent nature of most non-carbon energy sources as well as their high economic cost in the short-term [2]. The recent surge in shale gas reserves and its production, most notably in the U.S., has led to interest in utilizing NG as a bridge for the transition to a sustainable economy.

Towards reducing the CO₂ emissions associated with the transportation sector, we investigate the design of carbon and energy efficient processes for integrated biomass and natural gas (NG) conversion to liquid fuel. A process superstructure considering biomass conversion via gasification/Fischer-Tropsch (FT) synthesis and fast-hydropyrolsis/ hydrodeoxygenation described in [3], and NG conversion via reforming followed by FT synthesis is established. Subsequently, a mixed integer nonlinear programming model (MINLP) is formulated to identify the process configurations that maximize the energy output as liquid fuel for different ratios of NG to biomass carbon feeds (δ_ng). For 1 % ≤ δ_ng≤ 150 %, the optimal process configurations are capable of producing ~5-14 % more liquid fuel output than the combined fuel output of individual standalone processes converting the same amount of biomass and NG. This synergy originates from synthesizing additional liquid fuel by combining the residual biomass carbon with the excess hydrogen per carbon available from the NG feed. These integrated processes are also estimated to achieve up to 80 % reductions in greenhouse gas (GHG) emissions relative to petroleum-based fuels.

[1]       Agrawal R, Singh NR. Synergistic Routes to Liquid Fuel for a Petroleum deprived future AIChE Journal 2009;55:1898.

[2]       Singh N, Mallapragada D, Agrawal R, Tyner W. Economic analysis of novel synergistic biofuel (H2Bioil) processes. Biomass Conversion and Biorefinery 2012;2:141.

[3]       Mallapragada DS, Agrawal R, Tawarmalani M. Synthesis of augmented biofuel processes using solar energy. AIChE Journal 2014.