Optimal use of hybrid feedstock, switchgrass and shale gas for the simultaneous production of hydrogen and liquid fuels

• The use of hybrid raw materials for liquid fuels, biomass and shale gas, is evaluated.
• We use a mathematical optimization based approach.
• Optimization-based sensitivity analysis is performed for hybrid production of fuels.
• Biomass is recommended as long as its price is below $100/t.
• Shale gas current low price supports its use until it reaches $5/MMBTU.

In this paper, we present a superstructure optimization approach for the integration of the simultaneous production of liquid fuels and hydrogen from switchgrass and shale gas. The process is based on Fischer-Tropsch technology in which the shale gas is reformed with steam, while the switchgrass is gasified and reformed (with steam or partial oxidation). The raw gas is cleaned up and its composition may be adjusted (using either water gas shift reaction or pressure swift adsorption). Next, the sour gases are removed before the liquid fuels are produced using an FT reactor. The heavy liquids are upgraded using hydrocracking to increase the yield towards FT-diesel. A sensitivity study on the raw material prices reveals that production costs for the biomass-shale gas facility are below $1/gal as long as biomass price is below $100/t and the price of the shale gas is not higher than $11.5/MMBTU. Furthermore, hydrogen is produced as long as the demand for liquid fuels can be met and there is enough shale gas available.