Effects of Coproduct Uses on Environmental and Economic Sustainability of Hydrocarbon Biofuel from One- and Two-Step Pyrolysis of Poplar

Abstract

This study investigated the environmental and economic sustainability of liquid hydrocarbon biofuel production via fast pyrolysis of poplar biomass through two pathways: a one-step pathway that converted poplar via fast pyrolysis only, and a two-step pathway that includes a torrefaction step prior to fast pyrolysis. Optimization of these fast pyrolysis-based biofuel processes were investigated through heat integration and alternative uses of the coproduct biochar, which can be sold as an energy source to displace coal, soil amendment or processed into activated carbon. The impacts of optimization on the cost of hydrocarbon biofuel production as well as the environmental impacts were investigated through a technoeconomic analysis (TEA) and life cycle assessment (LCA), respectively, with two-step and one-step processing compared to fossil fuels. The TEA indicates that a one-step heat integrated pathway with the production of activated carbon has a minimum selling price of $3.23/gallon compared to $5.16/gallon for a two-step heat integrated process with burning of the coproduct biochar to displace coal. The LCA indicates that using the displacement analysis approach, a two-step heat integrated pathway had a global warming potential of −102 g CO2 equivalent/MJ biofuel compared to 16 CO2 equivalent/MJ biofuel for the heat integrated one-step pathway.