(726a) Effects of Co-Product Uses on Environmental and Economic Sustainability of Hydrocarbon Biofuel from One- and Two-Step Pyrolysis of Poplar

Authors: 
Kulas, D., Michigan Technological University
Winjobi, O., Michigan Technological University
Zhou, W., Michigan Technological University
Shonnard, D. R., Michigan Technological University
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 (Kulas et al. 2018). Fast pyrolysis involves rapid thermal degradation of wood in the absence of air at a temperature of approximately 500-550OC with a short residence time of less than 2 seconds. The bio-oil product from pyrolysis is catalytically upgraded with hydrogen into hydrocarbon biofuel. Torrefaction, often referred to as mild pyrolysis, tends to enhance bio-oil properties by reducing water content, minimizing acidity, and reducing size reduction energy. The development of a two-stage fast pyrolysis process that involves a torrefaction pretreatment step prior to pyrolysis was investigated as an approach to minimize the energy consumption associated with size reduction and enhance the bio-oil quality.

Optimization of these fast pyrolysis-based biofuel processes were investigated through heat integration and alternative uses of the co-product biochar, which can be sold as an energy source to displace coal or natural gas, soil amendment or processed into activated carbon. The impacts of optimization through heat integration on the cost of hydrocarbon biofuel production as well as the environmental impacts were investigated through a techno-economic 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 co-product 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.

References

1. Kulas, D. Winjobi, O., Zhou, W., Shonnard, D.R. (2018), Effects of Co-product Uses on Environmental and Economic Sustainability of Hydrocarbon Biofuel from One- and Two-Step Pyrolysis of Poplar, ACS Sustainable Chemistry & Engineering, March 21, 2018, DOI: 10.1021/acssuschemeng.7b04390

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