Environmental, exergetic and economic tradeoffs for catalytic and fast pyrolysis-to-renewable diesel

Authors: SPATARI, SABRINA - Drexel University; LARNAUDIE, VALERIA - Drexel University; MANNOH, IDA - Drexel University; WHELLER, MICHAEL - University Of Maine; MACKEN, NELSON - Swarthmore College; Mullen, Charles; Boateng, Akwasi

Submitted to: Renewable Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2020
Publication Date: 8/13/2020
Citation: Spatari, S., Larnaudie, V., Mannoh, I., Wheller, M.C., Macken, N.M., Mullen, C.A., Boateng, A.A. 2020. Environmental, exergetic and economic tradeoffs for catalytic and fast pyrolysis-to-renewable diesel. Renewable Energy. 162:371-380. https://doi.org/10.1016/j.renene.2020.08.042.
DOI: https://doi.org/10.1016/j.renene.2020.08.042

Interpretive Summary: The largest source of renewable carbon available for conversion to fuels and chemicals to replace those currently sourced from fossil fuels is lignocellulosic biomass which includes purpose grown energy crops (e.g. grasses) as well as forest and crop residues. One promising process that is able to convert these materials to drop in hydrocarbon biofuels that will be direct replacements for petroleum derived gasoline and diesel fuel is fast pyrolysis (FP). Fast pyrolysis produces a liquid called bio-oil, which needs to be deoxygenated in order to be refined into gasoline or diesel fuel. This deoxygenation can take place partially during its production by adding a catalyst to the pyrolysis process which is then called catalytic fast pyrolysis (CFP). Pyrolysis oils from both CFP and non-catalytic FP need to be further refined but the advantage of CFP is that the pyrolysis is stable and it therefore reduces the expense and difficultly required for the upgrading process. The disadvantages to CFP are complication of the initial pyrolysis process, need for additional materials (catalysts) and reduction of the pyrolysis oil yields. Which route to renewable fuels is better depends on the cost of the process and the environmental impact resulting from the overall production of the fuel. In this work, the conversion of forest residues through the two above describe path was evaluated by techno economic analysis (TEA), life cycle analsyis (LCA) and exergetic analysis. TEA estimates the cost of the process, LCA determines how much greenhouse gas emissions are reduced compared with the use of petroleum fuels and exergy analysis determines the resource impact of the process. Results from the analysis indicate a tradeoff between biofuel yield and environmental impact for the CFP process, where low renewable diesel yield corresponds with potentially the best life cycle GHG emission reduction (-71 g CO2e/MJ). However, fast pyrolysis and ex-situ catalytic upgrading maintains a high fuel yield while also meeting a low global warming intensity (GWI) measure that meets energy policy objectives. With continued research to optimize catalyst performance, improve product yield, and reduce production costs, both processes could be promising means of producing low carbon transport fuels.

Technical Abstract: Life cycle assessment and techno-economic analysis are used to evaluate the upgrading of bio-oils derived from forest residues to renewable diesel through catalytic fast pyrolysis (CFP) and hydrocracking and fast pyrolysis (FP) and catalytic upgrading by hydrotreating and hydrocracking processes. Multiple metrics corresponding with environmental, exergetic, as a measure of maximum theoretical work and resource intensity, technological and economic aspects are used to evaluate both pathways for producing renewable diesel for meeting renewable transport fuel policy goals. The LCA model shows that daily catalyst regeneration is a significant process input and constitutes a sizeable contribution to life cycle greenhouse gas (GHG) emissions for catalytic upgrading (33%) and catalytic pyrolysis (12%). Catalyst regeneration also affects exergy and production cost. Results from the analysis indicate a tradeoff between biofuel yield and environmental impact for the CFP process, where low renewable diesel yield owing to a high product ratio of bio-char to renewable diesel corresponds with potentially the most negative life cycle GHG emissions (-71 g CO2e/MJ). However, fast pyrolysis and ex-situ catalytic upgrading maintains a high fuel yield while also meeting a low global warming intensity (GWI) measure that meets energy policy objectives. With continued research to optimize catalyst performance, improve product yield, and reduce production costs, both processes could be promising means of producing low carbon transport fuels.