Ex Situ Catalytic Fast Pyrolysis of Lignocellulosic Biomass to Hydrocarbon Fuels: 2018 State of Technology and Future Research

This report documents the progress in research funded by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office, for the conversion of biomass to infrastructure-compatible liquid hydrocarbon fuels via catalytic fast pyrolysis (CFP). This research is focused on an ex situ CFP pathway where biomass undergoes a rapid deconstruction in a fast pyrolysis reactor at approximately 500°C (932°F), followed by the separation of vapors from solids (char and mineral matter); the vapors are then sent to an ex situ catalytic reactor for upgrading. Upgrading involves deoxygenation, hydrogenation, and carboncarbon coupling, and this renders the vapors significantly less reactive and more amenable to further processing upon condensation (condensation produces CFP oil). Solids removal prior to the ex situ upgrading step provides an advantage with respect to catalyst stability and choices; catalyst choices can be further broadened to include noble metals in fixed bed systems. The effectiveness of this ex situ vapor upgrading step for CFP oil quality improvement has been verified, with experiments proving that single-step hydrotreating can deoxygenate the liquid product to <1wt% oxygen. Catalyst stability during hydrotreating of raw fast pyrolysis bio-oil is a major challenge; it requires multiple hydrotreating steps unless vapor upgrading (CFP) is included.

Significant advancements have been made with this research since it started in 2014. Catalyst development and testing has resulted in a >60% relative increase in carbon efficiency. This has allowed a quicker reduction in the modeled minimum fuel selling price (MFSP) compared to initial out-year projections documented in previous Bioenergy Technologies Office Multi-Year Program Plans. Modeled reduction in the MFSP since 2014, based on bench-scale experimental results, are shown in Figure ES-1; further details for the 2018 state of technology (SOT) are in Table ES-1 and Table ES-2. Updated 2022 goals show future technical and cost projections based on an extrapolation of the current research and its estimated trajectory (Figure ES-1, Table ES-1, and Table ES-3).

With the recent gains in process efficiency, research focus through 2022 will include considerations of future industrial relevance, in addition to further yield improvements primarily by reducing carbon loss to light gases (CO and CO2). Research will include: establishing longer CFP catalyst lifetimes and longer onstream times before requiring regeneration; developing more rapid regeneration; enabling the use of lower cost (and less pristine) feedstocks to allow further cost reduction and added diversity in the feedstock supply chain; and targeting improvements in fuel quality making the product fuel blendstocks more desirable for end use in transportation. Research through 2022 and beyond will include the improvement and tailoring of CFP oil composition through further catalyst research; this can enable reduced hydroprocessing costs including the option of coprocessing at petroleum refineries, improvements in downstream fuel quality, and the production of valuable and separable coproducts.