4.6 Article

High-Efficiency Conversion of Ionic Liquid-Pretreated Woody Biomass to Ethanol at the Pilot Scale

Journal

ACS SUSTAINABLE CHEMISTRY & ENGINEERING
Volume 9, Issue 11, Pages 4042-4053

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acssuschemeng.0c07920

Keywords

woody biomass; ionic liquid; ethanol; scale-up; pilot scale; carbon footprint; technoeconomic analysis

Funding

  1. California Energy Commission [GFO-17-902]
  2. Lawrence Berkeley National Laboratory
  3. U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research [DE-AC02-05CH11231]
  4. Bioenergy Technology Office within the DOE Office of Energy Efficiency and Renewable Energy

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Using an IL pretreatment solvent, this study optimized the conversion of California woody biomass to ethanol, achieving nearly full conversion of glucose and xylose to ethanol. Demonstrating high efficiency in biomass-to-ethanol conversion, the process achieved >80% deconstruction efficiency, >90% fermentation efficiency, and high ethanol distillation efficiency.
With a diverse and widely distributed global resource base, woody biomass is a compelling organic feedstock for conversion to renewable liquid fuels. In California, woody biomass comprises the largest fraction of underutilized biomass available for biofuel production, but conversion to fuels is challenged both by recalcitrance to deconstruction and by toxicity toward downstream saccharification and fermentation due to organic acids and phenolic compounds generated during pretreatment. In this study, we optimize pretreatment and scale-up of an integrated one-pot process for deconstruction of California woody biomass using the ionic liquid (IL) cholinium lysinate [Ch][Lys] as a pretreatment solvent. By evaluating the impact of solid loading, solid removal, yeast acclimatization, fermentation temperature, fermentation pH, and nutrient supplementation on final ethanol yields and titers, we achieve nearly full conversion of both glucose and xylose to ethanol with commercial C5-utilizing Saccharomyces cerevisiae. We then demonstrate process scalability in 680 L pilot-scale fermentation, achieving >80% deconstruction efficiency, >90% fermentation efficiency, 27.7 g/L ethanol titer, and >80% ethanol distillation efficiency from the IL-containing hydrolysate post fermentation. This fully integrated process requires no intermediate separations and no intermediate detoxification of the hydrolysate. Using an integrated biorefinery model, current performance results in a minimum ethanol selling price of $8.8/gge. Reducing enzyme loading along with other minor process improvements can reduce the ethanol selling price to $3/gge. This study is the largest scale demonstration of IL pretreatment and biofuel conversion known to date, and the overall biomass-to-ethanol efficiencies are the highest reported to date for any IL-based biomass-to-biofuel conversion.

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