Electrocatalytic Co-Processing of Biomass-Derived Aqueous Waste Streams and Bio-Oils for Renewable Fuel Production at Normal Temperature and Pressure

Electrocatalytic conversion is emerging as a potentially attractive low-cost approach to valorize biomass-derived streams. Conventional upgrading processes require moderate temperatures between 433 and 678 K, pressures of 14,000 kPa, and external sources of dihydrogen; however, the same upgrading reaction can be performed using electrochemical reactors and much lower temperatures and pressures (293 K and 101 kPa) and with no supplied hydrogen (H2).1-4 In this work, we evaluate the electrocatalytic conversion of aqueous waste and bio-oils generated during biomass liquefaction via hydrothermal liquefaction (HTL) and pyrolysis. Our work shows that the main biomass-derived compounds (carboxylic acids, alcohols, ketones, etc.) were successfully converted via electrocatalytic oxidation (ECO) into olefins, paraffins, and alcohols.2, 5 Alternatively, the same compounds could not be upgraded via electrocatalytic hydrogenation (ECH) over a variety of noble and base metals, instead H2 evolution was the preferred reaction.1, 3 Figure 1 shows that the operation (electricity) cost can be offset by the sale of the excess H2 generated (valued at >$2/kgH2) specially when operating at low full cell potentials (<4.5 V) and using low electricity cost (<¢4/kwh).2 Additionally, a preliminary techno-economic analysis shows the capital cost associated with the integrated electrocatalytic process for the aqueous waste treatment and H2 generation can be up to 80% lower than the combined cost for traditional thermal (e.g., gasification) and biological (e.g., anaerobic digestion) wastewater treatment, and H2 generation (via natural gas steam reforming), and can lower the minimum fuel selling price (MFSP) by up to $0.84/GGE. References Andrews, E.; Lopez-Ruiz, J. A.; Egbert, J.; Koh, K.; Sanyal, U.; Miao, S.; Li, D.; Karkamkar, A.; Derewinski, M. A.; Holladay, J.; Gutiérrez, O. Y.; Holladay, J. D., Performance of Base and Noble Metals for Electrocatalytic Hydrogenation of Bio-Oil-Derived Oxygenated Compounds. ACS Sustainable Chem. Eng. 2020, 8 (11), 4407-4418. Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. J. Appl. Electrochem. 2020, Accepted. Lopez-Ruiz, J. A.; Andrews, E. A.; Akhade, S. A.; Lee, M.; Koh, K.; Sanyal, U.; Yuk, S. F.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Glezakou, V. A.; Rousseau, R.; Gutiérrez, O. Y.; Holladay, J. D., Understanding the role of metal and molecular structure on the electrocatalytic hydrogenation of oxygenated organic compounds. ACS Catal. 2019, 9 (11), 9964-9972. Lopez-Ruiz, J. A.; Sanyal, U.; Egbert, J.; Gutiérrez, O. Y.; Holladay, J., Kinetic Investigation of the Sustainable Electrocatalytic Hydrogenation of Benzaldehyde on Pd/C: Effect of Electrolyte Composition and Half-Cell Potentials. ACS Sustainable Chem. Eng. 2018, 6 (12), 16073-16085. Qiu, Y.; Lopez-Ruiz, J. A.; Sanyal, U.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Anodic electrocatalytic conversion of carboxylic acids on thin films of RuO2, IrO2, and Pt. Appl. Catal. B-Environ. 2020, 277, 119277. Snowden-Swan, L. J.; Hallen, R. T.; Zhu, Y.; Hart, T. R.; Bearden, M. D.; Liu, J.; Seiple, T. E.; Albrecht, K. O.; Jones, S. B.; Fox, S. P.; Schmidt, A. J.; Maupin, G. D.; Billing, J. M.; Elliott, D. C. Conceptual Biorefinery Design and Research Targeted for 2022: Hydrothermal Liquefaction Processing of Wet Waste to Fuels; PNNL-27186. BM0108010; Pacific Northwest National Lab. (PNNL), Richland, WA (United States): 2017. Figure 1