Solvent liquefaction of fast pyrolysis bio-oil distillate residues for solids valorization

Authors: Elkasabi, Yaseen; Mullen, Charles

Submitted to: Industrial and Engineering Chemistry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2024
Publication Date: 6/22/2024
Citation: Elkasabi, Y.M., Mullen, C.A. 2024. Solvent liquefaction of fast pyrolysis bio-oil distillate residues for solids valorization. Industrial and Engineering Chemistry Research. 63:11701-11709. https://doi.org/10.1021/acs.iecr.4c01364.
DOI: https://doi.org/10.1021/acs.iecr.4c01364

Interpretive Summary: Renewable chemicals can be made from plants using a process called pyrolysis. When done correctly, pyrolysis produces an oil ("bio-oil") that can be refined into fuels and chemicals. After refining, solid waste from the bio-oil can be made into other valuable solid products, but it is sometimes desirable to produce more liquid chemicals from the solid waste materials. This work examined how solvents, temperature and pressure can be used to liquefy these solids for applications in fuel blends. Depending on the type of biomass examined (spirulina or switchgrass), we find that greater amounts of oil can be made with spirulina, partly due to the nature of biomasses like spirulina that have higher amounts of protein.

Technical Abstract: Viable thermochemical biorefineries require valuable outputs with optimized carbon distributions. While catalytic refining of biomass pyrolysis oils can produce fuel-grade hydrocarbons, more carbon-efficient pathways are needed to sustainably produce both renewable hydrocarbons – including those suitable for sustainable aviation fuel (SAF) – and carbonaceous solid materials. Bio-oils of sufficient quality and stability can undergo distillation, and catalytic hydrotreatment can upgrade the distillates without interference of high molecular weight coke precursors. To further utilize the residues, we tested solvent liquefaction for the upgrading of bio-oil distillate residues. Pyrolysis bio-oils from a lignocellulosic (switchgrass) and an oleaginous/proteinaceous (spirulina) biomass were distilled, and the distillate residues underwent liquefaction in microreactors with various solvents (water, ethanol, NaOH (aq), formic acid (aq)). Optimal conditions were downselected based on GC-MS of the products. For spirulina oil residues, ethanol-based liquefaction produced the most volatile compounds, whereas 2M NaOH (aq) produced the best results for switchgrass-oil residues. Larger scale reactions of optimal conditions (100 mL Parr reactor, 300 oC, 1500 psi) produced oils and hydrochar, the latter which can be calcined into coke for manufacturing applications. The oils contained straight-chain aliphatic compounds, which can potentially improve processability for SAF applications.