Solvent liquefaction of pyrolysis bio-oil distillation residues into upgraded products

Abstract: Fast pyrolysis of biomass can convert a wide variety of biomass feedstocks into bio-oils and higher value products. While catalytic refining of bio-oils can produce fuel-grade hydrocarbons, more efficient pathways are needed to ensure production of sustainable aviation fuel (SAF) compounds and carbonaceous solid materials. Bio-oils of sufficient quality and stability can undergo distillation, and catalytic hydrotreatment can upgrade the distillates without the interference of high molecular weight coke. However, more utilization of the residues can be realized.
To this end, we utilized solvent liquefaction for the upgrading of bio-oil distillate residues. Fast pyrolysis bio-oils from lignocellulosic (switchgrass) and oleaginous (spirulina) biomasses were distilled, and the distillate residues underwent liquefaction in microreactors with various solvent environments (water, ethanol, NaOH, formic acid). Optimal conditions were downselected based on GC-MS results. For spirulina residues, ethanol liquefaction produced the most compounds, whereas 2M NaOH (aq) produced the best results for switchgrass-based residues. Larger scale reactions of optimal conditions (100 mL Parr reactor, 300 ^oC, 1500 psi) produced oils and hydrochar product, the latter of which can be calcined into coke for manufacturing applications. The liquefaction oils from spirulina contained straight-chain aliphatic compounds, which can potentially improve processability for SAF applications.