Petrological analysis of fast pyrolysis bio-oil distillation residues

Distillation of fast pyrolysis bio-oil leaves solid residues analogous to those from distillation of fossil fuels, potentially also mimicking subsurface petroleum formation or other natural carbon concentration processes. As in petroleum-based residues, bio-oil residues vary in terms of quality, yield, and versatility for downstream applications. The goal of this work was to elucidate parallels and contrasts between bio-oil distillation residues and fossil-derived solid fuels using petrological analysis techniques (reflectance and fluorescence microscopy, Raman and infrared spectroscopy) supported by geochemical analysis (elemental and programmed temperature pyrolysis analysis). Continuous dual-bed fast pyrolysis was used to convert hardwood and switchgrass biomass into oils. Compositions and petrographic presentation of the biomass distillation residue solids were compared to natural solid hydrocarbon products and lignite-subbituminous coal. Microscopic evaluation showed distillation residues are similar to low to moderate thermal maturity solid hydrocarbons in reflectance, fluorescence, isotropism, and the absence of biological structure. Bio-oil distillation residues contained significantly more structural oxygen than solid hydrocarbons, and as such present similarities to coal. This significant content of weakly bound oxygen-containing terpenoid compounds indicates the volatility and environmental reactivity of bio-oil distillation residue solids, potentially suggesting these materials could be re-processed and recycled into the industrial process as a byproduct energy fuel.