Spinning band distillation of biomass pyrolysis oil phenolics to produce pure phenol

Abstract

Competitive pricing for biofuels will require the coproduction of biobased products and chemicals to improve the economic outlook of biorefineries. Phenolics have been eyed due to their natural abundance in bio-oils relative to petroleum, as well as their potential profit margins. In bio-oils, the wide product distribution (especially phenolics) prevents meaningful separation. We’ve shown previously that bio-oils with relatively low oxygen (<15 wt%) from advanced pyrolysis processes can be distilled and/or extracted, producing a fraction rich in phenol and cresols. To further improve separation, we utilized a spinning band column distillation system, designed to perform at 200 theoretical plates. Catalytic (HZSM-5) pyrolysis bio-oils from switchgrass biomass first underwent extraction directly, producing a phenolic fraction and a hydrocarbon fraction. Subsequently, the phenolic fraction underwent a preliminary flash distillation ahead of spinning band distillation, in order to remove residues. Spinning band distillation resulted in fractions with more than 80 wt% phenol (the balance o-cresol), which can be purified by recrystallization in pentane. Both GC/MS and NMR indicate phenol crystals were obtained at ∼92 wt% purity. To complete the biorefinery concept, the hydrocarbon fraction was distilled to obtain a fuel product and heavy polyaromatic residues. The residues were thermally treated to produce bio-pitch.