The valorization of co-pyrolysis bio-oil derived from bio-oil distillation residue and walnut shell via coupling fractional condensation and lyophilization

Abstract

In this study, walnut shells and bio-oil distillation residues were co-pyrolyzed at varying ratios (i.e. 1:3, 1:1, and 3:1) and the resulting bio-oils were collected via fractional condensation. Furthermore, the effect of lyophilization on the collected bio-oils was analyzed. The results indicated that the temperature of fractional condensation effectively controlled the co-pyrolytic oil yield in first condenser, while the total bio-oil yield and condensation efficiency were dominated by the co-pyrolytic blend mass ratios. Meanwhile, the lower ratio of mixed walnut shell and higher condensation temperature would improve the element distribution of bio-oil, namely weakened oxygen content and intensified carbon content. Moreover, the introduction of bio-oil distillation residue not only decreased the content of carboxylic acids in co-pyrolytic oils, but also accelerated the conversion of lignin oligomers to aromatic monomers. The product distribution of fractional co-pyrolytic oil was also improved, in which the total detectable phenols enhanced to 9.73 wt% (with a maximum increase of 22.79 times). Additionally, lyophilization had a positive effect on separation and purification of aqueous bio-oil, endowing 4.79–10.81 times enhancement of detectable phenols and exhibiting a maximum increase of furfural content as surprising 2.22 wt%.