Hydrothermal and supercritical ethanol processing of woody biomass with a high-silica zeolite catalyst

Abstract

The effects of high-silica ZSM-5 on the yields, as well as compositions, of bio-oil and solid residue obtained from oak wood sawdust were investigated. The catalyst, in concentrations from 5 to 40 wt% of the raw lignocellulose material, was tested in hydrothermal (HT) and supercritical ethanol (SCE) media. The highest bio-oil yields were 11.0 and 32.4 wt% for HT and SCE processing, respectively, and were obtained by using 20 wt% ZSM-5. After the noncatalytic and catalytic HT processing and noncatalytic SCE processing of lignocellulose, the major products were phenols, whereas esters were the major products in the bio-oils obtained from the catalytic SCE processing of oak wood sawdust. The use of ZSM-5 increased the relative contents of the ester compounds in the bio-oils from the SCE processing, while the catalyst did not significantly change the composition of the bio-oils produced from the HT processing of oak wood sawdust. The highest heating values of the bio-oils were 27.11 and 25.65 MJ kg−1 for HT and SCE processing, respectively, and were obtained from the noncatalytic runs. The amount of recovered carbon in the bio-oils from the catalytic runs was higher than that from the noncatalytic runs for both HT and SCE processing. The carbon content of the solid residues for both HT and SCE processing decreased with the use of a catalyst. An increase in the catalyst concentration led to a decrease in the carbon content of the solid residues in SCE and HT processing.