Catalytic liquefaction of pine sawdust for biofuel development on bifunctional Zn/HZSM-5 catalyst in supercritical ethanol

•Integration of Zn/HZSM-5 and supercritical ethanol was used for biomass liquefaction.•Zn/HZSM-5 exhibited higher catalytic performance than HZSM-5.•10%Zn/HZSM-5 produced biofuel with the highest hydrocarbons content at 15.03%.•Mechanism of biomass liquefaction reactions on Zn/HZSM-5 catalysts was proposed.

Catalytic liquefaction can effectively convert solid biomass into liquid bio-crude that could be upgraded to advanced biofuel, but the exploration of green and efficient catalysts remain a challenge. In this study, bifunctional Zn/HZSM-5 catalysts were firstly combined with supercritical ethanol to produce bio-crude in pine sawdust catalytic liquefaction. The catalysts were characterized by BET, NH3-TPD, XRD and TEM. The effects of Zn/HZSM-5 catalysts with different Zn loading ratios on the yield and quality of bio-crude and gas were investigated. The results showed that Zn/HZSM-5 and HZSM-5 catalysts improved the yields of bio-crude compared to no catalyst treatment. The use of HZSM-5 based catalysts reduced the contents of oxygenated compounds including acids, ketones, phenols and alcohols in bio-crude products. Hydrocarbons content of the bio-crudes produced by HZSM-5 based catalysts increased compared to bio-crude produced by no catalyst treatment. Compared to HZSM-5 catalyst, Zn/HZSM-5 catalysts exhibited better catalyst performance to improve bio-crude quality due to the additional decarbonylation, decarboxylation and dehydrogenation reactions induced by Zn loading. 15%Zn/HZSM-5 catalyst resulted in the highest yields of bio-crude at 59.09 wt.%, and 10%Zn/HZSM-5 catalyst produced bio-crude with the highest hydrocarbons content at 15.03%. The four stages of mechanism for biomass liquefaction reactions on Zn/HZSM-5 catalysts in supercritical ethanol was proposed.