Hydrocarbon-rich bio-oil production from the coupling formaldehyde-pretreatment and catalytic pyrolysis of poplar sawdust

Abstract

The efficient preparation of hydrocarbon-rich bio-oil is a promising method for biomass utilization. However, the complicated bio-oil composition and low hydrocarbon yield reduced the utilization efficiency of biomass. To solve this problem, a novel technology of coupling formaldehyde-pretreatment (FA) and catalytic fast pyrolysis (CFP) was proposed and tested on poplar sawdust. This coupling technology (FACFP) was featured by introducing catalyst in the pretreatment process, which not only promoted the dissolution of lignin but also enhanced the conversion of lignin-deficient biomass residues into hydrocarbons. Effects of other pretreatment parameters (e.g., solvents, temperature, processing time) on bio-oil production were studied in detail. Compared to water, the utilization of FA as pretreatment solvent was advantageous in lignin removing and improving the accessibility of cellulose to catalyst during pyrolysis. The FACFP of poplar sawdust conducted at a moderate FA-pretreatment temperature (180 °C) and processing time (3 h) was superior in producing hydrocarbon-rich bio-oils, which led to a 1.7-fold hydrocarbon selectivity and a 1.3-fold bio-oil yield as compared to the two-staged FA + CFP mode. Finally, a reaction mechanism for the coupling FACFP of biomass was proposed by highlighting the crucial role of HZSM-5 and FA solvent.