Ionic liquid coupled with nickel salt for enhancing the hydro-liquefaction efficiency of the major biomass components

Abstract

Ionic liquid combined with metal species is considered as a promising catalytic system for biomass liquefaction, which complies with the requirement of green chemistry and promotes utilization of biomass resources. The catalytic systems containing imidazolium-based ionic liquids and nickel chloride were applied to the hydro-liquefaction of major biomass constituents (cellulose, xylan and lignin) in this work. The anion type in ionic liquid played a vital role in the liquefaction of feedstock. The results indicated that the maximum conversion and bio-oil yield were achieved in 1-butyl-3-methylimidazolium bromide ([BMIM]Br)/NiCl2 system, which was attributed to the strong nucleophile and coordinating capacity of bromide ion. The ionic liquid-based catalyst was more effective in the conversion of cellulose and xylan, due to their high reactivity. Additionally, the ionic liquid-based catalyst facilitated the thermal degradation of feedstocks and intermediates, resulting in the increased content of organics with the smaller molecular sizes. The deoxy-hydrogenation reaction was enhanced over ionic liquid-based catalyst, improving the quality of the resulting bio-oils.