Copper and zinc-impregnated mesoporous gamma-alumina catalyst for hydrothermal liquefaction of alkali lignin

Abstract

The complete utilization of lignocellulose is a sustainable key for bio-refineries, where the utilization of evitable lignin is a great challenge owing to its structural complexity. Here, the effect of Cu and Zn-loaded mesoporous γ-Al2O3 catalysts was examined for the first time for the hydrothermal liquefaction of alkali lignin in an ethanol/water solvent system. It showed excellent performance towards the liquefaction as compared to that of (commercial) com-5Cu/γ-Al2O3 catalyst. Here, the bio-oil yield was observed to be 47.7 wt% for com-5Cu/Al catalyst which was increased to 59.1% for syn-5Cu/Al. It was increased substantially to 65.4 wt% for syn-10Cu/Al. However, only a 40 wt% bio-oil yield was found for the non-catalytic (NC) reaction. Additionally, a further significant improvement to 74.7 wt% was noticed for Zn (5 wt%) modified syn-10Cu/Al catalyst. Here, the screening of the water-ethanol mixture, and reaction parameters were also evaluated which showed a small increase in bio-oil yield to 77.4 wt% for ethanol/water (75/25, v/v). The GC-MS analysis of bio-oil exhibited the high specificity of vanillin (69.3%) for syn-10Cu-5Zn/Al. The 1H NMR and FT-IR investigation also validate the diverse functionality of bio-oils. The reusability of the optimum catalyst (syn-10Cu-5Zn/Al) was also tested for three successive catalytic cycles that exhibited the good performance of the catalyst up to the second cycle.