Use of a Lewis acid, a Brønsted acid, and their binary mixtures for the liquefaction of lignocellulose by supercritical ethanol processing

Abstract

Supercritical ethanol liquefaction of teak wood was carried out at 300 °C for 30 min without and with the use of Mg(ClO₄)₂, HClO₄, and HClO₄/Mg(ClO₄)₂ at various loadings (2–10 mmol). The bio-oil yield from the non-catalytic supercritical ethanol liquefaction of teak wood was ∼41 wt%. The highest bio-oil yield (∼58.2 wt%) was obtained with the catalytic run using 2 mmol of Mg(ClO₄)₂. In the catalyzed trials, with the use of either Mg(ClO₄)₂ or HClO₄, an increase in catalyst amounts resulted in a decrease in bio-oil yields. There was no clear trend for the use of co-catalysts. A degree of de-oxygenation was observed with the use of the catalysts studied. The O/C atomic ratio of the bio-oil from the non-catalytic was 0.44. The O/C atomic ratios in the bio-oil produced from catalytic runs ranged from 0.25 to 0.38. In the bio-oil from the non-catalytic run, the major compound was phenolic species, whereas esters were dominant in the bio-oils from the catalytic runs. The type of catalyst and its amount had significant effects on the product distributions and compositions. The prominent ester compounds were ethyl lactate and ethyl levulinate. The highest relative yield of ethyl levulinate was 49.1% and obtained with the use of the Mg(ClO₄)₂/HClO₄ (2 mmol : 10 mmol) catalyst. The heating values of the bio-oils from catalytic runs were higher than that of the non-catalytic run. The highest heating value of 31.21 MJ kg⁻¹ was obtained with the Mg(ClO₄)₂/HClO₄ (2 mmol : 10 mmol) catalyst.