Microwave-assisted Organosolv pretreatment of a sawmill mixed feedstock for bioethanol production in a wood biorefinery

Abstract

A mixture of sawmill feedstocks comprising four softwood species (fir, spruce, Scots pine, and Douglas fir) was subjected to a microwave-assisted Organosolv pretreatment. The influence of H₂SO₄ as a catalyst, ethanol-water ratio as the solvent, and temperature on wood fractionation, cellulose yield and purity, lignin recovery, and inhibitor formation were investigated. Minute addition of H₂SO₄ (0.25% w/w) was found to enhance lignin extraction and hemicellulose hydrolysis, thus providing cellulose yield and purity above 68% ± 2% and 61% ± 3%, respectively. The increase in H₂SO₄ up to 1% and temperature up to 190 °C, impaired cellulose yields a result of intense hydrolysis, thus degrading cellulose and hemicellulose. Conversely, the increase in ethanol-water ratio enhanced delignification without cellulose degradation. Similarly, inhibitor formation increased with pretreatment severity (H₂SO₄ content and temperature), but was mitigated by higher ethanol-water ratio. Finally, under best conditions (60:40 ethanol-water, 175 °C, 0.25% H₂SO₄), cellulose yield and purity reached 82% ± 3% and 71% ± 3%, respectively.

Keywords: Cellulose; Ethanol; Lignin; Mixed sawdust; Organosolv pretreatment.