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

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 degrees 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 degrees C, 0.25% H2SO4), cellulose yield and purity reached 82% +/- 3% and 71% +/- 3%, respectively.