14.2.3.1 General Process of Organosolv Pretreatment

A general process of organosolv pretreatment is described in Fig. 14.2. Pure or aque­ous organic solvents, such as methanol, ethanol, acetone, ethylene glycol, triethylene glycol, and phenol, were typically used as the working medium. Biomass was ther­mochemically treated in these working medium by mixing with (or without) the addition of acid, alkaline, or neutral catalysts, such as H2SO4, NaOH, or MgCl2, at a

relatively lower (< 180 °C) or higher temperature (> 180 °C) [23,24,55,56]. Organo­solv pretreatment also dictated a unique pathway of downstream refinery process: Af­ter treating the substrate for several minutes or days, the cellulose-rich solid fraction was separated by filtration and washed by the same solvent and, subsequently, water, and then was ready for hydrolysis. The liquid stream, which contained the solvent, alone with lignin and sugars from hemicellulose, as well as their derived products (e. g., furfural, 5-hydroxymethylfurfural(5-HMF),depolymerizedlignin), was recov­ered by distillation. After distillation, the residual was washed by water to precipitate the organosolv lignin. Chemicals recovered from the water-soluble fraction include xylose, glucose, oligomeric sugars, organic acids, 5-HMF, and other lipophilic extracts. They can be further utilized after separation and concentration [24].