Wood solubilization and depolymerization using supercritical methanol. Part 1: Process optimization and analysis of methanol insoluble components (bio-char)

Conversion of wood into a methanol soluble liquid (bio-oil) was shown to occur under supercritical methanol treatment (SCM). The particle size of the solid material (bio-char) left after evaporating the solvent from the bio-oil was analyzed. Expectedly, the degradation of the particle size was more pronounced during a severe SCM treatment in comparison to subcritical solubilization conditions. Molecular mass was reduced by 90% under optimal conditions of SCM treatment under which the highest degree of solubilization (degradation) was obtained. The bio-char was also analyzed by pyrolysis GC-MS. The composition of the bio-char after sub- and moderate SCM treatments consisted mainly of carbohydrate derived degradation products, which was mixed with some lignin moieties. At near to optimal SCM treatment conditions, the remaining bio-char was composed mainly of modified cellulose and lignin. The optimization of the liquefaction process was performed by means of the statistical design called response surface model with a central composite design.