Supercritical methanol treatment of wood for chemical production.

摘要

Ponderosa pine wood was solubilized in a single step process using supercritical methanol (SCM). The solubilization of wood was optimized using a response surface method with a central composite design, using as independent variables biomass quantity, the methanol volume fraction (VF) and temperature. The optimal conditions resulting in 98% solubilization were temperature of 500°C, VF of 0.47. Statistical analysis also shows that temperature, the VF and their interactions had statistical significance in liquefying wood. Based on the optimization study, five treatment regimes were developed to summarize all experimental conditions studied, based on variables temperature (T) and VF, as follows: T235/VF0.46, T235/VF0.59, T367/VF0.52, T500/VF0.46 and T500/VF0.59. Within these ranges, the near optimal conditions were found at T500/VF0.46 with a SCM density of 0.325 g cm-1. After treatment, the reactor mixture was fractionated into solids, methanol solubles and gases. The solid fraction was analyzed by Pyrolysis GCMS and FTIR spectroscopy showing the presence of mainly polysaccharides and a minor amount of lignin. The volatile components of the methanol soluble fraction were analyzed by GCMS showing the presence of extractives, monomeric lignin structures and carbohydrate dehydration and thermal breakdown products. The water soluble non-volatile components in the methanol soluble fraction were analyzed by HPLC and showed presence of disaccharides, monosaccharides, methylglycosides and 1,6 anhydro monosaccharides. The organic soluble non-volatile components were analyzed by GPC which showed the presence of mainly monomeric, oligomeric and polymeric lignin fragments, indicating the validity of the supercritical methanol treatment in breaking down the natural wood polymer matrix into its building block components. Gas analysis showed CO2 as the main component, indicating the thermal degradation of wood. For the optimal SCM wood depolymerization conditions it was found that extractives are readily removed, with lignin polymers undergoing cleavage of the beta-ether bonds and going into solution. As the lignin solubilizes, exposed wood polysaccharides become exposed and can depolymerize and be solubilized in methanol. The process described in this dissertation can be used to identify several species of interest to drive future endeavors in bio-refinery applications, and for finding potential substitutes for chemical commodities currently generated by petroleum resources.