The solubilization of wood in potentially wood derivable solvents

This study is concerned with the conversion of biomass to higher value products. The medium to long term possibility of substituting oil-derived fuels and chemicals as well as developing compact and low capital investment technologies is the main reason for this work. One of routes being explored is direct liquefaction, which consists of mixing wood with a recycle liquid and converting the slurry under the action of temperature, pressure and often catalysts. The study is composed of two parts: (1) a literature review of same basic aspects of wood liquefaction and (2) an experimental investigation of the initial solubilization of wood under liquefaction conditions. The rationale behind this study is based on concepts put forward by the Sherbrooke liquefaction group. The key concept is that, to achieve a controlled and selective conversion of wood to liquids, a well designed pretreatment is needed to solubilize the wood components (or major families) under conditions in which little or nochemical degradation other than depolymerization takes place. Under these circumstances the primary products can be subsequently upgraded via selective catalytic processes. In this study, the swelling, the dissolution and the depolymerization of wood and wood components are reviewed together with the effects of the important physiochemical parameters on wood solubilization. In the experimental study, poplar wood was treated with water as well as with five potentially wood-derivable solvent systems (methanol, methanol/water, diethyleneglygol, phenol/water, toluene) using a 250 ml autoclave and at temperatures between170 and 235 °C. Heating rates of ant 10 °C/min were used and the time at reaction temperature was typically 10 minutes. The yields of ethanol solubles ranged between10 and 63 % of m.a.f. wood at 235 °C. A correlation between the swelling power of the solvent and the hemicellulose solubilization was found. This result is also of significance for lignin removal since hemicellulose solubilization and hydrolysis (i.e. autohydrolysis presumably) precedes lignin solubilization. The highest lignin conversion to ethanol solubles was found to be 90 %. No cellulose was converted to ethanol solubles below 235 °C except in the presence of water and phenol/water mixtures where the amorphous cellulose could be partially solubilized.