Liquefaction of torrefied wood using microwave irradiation
Torrefaction is an effective pretreatment method to improve the uniformity and quality of lignocellulosic biomass before further thermal processing (e.g., gasification, combustion). The objective of this study was to determine the impacts of torrefaction as a pretreatment before liquefaction. Wood chips were torrefied for 2 h at three different temperatures (230, 260, 290° C) and then subjected to microwave-assisted liquefaction, as was the untreated wood control. The dielectric properties of liquefaction materials, including the biomass samples and liquefaction reagent, were measured to evaluate their abilities to convert electromagnetic energy to heat. The effects of liquefaction time, temperature, and catalyst concentration on the liquefaction efficiency were also investigated. It showed that torrefaction temperature had significant influence on the liquefaction behavior of wood materials. Wood treated at the lowest torrefaction temperature (230° C) retained the most structural/compositional characteristics of untreated wood and therefore they both exhibited similar liquefaction behaviors. The higher treatment temperature (290° C) led to higher liquefaction residue contents, attributed to the increase in carbon content and hydrophobicity from torrefaction.