Modelling of pine wood sawdust thermochemical liquefaction

Abstract

This work presents the study of direct liquefaction of pine sawdust. The effect of the temperature, solvent, catalyst and biomass concentration was investigated in a 100 mL reactor. The optimal operating conditions are 20% biomass, catalyst – acid p-toluenesulfonic (3%), solvent – diethylene glycol and 2-ethyl-hexanol (1:1), 160 °C and 2 h to achieve a conversion of 97%. In these conditions, identical conversion was obtained in a 1 L reactor, but the viscosity of the liquefied biomass increased drastically with the concentration of biomass (≥40%) and with the reaction time (>1 h). The factorial design of experiments was used to establish the model that relates the conversion with the temperature and the catalyst concentration. This study showed that the temperature was the most important variable and that it is possible to obtain conversions higher than 90% using low percentages of catalyst (2.6%) but high temperatures (>170 °C). However, for temperatures lower than 160 °C it is impossible to achieve excellent yields, even when using 3.5% of catalyst. The kinetic study allowed the establishment of the equation that describes the variation of the biomass conversion with the reaction time and temperature. The optimization carried out allowed to estimate the reaction order (≈1) and the activation energy (kJ/mol) characteristic of processes controlled by the rate of the chemical reaction. The liquefied wood products were characterized by mid infrared spectroscopy, and the density, viscosity, water content and hydroxyl and acid values were also determined.