Thermal Devolatilization Kinetics of Switchgrass Pretreated with Torrefaction and Densification

Abstract

<abstract> <bold><sc>Abstract.</sc></bold> Pretreatment of switchgrass by torrefaction or densification can improve its physical and chemical characteristics by making it hydrophobic, increasing the bulk density and energy content, and improving ability to store and transport. The goal of this study was to investigate the effects of four pretreatments (torrefaction at 230°C, torrefaction at 270°C, densification, and combined torrefaction and densification) and heating rates on the thermal devolatilization characteristics of switchgrass in both inert and oxidizing atmospheres. The thermal devolatilization characteristics of biomass were determined using a thermogravimetric analyzer. Torrefaction of switchgrass increased its carbon content and higher heating value but decreased hydrogen and oxygen contents. These effects increased with increase in torrefaction temperature from 230°C to 270°C. However, the rate of devolatilization of switchgrass torrefied at 230°C was higher than that of switchgrass torrefied at 270°C in both inert and oxidizing atmospheres. The weight loss of switchgrass occurred in three stages in both inert and oxidizing atmospheres. In both atmospheres at a heating rate of 50°C min^-1, switchgrass pretreated with combined torrefaction and densification showed the highest rate of weight loss peak (34 and 44 mg min^-1 in inert and oxidizing atmospheres, respectively) and the lowest start and end temperatures of the rate of weight loss peak. Overall, in both inert and oxidizing atmospheres, switchgrass pretreated with combined torrefaction and densification had the highest rate of devolatilization, followed by switchgrass pretreated with densification, switchgrass pretreated with torrefaction at 230°C, switchgrass pretreated with torrefaction at 270°C, and raw switchgrass. Heating rate also had significant effects on the weight loss and rate of weight loss of switchgrass but did not have significant effects on the start and end temperatures of the rate of weight loss peaks.