Thermal behavior and kinetics of the pyrolysis of the raw/steam exploded poplar wood sawdust

Steam explosion (SE) pretreatment has been an effective method for the upgrade of biomass, including poplar wood sawdust (PWS). The change of PWS components after SE treatment was investigated, e.g., a significant increase of extractives and decrease of hemicellulose content, while slight change in cellulose and lignin contents. The pyrolysis characteristics of raw PWS and SE PWS were investigated by thermogravimetric analysis/infrared spectrometry (TG-IR) analytical technology. Pyrolysis of PWS was performed on a thermogravimetric analyzer at multiple heating rates of 10, 20, 40, and 80 °C/min up to 1000 °C to obtain the pyrolysis characteristics of PWS. TG results showed that both raw PWS and SE PWS presented three weight loss stages, respectively. It could be concluded that the pyrolysis process of the two PWS samples has similar characteristics, and the main pyrolysis temperature range of PWS is from 200 °C to 500 °C. The significant difference between two types of PWS is that the SE pretreated PWS displayed a lower volatile content and higher fixed carbon content than raw PWS, which could make SE PWS much more favorable in thermochemical application. Derivative thermogravimetric also showed that one major decomposition reaction took place at a specific heating rate for two PWS feedstocks. The heating rate mainly influences the primary pyrolysis stage of the PWS, while the maximum weight loss rate and corresponding temperature change with increasing of heating rate. The evolved gaseous products during PWS pyrolysis such as H2O, CO, CO2, CH4 and other volatile compounds were found. Assuming that the decomposition obeys first-order kinetics, kinetic parameters of PWS pyrolysis were determined using two methods proposed by Kissinger and Ozawa, respectively. Both methods gave analogous values of activation energy for raw PWS and SE PWS samples, ranging from 134 kJ mol−1 to 142 kJ mol−1. This study gave further confirmation that the steam explosion pretreatment process could transform lignocellulosic biomass into an intermediate feedstock with favorable properties for thermo-chemical applications.