Intrinsic kinetics study of microwave catalytic pyrolysis of cellulosic biomass using a novel microwave thermogravimetric analyzer

A novel microwave thermogravimetric analyzer (microwave TGA) has been developed and applied to study the intrinsic reaction kinetics of microwave-assisted catalytic pyrolysis of cellulosic biomass particles. Constant heating rate was achieved by exposing the sample directly to the microwave irradiation, monitoring the particle surface temperature by an infrared temperature sensor and controlling the magnetron power output via a feedback PID controller. Compared with a conventional TGA operated with the same sample at identical loading and heating rate, the peak weight loss temperature measured in the microwave TGA was 30–50 °C lower. This systematic offset arises from the distinct temperature measurement strategy and heat transfer pathways in two systems. In the microwave TGA, the IR sensor records the particle surface temperature, which is lower than the particle core because the heat is generated volumetrically and flows outward. By contrast, the conventional TGA the reported temperature reflects the carrier gas (or furnace) temperature, which is generally higher than particle interior with inward conductive/convective heat transfer. Consequently, the same conversion is reached at a lower measured temperature in the microwave TGA than in the conventional TGA. Consistent with this behavior, the activation energy extracted from the constant heating rate data using model-free kinetic models is 50–80 % lower in microwave-assisted pyrolysis than in conventional pyrolysis. Our results generated from a well-designed microwave TGA operated at constant heating rates confirmed those results in the literature showing much lower activation energy of microwave reactors and thus much lower microwave reactor temperature to achieve similar conversions in conventional conductively/convectively heated reactors. • A novel microwave TGA with sensor-feedback controlled constant heating rates • Delivered 1–50 °C /min constant ramp rates and stable isotherms at 700 °C • Revealed 50–80 % lower activation energy for biomass pyrolysis under microwave