A comprehensive evaluation on pyrolysis behavior, kinetics, and primary volatile formation pathways of rice husk for application to catalytic valorization

Catalytic fast pyrolysis is a prospective and effective route to produce value-added products from rice husk (RH). Understanding the volatile compositions and its formation pathways as well as kinetics during RH pyrolysis is crucial and fundamental to regulate the quality of the target products since catalysts interact directly with primary volatiles. In this study, two pyrolysis coupled real-time volatile monitoring techniques (TG-FTIR and PyGC/TOF-MS) were employed to conduct comprehensive experiments for RH. The results showed that RH presented three mass loss and gaseous product evolution stages in the temperature range of 200 to 330 degrees C, 330 to 390 degrees C, and 390 to 600 degrees C, respectively. After speculating the formation pathways of the 24 main volatile species, it was indicated that 2,3-dihydro-benzofuran was the major product for hemicellulose, while 2-methoxy-4-(1-propenyl)-phenol was potentially a key active intermediate and very unstable during pyrolysis of lignin constituent in RH. In addition, pyrolysis of RH could be divided into two kinetic stages at cut-off point of 25% conversion. The first kinetic stage obeyed three-dimensional (D3) diffusion model and E-a was within 140-170 kJ/mol. In the secondary kinetic stage, Ea raised gradually to about 200 kJ/mol and pyrolysis reactions followed the second-order reaction model.