Effect of torrefaction on the structure and reactivity of rice straw as well as life cycle assessment of torrefaction process

Biomass structure and reactivity of torrefied products are a matter of great concern to explore the fuel properties, pyrolysis characteristics, and microcosmic appearance, and life cycle assessment (LCA) is of great importance to evaluate the environmental impact of the torrefaction process. This study investigates the properties and microstructure of torrefied rice straw, including fuel properties, pyrolysis kinetics, crystallinity, surface functional group changes, and microscopic appearance. Results show that a good linear distribution appears between the comprehensive pyrolysis index (CPI) and atomic H/C ratio, and CPI and crystallinity index (CrI). Fourier transform infrared spectra depict dehydration, decarboxylation, and decarbonylation occur during the torrefaction process. The scanning electron microscope images illustrated the surface characteristics are closely related to the release of volatiles during the torrefaction process. The solid ¹³C NMR spectra of raw and torrefied rice straw reflect that the aromaticity will improve with increasing the torrefaction severity. For LCA analysis, the environmental impact of the torrefaction process shows a positive correlation with torrefaction temperature, and the global warming potential is in the range of 0.1469–0.2707 kg CO₂ emission. This study is meaningful for the evaluation of fuel properties and torrefaction performance as well as microstructure and reactivity of torrefied rice straw.