Pyrolysis characteristics of tea oil camellia (Camellia oleifera Abel.) shells and their chemically pre-treated residues: Kinetics, mechanisms, product evaluation and joint optimization

Abstract

Tea oil camellia (Camellia oleifera Abel.) is a widely distributed oilseed plant in China that yielded around 3.14 million tons of camellia seeds in 2020. Consequently, millions of tons of tea oil camellia shells (TOCS) are produced as processing residues. They are mainly discarded or burned due to the lack of effective large-scale utilization strategies. In this study, the pyrolysis characteristics of raw/extracted/alkali-treated tea oil camellia shells (RTOCS/EXTOCS/ALTOCS) were elucidated via thermogravimetry-infrared spectroscopy, pyrolysis-gas chromatography/mass spectroscopy and artificial neural network (ANN) to demonstrate the application of TOCS in mass pyrolysis. The Coats–Redfern method was used for thermokinetic and thermodynamic analyses under different models. The 1.5-order reaction (F1.5) mechanism could best describe the main pyrolysis stages of RTOCS, EXTOCS and ALTOCS, with an activation energy of 40.14, 66.54 and 76.73 kJ/mol, respectively. Moreover, the pyrolysis gases were mainly released at 200–400 °C. EXTOCS pyrolysis produced more compounds containing CO and C-O functional groups, while ALTOCS produced more CH4. Nine types of organic compounds were identified. Multi-objective optimization based on ANN simulations indicated that ALTOCS pyrolysis at 800 °C was the optimal condition as it provided the highest pyrolysis efficiency. This study suggests that RTOCS, EXTOCS, and ALTOCS were suitable as biomass pyrolysis feedstocks. Therefore, this million-ton-level biomass is expected to serve full-component and high-value industrial utilization.