CO2 pyrolysis kinetics and characteristics of lignin-rich hydrolysis residue produced from a tandem process of steam-stripping and acid hydrolysis

High-value utilization of lignin-rich hydrolysis residue (LIHS) from sustainable aviation fuel pilot system by pyrolysis under CO2 atmosphere was proposed to co-produce the carbon-based products in order to improve the techno-economic level and low carbon dioxide emission. Thermal decomposition characteristics and kinetics of the LIHS under CO2 atmosphere was for the first time investigated by using the distributed activation energy models with distributed-free and distributed-fitting methods. The thermal decomposition process of lignin-rich hydrolysis residue in CO2 atmosphere can be divided into drying, devolatilization, carbonization and carbon-loss stages. A middle difference method with variable step was developed for the approximation of the differ-ential term in the Friedman method. The values of activation energy and pre-exponential factor at selected conversion degrees were obtained. The kinetic compensation effect between activation energy and pre-exponential factor was found. The mean activation energy was estimated based on the Maximum Likelihood Estimation. The effective values of the standard deviation and pre-exponential factor were determined by inverse problem method that combines Gauss-Hermite quadrature numerical method and Pattern Search Method (PSM) optimization algorithm. The results showed that the mean activation energy, the standard deviation and pre-exponential factors for the integral method are 261.26 kJ mol(-1), 28.760 kJ mol(-1) and 1017.658 s(-1), those for differential method are 271.36 kJ mol(-1), 29.910 kJ mol(-1) and 1018.418 s(-1). The unavailability of activation energy distributed function for distributed-free method may lose its prediction ability. Finally, the developed distributed activation energy model with distributed-fitting method not only could obtain the real kinetic pa-rameters of the LIHS pyrolysis process, and have a good ability on predicting the reaction process. This work may provide an alternative technical scheme for the non-thermal valorization of the LIHS, and a comprehensive and systematic kinetic analysis of the thermal decomposition of the LIHS for process design.