Decoupling study on the influence of the interaction between biomass hydrochar and coal during co-pyrolysis on the char structure evolution

Co-pyrolysis of biomass hydrochar (biomass processed by hydrothermal carbonization, HTC) and coal, is a viable method for the clean and high-efficiency co-utilization of conventional and renewable resources. Interaction between biomass hydrochar and coal during co-pyrolysis directly impacted the physiochemical structure evolution of char and its downstream application. However, interaction mechanism hasn't been systematically revealed till now. Therefore, this study conducted a decoupling investigation on co-pyrolysis of rice straw hydrochar (RSH) prepared at different HTC conditions and bituminous coal (BC) using a staged fixed-bed reactor. The results demonstrated that RSH volatiles increased the number of deposits and cracks formed on the surface of co-pyrolysis decoupled BC char. Additionally, volatiles from RSH prepared at higher HTC temperatures led to the decrease of surface deposits, surface functional groups (such as –OH, C–H, and C–O) and graphitization degree of BC char. However, volatiles prepared at different solid-liquid ratios had a negligible impact on physicochemical structure of BC char. At HTC temperature of 200 °C, volatiles from BC led to increased surface functional groups (such as –OH and CC) and graphitization degree of co-pyrolysis decoupled RSH char. Furthermore, volatiles from BC showed more noticeable effect on graphitization process of RSH char prepared at higher solid-liquid ratio.