Near-isothermal hydrothermal carbonization of glucose: Estimating continuous reactor performance from batch kinetics

Hydrothermal carbonization (HTC) is a promising thermochemical process for converting biomass into value-added products such as hydrochar. Most HTC research is conducted in batch reactors due to their simplicity, resulting in a lack of studies on continuous operations. Batch reactors have limitations primarily related to a smaller throughput preventing further process development. Continuous reactors, by contrast, offer significant throughput, but design and performance remain largely underexplored. This study investigates the HTC of glucose in both batch and continuous reactors under near-isothermal reaction conditions, with a focus on understanding reaction kinetics. Batch HTC was conducted at 230 °C by injecting a 10 g/L mixture of glucose and water. With use of a sophisticated injection port, biomass reactants were rapidly heated to reaction temperature, allowing for near isothermal reaction conditions. Our approach overcomes the long-time delay resulting from heating a heavy steel reactor. A continuous HTC system was designed, fabricated, and tested with a throughput of 0.30 L/min. The reactor is configured as a baffled plug flow reactor consisting of three main sections: biomass feeding and, the continuous HTC reactor zone, and an energy recovery and depressurization unit. A kinetic model was developed from batch experiments and applied to predict the performance of a continuous HTC reactor using the segregation model. The predicted glucose conversions were 94.80 % for the continuous reactor and 96.30 % for the batch reactor at the same mean residence time of 13.25 min.