MODELING THE REACTION KINETICS DURING HYDROTHERMAL CARBONIZATION OF WASTE BIOMASS

In this paper, a study on the reaction kinetics of the hydrothermal carbonization (HTC) process is presented. A fundamental piece of information for the design of a HTC process is the knowledge of its kinetics: the process conditions do not allow the establishment of thermodynamic equilibrium and the reaction kinetics approach becomes mandatory for understanding how the process occurs, evolves over time and depends on the operating conditions. Experimental data have been collected applying the HTC process to an organic waste residue coming from the wine-making industry: the grape marc. Starting from the yield and analytical results, a kinetic model based on a two-step kinetic mechanism was calibrated. The activation energy and pre-exponential factors of the various degradation reactions were determined by means of least square optimization versus the experimental data. The calibrated model allowed a characterization of the HTC time scale under different process conditions, showing that a two-step reaction mechanism can be suitably used to describe the evolution in time of the hydrochar yield at different process temperature