A novel reaction kinetics model for estimating the carbon content into hydrothermal carbonization products

This paper presents an original reaction kinetics model as a tool for estimating the carbon yield and distribution among the product phases originating from hydrothermal carbonization (HTC) of biomass. The kinetics model, developed in MATLABTM, was used in a best fitting routine with HTC experimental data obtained for a representative ligno-cellulosic biomass (grape marc) and it is easily applicable to any kinds of feedstock. Levenberg–Marquardt algorithm was used for best fitting. The HTC reaction pathway was described through a lumped model, in which biomass is converted into solid (primary and secondary char), liquid and gaseous products. Runge-Kutta method was used to solve the system of 6 differential equations - mass balances - accounting for the different HTC lumped reactions, through the estimation of 5 Arrhenius kinetics parameters (݇ଵ ݇ଶ ݇ଷ ݇ସ ݇ହ). The ݇௜ parameters were used to graphically determine the preexponential factors (݇଴,௜) and the activation energy (ܧ (௜,௔values for each reaction. Modelling predictions are in very good agreement with experimental data, i.e. carbon content calculated from hydrochar and gas mass yields and ultimate analysis data. For all the examined conditions (T=180-250 °C, t=0-8 h), the model fitting errors resulted lower than 10%. The developed reaction kinetics model is therefore a reliable tool for the prediction of carbon distribution among HTC products.