A holistic kinetic model for the hydrothermal carbonisation of lignocellulosic biomass

Abstract

This research presents the first holistic kinetic model for hydrothermal carbonisation (HTC) of lignocellulosic biomass, based on the composition of cellulose, hemicellulose, and lignin. The model predicts product outcomes for hydrochar, gas and liquid residuals over a wide range of processing conditions: temperatures (200 – 260 °C), residence times (0 – 12 hours), and biomass-to-water ratios (1:4 to 1:50). Individual kinetic models for the macromolecular compounds were developed and validated with experimental data. The combination into a holistic model demonstrated accurate predictions of the solid phase (hydrochar), where 258 data points from 58 lignocellulosic biomass sources (49 different types, from 41 studies including this one) were processed. The accuracy of the holistic kinetic model was improved when considering the interaction effects between the macromolecular compounds in lignocellulosic biomass and by determining optimised distribution factors for the non-macromolecular fraction into the solid, liquid and gas phases. The finalised R^2 value for hydrochar was 0.966. Prediction of the gas phase was evaluated and a correlation determined, however, further developments with more experimental quantification of this phase is necessary to improve prediction capabilities, with the final model resulting in an R^2 of 0.120 for this phase. The finalised holistic kinetic model shows promise for predicting the hydrochar produced from several non-traditional lignocellulosic biomass types, presenting an advanced future application of this research