New insights into the evolution of solid and liquid phases during hydrothermal carbonization of lignocellulosic biomasses

This paper is the first illustration of an innovative procedure for studying the dynamics of condensed phases in hydrothermal carbonization of lignocellulosic scraps and wastes. A novel technique, based on a particular implementation of van Krevelen plots, shows how to monitor precisely the compositions during the process. Two fundamental laws describe the system evolution: a double-exponential decay and a modified form of the Hill equation. The modeling is tested using batch experiments (200 °C, up to two hours) performed with three different lignocellulosic materials (silver fir, beech wood, olive pruning). The quality of the fittings (R2 as high as 0.999) seems to give a reason for the goodness of the approach and heuristically indicate the way for further extensions. The method allows predicting the time course of solid yield, heating value, atomic ratios, and other relevant process variables. The technique also provides valuable and easy-to-obtain information to address the process optimization of industrial plants.