Hydrothermal carbonization: combination of heat of reaction measurements and theoretical estimations

Abstract

Experimental data for the heat of reaction during the hydrothermal carbonization (HTC) of biomass are scarce. Theoretical approaches can be found in literature, but the values are in a wide range. Up to now, there is no publication that presents a combination of theoretical estimation and experimental determination of the heat of reaction. The comparison is very important, for example to improve and validate the theoretical approaches. In this study, a new experimental setup at a heat flow DSC in temperature scanning mode is presented. It allows for the first time a comparison between measured and estimated values for the heat of reaction from the same HTC experiment: a sample mass of about 1.25 g, composed of biomass from a nature protection area and water, is carbonized while the heat of reaction is recorded. The usage of a removable glass container as inset allows to balance the process. The sample volume allows CHN analysis of the HTC-coal for theoretical estimations of the heat of reaction. The results show that the setup leads to reproducible results for the recorded heat flows and the CHN composition of the HTC-coal. Compared to the experimentally determined value for the heat of reaction of biomass in HTC process of $(-715.1\,\pm \,15.3)\, {{\text{J\,g}}^{-1}_{\text {daf}}}$, the estimation for the heat of reaction leads to an overrated value, even if the dissolved organic matter (dried on the coal) is considered in the energy balance.