Abstract
In this work, the effect of the water formation on the enthalpy change of the hydrothermal carbonization (HTC) process was assessed by the direct application of the Hess’s Law to HTC reactants and products. The data concerning HTC of grape-marc at different temperatures (180, 220, and 250 °C), and for different residence times (1, 3, and 8 hours), were retrieved from the literature. The amount of water formed during the process was calculated by means of mass balances on reactants and products. The enthalpy change of HTC was computed first neglecting the enthalpy of formation of the produced water, and then including the enthalpy value derived from the calculated amount of water formed inside the enthalpy balance. In the first case, the enthalpy change was negative (exothermic process) but the trend was parabolic, while considering the enthalpy of the water formed during the process led to exothermicity proportional to the severity factor, which agrees with the literature.