Evaluation of the overall reaction enthalpy change of hydrothermal carbonization process by means of differential scanning calorimetry at high pressure

In this work, heat flux Differential Scanning Calorimetry (DSC) was used coupled with high-pressure crucibles to evaluate the enthalpy change of Hydrothermal Carbonization (HTC) applied to cellulose, wood, and digestate from an anaerobic digestion plant. The temperature program, constant heating rate of 5 °C/min up to 250 °C, then 3 hours at 250 °C, was run twice on each crucible containing the sample: in the first run the HTC process takes place and completes, in the second run (the blank) the thermal effect is not related to the process. The two curves are then subtracted to obtain the process enthalpy change. 8 mg of dry substrates and 64 mg of distilled water were used for each run. For each substrate, three replicates were performed. Results showed high reproducibility and agreed with the available literature about DSC of wood and cellulose. The results for digestate were in the same range, but lower due to the less energetic nature of the substrate. Interestingly, the enthalpy value related to wood showed higher standard deviation with respect to the one related to digestate.