*Article* **Thermal Analysis and Kinetic Modeling of Pyrolysis and Oxidation of Hydrochars**

**Gabriella Gonnella 1, Giulia Ischia 1, Luca Fambri <sup>2</sup> and Luca Fiori 1,\***


**Abstract:** This study examines the kinetics of pyrolysis and oxidation of hydrochars through thermal analysis. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques were used to investigate the decomposition profiles and develop two distributed activation energy models (DAEM) of hydrochars derived from the hydrothermal carbonization of grape seeds produced at different temperatures (180, 220, and 250 ◦C). Data were collected at 1, 3, and 10 ◦C/min between 30 and 700 ◦C. TGA data highlighted a decomposition profile similar to that of the raw biomass for hydrochars obtained at 180 and 220 ◦C (with a clear distinction between oil, cellulosic, hemicellulosic, and lignin-like compounds), while presenting a more stable profile for the 250 ◦C hydrochar. DSC showed a certain exothermic behavior during pyrolysis of hydrochars, an aspect also investigated through thermodynamic simulations in Aspen Plus. Regarding the DAEM, according to a Gaussian model, the severity of the treatment slightly affects kinetic parameters, with average activation energies between 193 and 220 kJ/mol. Meanwhile, the Miura–Maki model highlights the distributions of the activation energy and the pre-exponential factor during the decomposition.

**Keywords:** hydrothermal carbonization; modeling; kinetics; thermal analysis; Aspen Plus; biomass; hydrochar
