MgO Assisted Catalytic Hydrothermal Carbonization Followed by Pyrolysis of Sunflower Stalks for the Determination of Kinetic and Thermodynamic Parameters

The current study aimed to produce hydrochar from sunflower stalks using the catalytic hydrothermal carbonization (HTC) technique and to evaluate its effectiveness in the pyrolysis process. The hydrochar was pyrolysed in a thermogravimetric analyser at three different heating rates (10, 20, and 40°C/min) for the evaluation of kinetic, thermodynamics and reaction mechanisms. Characterization methods such as Fourier transform infrared spectroscopy and X-ray diffraction were applied to examine the functional groups and phases, respectively. The isoconversional methods were applied for the estimation of kinetic parameters, which included Kissinger Akahira Sunose (KAS), Vyazovkin (VZK), and Ozawa Flynn Wall (OFW). The average activation energy obtained for the catalytic hydrochar based on the VZK method was 125.81 kJ/mol, significantly lower than those for the raw biomass and sole hydrochar pyrolysis. The z(α) master plot approach was applied to deduce the reaction mechanism. The use of catalytic hydrochar may reduce the total environmental effect and greenhouse gas footprint of solid fuel combustion, easing the transition to low-carbon power generation.