The Effect of Temperature on the Properties of Hydrochars Obtained by Hydrothermal Carbonization of Waste Camellia oleifera Shells

Hydrothermal carbonization (HTC) is a thermochemical conversion technique that can produce renewable solid biofuel by all types of waste. Waste Camellia oleifera shells (WCOSs) can be used to produce hydrochars via HTC. The effect of HTC temperature on the physicochemical properties and combustion behaviors of hydrochars was analyzed by varying from 150 to 300 °C. The mass yield of hydrochars decreased from 72.45% at 150 °C to 41.88% at 300 °C with the increase in temperature, and the higher heating value increased from 19.22 MJ/kg at 150 °C to 29.97 MJ/kg at 300 °C. The H/C and O/C values reduced from 1.30 and 0.66 of HTC150 to 0.77 and 0.27 of HTC300, respectively. Fourier transform infrared spectroscopy analysis indicated that the functional groups of hydrochar have changed because of the dehydration and decarboxylation reaction. The surface structure of hydrochars was rougher, and many pore structures were found at 240–300 °C by scanning electron microscopy analysis. The combustion behaviors of WCOSs and their hydochars are distinct via thermogravimetric analysis, and the stability of hydrochars was strengthened with the increase in HTC temperature.