Effect of residence time on hydrothermal carbonization of corn cob residual

Hydrothermal carbonization is a promising technique for conversion of industrial waste into valuable products. Producing hydrochar from corn cob residual (CCR) in a cost-effective way is key, from an economic standpoint. For this purpose, the effect of residence time in the range of 0.5 to 6 h was studied under the optimal temperature of 250 °C. Results showed that the higher heating value (HHV) of hydrochar increased approximately 40% in comparison to that of the raw material; however, prolonging the residence time beyond 0.5 h had a negligible effect on the HHV increase. Chemical compositions and H/C and O/C ratios of hydrochars revealed a minimal effect of longer residence time. Furthermore, thermogravimetric and derivative thermogravimetric analysis (TG/DTG), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analysis of hydrochars also verified that the pyrolysis behavior and chemical structure of hydrochars with various residence times were similar.