Characteristic evolution of hydrochar from hydrothermal carbonization of corn stalk

• Hydrothermal carbonization of corn stalk was carried out at reaction severity of 5.05–8.29.
• The hydrochar exhibited coal-like O/C and H/C atomic ratios at the reaction severity log R0 > 7.11.
• Correlations between the hydrochar properties and the reaction severity were modeled by dose-response functions.
• The FTIR functional groups showed different profiles with reaction severity.

Reaction severity is a comprehensive parameter which combines temperature and time to describe the severity of a process. In this work, hydrothermal carbonization (HTC) of corn stalk was carried out at reaction severity levels of 5.05–8.29. The effect of reaction severity on the solid yield, the chemical, energetic, and structural properties of hydrochar products were studied in detail. The hydrochar yield varied from 71 to 36%. The higher heating value increased from 20.8 MJ/kg at reaction severity of 5.05 to the maximum value of 29.79 MJ/kg at severity of 8.29. When the reaction severity was greater than 7.11, the hydrochar exhibited coal-like oxygen/carbon and hydrogen/carbon atomic ratios. The evolution of microcrystalline structure for hydrochar was examined by XRD and the results showed that the component degradation led to develop hydrochar structure. The functional group results revealed that the high aromatization performance and carbonization extent of the hydrochar could be achieved with reaction severity increasing. The correlations between solid yield, carbon content, oxygen content, HHV, relative peak intensity ratios of the functional groups for hydrochar and reaction severity were fit with the experimental data. The results indicated that the dose-response models fit these characteristics data well, which would be favorable to understand and design the hydrothermal carbonization process for corn stalk.