Comparative study on fuel characteristics and pyrolysis kinetics of corn residue-based hydrochar produced via microwave hydrothermal carbonization

Corn residues are an important source of bioenergy. Due to their highly diverse lignocellulosic structures, the hydrochar produced from microwave-assisted carbonization of different corn residues may have distinct fuel properties and pyrolysis kinetics. This study comprehensively investigated the effect of processing temperature on the basic fuel properties of hydrochar and examined the pyrolysis behavior of hydrochar as a precursor through kinetic analysis. The results indicate that the fuel quality of corn straw hydrochar prepared by microwave-assisted hydrothermal carbonization at 230 degrees C was significantly improved over that of its feedstock, with a higher heating value of approximately 20.7 MJ/kg. Hydrochar prepared by microwave-assisted hydro-thermal carbonization of corn cob at 230 degrees C presents noticeable environmental advantages because it contains the lowest ash and nitrogen contents (0.5% and 0.5%, respectively) and lower sulfur content (0.05%). Moreover, regarding the kinetic modeling, the Doyle and Coats-Redfern models, which are both first-order and single-step kinetic models, were identified as satisfactory in interpreting the key pyrolysis kinetic parameters. Additionally, the microwave-assisted hydrothermal process increased the apparent activation energy of hydrochar due to the increase in crystallinity and the increase in the number of C=C and C=O bonds.

Automated summary

Corn residues are an important source of bioenergy. This study investigated the effect of processing temperature on the fuel properties of hydrochar produced from different corn residues. The results showed that microwave-assisted hydrothermal carbonization improved the fuel quality of corn straw and corn cob hydrochar, with lower ash, nitrogen, and sulfur contents. The kinetic analysis indicated that first-order and single-step kinetic models were satisfactory in interpreting the pyrolysis behavior. The microwave-assisted hydrothermal process increased the apparent activation energy of hydrochar.