Thermal decomposition kinetics of dairy manure hydrochars

Abstract

Hydrothermal processes, as well as hydrothermal carbonization (HTC), have emerged as a promising technology for the conversion of high-moisture feedstocks. A total of six hydrochars were generated from dairy manure via H3PO4-catalyzed HTC at varying reaction temperatures and residence times. The heating value of hydrochars produced using HTC (25.64 MJ/kg) has improved significantly from raw dairy manure (17.16 MJ/kg). The kinetic parameters for the thermal decomposition of the manure and its hydrochars were estimated using the Friedman mathematical model. In a comparison of three reaction atmospheres (CO₂, N₂, and air), it was observed that lower activation energies were required in air environments for all specified hydrochars relative to the raw manure. Furthermore, Py-GC-MS studies revealed that light-oxygenated compounds were produced at 500 °C from the hydrochars upon flash pyrolysis. The acid treatment under autogenous pressure, significantly improved manure hydrochars physiochemical properties. The comprehensive theoretical and practical guidelines presented in this study for acid-promoted manure hydrochars indicate that dairy manure can be converted into a substitute energy source using the hydrothermal carbonization process. Additionally, a thorough comprehension of the kinetics of combustion, gasification, and pyrolysis is crucial for the design of industrial processes, feasibility assessments, and scale-up.