Study on the pyrolysis characteristics and kinetic mechanism of cow manure under different leaching solvents pretreatment

Abstract

Cow manure (CM) is a kind of biowaste with potential for heat recovery and energy. The effects of different leaching solvents on the physicochemical structure of CM and the catalysis role of AAEMs on the thermal behavior were studied. TGA experiments showed that the maximum weight loss rate and the peak temperature of hemicellulose and cellulose increased after leaching, while the TG/DTG curve moved to a high temperature direction. The devolatilization index (Di) value of the raw and leaching samples increased with the increase of the heating rate, indicating that the higher heating rate promoted the release of volatile. The treatment with leaching not only removed AAEMs in CM effectively, but also led to a larger specific surface area and pore volume, and reduced the crystallinity of cellulose and crystal size in CM. Na salt and K salt were mainly in water soluble state, while Ca salt and Mg salt were mainly in acid soluble salt. Compared with the change of physical and chemical structure caused by leaching, the removal of AAEMs played a dominant role in the pyrolysis characteristics of the samples. The removal efficiency of AAEMs increased with the strength of acid. Based on Kissinger model, the Eα of Raw-CM, H2O-CM, CH3COOH-CM, HCl-CM, HNO3-CM and H2SO4-CM is 171.30 kJ/mol, 187.58 kJ/mol, 190.86 kJ/mol, 292.10 kJ/mol, 287.79 kJ/mol and 280.69 kJ/mol respectively. Both the raw and leaching samples followed the reaction order mechanism and tended to react according to a higher-order reaction model between n = 1.5 and n = 4. In contrast, CH3COOH is an ideal solvent for leaching pretreatment.