The influence of NaCl during hydrothermal carbonization for rice husk on hydrochar physicochemical properties

NaCl was used to solubilize organic matter from rice husk (RH), followed by subsequent hydrothermal carbonization (HTC) to explore the catalysis role of Cl− to components of lignocellulose during the HTC due to the interactions of NaCl (Na+ and Cl−) with –OH group would promote cellulose and hemicellulose hydrolysis to improve carbonization. Ultrasonic pretreatment was also used to enhance the process. The results demonstrated that ultrasonic pretreatment could effectively destroy the structure of RH, and enhanced the hydrolysis of RH during the HTC. The ultrasonic pretreatment could benefit dehydration and inhibit decarboxylation during the HTC for its free radical role. The addition of NaCl could improve the hydrolysis, dehydration and decarboxylation performance and the NaCl would be absorbed on the surface of hydrochar. It was found that NaCl would promote the removal of hemicellulose and enhance the depolymerization of lignin to form monomers during the HTC, resulting in crack formation on the surface of hydrochar for RH. The results would give more help to understand the role about Cl− during HTC of lignocellulose and other organic waste.