Pyrolysis of torrefied herbal medicine wastes: Characterization of pyrolytic products

Torrefaction is beneficial for improving the pyrolysis product quality. To study the feasibility of utilizing herbal medicine wastes (HMWs), pyrolysis of torrefied HMWs was performed. The effects of torrefaction on the properties of products and the evolution law were examined. The results show that the torrefaction temperature exerts a greater influence on the yield and quality of products from HMWs pyrolysis than that of the torrefaction atmosphere. CO was the predominant component in the gas, and its yield increased with both the torrefaction and pyrolysis temperatures. H-2 and CH4 started to be released at >= 600 degrees C due to dehydrogenation and condensation reactions. Acids, ketones and anhydro-saccharides (AS) were the major compounds in bio-oil from 400 to 600 degrees C, while phenols, aromatics and N-containing compounds dominated at high temperatures. Torrefaction at high temperatures and under oxygenated atmospheres facilitated the formation of larger aromatic ring structures. Pyrolysis of torrefied HMWs under CO2 and O-2 and 260 degrees C produced more CO, CO2 and acids but fewer phenols than that under N-2. The obtained results are beneficial for the development of an effective utilization method for HMWs. (C) 2020 Elsevier Ltd. All rights reserved