Formation of persistent free radicals in biochar derived from rice straw based on a detailed analysis of pyrolysis kinetics

• Published in: The Science of the total environment 2020-05, Vol.715, p.136575-136575, Article 136575
• Main Authors: Tao, Wenmei, Duan, Wenyan, Liu, Chunbo, Zhu, Dongdong, Si, Xiaoxi, Zhu, Ruizhi, Oleszczuk, Patryk, Pan, Bo
• Format: Article
• Language: English
• Subjects: Charcoal; Free Radicals; Kinetics; Lignin; Oryza; Persistent free radicals; Pyrolysis; Pyrolysis kinetics; Rice straw
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.136575

The presence of persistent free radicals (PFR) in biochars may greatly broaden the application of biochars in pollution control, but may also cause negative impacts to the environment. Understanding the structural basis and the formation mechanisms of PFR is essential for a targeted biochar production and application. This study used rice straw (RS), a ubiquitous agricultural waste, to investigate the generation processes of PFR in relation to RS pyrolysis kinetics. Based on a detailed thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis, the activation energy was calculated by Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods. This work combined pyrolysis kinetics analysis and solid particle characterization. Our results showed that lignin started to pyrolyze at a lower temperature than cellulose and hemicellulose. Lignin was the main factor for PFR generation. Chemical bond breaking contributed only slightly to PFR formation. The reconfiguration of the carbonaceous structures may be a more important contributor to PFR formation, while the cross-linking between different compositions and the interactions between the chemical compositions and inorganic minerals may play a significant role for PFR generation and stabilization in RS. This study provides useful theoretical basis to understand the thermal pyrolysis process of RS and the manipulation of biochar properties. [Display omitted] •Similar activation energies are obtained by KAS and FWO methods.•Lignin pyrolyzes at a lower temperature than cellulose and hemicellulose•Lignin is a main contributor to PFR generation in rice straw biochar.•Carbonization of the structures is the major process for PFR generation.