Volatile–char interactions: Roles of in situ volatiles with distinctly-different chemistry in determining char structure and reactivity

Abstract

This study reports the roles of volatiles with distinctly-different chemistry in determining char reactivity and char structure during in situ volatile–char interactions under non-catalytic conditions. Volatiles were generated in situ from polyethylene (PE), double-acid washed biosolid (DAWB), polyethylene glycol (PEG) or cellulose and interacted with char prepared from DAWB that is free of catalytically-active inorganic species in a two-stage reactor at 1000 °C. The experimental results show that both H- and O-containing reactive species play different roles during in situ volatile–char interactions. It has been found that char reactivity decreases substantially after in situ volatile–char interactions. Results from Raman analysis of the char after in situ interactions with the PE volatiles show H-containing reactive species substantially enhance the condensation of the aromatic ring systems within the char, thus slightly decreasing the H content in char and also making char carbon structure considerably less reactive. It has also been found that the reactivity of char after in situ volatile–char interactions increases with increasing O/H molar ratio of volatiles. The results indicate that O-containing reactive species in volatiles can react with char to form CO complex oxides that mitigate the carbon structure from condensing into large aromatic ring systems, thus increasing O and H contents in char and enhancing char reactivity.