Pyrolysis characteristics and kinetic analysis of tobacco stem pretreated with different solvents

In the present study, the effects of pretreatments with different solvents (hydrochloric acid, sodium hydroxide, and ethanol) on the physicochemical structure and pyrolysis behavior of tobacco stem (TS) were investigated. Elemental compositions analysis showed that acid washing increased the carbon content and exhibited a high removal percentage for the inorganic species. SEM, BET, and FTIR analysis showed that the pretreatments exerted different effect on the surface and microstructure. Furthermore, the pyrolysis characteristics analysis indicated that solvent pretreatment increased the initial pyrolysis temperature due to the removal of unstable volatile components, especially for the acid and alkali washing samples. Meanwhile, hydrochloric acid pretreatment increased the maximum pyrolysis rate temperature of cellulose decomposition stage and decreased the char residues due to the large removal of inorganic species, while alkali treatment produced the opposite result. Pyrolysis kinetic analysis based on Coats-Redfern method showed that F1.5 chemical reaction model can be used to describe the pyrolysis stages of TS samples and a decreased activation energy was observed during the decomposition of cellulose stage for the acid and alkali washed samples. The released gaseous products during the pyrolysis process were also monitored by using TG-FTIR technique, and the gaseous release behavior was different from each other.