Study on the effect of different solvent pretreatment on the pyrolysis characteristics of tobacco

Solvent pretreatment can remove some components in biomass and change the distribution of its pyrolytic products. Combined with the physicochemical analysis of tobacco before and after solvent pretreatment, the pyrolysis characteristics of tobacco and the changes of pyrolysis oil components after the removal of some components of tobacco by deionized water, 75% ethanol, and 3% lactic acid were evaluated by thermogravimetry (TG) and high-temperature pyrolysis experiments. The results showed that the O/C atomic ratio of tobacco decreased after solvent pretreatment, and the high concentration of ethanol had a huge effect on the intensity of the peaks associated with aromatic and pyranic rings. TG analysis showed that the pyrolysis of pretreated tobacco was mainly characterized by the thermal decomposition of cellulose and hemicellulose. For ethanol and lactic acid-washed samples, the weight loss in the last stage decreased and the amount of the char residues increased, with the highest of 22.7% for the lactic acid-washed sample. Gas chromatography-mass spectrometry analysis of high-temperature pyrolysis oil showed that water pretreatment could effectively reduce the production of aromatics and cresols, while ethanol was able to elute chlorogenic acid, a precursor of hydroquinone. Lactic acid pretreatment increased the relative content of long-chain hydrocarbons and acids, causing the relative peak area percentages of n-hexadecanoic acid to increase from 1.8% to 8.91% compared with the raw sample of tobacco. In addition, organic solvent pretreatment promoted the formation of ketones in the pyrolysis oil and also inhibited the formation of substituted pyridines at the C-3 position on the pyridine ring.