Toluene gas treatment by combination of ionic liquid absorption and photocatalytic oxidation

Toluene exhaust gas is a nuisance to the environment and human beings. In this study, 1-dodecyl-3-methylimidazolium chloride (DDMIM Cl) was selected as the absorbent solution and was combined with photocatalytic oxidation (PCO) for the treatment of toluene gas. The effects of toluene concentration, UV lamp power, catalyst dosage, coexisting ions and pH on the toluene removal ratio by PCO were investigated. Changes to the absorbent structure after four reuses were compared according to the UV-vis absorption spectrum, and the anti-oxidation ability of the absorbent was evaluated. The results showed that the absorbent concentration was an important factor in the absorption of toluene. At the absorbent concentration of 5%, the initial absorptivity reached 96.79%, and the saturated absorption capacity was 43.8 mg/L. With a toluene concentration of 13.1 mg/L, an 18-W UV lamp, a photo catalyst dosage of 400 mg/L, and a reaction time of 80 min, the removal ratio of toluene reached 91.3%. The PCO of toluene followed pseudo-first-order kinetics. The main intermediates of toluene oxidation were benzoic acid and benzaldehyde, while traces of cresol and benzyl alcohol were also found. After four reuses, the absorption capacity of the absorbent was not weakened, and the molecular structure of DDMIM Cl remained stable, reflecting its oxidation resistance. Therefore, the use of an ionic liquid as an absorption solution combined with PCO for the treatment of toluene waste gas is theoretically feasible.