Adsorption of Gaseous Toluene by an Aqueous N,N-Dimethylformamide Solution: An Experimental Study

The synthetic leather industry emits organic waste gases predominantly composed of N,N-dimethylformamide (DMF), with trace amounts of toluene, butanone, and ethyl acetate as secondary components. Conventional treatment methods rely on water absorption processes, which generate aqueous absorbent solutions enriched with DMF. This study systematically investigates the absorption efficiency of hydrophobic toluene in DMF aqueous solutions using a spray-packed column, focusing on the characteristics of exhaust gas components. Through molecular interaction analysis (DMF-toluene-water ternary system) and experimental validation, we demonstrate that DMF addition significantly enhances intermolecular interactions between toluene and the absorbent matrix. Analysis based on density gradient theory (DGT) reveals that only weak interactions exist between toluene and water molecules or between toluene and DMF molecules, whereas strong hydrogen bonding is present between DMF and water molecules. Therefore, the addition of DMF to an aqueous solution enhances the intermolecular interactions between toluene and the absorbent, enabling efficient absorption and resource recovery of toluene. Experimental results indicate that DMF enhances the interaction force between toluene and the absorbent. In dynamic absorption experiments, the absorption efficiencies of 40% DMF absorbent and deionized water were 32.0% and 12.7%, respectively, representing a 2.5-fold increase in absorption efficiency. Residence time and liquid-to-gas ratio significantly influenced the toluene absorption efficiency of the DMF aqueous solution. Increasing the residence time from 10 s to 25 s improved the absorption efficiency from 10.0% to 24.0% over a 30-minute operational period. Additionally, the system achieved peak absorption performance at a liquid-to-gas ratio of 15 L/m3, with a maximum efficiency of 24.3%. The saturated absorption capacity of toluene in the 30% DMF aqueous solution was 14 mg/L. The quasi-Henry′s law constant of toluene in the 30% DMF aqueous solution was significantly lower than that in water, further confirming the enhancement effect of DMF on toluene absorption. Heating distillation at 50 ℃ efficiently recovered toluene from the DMF absorbent solution, and the regenerated absorbent retained nearly the same initial toluene absorption capacity. At a desorption temperature of 50 ℃, the desorption efficiency of toluene reached 91.2%. Remarkably, the absorption saturation capacity of the DMF aqueous solution for toluene remained stable without significant degradation even after 8 consecutive adsorption-desorption cycles. These findings systematically demonstrate the feasibility of utilizing DMF aqueous solutions for the effective absorption of low-concentration toluene emissions, supported by comprehensive theoretical analysis and extensive experimental investigations. Moreover, they highlight the significant potential of this approach for practical applications in treating low-water-solubility volatile organic compounds (VOCs).