Degradation of toluene by pulse-modulated multistage DBD plasma: Key parameters optimization through response surface methodology (RSM) and degradation pathway analysis

In the present work, a pulse-modulated high-frequency (HF) dielectric barrier discharge (DBD) plasma has been employed and utilized to evaluate the feasibility of toluene degradation in a multistage rod-type reactor at room temperature. Experimental result indicates that the energy consumption is significantly reduced and heating effect can be effectively suppressed when the DBD plasma is ignited in pulse-modulated mode instead of continuous mode. The response surface methodology (RSM) based on central composite design (CCD) model has been proposed to evaluate the contribution of key operating parameters including duty cycle and modulation frequency. The proposed model offers a good fit for actal data. The contribution of the modulation frequency is observed to be more dominant compared to the duty cycle for both the degradation efficiency and the energy yield. According to the results provided by the proposed model, the toluene degradation efficiency of 62.9 % and the energy yield of 0.90 g/kWh are obtained under the optimal conditions of 400 Hz modulation frequency and 56 % duty cycle. The effect of initial toluene concentration and gas flow rate have also been investigated. Increasing toluene initial concentration and gas flow rate are found to be unfavorable for the degradation of toluene, however, which are of benefit to the energy yield. A long-time experiment to assess the stability of pulse-modulated DBD has been successful performed. The possible pathways in plasma degradation of toluene is proposed based on the intermediates identification using GC-MS and FTIR.