Removal Of Volatile Organic Compounds By Plasma Coupled With Catalyst

The problem of photochemical smog, haze, carcinogenic caused by volatile organic compounds(VOCs), which harmful to humans and the environment, has been growing concern. So the removal technology with higher efficiency, energy saving, non-pollution is of great significance. In this study, formaldehyde and toluene were chosen as the target pollutants, self-made wire-cylinder dielectric barrier discharge(DBD) reactor energized by AC power supply was used in our experiment. Removal of low concentrations of formaldehyde and toluene by the combination of non-thermal plasma(NTP) and various catalysts was investigated in this study. The feasibility of NTP coupled with adsorption to decompose toluene was discussed. The mechanism of NTP coupled with catalyst removal of toluene was analyzed. The foundation was layed for the wide application of non-thermal plasma. The main research contents and the corresponding findings could be summarized as follows:The effects of NTP coupled with catalysts on the removal of HCHO were studied. Firstly, the effects of NTP on the removal of HCHO were investigated, mainly on the effects of power parameters and operating parameters. Secondly, the effects of NTP coupled with Ba Ti O3/γ-Al2O3 and Ba Ti O3-Ti O2/γ-Al2O3 catalysts on the removal of HCHO were investigated. The results showed that the HCHO removal rate and removal amount increased with the voltage, the frequency and the effective length of discharge area increasing. But the removal rate decreased with the inlet concentration increasing and the removal amount increased with the inlet concentration increasing. The HCHO removal rate firstly increased and then decreased with loading amount of Ba Ti O3 and Ba Ti O3-Ti O2 being increased. The optimum loading amounts in the experiment were 16.2% and 16.5%, respectively. The degradation efficiency of HCHO for the reactor filled with Ba Ti O3/γ-Al2O3 catalyst was slightly higher than that filled with Ba Ti O3-Ti O2/γ-Al2O3, which may be because the molecule of formaldehyde was simple. The more micro discharge for the Ba Ti O3 reactor, the higher decomposition of HCHO was. Compared with NTP, NTP coupled with Ba Ti O3/γ-Al2O3 and Ba Ti O3-Ti O2/γ-Al2O3 catalyst could distinctly increase the energy density, removal rate, removal amount. Under the conditions of higher voltage, ozone could be decomposed, but could not decrease the energy consumption.The effects of NTP coupled with catalysts on the removal of toluene were studied. Firstly, the effects of NTP on the removal of toluene were investigated, mainly on the effects of power parameters and operating parameters. Secondly, the effects of NTP coupled with Mn-Ag, V-Ti and fluorine modified Ti O2 catalyst on the removal of toluene were investigated. The results showed that the toluene removal rate and removal amount increased with the voltage, the frequency, and the effective length of discharge area increasing. But the removal rate decreased with the inlet concentration and gas flow rate increasing, the removal amount increased with the higher inlet concentration, and firstly increased and then decreased with gas flow rate increasing. The maximum removal amount was at 18.5 cm/s. The reactors filling with Mn-Ag, V-Ti and fluorine modified Ti O2 catalysts could significantly promote the degradation of toluene, decrease the generation amount of ozone and improve energy efficiency. Among the Mn-Ag catalysts, the highest removal rate was 86.9% for Mn O2-Ag O-Ce O2 catalyst. Ce O2 could improve removal efficiency of Mn-Ag catalyst. Among the V-Ti catalysts, V2O5-Ti O2 has the highest removal rate, up to 88.6%. Stability test of V2O5-Ti O2/γ-Al2O3 catalyst showed that toluene conversion decreased slowly with the reaction time, the average removal efficiency at 83% within 900 min, which indicating that the catalyst suffered slow deactivation, probably due to the accumulation of by-products over the catalyst surface. After calcinations in air for 3 h at 500 °C, activity of the catalyst could be recovered. Through the toluene degradation by the fluorine modified Ti O2 catalyst experiments, it was found after toluene removal efficiency firstly increased and then decreased with the increase of fluorine content. When the mass content of fluorine was at 4.4%, the removal rate was the highest, up to 95.2%.The effects of NTP coupled with adsorption on the removal of toluene were studied. The activated carbon fiber(ACF)was chosen as the adsorbent. The results of orthogonal experiment showed that the effect of five factors on the toluene removal was: the length of effective discharge area > toluene concentration > gas flow rate > applied voltage > frequency. The results of single factor experiment showed that toluene removal rate and removal amount increased with the length of effective discharge area, applied voltage and frequency increasing, while removal rate reduced, removal amount increased with gas flow rate and inlet concentration increasing. NTP coupled with ACF can greatly improve toluene removal rate and removal amount. When the frequency was at 150 Hz, the removal rate and removal amount of DBD-ACF was 100% and 9600.0 mg/h, respectively, while the removal rate and removal amount of NTP was only 19.5% and 1869.1 mg/h. Toluene removal rate could maintain 100% within 90 min and the generation of O3 could significantly inhabited. But the lower energy efficiency of DBD-ACF should be further studied.The main solid and gaseous by-products during the degradation of toluene were analyzed by GC-MS, FT-IR. Catalyst could reduce the generation of the by-products, and improve the degree of mineralization, convert into other simpler substances such as CO2. The mechanism of NTP coupled with catalyst removal of toluene was analyzed.