•The BaTiO3 packed bed reactor enhances CO2 conversion and energy efficiency.•The packed bed reactor is proved to be more efficient than unpacked DBD reactors.•Ar or N2 dilution increased CO2 conversion by changing plasma electrical properties.Carbon dioxide conversion upon dilution by argon and nitrogen at atmospheric pressure has been studied using a barium titanate packed bed, non-thermal plasma reactor. The results show that the packed bed reactor with the BaTiO3 ferroelectric packing material directly contacting to electrodes provided a higher CO2 conversion and energy efficiency than a dielectric barrier discharge reactor with and without packed materials using electrodes covered by dielectric layers. In the packed bed reactor, the CO2 conversion increased from 19% in pure CO2 to 36% upon diluting the CO2 with 80% argon and to 35% with 80% nitrogen at a specific energy input (SIE) of 36 kJ L−1. The energy efficiency was approximately constant at ca. 0.24 mmol kJ−1 for pure CO2 dissociation upon increasing SIE, but decreases upon dilution by Ar and is more pronounced by N2. In addition to the major products of CO and O2, up to 100 ppm of ozone was produced in a CO2/Ar plasma, but not in a CO2/N2 plasma where some nitrogen oxides (N2O, NO and NO2), were observed with a total maximum concentration of 3120 ppm. Possible mechanisms are presented for the effect of Ar and N2 on the dissociation of CO2 and for the formation of O3, N2O and NOx based on discharge processes in the plasma and the subsequent chemistry. Electrical characterisation of the pure CO2, CO2/Ar and CO2/N2 plasmas was also undertaken. The results suggest the formation of by-products can be controlled by varying the dilution gas fraction and operating conditions.Download high-res image (66KB)Download full-size image

The plasma decomposition of gaseous dodecane has been investigated in a non-thermal BaTiO3 packed-bed plasma reactor in the atmospheric pressure streams of N2–O2 mixtures using FTIR and OES spectroscopy. Results suggest that energy transfer reactions of the electronically-excited nitrogen metastable, N2(A), with dodecane play an important role in the initiation steps that lead to the dissociation of C–H and C–C bonds at the different positions. Increasing the percentage of oxygen in the nitrogen (up to 40 %) does not increase the dodecane decomposition, as metastable nitrogen reacts with the additional oxygen to create increasing NO and NO2 instead. N2O formation does not change significantly with increasing oxygen concentration but this is strongly correlated to the oxygen lattice in the BaTiO3 pellets used in the reactor. The maximum degradation efficiency found was to be ~21 % with an energy efficiency of 2.63 mg kJ−1.

A novel, multistage, dielectric, packed-bed, plasma reactor has been developed and is used to efficiently destroy environmental pollutants, such as volatile organic compounds (VOCs). A three cell plasma reactor, operated at ambient pressure and low temperatures, is found to be an effective technology for complete VOC remediation in air. The combination of plasma cells in series can significantly improve the efficiency of VOC decomposition, but the combined destruction rate is not simply an additive effect, there is a synergistic enhancement related to the effect on the plasma chemistry of sequential processing in the three cells. At the same time, the formation of byproduct such as NOx is strongly suppressed, and it is possible to remediate toluene and ethylene in air, with no detectable formation of NOx or nitric acid.

Results for the destruction of environmental pollutants, using a novel multistage dielectric packed bed discharge plasma reactor (DPBD), carried out at an industrial scale flow rate of 300 L min−1 are presented. Some initial results on the combination of a MnO2 catalyst with the system are also given. Complete destruction of toluene is seen for an initial concentration of 10 ppm at a deposited energy density of 23 J L−1 (0.006 kW h Nm3−). This is an order of magnitude better than previous values indicating high energy efficiency. No NOx, a previously common byproduct in plasma processing, can be detected

This study investigated the decomposition of hydrofluorocarbons (HFCs) having high global warming potentials by using a dielectric-packed-bed nonthermal plasma reactor with barium titanate beads as the packing material. The target HFCs were 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1-difluoroethene (HFC-132a). The effects of several parameters such as reaction temperature, oxygen content, and initial concentration on the HFC decomposition efficiency were evaluated. There was essentially no temperature dependence of the HFC decomposition efficiency in the range 150−250 °C. The optimum oxygen content for HFC decomposition was found to be about 0.5 vol %. Variations in the initial concentration did not affect the decomposition efficiency. The decomposition products were analyzed, and some decomposition pathways were elucidated. The energy requirements for the decomposition of HFC-134a and HFC-132a were found to be 0.038 and 0.062 mol MJ−1, respectively, based on the initial concentrations of 200 and 120 ppm (parts per million, volumetric).

The oxidative destruction of propane at low temperature (∼150 °C) in a nonthermal, atmospheric pressure plasma can be significantly enhanced without the use of a catalyst by the simple addition of an unsaturated alkene. An enhancement in the destruction of propane of up to 45% can be achieved by the addition of propene. Propene acts as a supply of OH radicals, which accelerate the breakdown of the propane. Ethene also enhances the destruction of propane but to a more limited extent. The experimental results are interpreted by chemical modeling, which is used to elucidate the reaction mechanisms.

A non-thermal, atmospheric pressure plasma with a titanium dioxide catalyst were combined to destroy difluorochloromethane, CCl2F2, (CFC-12) in gas streams of nitrogen and air using two configurations; one where the catalyst was incorporated directly into the plasma and the other where the catalyst was downstream of the plasma. The single stage reactor, in both gas streams, gave significant enhancement of the CFC-12 destruction with high energy efficiency. Both configurations decreased NOx production when processing in air. No loss in catalyst surface area or activity was observed.