Renxi Zhang

Feasibility of destruction of gaseous benzene with dielectric barrier discharge

Destruction of gaseous benzene (C(6)H(6)) by dielectric barrier discharge (DBD) was studied in both laboratory-scale and scale-up DBD systems. The effects of input power, gas flow rate as well as initial concentration on benzene decomposition and energy yield were investigated. In addition, qualitative analysis on byproducts and relatively detailed discussion on mechanisms were also presented in this paper. At last, we systematically illustrated the feasibility of benzene removal with DBD on basis of three aspects: estimation of treatment cost per unit volume, comparison with other plasmas, and problems existed in DBD system. The results will help impel actual application of DBD on waste gas containing benzene.

Photoreductive degradation of sulfur hexafluoride in the presence of styrene

Sulfur hexafluoride (SF6) is known as one of the most powerful greenhouse gases in the atmosphere. Reductive photodegradation of SF6 by styrene has been studied with the purpose of developing a novel remediation for sulfur hexafluoride pollution. Effects of reaction conditions on the destruction and removal efficiency (DRE) of SF6 are examined in this study. Both initial styrene-to-SF6 ratio and initial oxygen concentration exert a significant influence on DRE. SF6 removal efficiency reaches a maximum value at the initial styrene-to-SF6 ratio of 0.2. It is found that DRE increases with oxygen concentration over the range of 0 to 0.09 mol/m3 and then decreases with increasing oxygen concentration. When water vapor is fed into the gas mixture, DRE is slightly enhanced over the whole studied time scale. The X-ray Photoelectron Spectroscopy (XPS) analysis, together with gas chromatography-mass spectrometry (GC-MS) and Fourier Transform Infrared spectroscopy (FT-IR) analysis, prove that nearly all the initial fluorine residing in the gas phase is in the form of SiF4, whereas, the initial sulfur is deposited in the form of elemental sulfur, after photodegradation. Free from toxic byproducts, photodegradation in the presence of styrene may serve as a promising technique for SF6 abatement.

Decomposition of dimethylamine gas with dielectric barrier discharge

The decomposition of dimethylamine (DMA) with gas under high flow rate was investigated with dielectric barrier discharge (DBD) technology. Different parameters including removal efficiency, energy yield, carbon balance and CO2 selectivity, secondary products, as well as pathways and mechanisms of DMA degradation were studied. The experimental results showed that removal efficiency of DMA depended on applied voltage and gas flow rate, but had no obvious correlation with initial concentration. Excellent energy performance was obtained using present DBD technology for DMA abatement. When experiment conditions were controlled at: gas flow rate of 14.9 m(3)/h, initial concentration of 2104 mg/m(3), applied voltage of 4.8 kV, removal efficiency of DMA and energy yield can reach 85.2% and 953.9 g/kWh, respectively. However, carbon balance (around 40%) was not ideal due to shorter residence time (about 0.1s), implying that some additional conditions should be considered to improve the total oxidation of DMA. Moreover, secondary products in outlet gas stream were detected via gas chromatogram-mass spectrum and the amounts of NO3(-) and NO2(-) were analyzed by ion chromatogram. The obtained data demonstrated that NOx might be suppressed due to reductive NH radical form DMA dissociation. The likely reaction pathways and mechanisms for the removal of DMA were suggested based on products analysis. Experimental results demonstrated the application potential of DBD as a clean technology for organic nitrogen-containing gas elimination from gas streams.

Removal of Isobutyl Acetate in Flowed Air Stream with DBD Plasmas

Removal of isobutyl acetate (IA) gas using dielectric barrier discharge (DBD) technology were reported. The experimental results showed that IA removal efficiency can reach 75.3% when applied voltage, initial IA concentration and gas flow rate were set at 9 kV, 1788 mg/m3 and 2.85 m3/h, respectively. IA removal efficiency increased with increasing applied voltage but decreased with ascending initial concentration and gas flow rate. Energy yield continued rising with initial concentration of IA gas, its maximal value was up to 32.9 g/(kW.h). In addition, practical industrial waste gas containing IA from pharmacy were treated with DBD technology. The test result indicated that IA removal efficiency exceeds 80% as IA waste gas of 2000 m3/h flowed through reaction region of DBD (flow-velocity of 5.4 m/s). Treatment cost of IA waste was only 0.012 RMB/m3 as calculated. At last, qualitative analysis on byproducts via Ion chromatograph (IC) and Gas chromatogram-mass spectrometry (GC-MS) was performed.

Different reaction mechanisms of diphenylether and 4-bromodiphenylether with nitrous acid in the 355 nm laser flash photolysis of mixed aqueous solution.

The microscopic reaction mechanisms of diphenylether (DPE) and 4-bromodiphenylether (4-BrDPE) with nitrous acid (HNO(2)) in the absence of O(2) have been explored by the 355nm laser flash photolysis. It was proposed that OH radical, from the photolysis of HNO(2), added to DPE forms the C(12)H(10)O-OH adduct while added to 4-BrDPE forms the 4-BrDPE-OH and 4-BrOH-DPE adducts. The first-order decay rate constants of the C(12)H(10)O-OH adduct, 4-BrDPE-OH adduct and 4-BrOH-DPE adduct were measured to be (1.86+/-0.14)x10(5)s(-1), (2.19+/-0.04)x10(5)s(-1) and (1.56+/-0.03)x10(5)s(-1), respectively. The final photolysis products of DPE and HNO(2) identified by GC/MS analysis were phenol, o-hydroxydiphenylether, p-hydroxydiphenylether and p-nitrodiphenylether, while the final photolysis product of 4-BrDPE and HNO(2) identified by LC/MS analysis was mainly the dimer.

Reaction Mechanism of C6F6-HNO2 Aqueous Solution under Irradiation at 355 nm

Abstract The reaction mechanism of C 6 F 6 -HNO 2 aqueous solution was studied using the laser flash photolysis-transient absorption spectrum technique under irradiation at 355 nm. The characteristic absorption peaks and the kinetic parameters of transient species were also investigated. The hydroxyl radical derived from the photolysis of HNO 2 was added to hexafluorobenzene with a second-order rate constant of 1.8×10 9 L·mol −1 ·s −1 to form an adduct, C 6 F 6 ···OH, which had absorption peaks at 250, 270, and 400 nm. The C 6 F 6 ···OH adduct decayed by the elimination of HF to yield C 6 F 5 O· with an apparent first-order rate constant of 6.1×10 5 s −1 . In the presence of O 2 , C 6 F 6 ···OH underwent a complex reaction with a rate constant of 2.8×10 6 L·mol −1 ·s −1 to form C 6 F 6 OHO 2 , which had the same absorption bands as C 6 F 6 ···OH. The final products were identified using the GC-MS technique and the possible reaction pathways were also discussed.