Huiqi Hou

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.

Photolysis of low concentration H2S under UV/VUV irradiation emitted from microwave discharge electrodeless lamps

The photolysis of simulating low concentration of hydrogen sulfide malodorous gas was studied under UV irradiation emitted by self-made microwave discharge electrodeless lamps (i.e. microwave UV electrodeless mercury lamp (185/253.7 nm) and iodine lamp (178.3/180.1/183/184.4/187.6/206.2 nm)). Experiments results showed that the removal efficiency (eta H2S) of hydrogen sulfide was decreased with increasing initial H2S concentration and increased slightly with gas residence time; H2S removal efficiency was decreased dramatically with enlarged pipe diameter. Under the experimental conditions with pipe diameter of 36 mm, gas flow rate of 0.42 standard l s(-1), eta H2S was 52% with initial H2S concentration of 19.5 mg m(-3) by microwave mercury lamp, the absolute removal amount (ARA) was 4.30 microg s(-1), and energy yield (EY) was 77.3 mg kW h(-1); eta H2S was 56% with initial H2S concentration of 18.9 mg m(-3) by microwave iodine lamp, the ARA was 4.48 microg s(-1), and the EY was 80.5mg kW h(-1). The main photolysis product was confirmed to be SO4(2-) with IC.

Removal of H2S from gas stream using combined plasma photolysis technique at atmospheric pressure.

In this paper, H(2)S in gas stream was successfully decomposed at atmospheric pressure by dielectric barrier discharge plasma and VUV-UV radiation from a combined plasma photolysis reactor (CDBD). In comparison with DBD, CDBD enhanced H(2)S removal efficiency significantly at the same applied voltage, inlet H(2)S concentration and gas residence time. H(2)S removal efficiency was determined as a function of Kr pressure, applied voltage, inlet H(2)S concentration, and gas residence time. H(2)S removal efficiency could reach as high as 93% at inlet H(2)S concentration of 27.1 mg m(-3), residence time of 0.4 s, and applied voltage of 7.5 kV. The main products were discerned as H(2)O and SO(4)(2-) based on FTIR and IC analysis.

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.

Photolysis of gaseous butyl acetate using built-in microwave discharge electrodeless lamps.

This paper examined the photolysis of gaseous butyl acetate by built-in microwave discharge electrodeless lamps. Bromine and iodine lamps were used to investigate the effects of microwave input power, inlet concentration, gas residence time, and different filling materials on butyl acetate decomposition and energy yield. Water vapor and ammonia were utilized as additional chemicals to determine if they can improve removal efficiency. Built-in structure and external structure were also compared. When the gas flow velocity is 0.025 m/s, and the inlet concentration is 1.5 mg/m(3), the removal efficiency of butyl acetate can reach over 78%, which is the highest in this study. Additional water vapor and ammonia can hardly improve the degradation. To some extent, built-in MDELs are better than external MDELs. The results will help promote the study of microwave discharge electrodeless lamps and their effect on the degradation of gaseous pollutants. Maybe, as the research goes on, it could realize the span from laboratory scale to practical application, and will become an advanced technology for the gaseous pollutants control.

Destruction of benzene in an air stream by the outer combined plasma photolysis method

An outer combined plasma photolysis (OCPP) reactor that simultaneously utilized a dielectric barrier discharge (DBD) plasma and UV radiation from DBD-driven KrI* excimer was designed and constructed. Gas streams containing benzene were treated with normal DBD and OCPP at atmospheric pressure. In contrast to DBD, benzene removal efficiency increased by 15.9% in OCPP when applied voltage, gas flow rate and initial concentration of benzene were set at 9 kV, 35 L min−1 and 800 mg m−3, respectively. Thus, the applied voltage could be reduced to a certain extent in the plasma decomposition of pollutants with OCPP. In addition, the effects of various operational parameters including pressure of filled Kr, ratio of Kr/I2 and quartz dielectric characteristics on OCPP performance were investigated. Finally, the likely reaction mechanisms for the removal of benzene by OCPP were suggested on the basis of the emission spectra of KrI* excimer and byproducts analysis. Those results would offer prospective commercial applications for pollutant decomposition with OCPP.

Study on the reaction of carbon disulfide with hydroxyl radical in aqueous solution

The laser flash photolysis technique is employed to investigate the reaction mechanism of CS2 with ·OH in the nitrogen-saturated aqueous solution. By comparison of the transient absorption spectra obtained at different phases and pHs and through the addition of proper radical cation scavenger, CS2 is determined to react with · OH to form · CS2OH adduct, instead of the CS2+ radical cation. At pH 1–5, · CS2OH decomposes into COS and · HS, while at pH > 5, it further reacts with OH- to form CS2O-. The temperature dependent kinetics for the reaction CS2 + · OH → · CS2OH is also reported in this paper with an estimated activation energy of (26.9±1.0) kJ · mol−1.

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.