TCE Decomposition Research Articles

Air trichloroethylene oxidation in a corona plasma-catalytic reactor

The oxidative decomposition of trichloroethylene (TCE; 300 ppm) by non-thermal corona plasma was investigated in dry air at atmospheric pressure and room temperature, both in the absence and presence of catalysts including MnO x, CoO x. The catalysts were synthesized by a co-precipitation method. The morphology and structure of the catalysts were characterized by BET surface area measurement and Fourier Transform Infrared (FTIR) methods. Decomposition of TCE and distribution of products were evaluated by a gas chromatograph (GC) and an FTIR. In the absence of the catalyst, TCE removal is increased with increases in the applied voltage and current intensity. Higher TCE removal and CO 2 selectivity is observed in presence of the corona and catalysts, as compared to those with the plasma alone. The results show that MnO x and CoO x catalysts can dissociate the in-plasma produced ozone to oxygen radicals, which enhances the TCE decomposition.

Catalysts used for microwave-assisted TCE decomposition by hydrogen

Abstract Microwave-assisted trichloroethylene decomposition by hydrogen over a series of catalysts was investigated. Comparing their activity for decomposition of TCE, we found that when we chose different support, the suitble active metal for TCE decomposition was also different. If HZSM-5 was chosen as support, active metal should be Co. For X-zeolite, Fe should be chosen. For 5A, Ni was the active metal. We also found that the catalysts with Al2O3 support showed the highest activity under microwave conditions than that under conventional conditions, which was opposite to the result over SiO2 support.

Complete Removal of Chloro-Based Volatile Organic Compounds by Thermally Activated Oxide Semiconductors

Chloro-based volatile organic compounds (VOCs) are known to exert noxious effects on the environment, and their destruction by catalytic combustion, for example, accompanies a production of hydrochloric acid (HCl) that damages the catalyst. We have been interested in complete removal of VOCs by our system based on thermally activated oxide semiconductors (i.e., catalysts) such as Cr2O3, TiO2, NiO, � -Fe2O3. In the present investigation, we have fundamentally studied the decomposition process of dichloromethane (CH2Cl2: DCM) and trichloroethylene (CHCCl3; TCE) on the basis of the mass- and Raman spectra in an attempt to identify the formation temperature of HCl. Then, we found that the decomposition of DCM and TCE starts at about 100 and 200 � C, respectively; whereas HCl is abruptly formed at a critical temperature of about 350 � C in both compounds. Based on this result, we have optimized the operation temperature below 300 � C for Cr2O3-impregnated honeycomb systems and achieved the complete removal of DCM and TCE that accompanies no formation of HCl. [doi:10.2320/matertrans.M2011028]

대기압플라즈마 및 오존 분해촉매를 이용한 트리클로로에틸렌의 분해효율 증진 연구

본 논문은 비열평형 플라즈마와 촉매를 이용하여 트리클로로에틸렌의 효과적인 분해방법을 재안하였다. 이를 위하여 이산화망간과 알루미나 펠렛을 플라즈마 리액터 내부에 충진한 리액터를 설계하였다. 이산화망간 충진 리액터를 이용할 경우에는 산소를 포함한 가스중의 방전에 의해 발생된 오존이 촉매 표면애서 분해되는 동안에 발생된 산소원자 라디칼에 의하여 TCE의 분해율이 향상됨을 알 수 있었다. 그리고 알루미나를 충진한 경우에는 TCE는 DCAC로 산화되었으며, COx 및 Cl₂와 같은 저분자상으로 많이 분해되지 않았다. 그러나 알루미나 충진 리액터에 의한 플라즈마 처리된 가스를 리액터 후단에 설치한 이산화밍간 촉매를 통과시킴에 의하여 분해율이 매우 향상됨을 알 수 있었다. 따라서, 플라즈마 프로세스에 이산화망간을 응용함에 의하여 오존 분해에 따른 촉매 표면의 산소 원자 라디칼에 의하여 TCE 및 분해 생성불(DCAC)를 효율적으로 분해하는 것이 가능하다.

Nonthermal Plasma Abatement of Trichloroethylene Enhanced by Photocatalysis

Abatement of trichloroethylene (TCE, 250 ppm in air) was studied in a novel nonthermal plasma (NTP) dielectric barrier discharge reactor with an inner electrode made of sintered metal fibers (SMF). The SMF electrodes modified with TiO2 and MnO2 were observed to be catalytically active. Their efficiency in TCE decomposition was compared with a Cu inner electrode. The SMF electrode modified with MnO2 and TiO2 catalyst effectively destroys TCE due to the synergy between plasma excitation of the TCE molecules and their catalytic oxidation. The latter process was observed to be further enhanced by photocatalysis since TiO2 absorbs the UV light produced by the NTP. These innovative TiO2-modified SMF electrodes were characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), confirming formation of titania anatase, whereas the emission spectrum of the plasma showed the presence of ultraviolet light.

Study on Reactive Non-thermal Plasma Process combined with Metal Oxide Catalyst for Removal of Dilute Trichloroethylene

In order to improve energy efficiency in the dilute trichloroethylene removal using the nonthermal plasma process, the barrier discharge treatment combined with manganese dioxide was experimentally studied. Reaction kinetics in this process was studied on the basis of final byproducts distribution. Decomposition efficiency was improved to about <TEX>$99\;\%$</TEX> at the specific energy of 40 J/L with passing through manganese dioxide. C=C <TEX>${\pi}$</TEX> bond cleavage of TCE substances gave DCAC, which has the single bond of C-C through oxidation reaction during the barrier discharge plasma treatment. Those DCAC were broken easily in the subsequent catalytic reaction due to the weak bonding energy about <TEX>$3{\sim}4\;eV$</TEX> compared with the double bonding energy in TCE molecules. Oxidation byproducts of DCAC and TCAA from TCE decomposition are generated from the barrier discharge plasma treatment and catalytic surface chemical reaction, respectively. Complete oxidation of TCE into COx is required to about 400 J/L, but <TEX>$CO_2$</TEX> selectivity remains about <TEX>$60\;\%$</TEX>.

TiO2에 담지된 금속 산화물 촉매상에서 TCE 산화분해반응

Oxidative TCE decomposition over <TEX>$TiO_2$</TEX>-supported single and complex metal oxide catalysts has been conducted using a continuous flow type fixed-bed reactor system. Different types of commercial <TEX>$TiO_2$</TEX> were used for obtaining the supported catalysts via an incipient wetness technique. Among a variety of titanias and metal oxides used, a DT51D <TEX>$TiO_2\;and\;CrO_x$</TEX> would be the respective promising support and active ingredient for the oxidative TCE decomposition. The <TEX>$TiO_2-based\;CrO_x$</TEX> catalyst gave a significant dependence of the catalytic activity in TCE oxidation reaction on the metal loadings. The use of high <TEX>$CrO_x$</TEX> contents for preparing <TEX>$CrO_x/TiO_2$</TEX> catalysts might produce <TEX>$Cr_2O_3$</TEX> crystallites on the surface of <TEX>$TiO_2$</TEX>, thereby decreasing catalytic performance in the oxidative decomposition at low reaction temperatures. Supported <TEX>$CrO_x$</TEX>-based bimetallic oxide systems offered a very useful approach to lower the <TEX>$CrO_x$</TEX> amounts without any loss in their catalytic activity for the catalytic TCE oxidation and to minimize the formation of Cl-containing organic products in the course of the catalytic reaction.

The Catalytic Incineration of Trichloroethylene over γ-Alumina Supported Manganese Oxide Catalysta

TCE decomposition over a Mn2O3/γ-Al2O3 catalyst in a fixed bed reactor was conducted in this study. Preliminarily, three catalysts including Mn2O3/γ-Al2O3, NiO/γ-Al2O3, and Pt/γ-Al2O3 were used to incinerate TCE and the results show that the Mn2O3/γ-Al2O3 catalyst has the best performance. The effects of operating parameters, such as inlet temperature, space velocity, TCE inlet concentration, and oxygen concentration on the catalytic incineration of TCE over the Mn2O3/γ-Al2O3 catalyst were then performed. The results show that conversion of TCE increases as inlet temperature and oxygen concentration increase, and decreases with the increases of TCE concentration and space velocity. The activity of the catalyst decreases significantly while TCE incineration is operated under a low temperature, 365°C. However, the activity of the catalyst does not change much while the operating temperature is as high as 500°C. The catalysts were characterized by the surface and pore size analysis, XRD, XPS, EDS, and SEM before and after the tests. The results show that the catalytic crystal is Mn2O3, the catalytic deactivation is not due to carbonaceous material, and the chlorine element is adsorbed on the surface of catalysts.

トリクロロエチレンを吸着した粒状活性炭の酢酸水溶液を用いた再生

The objective of this study was to develop a regeneration system for GAC and a solvent for use in TCE treatment. Thus, we evaluated the characteristic of TCE desorbed from GAC by acetic acid solution, the degradability of TCE in acetic acid solution by ozone, and the adsorption performance of TCE for GAC regenerated by acetic acid solution. The conclusions obtained from this study are as follows: The amount of TCE desorbed from GAC increased with increasing concentration of acetic acid. Almost all TCE was desorbed by more than 50% acetic acid solution. TCE in acetic acid solution was effectively decomposed by ozone. The specific amount of TCE decomposition in acetic acid solution in relation to ozone consumption was 4.0-48.0% higher than that in pure water. The adsorption capacity of the regenerated GAC was the same as that regenerated with new GAC. This result indicates that GAC regenerated by acetic acid solution can be recycled for TCE adsorption.

Comparison of reactor performance in the nonthermal plasma chemical processing of hazardous air pollutants

The performance of three different types of plasma reactors such as ferroelectric packed-bed (FPR), pulsed corona (PCR), and silent discharge (SDR) were compared in the decomposition of trichloroethylene (Cl/sub 2/C=CHCl, TCE), bromomethane (CH/sub 3/Br), and tetrafluoromethane (CF/sub 4/). Irrespective of reactors, hazardous air pollutant (HAP) reactivity in dry N/sub 2/ decreased in the order: TCE>CH/sub 3/Br>CF/sub 4/. Similar byproducts were obtained with any of the above reactors, and similar trends were observed in the HAP decomposition rate-retarding effect by water. Only for SDR, TCE decomposition was accelerated by O/sub 2/ in the background gas. The most plausible active oxygen species is considered to be the triplet oxygen atom. In the reaction systems where chemically induced decomposition of HAPs can occur, as in the case of TCE, PCR is expected to exceed FPR and SDR in performance. In the cases of CH/sub 3/Br and CF/sub 4/, residence time has been the most important factor governing their decomposition rates, and FPR and SDR have shown higher performance than PCR.

Paint spraying device

Microwave-assisted trichloroethylene decomposition by hydrogen over a series of catalysts was investigated. Comparing their activity for decomposition of TCE, we found that when we chose different support, the suitble active metal for TCE decomposition was also different. If HZSM-5 was chosen as support, active metal should be Co. For X-zeolite, Fe should be chosen. For 5A, Ni was the active metal. We also found that the catalysts with Al2O3 support showed the highest activity under microwave conditions than that under conventional conditions, which was opposite to the result over SiO2 support.

Anatase-phase titania: preparation by embedding silica and photocatalytic activity for the decomposition of trichloroethylene

Nanophase titania particles were prepared by the sol–gel process using two different precursors; titanium isopropoxide(TTIP) and titanium ethoxide (TEOT). Silica-embedded titania particles was also prepared from TEOT and tera-ethyl-ortho-silicate (TEOS). In the case of nanophase titania particles prepared from TTIP, the rutile/anatase mixed phase had higher photoactivity than the pure anatase in the decomposition of TCE. However, in the nanophase titania prepared from TEOT, the photoactivity was increased with the heat treatment temperature until rutile phase began to be formed. The surface area was decreased with the heat treatment temperature. The photoactivity of the pure anatase titania prepared from TEOT was higher than that of Degussa P25 and the anatase/rutile mixed titania prepared from TTIP. Therefore, we concluded that, in order to achieve high photocatalytic activity, it was important to prepare titania particles at high temperature, preferably without forming rutile phase but not necessarily. This conclusion was confirmed by the experimental result that the silica-embedded titania particle of pure anatase phase had higher photoactivity than that of Degussa P25 and the pure anatase titania prepared from TEOT. The embedding of small amount of silica into anatase titania matrix enhanced the thermal stability of nanophase titaina particle resulting in the suppression of the phase transformation from anatase to rutile phase. This thermal stability enables us to calcine the silica-embedded particles at higher temperature without accompanying the phase transformation and to reduce the bulk defects, which are responsible for the low photocatalytic activity.

揮発性有機塩素化合物の加熱酸化分解処理

Tests were carried out on a heater-type, oxidation-decomposition system to study whether this system could achieve complete decomposition of volatile chlorinated organic compounds (TCE, PCE), major contaminants of groundwater and soil. Test results revealed a decomposition characteristic that there is less residual TCE/PCE (higher decomposition percentage) with greater inflow load, longer retention time, and higher temperature of the reactor used. This system was capable of about 100% decomposition of TCE into CO2 and HCI, when the temperature of the reactor was 950°C, the retention time was over 8.0 seconds, and the TCE concentration was over 3%. Under these conditions, it was possible to carry out stable continuous treatment. CCl4, PCE, CHCl3 were detected below the limited value as by-products and there was no forming of Dioxins under these conditions. Tests which involved the treatment of a gas which contained both TCE and PCE revealed a TCE decomposition of approximately 100%, and a PCE decomposition of below the limited value, when the reactor temperature was 950°C, the retention time was over 8.0 seconds, and the TCE and PCE concentrations were over 3% and 0.3%, respectively. This system has the efficiency of more than two times that of a UV system.

Generation of aerosol particles in the process of xylene, and TCE decomposition from air stream by a ferroelectric packed-bed barrier discharge reactor

Generation of aerosol particles in the process of xylene, and TCE decomposition from air stream by a ferroelectric packed-bed barrier discharge reactor

The effect of a carbon-carbon double bond on electron beam-generated plasma decomposition of trichloroethylene and 1,1,1-trichloroethane

The effect of a carbon-carbon double bond on the energy required for decomposition in an electron beam-generated plasma reactor is studied by comparing the decomposition of trichloroethylene and 1,1,1-trichloroethane. A reaction mechanism for TCE decomposition based on a chlorine radical chain reaction is presented which accounts for the formation of all of the experimentally observed reaction products. TCE decomposition is autocatalyzed by reaction products, whereas TCA decomposition is inhibited. The rate expression for the decomposition of TCE in the reactor is determined to be r=−[T](15.07[T0]−0.40+0.006{[T0]−[T]}), where [T] and [T0] are both in ppm, and r is in ppm Mrad−1. The energy expense ɛ for TCE decomposition is determined as a function of inlet concentration. For 99% decomposition of 100 ppm TCE in air, ɛ=28 eV/molecule, and ɛ=2.5 eV/molecule at 3000 ppm. This is only 2.5–5% of the amount of energy required to decompose a similar amount of TCA as reported by the authors in a previous study. By comparing the energy requirements for TCE decomposition to those for TCA decomposition, the TCE reaction chain length is determined to increase from approximately 20 at 100 ppm initial TCE concentration, to 40 at 3000 ppm.