Decomposition Of Trichloroethylene Research Articles

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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.

Application of spinel-type cobalt chromite as a novel catalyst for combustion of chlorinated organic pollutants.

Various chromium-containing catalysts were tested for the total oxidation of trichloroethylene (TCE) as a model reaction for the catalytic combustion of chlorinated organic pollutants. A spinel-type cobalt chromite (CoCr2O4) among others was proven to be a very promising catalyst showing higher activity and higher CO2 selectivity than traditional alumina supported chromia. Even if both Cr3+ and Cr6+ species were observed on the surface of CoCr2O4, the Cr6+ species was stable under reducing environment. The presence of Cr3+-Cr6+ pair sites and the effect of redox treatments on the activity were investigated to explain the nature of possible active sites for TCE decomposition. Higher selectivity to CO2 of CoCr2O4 was ascribed to the abundance of its Cr3+ species, together with its activity for water gas shift reaction.

Biodegradation of trichloroethylene (TCE) adsorbed on granular activated carbon (GAC)

The objective of this study is to clarify the possibility of biodegradation of TCE adsorbed on granular activated carbon (GAC) and to determine the adsorption capacity of bioregenerated GAC. The amount of desorption and mineralization was estimated to account for 82.5% of the total TCE (26.2 mg) adsorbed in the GAC. It indicates that incinerators were saved from the damage by HCl gas generated by decomposition of TCE. The adsorption capacity of the bioregenerated GAC was very low compared to that of new GAC indicating that the bioregenerated GAC cannot be recycled for TCE adsorption without thermal regeneration.

Phase-transfer catalysis applied to the oxidation of nonaqueous phase trichloroethylene by potassium permanganate

The use of potassium permanganate to oxidize chlorinated solvents has been demonstrated as an effective process for treating nonaqueous phase liquids in ground-water systems. This study evaluates the effectiveness of phase-transfer catalysts (PTCs) in enhancing the degradation rate. PTCs work by transferring permanganate ion into the nonaqueous phase where it initiates oxidative decomposition. We studied the oxidation of trichloroethylene (TCE) by potassium permanganate, conducting kinetic batch experiments in conjunction with three PTCs that varied in terms of their extraction constants and molecular structures. Using the same batch technique, we examined whether PTCs could enhance the aqueous solubility of TCE. Solubilization could also increase oxidation rates in the aqueous phase. Rates of TCE oxidation in solutions containing the PTCs and a blank were estimated separately by measuring chloride concentration and UV–Vis absorbance in the aqueous phase. The enhanced rate of TCE destruction by the PTCs was reflected by an increase in the rate of consumption of permanganate ion and production of chloride ion. There was no tendency for the PTCs, however, to solubilize TCE in the aqueous phase. Therefore, the PTCs increased the rate of TCE decomposition by catalyzing permanganate oxidation in the organic phase. This study suggests that there is significant potential for testing this scheme under field conditions.

Enhanced photoactivity of silica-embedded titania particles prepared by sol–gel process for the decomposition of trichloroethylene

Silica-embedded titania photocatalyst (X-silica/titania, X denotes at.% of silicon) of improved photoactivity was prepared by the sol–gel technique. The photoactivity of the X-silica/titania particles was increased by increasing the silica content and reached a maximum. The highest photoactivity was obtained when silica content was 30% and five times higher than that of Degussa P25. The embedding of amorphous silica into nanophase titania matrix helped to increase the thermal stability of titania which suppressed the formation of anatase into rutile and made it possible to calcine the silica/titania particles at higher calcination temperature. This high temperature heat treatment resulted in the high crystallinity of the silica/titania particles. Surface area of X-silica/titania particles was monotonically increased by increasing the silica content. The average pore size and pore volume, however, has a maximum at 30%, at which mesopores larger than 30nm were observed. Therefore, we concluded that the large pore size and pore volume were responsible for the optimum composition of silica to titania. The enhanced photoactivity of silica-embedded titania particles was achieved by simultaneously increasing both the surface area and the crystallinity through embedding amorphous silica into titania.

Decomposition Mechanism for Electron Beam Irradiation of Vaporized Trichloroethylene−Air Mixtures

Decomposition of trichloroethylene (TCE) in electron beam irradiation was examined in order to get information on treatment of industrial off-gas. Air containing vaporized TCE was sealed into a glass vessel and irradiated with an electron beam. The concentration of TCE exponentially decreased with dose (air-absorbed energy). The doses necessary to decompose 90% of input TCE molecules had a value of 3.6 kGy independent of an initial concentrations ranging from 50 to 1800 ppmv. Between G values of decomposition and initial concentrations, the following equation was obtained: G(−TCE) [μmol J-1] = 1.5 [μmol J-1] + 0.020 [μmol J-1 ppmv-1] × conc [ppmv]. The equation shows that concentrations of Cl radicals remained constant at 6.3 × 10-4 ppmv (at 298 K and 1 bar) independent of concentrations of TCE and products under a dose rate of 2.1 kGy/s. Termination reactions in the decomposition mechanism for EB irradiation of TCE and tetrachloroethylene (PCE) were also clarified on the basis of the relation of G value of decomposition and the initial concentrations. Dichloroacetyl chloride, which was identified as a primary product, was decomposed and oxidized to give CO and CO2. Phosgene was also identified as a primary product. From the proportion of DCAC to COCl2 concentrations, a branching ratio was calculated to be 5.3 in the Cl radical chain reaction of TCE. Formation of HCl and/or Cl2 was analyzed and the collection of the products from the gas phase was examined with alkaline solution. The effect of water (400−25 000 ppmv) on decomposition efficiency was examined. The decomposition efficiencies had the same value as that in dry air.

Mechanism of Aqueous Decomposition of Trichloroethylene Oxide

The aqueous decomposition of trichloroethylene (TCE) oxide is shown to involve both pH-independent and hydronium ion-dependent regions. C−C bond scission is a major reaction at all pH values. Disappearance of TCE oxide is the rate-determining step for the formation of CO under the conditions studied. The product distribution of CO and three carboxylic acids (HCO2H, Cl2CHCO2H, and glyoxylic acid) did not change considerably over the pH range of −1.5−14, in general, even though the hydrolysis mechanism changes from hydronium ion-dependent to pH-independent. Mechanisms for the hydronium ion-dependent and pH-independent hydrolysis of TCE oxide were elucidated on the basis of the results of H218O and H incorporation and identification of products of the reaction of TCE oxide with lysine in both H216O and H218O. In the pH-independent hydrolysis, a zwitterionic intermediate could be formed and undergo an intramolecular rearrangement (Cl- shift) to generate dichloroacetyl chloride, which would subsequently decomp...

The kinetics of the combustion of trichloroethylene for low Cl/H ratios

A kinetic model has been developed for the combustion of trichloroethylene (TCE) under low Cl/H ratio conditions. Flame species concentration profiles, measured for CH 4/O 2/Ar flames, reveal that the most important reaction channels in the decomposition of TCE in the CH 4/TCE/O 2/Ar flame are the displacement by H atoms of Cl atoms from TCE, 1,1-dichloroethylene (DCE), and vinyl chloride. The displacement of Cl atoms from TCE by OH also contributes to the decomposition of TCE, and leads to the production of 2,2-dichloroethenol, a species unobserved in previous flame studies. Other species found in large concentrations in the present CH 4/TCE/O 2/Ar flames, but not observed in previous TCE/O 2/Ar flame studies at higher chlorine-to-hydrogen ratios, are ketene, chloroketene, and dichloroketene. Finally, the presence of TCE catalyzes the formation of C 3–C 6 hydrocarbons. The presence of significant concentrations of C 3H 3, C 3H 4, and C 6H 6 is consistent with “odd carbon species” mechanisms previously suggested for benzene formation in hydrocarbon flames.

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.

Thermal decomposition mechanism of chlorinated volatile organics at pyrolytic and oxidative conditions

Chlorinated hydrocarbons have been widely utilized due to their excellent physical properties and stability as solvents, coolants, propellants or raw materials etc. One of major problems in disposing of them is safe destruction or collection of recyclable components. One of most feasible methods for waste chlorinated organics is thermal treatment. In this study, experimental and theoretical analyses have been tried to investigate several fundamental operating parameters including temperature, residence time and background conditions like existence of oxygen. Vinyl chloride and trichloroethylene (TCE) were tested to observe their reaction mechanism. Vinyl chloride started to decompose at 725 dgC, and 99 % of initial amount was decomposed at 830 ‡C, 1 sec in pyrolytic environment, produing C2H2 and HC1 mainly and C2HC1, C2H4, H4as byproducts depending on experimental conditions. TCE, on the other hand, produced C2C12, C2C14, HC1 at pyrolytic conditions and CO and CO4 additionally through COC1 radical reactions at oxidative conditions. The supply of oxygen lowered the destruction temperature of TCE and C2C14 could be considered as an indirect indicator of TCE decomposition.

Economic Study of the Tunable Electron Beam Plasma Reactor for Volatile Organic Compound Treatment

ABSTRACT A tunable electron beam generated plasma system has been developed for selective cold plasma treatment of dilute concentrations (1-3,000 ppm range) of hazardous compounds in gaseous waste treatment. This system, referred to as the Tunable Hybrid Plasma (THP), has shown a high degree of efficiency and effectiveness in both laboratory and field tests. Decomposition energy requirements are in the 100 eV per molecule range for treatment of carbon tetrachloride and 10 eV for treatment of trichloroethylene. A cost comparison has been made between the Tunable Hybrid Plasma (THP) technology and three conventional technologies used for emission control of volatile organic compounds (VOCs): granular activated carbon, thermal incineration, and catalytic oxidation. In addition to its environmentally attractive features, THP technology has the potential to be lower cost than other technologies over a range of concentrations and flow rates. Cost projections for the THP system for decomposition of trichloroet-hylene are around 50 cents/lb for initial concentrations in the few hundred ppm range and flow rates of 5,000 cfm or greater and around $1/lb for 1,000 cfm flow rates. Cost projections for carbon tetrachloride and trichloroethane decomposition using the THP technology are several dollars per pound. The costs for THP treatment are generally significantly lower than costs for use of granular activated carbon and are also quite competitive with costs for thermal incineration and catalytic oxidation.

Decomposition of dilute trichloroethylene by nonthermal plasma

Decomposition performance of a dilute toxic organic compound, trichloroethylene (TCE), in air by using nonthermal plasma processing was studied extensively. The nonthermal plasma was generated by the high-frequency (2 kHz) or commercial-frequency (50 Hz) barrier discharge in a fused silica tube. Three types of reactors, bolt type, rod type (both are barrier-discharge type), and coil type (surface-discharge type), were tested. Analysis of byproducts, residual materials, and end products generated by the plasma process was performed by a gas chromatography mass spectrometer or gas chromatography. Most organic byproducts decrease with an increase of the electric discharge power, but only toxic phosgene increases with the increase of the discharge power. As a post process, NaOH solution was used to test effluent from the plasma reactor. The solution was found effective in phosgene absorption. Comparison between nonthermal plasma and UV irradiation for TCE decomposition was also made. In regard to the energy efficiency of TCE decomposition, UV irradiation is found much better than discharge plasma.

Modification of titania particles by ultrasonic spray pyrolysis of colloid

Composite fine particles such as ZnO-TiO2, CdS-TiO2, ZnS-TiO2 and Ag-TiO2 were prepared by ultrasonic spray pyrolysis of metal salt aqueous solution in which TiO2 (Degussa P25) particles were suspended. The crystallinity, chemical compositions, and morphologies of the produced particles were investigated by XRD, centrifugal particle size analyzer, and SEM/EDAX. The photocatalytic activity of the modified particles was investigated for the decomposition of trichloroethylene (TCE). The prepared particles were micro-porous and had spherical shapes of 0.3–1.5 μm in diameter. The size and size distribution of the prepared particles were not significantly changed by the type and loading of modifier. The crystallinity and crystallite size of TiO2 was not changed by these modifications. The photocatalytic activities of modified particles was slightly higher than pure titania when the loading was low. However, as the loading was further increased, the photocatalytic activity was sharply decreased and became almost constant.

Photoinduced Decomposition of Trichloroethylene on Soil Components

The photoinduced decomposition of trichloroethylene adsorbed on Ca-montmorillonite by long-wavelength UV irradiation has been studied in a quartz tube open to air or through which air or oxygen is passed. Solid-sample and liquid-solution NMR techniques were used to identify apparent products or intermediates of the photodecomposition. Dichloroacetic acid was identified as a major organic product/intermediate; substantial amounts of pentachloroethane and trichloroacetic acid were also identified. The formation of CO2 was characterized quantitatively by wet chemical analysis. About 40% and 57%, respectively, of the total carbon of trichloroethylene was converted to carbon dioxide in air and O2 environments over a period of 16 days. Phosgene and HCl were also detected. The photodecomposition of trichloroethylene adsorbed on whole soil, on Zn2+-exchanged and Cu2+-exchanged montmorillonites, on kaolinite, and on silica gel was also examined in less detail; qualitatively, the conversion of trichloroethylene to dichloroacetic acid in a 48-h period occurred with the following order of decreasing efficiencies: Zn2+-montmorillonite > silica gel > kaolinite > Ca2+-montmorillonite > whole soil > Cu2+-montmorillonite. These results show that the photoinduced decomposition of adsorbed trichloroethylene occurs on a variety of adsorbents, generating products and intermediates that are similar to what have been reported previously for TiO2-based photodecomposition but with much longer time scales. These conversions can, therefore, be expected to occur in sunlight at the air−soil interface.

Decomposition of Trichloroethylene by Microwave-Induced Ar Plasma Generated from SiC Ceramics under Atmospheric Pressure

Decomposition of Trichloroethylene by Microwave-Induced Ar Plasma Generated from SiC Ceramics under Atmospheric Pressure

Decomposition of gas-phase chloroethenes by UV/O 3 process

The photolytic behaviors of gas-phase 1,1-dichloroethylene (DCE), trichloroethylene (TCE), and perchloroethylene (PCE) in air streams by ultraviolet irradiation and UV/O 3 process were studied. The addition of ozone slightly improved the removal of TCE by UV/O 3 process, and excessive ozone would reduce the treatment efficiency of TCE. The enhancement of UV light intensity would promote the decomposition of TCE more effectively than the supplement of ozone. The mineralization and dechlorination of chloroethylenes by UV photolysis can be apparently promoted in presence with ozone and were affected by the number of chlorine atom substituted on the CC bond. The photolytic behaviors of TCE and the individual contribution to the decomposition of TCE by UV direct photolysis and by OH· destruction in the UV/O 3/TCE system were well modeled by the proposed decomposition scheme.

A study of photocatalytic degradation of trichloroethylene in vapor phase on TiO 2 photocatalyst

This investigation used a packed-bed reactor filled with coated titanium dioxide glass beads which was activated by a 365 nm UV light for heterogeneous photocatalytic decomposition of trichloroethylene under different conditions of flowrate, oxygen content, moisture and light intensity. For the flowrate of feed gas between 100–500 mL/min, the reaction rates increased with an increasing flowrate below 300 mL/min. When the flowrate was more than 300 mL/min, the reaction rate was not affected by the flowrate. For the oxygen content in the range of 0–20 %(v/v), it indicated that under 10 %(v/v) oxygen content the reaction rate increased as the oxygen content increased. The increase of moisture content lowered the reaction rates in the range of 230–30000 ppmv. The reaction rate of 6μM TCE increased as the light intensity increased, and was proportional to the 0.61 order of the light intensity. The deactivation of the TiO 2 described in the literature was not observed in this study.

Decomposition of Trichloroethylene by Microwave-Induced-Plasma Generated from SiC Ceramics under Atmospheric Pressure

Decomposition of Trichloroethylene by Microwave-Induced-Plasma Generated from SiC Ceramics under Atmospheric Pressure

Heterogeneous photocatalytic degradation of trichloroethylene in vapor phase by titanium dioxide

This investigation used a packed-bed reactor filled with titanium dioxide catalyst. It was activated by a 365 nm UV light source, for heterogeneous photocatalytic decomposition of trichloroethylene (TCE) under different conditions of flow rate, moisture, and light intensity. At a constant temperature of 30°C, the concentration of 6.5 μM for TCE decreased with increasing time, and reached an equilibrium state in 9 min. For the flow rate of feed gas between 100–900 mL/min, the conversion decreased with an increasing flow rate. The decomposition of TCE at 900 mL/min was only 2.22%, indicating feed gas rapidly passing through the catalyst layer without a reaction. For moisture in the range of 3000-20 000 μL/L, the conversion of TCE decreased with increasing humidity, and the decomposition of this could be inhibited by excessive moisture. The adsorbed water on the catalyst surface could compete with the adsorption of TCE on the sites. By adjusting light intensity in the range of 0.085-0.5 mW/cm 2, the stronger the illumination, the more the conversion of TCE, due to the increased supply of photons for reaction.

Removal of volatile organic compounds in water using low-energy electron beam

This paper presents the experimental results concerning removal of organic contaminants in water using low energy electron beam radiation. A laboratory scale apparatus for electron beam irradiation of water is described. The absorbed dose of radiation was controlled by water circulation time (1 to 10 min), accelerating voltage (100 to 170 kV), and electron beam current (0.5 to 1.2 mA) for a constant flow rate of 2 kg/min. The volume of the treated water was 1 dm/sup 3/. The electron beam was generated in vacuum (p<10/sup -5/ Pa), and electrons were injected into the water through the electron transparent window made of titanium foil with a thickness of 25 /spl mu/m TCE (trichloroethylene) and chloroform dissolved in deionized water were used in the experiment. The dependency of the relative concentration c=C/C/sub 0/; where C is the weight content of compound after electron irradiation and C/sub 0/ the initial contaminant concentration, on radiation energy density and the absorbed dose are presented. Although the initial contents of the compounds were higher than those occurring in real water sources, it has been found that it is possible to decompose both of the chemicals with high efficiency (total decomposition of TCE, and up to 90% reduction of chloroform) using a relatively low accelerating voltage (<200 kV). The results have indicated that the removal of TCE and chloroform mainly depended on the absorbed dose of electron radiation.