Decomposition Of Trichloroethylene Research Articles

Behaviour of Trichloroethylene Decomposition in a Plasma-Catalytic Combined Process

A nonthermal plasma processing combined with Cr2O3/TiO2 catalyst was applied to the decomposition of trichloroethylene (TCE). A dielectric barrier discharge reactor was used as the nonthermal plasma reactor. The effects of the reaction temperature and input power on the decomposition of TCE and the formation of byproducts including HCl, Cl2, CO, NO, NO2 and O3 were examined. With an identical input power, the increase in the reactor temperature lowered the decomposition of TCE. The presence of the catalyst downstream the plasma reactor not only enhanced the decomposition of TCE but also affected the distribution of byproducts significantly. However any synergetic effect as a result of the combination of the nonthermal plasma with the catalyst was not observed, i.e., the TCE decomposition efficiency in the plasma-catalyst combined system was almost similar to the sum of those obtained with each process. To improve the decomposition of TCE argon as a plasma-assisting gas was added to the feeding gas and a large enhancement in the TCE decomposition was achieved.

Influences of H2 and O2 and in situ Ca(OH)2 absorption on nonthermal plasma decomposition of trichloroethylene in N2

Abstract The decomposition of trichloroethylene (TCE) with a wire-in-tube pulsed corona reactor was experimentally investigated. It was found that the decomposition of TCE was higher in N 2 gas, compared to the decomposition in the gas stream containing H 2 or O 2 gas. The main gaseous products were HCl and Cl 2 for TCE decomposition in N 2 gas. With the existence of 2% H 2 in gas stream, the yield of HCl was three times higher than that in N 2 gas. When O 2 gas was added into N 2 gas stream, the main decomposition products were COCl 2 , CO 2 and DCAC. In order to prevent the production of unwanted byproducts from TCE decomposition, a combination of plasma decomposition and in situ absorption was proposed by coating a layer of Ca(OH) 2 on the surface of the grounding electrode. It was demonstrated that the Ca(OH) 2 sorbent in the plasma reactor played an effective role as a scavenger participating in the TCE decomposition by in situ capturing of the unwanted products like HCl, therefore resulting in the increase of TCE decomposition.

Photocatalytic oxidation of gaseous trichloroethylene by UV/TiO2 process

The objective of this study was to investigate the reaction behavior of the photocatalytic oxidation of gaseous trichloroethylene (TCE) using titanium dioxide at room temperature. The experiments were carried out under various humidity levels and oxygen contents of carrier gas in an annular photoreactor. Experimental results indicated that the factors affecting the photocatalysis of TCE by UV/TiO2 process are carrier gases and humidity. It was found that increasing the relative humidity in inlet gas flow under low humidity could improve the decomposition of trichloroethylene and the mineralization of organic intermediates at an irradiation UV light intensity of 2.82 W m-2 by UV/TiO2 process. The photocatalytic kinetics of gaseous trichloroethylene can be described by the Langmuir-Hinshelwood rate equation.

Preparation and application of granular ZnO/Al 2O 3 catalyst for the removal of hazardous trichloroethylene

Trichloroethylene (TCE) is a volatile and nerve-toxic liquid, which is widely used in many industries as an organic solvent. Without proper treatment, it will be volatilized into the atmosphere easily and hazardous to the human health and the environment. This study tries to prepare granular ZnO/Al 2O 3 catalyst by a modified oil-drop sol–gel process incorporated the incipient wetness impregnation method and estimates its performance on the catalytic decomposition of TCE. The effects of different preparation and operation conditions are also investigated. Experimental results show that the granular ZnO/Al 2O 3 catalyst has good catalytic performance on TCE decomposition and the conversion of TCE is 98%. ZnO/Al 2O 3(N) catalyst has better performance than ZnO/Al 2O 3(O) at high temperature. Five percent of active metal concentration and 550 °C calcination temperature are the better and economic preparation conditions, and the optimum operation temperature and space velocity are 450 °C and 18,000 h −1, respectively. The conversions of TCE are similar and all higher than 90% as the oxygen concentration in feed gas is higher than 5%. By Fourier transform infrared spectrography (FT-IR) analyses, the major reaction products in the catalytic decomposition of TCE are HCl and CO 2. The Brunauer–Emmett–Teller (BET) surface areas of catalysts are significantly decreased as the calcination temperature is higher than 550 °C due to the sintering of catalyst materials, as well as the reaction temperature is higher than 150 °C due to the accumulations of reaction residues on the surfaces of catalysts. These results are also demonstrated by the results of scanning electron micrography (SEM) and energy disperse spectrography (EDS).

The Decomposition Property of Trichloroethylene and Ethylene using Ultra-Violet and Tio2 Catalyst

The decomposition processes of trichloroethylene, ethylene and trichloroethylene -ethylene mixtures were studied. Trichloroethylene decomposition was a gas-phase reaction, while ethylene decomposition was both a gas-phase reaction and surface reaction using ultra-violet and/or TiO2 catalyst.

Simultaneous and Sequential Photosonolysis of TCE and PCE

Aqueous solutions of trichloroethylene (TCE) and tetrachloroethylene (PCE) were treated in a flow-through reactor equipped with ultrasound and ultraviolet light sources. The reactor was operated as sonolysis (US), photolysis (UV), and simultaneous photosonolysis (UV/US) reactors; then as US, UV, and sequential UV/US reactors with the installation of a partition in the reactor. The reactor without the partition was simulated by using one continuously stirred-tank-reactor (1-CSTR) model, and the reactor with the partition was simulated by using the sequential CSTR model. Through model calibration, the decomposition rate constants and reactor efficiencies for the removal of TCE and PCE were evaluated. The results suggest that the combined effect of UV and US on the decomposition of TCE and PCE is synergistic in both the simultaneous and sequential UV/US modes, that the rate constants of sonolysis and photolysis are greater with the sequential combination than with the simultaneous combination, and that overall efficiency is higher for the reactor with the partition than for the one without it.

TCE Removal from Porous Media Using an Ozone-saturated Solvent

Abstract A new technique for rapid and complete removal of trichloroethylene (TCE) from porous media was developed on the basis of chemical decomposition by ozone added to flushing solvent. The rate of TCE removal by the combination process of ozone with acetic acid flushing was from 1.2 to 2.5 times as high as the flushing process without ozone due to the chemical decomposition of TCE not only dissolved in the solution but also adsorbed on the porous media.

Chemical adsorption of phosgene on TiO 2 and its effect on the photocatalytic oxidation of trichloroethylene

We observed the chemical adsorption with gas-phase phosgene on TiO 2 surfaces using in situ FT-IR, and examined its effect on the photocatalytic decomposition of trichloroethylene (TCE). The infrared spectrum of the adsorbed standard phosgene suggested that phosgene reacts with surface hydroxyl groups to form a bidentate carbonate compound, which binds to the TiO 2 surface through two Ti–O bonds. The surface species, adsorbed phosgene, derived from dichloroacetyl chloride (DCAC), which is generated during the photocatalytic decomposition of TCE, was also found to yield the same bidentate carbonate when decomposed photocatalytically. The adsorbed phosgene was formed stably on TiO 2 and was found to play an important role in accelerating the decomposition of TCE under irradiation with visible light as well as with UV. The active species was considered to be active oxygen on the structure of phosgene stably adsorbed to bidentate carbonate. The surface structure of adsorbed phosgene, bidentate carbonate may be used for the surface improvement of photocatalysts under visible light as well as UV.

습식 TCE 분해반응에서 CoO2/TiO2촉매의 반응활성 및 표면화학적 구조

From April 1992 and March 1993, morphometric characteristics and reproductive maturation were studied in Periophthalmus barbarus from subsistence catches in the mangrove swamps of Imo estuary. Morphometric equations for males and females at different stages of ovarian maturation are presented. Generally males were significantly heavier in weight than females, but the latter were heavier than the former of the same body length. Females with developing and mature ovaries were generally heavier than immature females of the same length. Analyses of the gonadosomatic index and percentage of mature males and females indicate all year-round breeding such that: February-May was spawning, June-October postspawning and November to January recovery period. Fecundity varied between 900 and 23,933 eggs per spawn and increased with fish size.

Dilute Trichloroethylene Decomposition in Air by the Non-Thermal Plasma Process Combined with the Manganese Oxide

AbstractThe non-thermal plasma is a very effective technique to decompose various kinds of gaseous organic compounds. The trichloroethylene (TCE) is one of the effective washing reagents to remove oily liquid materials or similar fatty materials from the solid surface but is harmful for human beings as the carcinogenic materials. The authors have been engaged in developing the non-thermal plasma technology to decompose that TCE efficiently. During the research on how to improve the decomposition efficiency of TCE, we found that the ozone generated in the air by the plasma can decompose TCE which is named as Indirect Process, comparing with the conventional plasma process named as Direct Process. We found that manganese oxide catalyst which can easily decompose the ozone and may generate oxygen radicals. The manganese oxide can improve the TCE decomposition efficiency, 20 or 80%, for Direct or Indirect Processes.

Decomposition of trichloroethylene and 2,4-dichlorophenol by ozonation in several organic solvents

The effects of chemical characteristics of organic solvents on the decomposition rate constants of undissociative trichloroethylene (TCE) and dissociative 2,4-dichlorophenol (2,4-DCP) by ozonation were studied. The TCE and 2,4-DCP decomposition by ozonation in organic solvents followed to the first-order reaction kinetics with respect to TCE or 2,4-DCP concentration. The orders of the rate constants among organic solvents for undissociative TCE and dissociative 2,4-DCP were different indicating that the ozonation rates for undissociative and dissociative compounds were dependent on the chemical property of organic solvent. The decomposition of undissociative TCE by ozonation was a simple electrophilic reaction, which was dependent on acceptor number (AN) of the solvent. On the other hand, the decomposition of dissociative 2,4-DCP was dependent on by the dissociation of the compounds and would be dependent on donor number (DN) of the solvent. Finally, TCE in acetic acid was transformed to chlorinated intermediates and chloride ion and then these intermediates were continuously oxidized to chlorine gas.

Catalytic Oxidation of Trichloroethylene over Pd-Loaded Sulfated Zirconia

The oxidative decomposition of trichloroethylene (TCE) was investigated using palladium catalysts supported on pure and sulfated zirconia. The reactions were performed under dry and wet conditions in the temperature between 200 and <TEX>$550^{\circ}C$</TEX> keeping GHSV of 14,000 <TEX>$h^{-1}.$</TEX> The products such as <TEX>$C_2Cl_4,\;C_2HCl_5,\;CO\;and\;CO_2$</TEX> were observed in the reaction. The addition of water in the feed affected the distribution of reaction product with dramatically improved catalytic activity. The spectroscopic investigations gave an evidence that the strong acid sites play an important role on controlling the catalytic activity. Among the catalysts investigated, the Pd-loaded sulfated zirconia catalyst with 1 wt% Pd was found to exhibit the highest catalytic activity in the presence of water vapor having the stability for 30 h of the reaction at <TEX>$500^{\circ}C$</TEX>. The successful performance of the catalyst might be attributed to promotional effect of Pd active sites and strong acid sites induced from surface sulfate species on zirconia.

TCE Decomposition by the Nonthermal Plasma Process Concerning Ozone Effect

Dilute trichloroethylene (TCE) and other volatile organic compounds (VOC) in air were decomposed by using the nonthermal plasma process combined with catalysts. To enhance the energy efficiency of the TCE decomposition, some catalysts were tested including their location. It was found that the newly proposed indirect process (VOC cannot be exposed in the plasma region) can also decompose TCE and other VOCs which is due to the ozone dissociation effect. The manganese oxide dissociates ozone to generate oxygen radicals which decompose TCE and other VOCs.

Photoactivity of SiO 2/TiO 2 and ZrO 2/TiO 2 mixed oxides prepared by sol–gel method

Silica/titania and zirconia/titania mixed oxides were prepared by the sol–gel technique and their photocatalytic activity for the decomposition of trichloroethylene was investigated as a function of the content of silica or zirconia. It was tried to interpret the change of photocatalytic activity in connection with the change of crystallite size of anatase phase. For both silica/titania and zirconia/titania particles, the photoactivity strongly depended on the crystallite size of anatase phase regardless of the content of silica or zirconia and the calcination temperature. On changing the crystallite size, silica/titania particles showed a different behavior in the change of the photoactivity with changing the crystallite size. The discrepancy was connected to the quantization of band structure which was identified by the blue shift in the UV/Visible absorption spectrum. On the other hand, for zirconia/titania particles the dependency of the photoactivity on the crystallite size was not affected by the content of zirconia. Finally, it was found that the photoactivity of titania-based mixed oxides prepared by the sol–gel method linearly depends on the crystallite of anatase phase.

Catalytic decomposition of TCE under microwave

The decomposition of trichloroethylene (TCE) by hydrogen over Co/γ-Al2O3 and Ni/γ-Al2O3 catalysts under microwave heating was studied. The comparison between the catalytic activity in the microwave heating mode and that in the conventional thermal mode demonstrated that the microwave heating could greatly reduce the reaction temperature, accelerate the TCE decomposition speed and improve the TCE decomposition ratio. The results suggest that the microwave heating has a novel effect in the decomposition of TCE.

Trichloroethylene catalytic conversion over acidic solid catalysts

The conversion of trichloroethylene (TCE) vapor (1000cm3/m3) in humid and dry conditions has been comparatively tested over several acidic catalists: HY zeolite, silica–alumina, tungsta–alumina, and pure γ-alumina. Among them, alumina shows the higher activity in TCE decomposition to COx and HCl at lower temperature (total conversion around 820K) and no deactivation phenomena occur at the laboratory scale time. Adding WO3 could even enhance catalytic activity. The use of alumina catalysts, although much less active than noble-metal containing catalysts, allows, in principle, the destruction of different chlorided organics and the recovery of HCl in a versatile authotermic process.

Decomposition of Trichloroethylene by a TiO2/Silica Gel Photocatalyst under Ultraviolet Light Irradiation

Decomposition of Trichloroethylene by a TiO<SUB>2</SUB>/Silica Gel Photocatalyst under Ultraviolet Light Irradiation

Characterization and Reaction Performance of the Ru-CrOx/Al2O3 Catalyst for the Oxidative Decomposition of Trichloroethylene

As the catalyst for the oxidative decomposition of trichloroethylene (TCE) in air, series of Ru-promoted CrOx/Al2O3 were prepared and studied. The catalysts were characterized using temperature programmed reduction (TPR), temperature programmed desorption of ammonia (NH3-TPD), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Ru-promoted effects were determined in the respects of the initial catalytic activity, the rate of catalyst deactivation, and the product concentrations of CO and Cl2 under dry or wet air conditions. The presence of a small amount of Ru as much as 0.4 wt% in a CrOx/Al2O3 catalyst turned out to promote the catalytic activity and improve the catalytic reaction performance. The Ru(0.4)Cr(9.6) catalyst was characterized to have better reducibility at lower temperature and higher fraction of more active Cr(VI) species over the catalyst surface. This Ru-promoted catalyst proved to be much less subject to the deactivation during the reaction and to produce less concentration of CO than the Cr(10). Such performance improvements of the Ru(0.4)Cr(9.6) catalyst was thought to attribute to its enhanced oxidation activity originated from the well dispersed coexisting Ru-oxide species, possibly being directly involved in the reaction as active centers activating molecular oxygen, and subsequently, facilitating the supply of activated oxygen to the reaction system.

The nature of low temperature deactivation of CoCr 2O 4 and CrO x/γ-Al 2O 3 catalysts for the oxidative decomposition of trichloroethylene

The CoCr 2O 4 and CrO x /γ-Al 2O 3 catalysts were used for the oxidative decomposition of trichloroethylene (TCE). Both catalysts showed an initial deactivation at low temperatures around 280 °C, mainly due to the dissociative adsorption of reactant TCE. This was confirmed by the temperature programmed oxidation of TCE where the carbon oxides were formed up to a temperature below 300 °C. Possible changes in the oxidation state of chromium species were observed with XANES and ESR. During the oxidation reaction at low temperatures, the Cr(VI) species were reduced to Cr(III) species, which seemed to be coupled with TCE adsorption. At higher temperatures, however, the Cr(VI) species appeared again and the catalytic activity was completely recovered.

Photocatalytic activities enhanced for decompositions of organic compounds over metal-photodepositing titanium dioxide

Three kinds of metals (Pd, Cu, and Pt) have been photodeposited either individually or simultaneously on a transparent thin film of titanium dioxide (TiO 2) that covers the inside surface of a Pyrex glass tube and the photocatalytic activities of these preparations have been investigated based on the oxidative decompositions of 2,4-dinitrophenol (DNP), formaldehyde (HCHO), and trichloroethylene (TCE) dissolved in aqueous solutions. The initial rate of DNP decomposition by Pd/TiO 2 is 2.5 times higher than that by TiO 2. Similarly, the initial rate of HCHO decomposition by Pd/TiO 2 is increased by 5.1 times. Such remarkable enhancements in the photocatalytic decompositions are also obtained with Pd–Cu/TiO 2 and Pd–Cu–Pt/TiO 2. Furthermore, Pd/TiO 2 is effective to promote the photocatalytic decomposition of TCE. This is different from the experimental result that was recently reported by other researchers, who used Pd/TiO 2 particles in the form of aqueous slurries. Microscopic observations of the metals deposited on the TiO 2 films reveal that the morphologies of the metal-photodepositing TiO 2 preparations are remarkably different from that of the TiO 2 film; each metal possesses its own coating pattern. A series of the photocatalytic reaction experiments indicate that the photocatalytic activities of the metal-depositing TiO 2 preparations are superior to that of the TiO 2 film and are highly stable.