Conversion Of Trichloroethylene Research Articles

Efficient low-temperature catalytic combustion of trichloroethylene over flower-like mesoporous Mn-doped CeO2 microspheres

Flower-like mesoporous Mn-doped CeO2 microspheres with three-dimensional (3D) hierarchical structures were successfully prepared by a hydrothermal method with the aid of glucose and acrylic acid and subsequent particular thermal treatment, and characterized by SEM, XRD, N2 adsorption/desorption, H2-TPR, XPS, Raman spectra and so on. The results show that the atomic ratios of Mn/(Ce+Mn) in the Ce–Mn–O samples as well as their morphologies affect obviously their catalytic performances for low-temperature catalytic combustion of trichloroethylene (TCE). These flower-like Ce–Mn–O microspheres have not only very excellent activity but also high stability, compared with pure flower-like CeO2 microspheres or bulk Ce–Mn–O samples. The flower-like sample with atomic ratio of Mn/(Ce+Mn) of 0.21 exhibits the best activity, for instance, T50 (the temperature for 50% conversion of TCE) is as low as 87°C, showing much higher catalytic activity than the sample prepared by a co-precipitation or sol–gel method. High surface area, high oxygen mobility and rich surface active oxygen species are responsible for the high catalytic performance of flower-like Mn-doped CeO2 microspheres, compared with general Ce–Mn–O mixed oxides.

Hybrid photocatalysts for the degradation of trichloroethylene in air

Hybrid photocatalysts based on an adsorbent SiMgOx and a photocatalyst TiO 2 were developed in a plate shape. The ceramic surface was coated with TiO 2 by the slip-casting technique. The effect of the support in the photocatalytic degradation of trichloroethylene (TCE) was analyzed by modifying TiO 2 loading and the layer thickness. Photocatalysts were characterised by N 2 adsorption–desorption, mercury intrusion porosimetry, SEM, UV–vis spectroscopy and XRD. A direct relationship between the TiO 2 content and the photocatalytic activity was observed up to three layers of TiO 2 (0.66 wt.%). Our results indicate that intermediate species generated on the TiO 2 layer can migrate through relatively long distances to react with the OH − surface groups of the support. By increasing the TiO 2 loading of the photocatalyst two effects were observed: trichloroethylene conversion is enhanced, while the efficiency of the oxidation process is decreased at expenses of increasing the selectivity to COCl 2 and dichloroacetylchloride (DCAC). The results are discussed in terms of the layer thickness, TiO 2 amount, TCE conversion and CO 2, and COCl 2 selectivity.

Degradation of gas-phase trichloroethylene over thin-film TiO 2 photocatalyst in multi-modules reactor

The present paper examined the photocatalytic degradation (PCD) of gas-phase trichloroethylene (TCE) over thin-film TiO 2. A large-scale treatment of TCE was carried out using scale-up continuous flow photo-reactor in which nine reactors were arranged in parallel and series. The parallel or serial arrangement is a significant factor to determine the special arrangement of whole reactor module as well as to compact the multi-modules in a continuous flow reactor. The conversion of TCE according to the space time was nearly same for parallel and serial connection of the reactors.

Effect of phosphoric acid on catalytic combustion of trichloroethylene over Pt/P-MCM-41

Abstract Pt-loaded MCM-41 catalysts modified with phosphorus acids at various Si/P ratios were prepared. Phosphoric acid molecules may react with surface Si–OH groups, which prevented the direct attack of H 2 PtCl 4 on mesostructure and improved the structural stability of Pt-loaded catalysts. Ammonia temperature-programmed desorption (NH 3 -TPD) indicated that P-MCM-41 samples possessed weak Bronsted acidities, and the Bronsted acidities on P-MCM-41 decreased with the incorporation of Pt, depending on the phosphoric acid loading. The interaction of Pt with phosphoric species resulted in the change of Pt oxidation state and the Bronsted acidity strength. The results of catalytic combustion of trichloroethylene over these catalysts showed that the modification with phosphoric acid endowed the catalysts with good catalytic performance of high trichloroethylene conversion and absence of tetrachloroethylene. The combination of Bronsted acidities and oxidation state Pt would propose a novel catalytic material suitable for the combustion of chlorinated volatile organic compounds. Carbon deposit over acid sites resulted in the deactivation of Pt/P-MCM-41 catalysts, and the deactivated catalysts were recovered at 500 °C in air.

Pt-loaded P-MCM-41 as a novel bifunctional catalyst for catalytic combustion of trichloroethylene

Abstract Pt-loaded P-MCM-41 catalysts with different Si/P ratio were prepared and used as novel bifunctional catalysts for catalytic combustion of trichloroethylene (TCE). Acidic materials, ZSM-5, P-SiO 2 and Al 2 O 3 as supports in Pt-loaded catalysts were also studied for comparison. The high activity for TCE conversion and low selectivity to tetrachloroethylene were observed on Pt/P-MCM-41 catalysts, indicating that phosphorus modified MCM-41 with an amount of weak Bronsted acid sites, in combination with Pt, was effective to form a bifunctional catalyst.

Analysis of the simultaneous catalytic combustion of chlorinated aliphatic pollutants and toluene over ceria-zirconia mixed oxides

Abstract In the present work the oxidation of representative VOCs, such as toluene, 1,2-dichloroethane and trichloroethylene, present in trace amounts in air streams over a series of Ce x Zr 1− x O 2 oxides (CeO 2 , Ce 0.8 Zr 0.2 O 2 , Ce 0.68 Zr 0.32 O 2 , Ce 0.5 Zr 0.5 O 2 , Ce 0.15 Zr 0.85 O 2 , ZrO 2 ) as catalysts was investigated with focus on the difference in catalytic performance in the oxidation of single and chlorinated VOC/toluene mixtures, and on the mixture effects on product selectivity. In general, the efficiency for the single VOC destruction decreased in the following order: toluene > 1,2-dichloroethane > trichloroethylene. For chlorinated compounds the best performance was observed for the mixed oxides with 50 and 85 mol% of zirconia content, while ceria exhibited the best behaviour for toluene oxidation. With regard to chlorinated compounds the combination of surface acidity and accessible lattice oxygen appeared to control the catalytic performance of the mixed oxides. On the contrary, the combustion of toluene was essentially controlled by surface oxygen species. Notable ‘mixture effects’ on both activity and selectivity were noticed when a given chlorinated feed was decomposed in the presence of toluene. On one hand, mutual inhibition took place but the conversion of trichloroethylene was retarded much more severely. On the other hand, the destruction of toluene was less affected by the presence of 1,2-dichloroethane. Competitive adsorption played an important role in the inhibition detected with CeO 2 -based catalysts. However, no one species was able to dominate the adsorption sites and thereby completely prevent the adsorption and reaction of other species. On the other hand, HCl selectivity was greatly enhanced by the presence of toluene in the feed stream.

Conversion of trichloroethylene to chloral using occupationally relevant levels

Conversion of trichloroethylene to chloral using occupationally relevant levels

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).

Combustion of trichloroethylene and dichloromethane over protonic zeolites: Influence of adsorption properties on the catalytic performance

The deep oxidation of dichloromethane (DCM) and trichloroethylene (TCE) over protonic zeolites (HA, HX, HY and H-ZSM-5) was studied in this work. Experiments were performed in dry air in the range 50–650 °C in a pulsed microreactor. Catalytic activity was correlated with the capacity of adsorption of DCM and TCE as well as the strength and specificity of these interactions, which parameters were determined by inverse gas chromatography (IGC). DCM is oxidized at lower temperatures than TCE, and at the same time, the interaction of this compound over the catalysts is also stronger than that of TCE. The increase of the TCE conversion in presence of the catalysts was very low, whereas these materials (specially the HY and H-ZSM-5 zeolites) have important catalytic activity for DCM oxidation. The best performance of these zeolites has been attributed to the higher density of strong acid sites, which act as active sites both in the adsorption of hydrocarbon and catalytic activation of hydrocarbon halides. The product distribution is also discussed in this work.

Destruction of Gas-Phase Trichloroethylene in a Modified Fuel Cell

A conventional fuel cell was used as a catalytic reactor to treat soil vapor extraction (SVE) gases contaminated with trichloroethylene (TCE). The SVE gases are fed to the cathode side of the fuel cell, where TCE is reduced to ethane and hydrochloric acid. The results obtained suggest that TCE reduction occurs by a catalytic reaction with hydrogen that is re-formed on the cathode's surface beyond a certain applied cell potential. Substantial conversion of TCE is obtained, even when competing oxygen reduction occurs in the cathode. The process has been modeled successfully by conceptualizing the flow passage in the fuel cell as a plug flow reactor.

FORMATION AND TOXICITY OF ANESTHETIC DEGRADATION PRODUCTS

Toxic degradation products are formed from a range of old and modern anesthetic agents. The common element in the formation of degradation products is the reaction of the anesthetic agent with the bases in the carbon dioxide absorbents in the anesthesia circuit. This reaction results in the conversion of trichloroethylene to dichloroacetylene, halothane to 2-bromo-2-chloro-1,1-difluoroethylene, sevoflurane to 2-(fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (Compound A), and desflurane, isoflurane, and enflurane to carbon monoxide. Dichloroacetylene, 2-bromo-2-chloro-1,1-difluoroethylene, and Compound A form glutathione S-conjugates that undergo hydrolysis to cysteine S-conjugates and bioactivation of the cysteine S-conjugates by renal cysteine conjugate beta-lyase to give nephrotoxic metabolites. The elucidation of the mechanisms of formation and bioactivation of degradation products has allowed for the safe use of anesthetics that may undergo degradation in the anesthesia circuit.

Reduced formation of undesirable by-products from photocatalytic degradation of trichloroethylene

Photocatalytic degradation of trichloroethylene (TCE) was investigated using a tubular photoreactor packed with TiO2 powders prepared by sol–gel techniques. Powders of the following metals: Cr, Fe, Ni, Cu and Pt, or Ca(OH)2 were uniformly mixed with the TiO2 powders and then their effect on the formation of COCl2, CHCl3, and CHCl2COCl as by-products was examined. Concentrations of COCl2 and CHCl3 were determined in a product gas stream by GC/MS while CHCl2COCl accumulated on the catalyst surface. When the catalysts were immersed in water after TCE photodegradation, the formation of Cl- and CHCl2COO− ions was confirmed by ion-chromatography. Of the chemicals tested, only Cu and Ca(OH)2 inhibited the formation of the chlorinated by-products. With increasing Cu and Ca(OH)2 content, TCE conversion decreased while the stoichiometric ratio ([CO2]formed/[TCE]degraded) increased. Concentrations of COCl2, CHCl3, and CHCl2COCl decreased with increasing Cu and Ca(OH)2 content. Especially, the formation of COCl2 was remarkably suppressed with Ca(OH)2.

Gas phase trichloroethylene (TCE) photooxidation and byproduct formation: photolysis vs. titania/silica based photocatalysis

Photooxidation of trichloroethylene (TCE) was examined in comparative study using photolysis and photocatalysis. Degussa P25 titania coated on reactor wall and deposited on silica based microporous support were used as photocatalyst. The destruction of TCE and formation of potential byproducts were investigated under steady state conditions using annular photoreactors. Experimental work involved passing polluted air containing TCE through the UV photoreactor at varying concentrations and residence times. Ultraviolet illumination was provided by low pressure mercury lamps with outputs at either 254 nm, 365 nm, or 185/254 nm. Silica supported photocatalyst yielded maximum removal capacity of up to about 6 kg TCE per m 3 per hour, nearly twice that provided by the coated titania. Direct photolysis with ozone generating UV also provided very high TCE conversion of up to 6 kg TCE per m 3 per hour. However, major quantities of phosgene and dichloroacetyle chloride (DCAC) were produced as byproducts. TCE removal using silica based photocatalyst did not result in any detectable DCAC. Only phosgene along with trace amounts of chloroform and carbon tetrachloride were identified as oxidation byproducts with silica based photocatalyst.

Photo-degradation characteristics of TCE (trichloroethylene) in an annulus fluidized bed photoreactor

The effects of gas velocity, annulus gap on solid (es) and gas phase holdups (eg), UV light transmittance and photocatalytic reduction of TCE (trichloroethylene) over TiO2/silica gel photocatalyst have been determined in an annulus fluidized bed photoreactor. The optimum TCE reduction efficiency exhibits at es/eg of 0.48, annulus gap of 8 mm and UV light transmittance around 0.20. The most pronounced effects on TCE conversion are found to be gas velocity (Ug) and annular gap in the photoreactor.

Photocatalytic degradation of trichloroethylene (TCE) over TiO 2/silica gel in a circulating fluidized bed (CFB) photoreactor

The effects of the ratio of TiO 2/silica gel, superficial gas velocity ( U g), solid circulation rate ( G s), initial trichloroethylene (TCE) concentration, wavelength of UV light, and concentrations of H 2O and O 2 on photodegradation of TCE over TiO 2/silica gel have been determined in a circulating fluidized bed (CFB) photoreactor. The TCE conversion decreases with wavelength of the UV light, the initial TCE and H 2O concentrations in the CFB reactor. The optimum concentration of O 2 for TCE degradation is found to be approximately 9 vol.% in the CFB photoreactor. The CFB photoreactor is an effective tool for high TCE degradation with efficient utilization of photon energy.

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.

Effect of impurities in TiO2 thin films on trichloroethylene conversion

Abstract In this study, we investigate the physical properties and photocatalytic activities of TiO2 thin films doped with low valence (Fe3+, Co2+, and Ni2+) and high valence (Mo5+, Nb5+, and W6+) cations. Clear difference in results from various analytical tools between groups was identified. The presence of different oxidation states and a higher degree of crystallinity in the high valence cation doped-TiO2 thin films seemed beneficial in terms of the transfer and separation of photo-generated electrons and holes in the TiO2 medium and on the surface, resulting in higher photocatalytic conversion of trichloroetylene.

Characterization of gamma-alumina-supported manganese oxide as an incineration catalyst for trichloroethylene.

Trichloroethylene (TCE) decomposition over a MnOx/ gamma-Al2O3 catalyst in a fixed-bed reactor was conducted in this study. The MnOx/gamma-Al2O3 powders were prepared by the incipient wetness impregnation method with aqueous solution of manganese nitrate. The catalysts were characterized by DTA-TGA, XRD, porosity analysis, SEM, EDX, and XPS. The results show that the main distinct weight loss is found at the temperature around 373 and 873 K,the MnO peaks (2theta = 34.9 degrees and 40.5 degrees) are only observed crystal phase on the fresh catalyst, the SEM image of the MnOx-impregnated gamma-Al2O3 support is much different from the calcined catalyst, and the Mn element quantity on the catalyst surface is higher than that of the impregnated support. The products and reactants distributions from the oxidation of TCE over MnOx/gamma-Al2O3 were analyzed by GC. The results show that the TCE conversion starts from 5% at 443 K and rises to very high values in the 673-873 K ranges and that the CO2 yield also pushes to 99% at the same temperature ranges. HCl and Cl2 are the other main products with little halogenated VOC intermediates.

Preparation of TiO 2 film by the MOCVD method and analysis for decomposition of trichloroethylene using in situ FT-IR spectroscopy

MOCVD (molecular organic chemical vapor deposition) method was demonstrated in this study to prepare TiO 2 thin film of anatase structure with high photo-activity. From the results of characterization of XRD and SEM spectroscopy, it was identified that a TiO 2 thin film exhibited pure anatase structure and it was stably attached on a substrate. To investigate the photo-catalytic performance of the TiO 2 film, the trichloroethylene (TCE) decomposition was done. The conversion of TCE remarkably increased over the TiO 2 film synthesized by CVD method compared with that of TiO 2 film prepared by Degussa P-25 colloidal solution, in particular, the conversion over TiO 2 film synthesized by the CVD method reached above 90% after 120 min, otherwise, it was 85% over Degussa P-25 film. On the other hand, the intermediates produced from TCE decomposition were investigated by in situ method using a FT-IR spectroscopy. As a result, it was confirmed that TCE was transferred into dichloroacetylchloride (DCAC) and trichloromethane (CHCl 3) in transition state, and then, finally, it turned to CO 2, HCl, and H 2O. In addition, the addition of H 2O enhanced TCE decomposition. However, it was not affected to mechanism of TCE photo-catalytic decomposition.

Reductive Dechlorination of Trichloroethylene: A Computational Study

Vitamin B12 catalyzes the reductive dechlorination of several ubiquitous pollutants including the conversion of trichloroethylene (TCE) to ∼95% cis-1,2-dichloroethylene (DCE) and small amounts of trans-DCE and 1,1-DCE. The origins of this unexpected selectivity were investigated using density functional and coupled-cluster theory. At all levels of theory considered, the initially formed trichloroethylene radical anion is an unstable species. Breakage of one of the three C−Cl bonds during the dissociative process gives the most stable ion complex when the two remaining chlorines occupy a cis geometry. Once formed, the cis-1,2-dichloroethen-1-yl radical is about 6 kJ/mol more stable than the corresponding trans radical and 21 kJ/mol more stable than the 1,1-dichloroethen-2-yl radical. The calculated relative energies can be rationalized by delocalization of the unpaired electron over the nonbonding orbitals of the α-chlorine. The computed geometries of the radicals suggest significant interactions between t...