Decomposition Of Trichloroethylene Research Articles

Comparison of the Effects of Fluidized-Bed and Fixed-Bed Reactors in Microwave-Assisted Catalytic Decomposition of TCE by Hydrogen

Trichloroethylene (TCE) decomposition by hydrogen with microwave heating under different reaction systems was investigated. The activities of a series of catalysts for microwave-assisted TCE hydrodechlorination were tested through the fixed-bed and the fluidized-bed reactor systems. This study found that the different reaction system is suitable for different catalyst type. And there is an interactive relationship between the catalyst type and the reaction bed type.

Catalyst restructuring studies: The facile synthesis of tripod-like carbon fibers by the decomposition of trichloroethylene

Carbon fibers with tripod-like morphology have been synthesized over a NiO xerogel catalyst using trichloroethylene as the carbon source. TEM analysis revealed that trichloroethylene causes the catalyst to continuously restructure to a tetrahedrally shaped catalyst particle, during carbon fiber growth, to give carbon tripods. Trichloroethylene not only acts as a source of carbon but actively controls the catalyst morphology during synthesis.

Trichloroethylene decomposition and in-situ dry sorption of Cl-products by calcium oxides prepared from hydrated limes

A comparison of CaOs produced by calcining two types of hydrated lime and calcium carbonate was made for decomposition of trichloroethylene and in-situ dry sorption of the decomposed Cl-products using a lab-scale gas flow type tubular packed bed reactor. About 20 mg of CaO sample was mixed with about 2 g of Al 2O 3 particles and packed in the reactor and allowed to react with a flowing standard gas containing 500 ppm of C 2HCl 3 (N 2 balance) at 673 and 873 K, under the condition that the reaction of CaO with C 2HCl 3 might be completed within a few hours. It was found that no thermal decomposition of C 2HCl 3 at or below 673 K was observed in a reactor packed only with Al 2O 3 particles. However, a considerable amount of decomposition of C 2HCl 3 was obtained in a reactor packed with CaO and Al 2O 3, even at 673 K. For 1 mol of CaO prepared by calcining highly reactive Ca(OH) 2 at 673 K, decomposition of 0.42 mol of C 2HCl 3 and in-situ absorption product of 0.53 mol of CaCl 2 were obtained. At 873 K, about 46% of C 2HCl 3 was thermally decomposed. The total amount of C 2HCl 3 decomposed in CaO–Al 2O 3 particle bed at 873 K became nearly twice larger than that at 673 K. For 1 mol of CaO prepared by calcining highly reactive Ca(OH) 2 at 873 K, decomposition of 0.59 mol of C 2HCl 3 and in-situ absorption product of 0.67 mol of CaCl 2 were obtained. Small amounts of C 2Cl 2, C 2Cl 4, CCl 4, etc. were detected during decomposition of C 2HCl 3 at 673 and 873 K. It was recognized that the data on decomposition of C 2HCl 3 as well as in-situ dry sorption of Cl-products in CaO particle bed were correlated with specific surface area of the CaO employed.

Qualitative By-Product Identification of Plasma-Assisted TCE Abatement by Mass Spectrometry and Fourier-Transform Infrared Spectroscopy

In this study, the formation of by-products resulting from the decomposition of trichloroethylene with a negative DC glow discharge has been investigated. By combining the qualitative data from mass spectrometry and Fourier-transform infrared spectroscopy, the formation of phosgene, dichloroacetylchloride and trichloroacetaldehyde have been confirmed as incomplete oxidation products. Hydrogen chloride, chlorine, carbon monoxide and carbon dioxide were also detected. Also, formation of ozone was found in the outlet stream. Based on this information, it is possible to chose an appropriate catalyst to combine with non thermal plasma. In this way emission of harmful, incomplete oxidation products can be further reduced at a lower energy cost.

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.

Decomposition of Trichloroethylene with Plasma-catalysis: A review

AbstractThe aim of this paper is to give a review of the research on the decomposition of trichloroethylene (TCE), a common industrial solvent, with combined use of non-thermal plasma and heterogeneous catalysis, i.e. plasma-catalysis. This air purification technique has been investigated over the last decade in an effort to overcome the disadvantages of non-thermal plasma treatment of waste air containing volatile organic compounds (VOCs). Some examples of different plasma technologies used for plasma-catalysis are given. These include the dielectric barrier discharge, the pulsed corona discharge and the atmospheric pressure glow discharge. In a plasma-catalytic hybrid system the catalyst can either be located in the discharge region or downstream of the plasma reactor. The mechanisms that drive both configurations are briefly discussed, followed by an extended literature overview of the removal of TCE with plasma-catalysis.

TiO2 photocatalyst for indoor air remediation: Influence of crystallinity, crystal phase, and UV radiation intensity on trichloroethylene degradation

Nanocrystalline TiO2 photocatalysts prepared through a simple sol–gel process followed by calcination at 100–800°C were evaluated for the decomposition of trichloroethylene (TCE) in simulated indoor air. Catalysts made of pure anatase, anatase/rutile mixture and pure rutile with crystal sizes of 5.8–75.8nm and surface areas of 4.3–498m2/g were immobilized as thick films on borosilicate glass and installed in a gas-phase, flat-plate photocatalytic reactor. Pure anatase TiO2 treated at 300–600°C exhibited higher activity than commercial TiO2 (P-25) under UV-A radiation with intensity of 5.1, 14.0 and 20.8W/m2. Conversely, pure rutile and mixed phase TiO2 materials showed significantly lower activity. The photocatalytic activity of fully grown anatase TiO2 with crystal size of 27nm was up to three-fold higher than that of P-25 despite exhibiting lower surface area. The increase in the crystallinity of anatase TiO2 upon calcination overcame the depreciation in its structural properties (decrease in surface area and porosity) for the decomposition of TCE. The dependence of the TCE oxidation rate on the intensity of the incident radiation in the range 5.2–20.8W/m2 was found to be first-order for the samples containing a rutile phase (including P-25) and 0.75-order for the sample containing pure anatase suggesting that “absorbed” photons are more effectively used when a rutile phase is present. However, less number of incident photons are absorbed by samples with pure rutile compared to samples with pure anatase. The crystallographic properties of TiO2 over its structural properties were found to be essential factors which determined the higher photocatalytic activity of TiO2 anatase for the photocatalytic decomposition of TCE. Rate equations for the photocatalytic oxidation of TCE over TiO2 films derived from an elementary reaction mechanism and with explicit effect of the incident photon flux were correlated with the catalyst properties.

The Influence of Soil and Organic Matter on Trichloroethylene Decomposition by Fenton Reaction

Contamination of soil and ground water by trichloroethylene (TCE) has become a serious problem in recent times. Fenton reaction can be used for the chemical decomposition of polluting substances. In this study, Fenton reagent was used as an in situ oxidizing agent for soils contaminated with TCE. We investigated the kinetics of TCE decomposition by Fenton reaction involving Fe(II). The results of our experiments show that the rates of TCE decomposition in the presence of all soils except Toyoura sand are lower than that in the absence of soils. TCE decomposition by Fenton’s reaction with Fe(II) in the presence and absence of black soil was found to be of the first order to concentrations of TCE and Fe(II) and half-order to hydrogen peroxide concentration. The reaction rate constants in the presence and absence of black soil were determined to be 1.048 and 0.568 (L·mol–1)1.5·s–1, respectively. Assuming the reaction order to be 2.5, the reaction rate constants in the presence of humic acid, Kanuma soil, Toyoura sand, and akadama soil were determined to be 0.849, 0.725, 1.050, and 0.354 (L·mol–1)1.5·s–1, respectively. The decrease in the rate is speculated to be affected by both specific surface area and carbon content of the soil.

Thermal decomposition of trichloroethylene under a reducing atmosphere of hydrogen

The thermal reaction of trichloroethylene (TCE: C2HCl3) has been conducted in an isothermal tubular flow reactor at 1 atm total pressure in order to investigate characteristics of chlorinated hydrocarbons decomposition and pyrolytic reaction pathways for formation of product under excess hydrogen reaction environment. The reactions were studied over the temperature range 650 to 900 °C with reaction times of 0.3–2.0 s. A constant feed molar ratio C2HCl3: H2 of 4: 96 was maintained through the whole experiments. Complete decay (99%) of the parent reagent, C2HCl3 was observed at temperature near 800 °C with 1 s reaction time. The maximum concentration (28%) of C2H2Cl2 as the primary intermediate product was found at temperature 700 °C where up to 68% decay of C2HCl3 occurred. The C2H3Cl as highest concentration (19%) of secondary products was detected at 750 °C. The one less chlorinated methane than parent increased with temperature rise subsequently. The number of qualitative and qualitative chlorinated products decreased with increasing temperature. HCl and dechlorinated hydrocarbons such as C2H4, C2H6, CH4 and C2H2 were the final products at above 800 °C. The almost 95% carbon material balance was given over a wide range of temperatures, and trace amounts of C6H6, C4H6 and C2HCl were observed above 800 °C. The decay of reactant, C2HCl3 and the hydrodechlorination of intermediate products, resulted from H atom cyclic chain reaction via abstraction and addition replacement reactions. The important pyrolytic reaction pathways to describe the important features of reagent decay, intermediate product distributions and carbon mass balances, based upon thermochemical and kinetic principles, were suggested. The main reaction pathways for formation of major products along with preliminary activation energies and rate constants were given.

Selective low temperature synthesis of carbon nanospheres via the catalytic decomposition of trichloroethylene

The catalytic growth of structured carbon from a C2H4 and C2HCl3 feed promoted by Ni/SiO2 in the presence of H2 over the temperature range 673 K ≤ T ≤ 1023 K has been examined. The supported Ni phase exhibited an exclusive cubic symmetry (XRD analysis) with a range of Ni particle sizes (TEM analysis) and a net shift in the distribution to larger particles with increasing reduction temperature (from 20 to 36 nm), accompanied by a decrease in H2 chemisorption. Conversion of C2H4 generated hydrogenation (C2H6), hydrogenolysis (CH4) and decomposition (C + H2) products. Ethane formation was favoured at lower temperatures with C formation increasingly preferred at higher temperatures so that C2H4 decomposition was the predominant process at T > 723 K; significant CH4 production was only observed at T > 900 K. Carbon yield from C2H4 passed through a maximum at 773 K and took the form of high aspect ratio graphitic nanofibres with a central hollow core and diameters in the range 5–180 nm. The carbonaceous product has been characterized by a combination of TEM-EDX, SEM, XRD, BET area and temperature programmed oxidation (TPO). Carbon formation from C2HCl3 exceeded (by a factor of up to an order of magnitude) that generated via the decomposition of C2H4 at the same inlet C:Ni ratio to deliver essentially a carbon yield invariance (9.1 ± 0.3 gC gNi−1) where 898 K ≤ T ≤ 1023 K, which represents a carbon efficiency (fraction of carbon in the inlet feed that is converted to a solid carbon product) in excess of 96%. Ni/SiO2 promoted a composite dehydrochlorination/decomposition of C2HCl3 to HCl + C. The nature of the carbon product generated from C2HCl3 is strongly temperature dependent with a shift from a pseudo-fibrous product at 773 K to a predominant nanosphere formation at 923 K. These nanospheres exhibit a wide diameter range (40–700 nm), a significant Cl content (1.1–2.6%, w/w) and a conglomeration or clustering to give a less ordered carbonaceous product than that generated at the lower temperature (773 K). A tentative carbon growth rationale is presented to account for the observed dependence of carbon structure on carbon-containing precursor and reaction temperature.

EFFECTS OF SEVERAL SURFACTANTS AND HIGH‐MOLECULAR‐WEIGHT ORGANIC COMPOUNDS ON DECOMPOSITION OF TRICHLOROETHYLENE WITH ZEROVALENT IRON POWDER

We investigated the effects of coexisting surfactants and high‐molecular‐weight organic compounds on the reductive dechlorination of trichloroethylene by zerovalent iron powder to determine whether these additives had utility as washing reagents for remediation of soil and groundwater pollution. During the dechlorination reaction, the amount of trichloroethylene decreased, and the formation of cis‐1,2‐dichloroethylene was observed. The decomposition of trichloroethylene was found to be first‐order with respect to the trichloroethylene and zerovalent iron concentrations when the solution contained no additives. The rates of decomposition of trichloroethylene in the presence of the additives were lower than the rate in the absence of the additives: the rate constant was reduced by a factor of 0.7 for the cationic surfactant cetyltrimethylammonium bromide; by a factor of 0.5 for the anionic surfactants sodium n‐dodecylbenzenesulfonate, sodium n‐dodecylsulfate, and sodium n‐dodecanesulfonate and for the high‐molecular‐weight organic compounds soluble starch, β‐cyclodextrin, and polyethyleneglycol 6000; and by a factor of 0.2 for sodium laurate and the nonionic surfactants Triton X‐100, Tween 20, Tween 60, Brij 35, and Brij 58. Comparison of the concentrations of the nonionic surfactants with their critical micellar concentrations indicated that the rate‐reducing effect of these additives was due to solubilization of trichloroethylene into the micellar phase. The adsorption of trichloroethylene onto the zerovalent iron surface was also affected by the presence of the additives. Thus, our results indicated that the changes in the decomposition rate of trichloroethylene were determined by several factors.

Efficient Decomposition of Trichloroethylene (TCE) in Groundwater by Ozone-Hydrogen Peroxide Treatment

It was verified that the ozone-hydrogen peroxide treatment (O3/H2O2) was very effective for decomposing trichloroethylene (TCE) in groundwater. The reaction efficiency of O3/H2O2 was 40% better than that of ozone treatment by using a diffuser type reactor and the optimum operating conditions were also revealed by laboratory-scale experiments and computer simulations. Taking these results into consideration, the 2-port ozone injection method using an ejector-type reactor was investigated to decompose TCE more rapidly and efficiently, and it was revealed that the ozone dose necessary for satisfying the Japanese water quality standard for drinking water (0.03mg/L) by the 2-port ozone injection method was 13% less than that by the conventional 1-port ozone injection method under the condition of the same amount of ozone injected. Also, the effectiveness of the 2-port injection method was proved by a sequential plant-scale experiment for about 40 days.

Ozonation of trichloroethylene in acetic acid solution with soluble and solid humic acid

The combined flushing and oxidation process using acetic acid and ozone has been used successfully to remove trichloroethylene (TCE) completely from contaminated soil. In this study, the effects of humic acid, a fraction of the organic matter in soil, over the performance of TCE decomposition was evaluated. TCE decomposition by ozone was enhanced by the presence of humic acid at concentrations lower than 8 mg C L −1 and then inhibited at higher concentrations. It is possible that the presence of the soluble humic acid fraction during the ozonation of TCE in acetic acid solutions produces hydroxyl radicals during the TCE ozonation which appears to be the reason for the enhanced TCE decomposition rate. Solid humic acid reduced TCE decomposition rate by acting as an ozone scavenger. Similarly, sorbed TCE reduced the amount of TCE available for decomposition by ozone in solution.

吸着相オゾン酸化によるトリクロロエチレン含有水処理装置の開発

A novel adsorbed phase ozonation process was developed, aiming at the low-cost treatment of Trichloroethylene (TCE)-polluted water. This process primarily consists of two operations: ‘adsorption of TCE’ and ‘regeneration of adsorbent by ozone’. In the step ‘adsorption of TCE’, TCE-polluted water is introduced to a bed packed with ZSM-5 (adsorbent) to realize a selective and high concentration of TCE inside the ZSM-5 owing to its molecular sieve effect and its strong affinity. In the subsequent step (‘regeneration of adsorbent by ozone’), the adsorbed TCE is decomposed by feeding an ozone aqueous solution into the packed bed instead of the TCE-polluted water, resulting in not only the selective decomposition of TCE in the adsorbed phase but also the quick regeneration of ZSM-5. To investigate its effectiveness, a prototype apparatus was designed and its performance was tested to estimate its initial and running costs. Results showed that this process could decompose TCE efficiently and economically.

Synthesis, characterisation and catalytic evaluation of iron–manganese mixed oxide pillared clay for VOC decomposition reaction

A series of iron and manganese mixed oxide pillared clay with varying manganese to iron ratio has been successfully synthesized. Prepared materials were characterized by low angle XRD, TG/DTA, hydrogen TPR and nitrogen adsorption desorption experiment. All the materials were found to be thermally stable up to 500°C having basal spacing ≥16.5Ǻ. Surface area and pore volume increases with the increase in the metal uptake irrespective of manganese to iron ratio. Catalytic decomposition of acetone and trichloroethylene was studied to find out the suitability of the material for VOC decomposition reaction. Catalyst (S-16/4) having high manganese content acts as better catalyst for the acetone decomposition reaction. Time on stream experiment justifies the stability of the prepared catalyst at least for 20h with minor change in the activity. However, in case of trichloroethylene (TCE) decomposition catalyst (S-8/12) with higher iron content shows better activity. Quick deactivation of the catalyst for TCE decomposition is noticed for all the prepared materials.

Catalytic decomposition of trichloroethylene over Pt-/Ni-catalyst under microwave heating

Microwave (MW)-activated catalytic reactor system was studied and the results were compared with that of a conventional system based on the thermal activation method. Trichloroethylene (TCE) was decomposed under various MW-powers supply. Results showed that there is an optimum film thickness that was loaded on supports in MW heating system. The threshold may be within 1–3 μm. Lower temperature cannot activate the catalyst, while higher temperature results in carbon deposition and catalyst deactivation. This means that the dechlorination reaction needs to fix an optimum film MW-power supply in order to avoid the deposition of carbon on the surface of the active phase. MW-activated system is also worth compensating the conventional system in VOCs decomposition reaction.

Use of an integrated photocatalysis/hollow fiber microfiltration system for the removal of trichloroethylene in water

This work focused on the degradation of toxic organic compounds such as trichloroethylene (TCE) in water, using a combined photocatalysis/microfiltration (MF) system. The performances of the hybrid system were investigated in terms of the removal efficiency of TCE and membrane permeability, in the presence or absence of background species, such as alkalinity and humic acids. The mass balancing of the fate of TCE during photocatalytic reactions was performed in order to evaluate the feasibility of the photocatalytic membrane reactor (PMR). Greater TCE degradation (>60%) was achieved with an increase in the TiO 2 dosage (up to 1.5 g/L) in PMR, but a substantially large TiO 2 dosage brought about a decrease in TCE degradation efficiency. The photocatalytic decomposition of TCE appeared to be more effective in acidic pH conditions than with a neutral or alkaline pH. The addition of alkalinity and humic acid into the feedwater did not have a significant effect on TCE degradation, while humic acids (whose dose was 1 mg/L as TOC) in the feedwater played a part in a decline of permeability by 60%. Membrane permeability in the PMR was also affected by tangential velocities. An improvement of 60% in flux was achieved when the tangential velocity increased from 0.19 to 1.45 m/s. This is because flow regimes can govern the deposition of TiO 2 particles on the membrane surface.

Plasma-assisted catalysis total oxidation of trichloroethylene over gold nano-particles embedded in SBA-15 catalysts

The oxidative decomposition of trichloroethylene (TCE) in dry air was investigated in non-thermal plasma at atmospheric pressure and room temperature, both in the absence and in the presence of gold containing mesoporous silica (GMS) catalysts. In the absence of catalyst, TCE removal reached 100% for average powers dissipated in the plasma above 3W, for a TCE concentration of 430ppmv. Carbon monoxide and carbon dioxide were the major reaction products with CO2 selectivity up to 25% and CO selectivity up to 70%. In the presence of gold containing mesoporous catalysts, the concentrations of CO and CO2 increased as compared to those obtained with plasma alone. The GMS catalysts can dissociate ozone produced in plasma to oxygen radicals that decompose TCE. Among these catalysts, the one containing the least amount of Au (0.5% GMS) showed the best catalytic performance. In the presence of ozone generated in the plasma, isolated gold cations might play a critical role for the catalytic behavior.

Improved performance of non-thermal plasma reactor during decomposition of trichloroethylene: Optimization of the reactor geometry and introduction of catalytic electrode

The decomposition of trichloroethylene (TCE) by non-thermal plasma was investigated in a dielectric barrier discharge (DBD) reactor with a copper rod inner electrode and compared with a plasma-catalytic reactor. The particularity of the plasma-catalytic reactor is the inner electrode made of sintered metal fibers (SMF) coated by transition metal oxides. In order to optimize the geometry of the plasma reactor, the efficiency of TCE removal was compared for different discharge gap lengths in the range of 1–5mm. Shorter gap lengths (1–3mm) appear to be more advantageous with respect to TCE conversion. In this case TCE conversion varies between 67% and 100% for input energy densities in the range of 80–480J/l, while for the 5mm discharge gap the conversion was lower (53–97%) for similar values of the input energy. As a result of TCE oxidation carbon monoxide and carbon dioxide were detected in the effluent gas. Their selectivity was rather low, in the range 14–24% for CO2 and 11–23% for CO, and was not influenced by the gap length. Several other chlorinated organic compounds were detected as reaction products.When using MnOx/SMF catalysts as the inner electrode of the DBD reactor, the TCE conversion was significantly enhanced, reaching ∼95% at 150J/l input energy. The selectivity to CO2 showed a major increase as compared to the case without catalysts, reaching 58% for input energies above 550J/l.

Dilute TCE Decomposition by the Nonthermal Plasma Combined with MnO2-supported Alumina

Atmospheric pressure nonthermal plasma has very high chemical reactivity and can decompose various toxic materials. The authors are engaged in decomposing the various kinds of VOCs (volatile organic compounds) by using the nonthermal plasma (typically barrier discharge reactor). To improve the energy efficiency, modification of the plasma reactor has been done. A new catalyst, manganese dioxide—supported alumina sphere of 3 mm in diameter was manufactured by ourselves for the combined process with the plasma. That can decompose the ozone very well, where the ozone is one of the typical byproducts produced by the strong barrier discharge in the air. At that ozone decomposition process, dilute TCE (trichloroethylene) is also oxidized very well. The ozone decomposition generates single atomic oxygen which oxidizes TCE very well. The total performance of that alumina assisted plasma process is investigated. The specific energy density (SED) is only 10 J/L when the TCE decomposition efficiency is more than 99 % which is the least record in our experiments. Moreover, the carbon balance from TCE to carbon oxide is also more than 90 % at the SED of 90 J/L.