Destruction Of Trichloroethylene Research Articles

The destruction of trichloroethylene by zinc dioxide using a modified Fenton reaction: Performance and a preliminary mechanism

The destruction of trichloroethylene by zinc dioxide using a modified Fenton reaction: Performance and a preliminary mechanism

Trichloroethylene Combustion in a Submerged Thermal Plasma: Results and Chemical Kinetics Model

This work deals with incineration of organic liquid wastes using an oxygen thermal plasma jet, submerged in water. The results presented here concern incineration of trichloroethylene (TCE). During a trial run, the CO2 and CO content in the exhaust gas is continuously measured; samples taken periodically from the solution are analyzed by appropriate methods: total organic carbon and chlorine content are measured. Process efficiency during tests with a few L/h of TCE is given by the mineralization rate. The trapping rate of chlorine as HCl is near 100 %. The TCE destruction and removal efficiency, measured by MS/GC, is better than 99.9999 %. A simplified kinetic model of gas quenching was constructed from a single-phase plug-flow reactor model taking into account 14 species and 34 reactions. It satisfies the requirements of heat balance and major components analysis, and reveals the major role of the OH radical on the concentrations of CO as well as HCl and/or Cl2 in the off-gas stream.

Modeling and Experimental Study of Trichloroethylene Abatement with a Negative Direct Current Corona Discharge

In this work, we study the abatement of dilute trichloroethylene (TCE) in air with a negative direct current corona discharge. A numerical model is used to theoretically investigate the underlying plasma chemistry for the removal of TCE, and a reaction pathway for the abatement of TCE is proposed. The Cl atom, mainly produced by dissociation of COCl, is one of the controlling species in the TCE destruction chemistry and contributes to the production of chlorine containing by-products. The effect of humidity on the removal efficiency is studied and a good agreement is found between experiments and the model for both dry (5 % relative humidity (RH)) and humid air (50 % RH). An increase of the relative humidity from 5 % to 50 % has a negative effect on the removal efficiency, decreasing by ±15 % in humid air. The main loss reactions for TCE are with ClO·, O· and CHCl2. Finally, the by-products and energy cost of TCE abatement are discussed.

Laboratory-scale column study for remediation of TCE-contaminated aquifers using three-section controlled-release potassium permanganate barriers

A laboratory-scale study with a sand column was designed to simulate trichloroethylene (TCE) pollution in the aquifer environment with three-section controlled-release potassium permanganate (CRP) barriers. The main objective of this study was to evaluate the feasibility of CRP barriers in remediation of TCE in aquifers in a long-term and controlled manner. CRP particles with a 1:3 molar ratio of KMnO4 to stearic acid showed the best controlled-release properties in pure water, and the theoretical release time was 138.5 days. The results of TCE removal in the test column indicated that complete removal efficiency of TCE in a sand column by three-section CRP barriers could be reached within 15 days. The molar ratio of KMnO4 to TCE in the three-section CRP barriers was 16:1, which was much lower than 82:1 as required when KMnO4 solution is used directly to achieve complete destruction of TCE. This result revealed that the efficiency of CRP for remediation of TCE was highly improved after encapsulation.

Enhanced nano-Fe 3O 4/S 2O 82− oxidation of trichloroethylene in a clayey soil by electrokinetics

The effectiveness of electrokinetically enhanced persulfate oxidation for destruction of trichloroethylene (TCE) in a spiked sandy clay soil was evaluated in this work. In addition, the effect of nanoscale Fe 3O 4 on activating persulfate oxidation was also evaluated. The TCE-spiked soil was compacted in the soil column of the electrokinetic (EK) treatment system, and both the anode and cathode reservoirs were filled with simulated groundwater. The electrode material for both the anode and cathode was graphite. An electrical potential gradient of 1 V cm −1 was applied to the EK treatment system by a DC power supply for a period of 7–14 d. Sodium persulfate (Na 2S 2O 8) was injected daily at a dose of 1.0–10.0 g L −1 into the anode or cathode reservoir, starting from the very beginning of the treatment. To evaluate the performance of persulfate alone in chemical oxidation of TCE in the EK treatment system, EK-alone test was also carried out for comparison. Experimental results have shown that the EK process greatly enhances the transport of injected persulfate from the anode reservoir to the cathode reservoir via the soil compartment by means of electroosmotic flow, aiding in situ chemical oxidation of TCE. In addition, nanoscale Fe 3O 4 was found to play a significant role in activating persulfate oxidation. Such a coupled process was found to be capable of effective destruction of TCE in the soil compartment and electrode compartments. Under optimal conditions, the residual TCE concentration in the soil compartment was found to be lower than Taiwan EPA's regulatory threshold (i.e., 60 mg kg −1). The residual TCE concentrations in both electrode reservoirs (i.e., not detectable and 0.01–1.74 mg L −1 for the anode and cathode reservoirs, respectively) also met the local regulatory standards for Type II groundwater quality (i.e., <0.05 mg L −1).

Application of microwave air plasma in the destruction of trichloroethylene and carbon tetrachloride at atmospheric pressure

In this study, the destruction rate of a volatile waste destruction system based on a microwave plasma torch operating at atmospheric pressure was investigated. Atmospheric air was used to maintain the plasma and was introduced by a compressor, which resulted in lower operating costs compared to other gases such as argon and helium. To isolate the output gases and control the plasma discharge atmosphere, the plasma was coupled to a reactor. The effect of the gas flow rate, microwave power and initial concentration of compound on the destruction efficiency of the system was evaluated. In this study, trichloroethylene and carbon tetrachloride were used as representative volatile organic compounds to determine the destruction rate of the system. Based on the experimental results, at an applied microwave power less than 1000W, the proposed system can reduce input concentrations in the ppmv range to output concentrations at the ppbv level. High air flow rates and initial concentrations produced energy efficiency values greater than 1000g/kWh. The output gases and species present in the plasma were analysed by gas chromatography and optical emission spectroscopy, respectively, and negligible amounts of halogenated compounds resulting from the cleavage of C2HCl3 and CCl4 were observed. The gaseous byproducts of decomposition consisted mainly of CO2, NO and N2O, as well as trace amounts of Cl2 and solid CuCl.

Destruction of trichloroethylene during hydration of calcium oxide

Quicklime (calcium oxide, CaO) is often used as part of soil cleanup operations to remove contaminants or to create more favorable physical soil conditions for treatment. The extent to which quicklime chemically reacts with trichloroethylene (TCE) was evaluated by reacting CaO with a TCE–water mixture in test vessels designed to minimize volatilization loss. The impact of excess water and the presence of air were evaluated. During the hydration of CaO, a fraction of the spiked TCE was destroyed, and several different byproducts were detected (chloride and several organic chemicals). The primary organic byproduct was dichloroacetylene (DCA). In the presence of air, the degradation of DCA resulted in the formation of perchloroethylene (PCE), hexachloro-1,3-butadiene (HCDE), and chloroacetylene (CA). The maximum amount of TCE degradation occurred with a CaO/H 2O ratio of 1:1 in the presence of air. The formation of DCA was hindered by the presence of excess water. In the presence of excess water (a CaO/H 2O ratio of 1:2) the detected byproducts accounted for less than 4% of the total chlorine originally spiked as TCE.

Destruction of Trichloroethylene and Perchloroethylene DNAPLs by Catalyzed H2O2 Propagations

The destruction of trichloroethylene (TCE) and perchloroethylene (PCE) dense nonaqueous phase liquids (DNAPLs) using catalyzed H2 O2 propagations (CHP), an in situ chemical oxidation process based on Fenton’s reagent, was investigated in batch, bench scale reactors. TCE and PCE masses were quantified over time in DNAPLs, aqueous phases, and off gasses, and the rate of DNAPL destruction was compared to the corresponding rate of gas purge dissolution. TCE and PCE DNAPLs were rapidly destroyed by CHP at 1.7 and 4.4 times the rate of gas purge dissolution, respectively. Use of reactions in which a single reactive oxygen species was generated demonstrated that both hydroxyl radical and superoxide were involved in TCE and PCE DNAPL destruction, with superoxide having the major role in the destruction of the DNAPLs. These results show that DNAPLs composed of contaminants highly reactive with hydroxyl radical, such as TCE and PCE, are destroyed primarily through reaction with superoxide.

PH dependence of persulfate activation by EDTA/Fe(III) for degradation of trichloroethylene

The ability of free ferrous ion activated persulfate (S 2O 8 2−) to generate sulfate radicals (SO 4 − ) for the oxidation of trichloroethylene (TCE) is limited by the scavenging of SO 4 − with excess Fe 2+ and a quick conversion of Fe 2+ to Fe 3+. This study investigated the applicability of ethylene-diamine-tetra-acetic acid (EDTA) chelated Fe 3+ in activating persulfate for the destruction of TCE in aqueous phase under pH 3, 7 and 10. Fe 3+ and EDTA alone did not appreciably degrade persulfate. The presence of TCE in the EDTA/Fe 3+ activated persulfate system can induce faster persulfate and EDTA degradation due to iron recycling to activate persulfate under a higher pH condition. Increasing the pH leads to increases in pseudo-first-order-rate constants for TCE, S 2O 8 2− and EDTA degradations, and Cl generation. Accordingly, the experiments at pH 10 with different EDTA/Fe 3+ molar ratios indicated that a 1/1 ratio resulted in a remarkably higher degradation rate at the early stage of reaction as compared to results by other ratios. Higher persulfate dosage under the EDTA/Fe 3+ molar ratio of 1/1 resulted in greater TCE degradation rates. However, increases in persulfate concentration may also lead to an increase in the rate of persulfate consumption.

Application of a Microwave Helium Plasma Torch Operating at Atmospheric Pressure to Destroy Trichloroethylene

We examined the influence of the gas flow-rate, microwave power and trichloroethylene concentration on the destruction of trichloroethylene with a system based on a microwave helium plasma operating at atmospheric pressure. Based on the experimental results obtained, the proposed system allows input concentrations of C2HCl3 in the ppmv range to be reduced to output concentrations in the ppbv range (i.e. virtually quantitative destruction) by using a microwave plasma power below 1000 W. High helium flow-rates and C2HCl3 concentrations allow energy efficiency values above 600 g/kW h to be obtained. Analyses of the output gases by gas chromatography and species present in the plasma by optical emission spectroscopy confirmed the negligible presence of halogen compounds resulting from the destruction of C2HCl3, and that of CCl4 and C2Cl4 as the sole chlorine species exceeding levels of 30 ppbv. Gaseous by-products consisted mainly of CO2, NO and N2O in addition to Cl2 traces.

Destruction of Trichloroethylene in a Two Stage Molten Salt Oxidation Reactor System

Destruction of Trichloroethylene in a Two Stage Molten Salt Oxidation Reactor System

Novel catalytic non-thermal plasma reactor for the abatement of VOCs

A novel dielectric barrier discharge (DBD) reactor has been designed and tested for the abatement of diluted volatile organic compounds (VOCs) of different nature. The novelty of the DBD reactor is that a metallic catalyst made of sintered metal fibers (SMF) also acts as the inner electrode. The SMF electrodes modified with oxides of Ti, Mn and Co were efficient during the destruction of toluene, isopropanol (IPA) and trichloroethylene (TCE). Total oxidation of IPA was achieved at lower specific input energy (SIE) compared to toluene and TCE. Among the catalysts studied, MnOx/SMF showed the best performance, involving the formation of active oxygen species by in situ decomposition of ozone on the catalyst surface. The selectivity to CO2 as the total oxidation product during TCE destruction was improved up to ∼70% by modifying MnOx/SMF with TiO2.

Photocatalysis of gaseous trichloroethylene (TCE) over TiO 2: The effect of oxygen and relative humidity on the generation of dichloroacetyl chloride (DCAC) and phosgene

Batch photocatalytic degradation of 80 ± 2.5 ppmV trichloroethylene (TCE) was conducted to investigate the effect of the oxygen and relative humidity (RH) on the formation of the dichloroacetyl chloride (DCAC) and phosgene. Based on the simultaneous ordinary differential equations (ODEs), the reaction rate constants of TCE ((2.31 ± 0.28) ∼ (9.41 ± 0.63) × 10 −2 min −1) are generally larger than that of DCAC ((0.94 ± 1.25) ∼ (9.35 ± 1.71) × 10 −3 min −1) by approximate one order. The phenomenon indicates the degradation potential of TCE is superior to that of DCAC. DCAC appreciably delivers the same degradation behavior with TCE that means there exists an optimum RH and oxygen concentration for photocatalysis of TCE and DCAC. At the time the peak yield of DCAC appears, the conversion ratio based on the carbon atom from TCE to DCAC is within the range of 30–83% suggesting that the DCAC generation is significantly attributed to TCE degradation. Regarding the phosgene formation, the increasing oxygen amount leads to the inhibitory effect on the phosgene yield which fall within the range of 5–15%. The formation mechanism of phosgene was also inferred that the Cl atoms attacking the C–C bond of DCAC results to the generation of phosgene rather than directly from the TCE destruction.

Destruction of trichloroethylene (TCE) and trichloromethane (TCM) in the presence of selected VOCs over Pt-Pd-based catalyst

Catalytic oxidation of trichloroethylene (TCE) and trichloromethane (TCM) oxidized alone and in two-component mixtures with selected volatile organic compounds (VOCs) such as toluene, n-hexane, ethanol or acetone was investigated over a Pt-Pd-based catalyst on a monolithic, metallic, γ-Al 2O 3-washcoated support. TCE and TCM were more difficult to oxidize than VOCs and temperatures of their 50% conversion ( T 50%) amouted to 420 and 330 °C, respectively. All the VOCs added were found to enhance the conversion of the two chlorinated compounds, drecreasing T 50% by 20 °C, at the most, for TCM in the presence of toluene and by 50 °C for TCE in the presence of acetone. Both the chlorinated compounds lowered the conversion of the VOCs added (except that of toluene), and this lowering was particularly distinct with n-heptane; they also raised the concentration of acetaldehyde formed during the oxidation of oxyderivative compounds.

Synthesis of Nanoscale Bimetallic Particles in Polyelectrolyte Membrane Matrix for Reductive Transformation of Halogenated Organic Compounds

Nanosized Fe/Ni and Fe/Pd particles were synthesized in the polyacrylic acid (PAA)/polyether sulfone (PES) composite membrane matrix for reductive transformation of halogenated organic compounds (HOCs). The advantages of using membrane to immobilize nanoparticles are the reduction of particles loss, prevention of particles agglomeration, and potential application of convective flow. Cross-linked PAA/PES composite membranes containing metal ions as particles precursor were prepared by heat treatment with ethylene glycol (EG) as a cross-linking agent. Nanoscale metal particles were formed and immobilized inside the membrane matrix after reduction with sodium borohydride. Membrane morphology and structure were observed by scanning electron microscopy (SEM). Particle size and distribution were characterized by SEM and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) was used to obtain the qualitative and quantitative element information of particles. A specimen-drift-free EDS line profile and EDS mapping system was performed in a scanning transmission electron microscopy (STEM) to determine the two-dimensional element distribution of iron and nickel in the nano domain. In the dechlorination study with trichloroethylene (TCE) as a representative HOCs, rapid and complete destruction of TCE was achieved by using nanosized bimetallic Fe/Ni or Fe/Pd in PAA/PES composite membranes. Typically more than 95% of 10 mg/l TCE was reduced within 1 h. Ethane was found in the headspace as the main product.

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.

UV Photolysis of Trichloroethylene: Product Study and Kinetic Modeling

Direct UV photolysis of trichloroethylene (TCE) in dilute aqueous solution generated chloride ions as a major end product and several reaction intermediates, such as formic acid, di- and monochloroacetic acids, glyoxylic acid, and, to a lesser extent, mono- and dichloroacetylene, formaldehyde, dichloroacetaldehyde, and oxalic acid. Under prolonged irradiation, these byproducts underwent photolysis, and a high degree of mineralization (approximately 95%) was achieved. TCE decays through the following major pathways: (1) TCE + h nu --> ClCH=C*Cl + Cl*; (2) TCE (H2O) + h nu --> ClCH(OH)-CHCl2; (3) TCE + h nu --> HC[triple bond]CCl + Cl2; (4) TCE + h nu --> ClC[triple bond]CCl + HCl; (5) TCE + Cl* --> Cl2HC-C*Cl2. A kinetic model was developed to simulate the destruction of TCE and the formation and fate of byproducts in aqueous solution under irradiation with polychromatic light. By fitting the experimental data, the quantum yields for the four photolysis steps were predicted as phi(1) = 0.13, phi(2) = 0.1, phi(3) = 0.032, and phi(4) = 0.092, respectively. The reaction mechanism proposed for the photodegradation of TCE accounts for all intermediates that were detected. The agreement between the computed and experimental patterns of TCE and reaction products is satisfactory given the complexity of the reaction mechanism and the lack of photolytic kinetic parameters that are provided in the literature.

Persulfate oxidation for in situ remediation of TCE. II. Activated by chelated ferrous ion

In situ chemical oxidation (ISCO) is a technique used to remediate contaminated soil and groundwater systems. It has been postulated that sodium persulfate (Na 2S 2O 8) can be activated by transition metal ions such as ferrous ion (Fe 2+) to produce a powerful oxidant known as the sulfate free radical (SO 4 − ) with a redox potential of 2.6 V, which can potentially destroy organic contaminants. In this laboratory study persulfate oxidation of dissolved trichloroethylene (TCE) was investigated in aqueous and soil slurry systems under a variety of experimental conditions. A chelating agent (i.e., citric acid) was used in attempt to manipulate the quantity of ferrous ion in solution by providing an appropriate chelate/Fe 2+ molar ratio. In an aqueous system a chelate/Fe 2+ molar ratio of 1/5 (e.g., S 2O 8 2−/chelate/Fe 2+/TCE ratio of 20/2/10/1) was found to be the lowest acceptable ratio to maintain sufficient quantities of Fe 2+ activator in solution resulting in nearly complete TCE destruction after only 20 min. The availability of Fe 2+ appeared to be controlled by adjusting the molar ratio of chelate/Fe 2+. In general, high levels of chelated ferrous ion concentrations resulted in faster TCE degradation and more persulfate decomposition. However, if initial ferrous ion contents are relatively low, sufficient quantities of chelate must be provided to ensure the chelation of a greater percentage of the limited ferrous ion present. Citric acid chelated ferrous ion appeared effective for TCE degradation within soil slurries but required longer reaction times. Additionally, the use of citric acid without the addition of supplemental Fe 2+ in soil slurries, where the citric acid apparently extracted native metals from the soil, appeared to be somewhat effective at enhancing persulfate oxidation of TCE over extended reaction times. A comparison of different chelating agents revealed that citric acid was the most effective.

Photocatalytic Oxidation of Trichloroethylene and Carbon Tetrachloride Using Titanium Dioxide Filter as a Catalyst

Destruction of trichloroethylene (TCE) and carbon tetrachloride by using TiO2 photocatalyst supported on an alumina filter prepared for this investigation was carried out using UV light. The kinetics of the rate of reaction were studied. The complete destruction of TCE and CCl4 occurred in 26 and 30 min, respectively, at room temperature and atmospheric pressure. The Langmuir?Hinshelwood rate expression was used to evaluate the rate constants from the experimental data.

Remediation of TCE contaminated soils by in situ EK-Fenton process

The treatment performance and cost analysis of in situ electrokinetic (EK)-Fenton process for oxidation of trichloroethylene (TCE) in soils were evaluated in this work. In all experiments, an electric gradient of 1 V/cm, de-ionized water as the cathode reservoir fluid and a treatment time of 10 days were employed. Treatment efficiencies of TCE were evaluated in terms of the electrode material, soil type, catalyst type, and catalyst dosage and granular size if applicable. Test results show that graphite electrodes are superior to stainless steel electrodes. It was found that the soil with a higher content of organic matter would result in a lower treatment efficiency (e.g. a sandy loam is less efficient than a loamy sand). Experimental results show that the type of catalyst and its dosage would markedly affect the reaction mechanisms (i.e. “destruction” and “removal”) and the treatment efficiency. Aside from FeSO 4, scrap iron powder (SIP) in the form of a permeable reactive wall was also found to be an effective catalyst for Fenton reaction to oxidize TCE. In general, the smaller the granular size of SIP, the lower the overall treatment efficiency and the greater the destruction efficiency. When a greater quantity of SIP was used, a decrease of the overall treatment efficiency and an increase of percent destruction of TCE were found. Experimental results have shown that the quantity of electro-osmotic (EO) flow decreased as the quantity of SIP increased. It has been verified that the treatment performances are closely related to the corresponding EO permeability. Results of the cost analysis have indicated that the EK-Fenton process employed in this work is very cost-effective with respect to TCE destruction.