Chlorinated Methanes Research Articles

Experimental study on alkylation of PCl3 for methyl-dichloride phosphine synthesis using mass spectrometry detection

An online sampling and mass spectrometry (MS) detection method was developed to study the alkylation of PCl3 with methane at high temperature for synthesis of methyl-dichloride phosphine (CH3PCl2, MDP), which was a free radical reaction on a millisecond time scale. Through qualitative analysis, the byproducts P4 and chloro-dimethyl-phosphine ((CH3)2PCl, CDMP) were identified, with their formation mechanisms elucidated for the first time. The effects of operation conditions, including temperature, residence time, and types and concentrations of chloromethanes (CH4-xClx, x = 2, 3, 4), on both MDP yield and selectivity, were systematically investigated. The optimal operation conditions were determined based on MDP yield and selectivity. The addition of chloromethanes significantly enhanced PCl3 conversion. Chloromethanes underwent conversion in the reaction, promoting PCl3 conversion while also continuously converting into lower chlorinated methane derivatives. These results are of great significance for guiding rational industrial process development.

Synergistic solvation effect and modeling of itraconazole solubility in eight binary mixtures (dichloromethane and chloroform + primary alcohol) at the range of 288.15 K to 308.15 K

In this study, the solubility and apparent thermodynamic parameters of itraconazole in chlorinated methane (dichloromethane and chloroform) + primary alcohol (methanol, ethanol, n-propanol, and n-butanol) mixtures were determined at 288.15–308.15 K utilizing the well-established shake-flask technique. The experimental mole fraction solubility of itraconazole in all studied binary solvent mixtures gradually increased as the temperature rises. Because of the synergy effect between chlorinated methane and primary alcohol mixtures, the solubility of itraconazole was maximal in chlorinated methane + primary alcohol mixtures with a 0.9 mass fraction of chlorinated methane at all tested temperatures. The solubility profile of itraconazole in chlorinated methane + primary alcohol mixtures can be explained by the synergistic effect and solubility parameters. Additionally, thermal and crystal analyses confirmed that no polymorphic transformation occurred during the dissolution processes of itraconazole. The experimental solubility of itraconazole in chlorinated methane + primary alcohol mixtures were adequately fitted and correlated with eight well-known correlation models. The modified van’t Hoff and Gibbs equations were applied to better understand and calculate the thermodynamics of itraconazole dissolved in chlorinated methane + primary alcohol mixtures. The experimental solubility and calculated solubility of itraconazole in eight binary mixtures can be helpful for drug development, such as pre-formulation study, separation, crystallization, extraction, purification, and solubilized drug formulation.

Phase Equilibrium Data of Ternary Mixtures (Water + Orthophosphoric Acid + Chlorinated Methanes)

In the present study, phase equilibrium data of the systems (water + orthophosphoric acid + chlorinated methanes) were measured in the temperature range of 298.2–318.2 K under ambient conditions. C...

Use of dual element isotope analysis and microcosm studies to determine the origin and potential anaerobic biodegradation of dichloromethane in two multi-contaminated aquifers

Many aquifers around the world are impacted by toxic chlorinated methanes derived from industrial processes due to accidental spills. Frequently, these contaminants co-occur with chlorinated ethenes and/or chlorinated benzenes in groundwater, forming complex mixtures that become very difficult to remediate. In this study, a multi-method approach was used to provide lines of evidence of natural attenuation processes and potential setbacks in the implementation of bioremediation strategies in multi-contaminated aquifers. First, this study determined i) the carbon and chlorine isotopic compositions (δ13C, δ37Cl) of several commercial pure phase chlorinated compounds, and ii) the chlorine isotopic fractionation (εCl = −5.2 ± 0.6‰) and the dual CCl isotope correlation (ΛC/Cl = 5.9 ± 0.3) during dichloromethane (DCM) degradation by a Dehalobacterium-containing culture. Such data provide valuable information for practitioners to support the interpretation of stable isotope analyses derived from polluted sites. Second, the bioremediation potential of two industrial sites contaminated with a mixture of organic pollutants (mainly DCM, chloroform (CF), trichloroethene (TCE), and mono-chlorobenzene (MCB)) was evaluated. Hydrochemistry, dual (CCl) isotope analyses, laboratory microcosms, and microbiological data were used to investigate the origin, fate and biodegradation potential of chlorinated methanes. At Site 1, δ13C and δ37Cl compositions from field samples were consistent with laboratory microcosms, which showed complete degradation of CF, DCM and TCE, while MCB remained. Identification of Dehalobacter sp. in CF-enriched microcosms further supported the biodegradation capability of the aquifer to remediate chlorinated methanes. At Site 2, hydrochemistry and δ13C and δ37Cl compositions from field samples suggested little DCM, CF and TCE transformation; however, laboratory microcosms evidenced that their degradation was severely inhibited, probably by co-contamination. A dual CCl isotopic assessment using results from this study and reference values from the literature allowed to determine the extent of degradation and elucidated the origin of chlorinated methanes.

Unravelling long-term source removal effects and chlorinated methanes natural attenuation processes by C and Cl stable isotopic patterns at a complex field site

The effects of contaminant sources removal in 2005 (i.e. barrels, tank, pit and wastewater pipe sources) on carbon tetrachloride (CT) and chloroform (CF) concentration in groundwater were assessed at several areas of a fractured multi-contaminant aquifer (Òdena, Spain) over a long-term period (2010–2014). Changes in redox conditions, in these chlorinated methanes (CMs) concentration and in their carbon isotopic compositions (δ13C) were monitored in multilevel wells. δ13C values from these wells were compared to those obtained from sources (barrels, tank and pit before their removal, 2002–2005) and to commercial solvents values in literature. Additionally, CMs natural attenuation processes were identified by C-Cl isotope slopes (Λ).Analyses revealed the downstream migration of the pollutant focus and an efficient removal of DNAPLs in the pit source's influence area. However, the removal of the contaminated soil from former tank and wastewater pipe was incomplete as leaching from unsaturated zone was proved, evidencing these areas are still active sources. Nevertheless, significant CMs degradation was detected close to all sources and Λ values pointed to different reactions. For CT in the tank area, Λ value fitted with hydrogenolysis pathway although other possible reduction processes were also uncovered. Near the wastewater pipe area, CT thiolytic reduction combined with hydrogenolysis was derived. The highest CT degradation extent accounted for these areas was 72 ± 11% and 84 ± 6%, respectively. For CF, the Λ value in the pit source's area was consistent with oxidation and/or with transport of CF affected by alkaline hydrolysis from upstream interception trenches. In contrast, isotope data evidenced CF reduction in the tank and wastewater pipe influence areas, although the observed Λ slightly deviates from the reference values, likely due to the continuous leaching of CF degraded in the non-saturated zone by a mechanism different from reduction.

Dual element (C[sbnd]Cl) isotope approach to distinguish abiotic reactions of chlorinated methanes by Fe(0) and by Fe(II) on iron minerals at neutral and alkaline pH

A dual element CCl isotopic study was performed for assessing chlorinated methanes (CMs) abiotic transformation reactions mediated by iron minerals and Fe(0) to further distinguish them in natural attenuation monitoring or when applying remediation strategies in polluted sites. Isotope fractionation was investigated during carbon tetrachloride (CT) and chloroform (CF) degradation in anoxic batch experiments with Fe(0), with FeCl2(aq), and with Fe-bearing minerals (magnetite, Mag and pyrite, Py) amended with FeCl2(aq), at two different pH values (7 and 12) representative of field and remediation conditions. At pH 7, only CT batches with Fe(0) and Py underwent degradation and CF accumulation evidenced hydrogenolysis. With Py, thiolytic reduction was revealed by CS2 yield and is a likely reason for different Λ value (Δδ13C/Δδ37Cl) comparing with Fe(0) experiments at pH 7 (2.9 ± 0.5 and 6.1 ± 0.5, respectively). At pH 12, all CT experiments showed degradation to CF, again with significant differences in Λ values between Fe(0) (5.8 ± 0.4) and Fe-bearing minerals (Mag, 2 ± 1, and Py, 3.7 ± 0.9), probably evidencing other parallel pathways (hydrolytic and thiolytic reduction). Variation of pH did not significantly affect the Λ values of CT degradation by Fe(0) nor Py.CF degradation by Fe(0) at pH 12 showed a Λ (8 ± 1) similar to that reported at pH 7 (8 ± 2), suggesting CF hydrogenolysis as the main reaction and that CF alkaline hydrolysis (13.0 ± 0.8) was negligible.Our data establish a base for discerning the predominant or combined pathways of CMs natural attenuation or for assessing the effectiveness of remediation strategies using recycled minerals or Fe(0).

Biofiltration of Chloroform in a Trickle Bed Air Biofilter Under Acidic Conditions.

In this paper, the application of biofiltration is investigated for controlled removal of gas phase chloroform through cometabolic degradation with ethanol. A trickle bed air biofilter (TBAB) operated under acidic pH 4 is subjected to aerobic biodegradation of chloroform and ethanol. The TBAB is composed of pelleted diatomaceous earth filter media inoculated with filamentous fungi species, which served as the principle biodegrading microorganism. The removal efficiencies of 5 ppmv of chloroform mixed with different ratios of ethanol as cometabolite (25, 50, 100, 150, and 200 ppmv) ranged between 69.9 and 80.9%. The removal efficiency, reaction rate kinetics, and the elimination capacity increased proportionately with an increase in the cometabolite concentration. The carbon recovery from the TBAB amounted to 69.6% of the total carbon input. It is postulated that the remaining carbon contributed to excess biomass yield within the system. Biomass control strategies such as starvation and stagnation were employed at different phases of the experiment. The chloroform removal kinetics provided a maximum reaction rate constant of 0.0018 s-1. The highest ratio of chemical oxygen demand (COD)removal/nitrogenutilization was observed at 14.5. This study provides significant evidence that the biodegradation of a highly chlorinated methane can be favored by cometabolism in a fungi-based TBAB.

Rapid quantitative estimation of chlorinated methane utilizing bacteria in drinking water and the effect of nanosilver on biodegradation of the trichloromethane in the environment.

Background:Halomethanes are toxic and carcinogenic chemicals, which are widely used in industry. Also they can be formed during water disinfection by chlorine. Biodegradation by methylotrophs is the most important way to remove these pollutants from the environment.Objectives:This study aimed to represent a simple and rapid method for quantitative study of halomethanes utilizing bacteria in drinking water and also a method to facilitate the biodegradation of these compounds in the environment compared to cometabolism.Materials and Methods:Enumeration of chlorinated methane utilizing bacteria in drinking water was carried out by most probable number (MPN) method in two steps. First, the presence and the number of methylotroph bacteria were confirmed on methanol-containing medium. Then, utilization of dichloromethane was determined by measuring the released chloride after the addition of 0.04 mol/L of it to the growth medium. Also, the effect of nanosilver particles on biodegradation of multiple chlorinated methanes was studied by bacterial growth on Bushnell-Haas Broth containing chloroform (trichloromethane) that was treated with 0.2 ppm nanosilver.Results:Most probable number of methylotrophs and chlorinated methane utilizing bacteria in tested drinking water were 10 and 4 MPN Index/L, respectively. Chloroform treatment by nanosilver leads to dechlorination and the production of formaldehyde. The highest growth of bacteria and formic acid production were observed in the tubes containing 1% chloroform treated with nanosilver.Conclusions:By combining the two tests, a rapid approach to estimation of most probable number of chlorinated methane utilizing bacteria is introduced. Treatment by nanosilver particles was resulted in the easier and faster biodegradation of chloroform by bacteria. Thus, degradation of these chlorinated compounds is more efficient compared to cometabolism.

Highly chlorinated unintentionally produced persistent organic pollutants generated during the methanol-based production of chlorinated methanes: A case study in China

The formation of unintentionally produced persistent organic pollutants (POPs) may occur during various chlorination processes. In this study, emissions of unintentionally produced POPs during the methanol-based production of chlorinated methanes were investigated. High concentrations of highly chlorinated compounds such as decachlorobiphenyl, octachloronaphthalene, octachlorostyrene, hexachlorobutadiene, hexachlorocyclopentadiene, hexachlorobenzene, and pentachlorobenzene were found in the carbon tetrachloride byproduct of the methanol-based production of chlorinated methanes. The total emission amounts of hexachlorocyclopentadiene, hexachlorobutadiene, polychlorinated benzenes, polychlorinated naphthalenes, octachlorostyrene, and polychlorinated biphenyls released during the production of chlorinated methanes in China in 2010 were estimated to be 10080, 7350, 5210, 427, 212, and 167kg, respectively. Moreover, polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) were formed unintentionally during chlorinated methanes production, the emission factor for PCDDs/DFs was 364μg toxic equivalency quotient (TEQ) t−1 product for residues, which should be added into the UNEP toolkit for updating. It was worth noting that a high overall toxic equivalency quotient from polychlorinated naphthalenes and PCDDs/DFs was generated from the chlorinated methanes production in China in 2010. The values reached 563 and 32.8g TEQ, respectively. The results of the study indicate that more research and improved management systems are needed to ensure that the methanol-based production of chlorinated methanes can be achieved safely.

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.

Gas Solubilities (CO2, O2, Ar, N2, H2, and He) in Liquid Chlorinated Methanes

Gas solubilities (CO2, O2, Ar, H2, N2, and He) in two liquid chlorinated methanes (dichloromethane and chloroform) from 283.15 K to 323.15 K were determined by measuring the decrease in pressure due to absorption. For all gases except for CO2, Henry’s law constant decreased with increasing temperature in both solvents. The order of solubility of the gases was CO2 > O2 > Ar > H2 > N2 > He in dichloromethane and CO2 > Ar > O2 > H2 > N2 > He in chloroform. On the basis of the measurements, semiempirical correlations for the solubility in that temperature range were then determined. The measured solubility data were theoretically analyzed using the method proposed by Wilhelm and Battino (J. Chem. Thermodyn. 1971, 3, 379; J. Chem. Thermodyn. 1971, 3, 743). to reveal the molecular basis of the solubility. The resulting theoretical Lennerd-Jones (LJ) potential parameters for both liquids are higher than those for methane but lower than those for carbon tetrachloride. The theoretical analysis also revealed that (...

Dechlorination of chlorinated methanes by Pd/Fe bimetallic nanoparticles

This paper examined the potential of using Pd/Fe bimetallic nanoparticles to dechlorinate chlorinated methanes including dichloromethane (DCM), chloroform (CF) and carbon tetrachloride (CT). Pd/Fe bimetallic nanoparticles were prepared by chemical precipitation method in liquid phase and characterized in terms of specific surface area (BET), size (TEM), morphology (SEM), and structural feature (XRD). With diameters on the order of 30–50 nm, the Pd/Fe bimetallic nanoparticles presented obvious activity, and were suited to efficient catalytic dechlorination of chlorinated methanes. The effects of some important reaction parameters, such as Pd loading (weight ratio of Pd to Fe), Pd/Fe addition (Pd/Fe bimetallic nanoparticles to solution ratio) and initial pH value, on dechlorination efficiency were sequentially studied. It was found that the maximum dechlorination efficiency was obtained for 0.2 wt% Pd loading. The dechlorination efficiency was observed to increase with increasing Pd/Fe addition. The optimal pH value for dechlorination reaction of chlorinated methanes was about 7. Kinetics of chlorinated methane dechlorination in the catalytic reductive system of Pd/Fe bimetallic particles were investigated. The dechlorination reaction complied with pseudo-first-order kinetics.

The interaction of CH3Cl, CH2Cl2, CHCl3, and CCl4 with ozone on the surface of ice under stratospheric conditions

The interaction of ozone with chlorinated methanes adsorbed on a thin ice film was studied over the temperature range 77–292 K. Ozone was shown to oxidize chlorinated methanes starting with 210 K to produce chlorine oxides of various compositions. The products formed in the oxidation of chlorinated methanes with ozone over the temperature range 77–292 K were analyzed by IR Fourier transform spectroscopy. Along with carbon dioxide and water, chlorine oxides in high oxidation states were predominantly formed.

Compound-specific carbon isotope analysis of volatile organic compounds in water using solid-phase microextraction

The compound-specific isotope analysis technique in conjunction with solid-phase microextraction using a carboxen–polydimethylsiloxane fiber was tested and implemented for isotopes analyses of organic compounds aiming for environmental application in contaminated groundwater. δ 13C values of several chlorinated methanes and ethenes, toluene and chlorobenzene were determined using a gas chromatograph coupled to an isotope ratio mass spectrometer through a combustion interface. Direct and headspace solid-phase microextraction (D-SPME, HS-SPME) methods were tested in order to determine the optimum conditions to obtain reproducible δ 13C values at very low concentration (μg/L range) and, to elucidate the carbon isotopic effects associated with the competitive extraction. For D-SPME, higher accuracy and precision of δ 13C results were obtained with no salted aqueous standards. Despite that the δ 13C of those compounds analyzed with both methods showed similar precision (<0.5‰) and accuracy, the highest sensitivity was reached with HS-SPME. Furthermore, the δ 13C values of cis-1,2-dichloroethylene, chorinated methanes and aromatic compounds obtained using HS-SPME showed measurable deviations with respect to the isotopic composition of pure phase compounds, however, these deviations are constant according to the analytical uncertainties, indicating that they are not affected by competitive extraction, and they could be corrected using standard correction technique based on internal calibrated standards.

Direct VUV photolysis of chlorinated methanes and their mixtures in an oxygen stream using an ozone producing low-pressure mercury vapour lamp

The gas-phase photooxidations of CCl(4), CHCl(3), CH(2)Cl(2) and their binary mixtures in an O(2) stream were studied in a flow reactor under various experimental conditions using a low-pressure mercury lamp as light source covered with a high-purity silica sleeve being used. The 184.9 nm VUV irradiation emitted is responsible for the Cl-C bond rupture in the chlorinated methanes and for the formation of O(3) from O(2). The rate of degradation of H-containing chlorinated methanes increased sharply on increase of their initial concentrations, most probably of a (*)Cl chain reaction, as indicated by the increase in the molar ratio of the amount of HCl formed to the amount of H-containing target substance decomposed. The experimental results suggested that the further transformations of the radicals and products formed play an important role as (*)Cl sources, causing a considerably higher rate of decomposition of the H-containing target substances. In a humidified O(2) stream, the (*)OH formed opens up another route for oxidation of the target substances. Thus, the rates of degradation of CH(2)Cl(2) and CHCl(3) increased on increase of the relative humidity, whereas the water vapour had no effect at all on the decomposition of CCl(4). At the same time, competition occurs between (*)Cl or (*)OH for reactions with the target substance. The photooxidation of binary mixtures was investigated too. The addition of CCl(4) or CHCl(3) to CH(2)Cl(2) strongly increased its degradation rate. The addition of CH(2)Cl(2) did not have a considerable effect on the rate of degradation of CHCl(3).

Fluxes and origin of halogenated organic trace gases from Momotombo volcano (Nicaragua)

In order to assess the contribution of quiescent degassing volcanoes to the global halo(hydro)carbon inventory, we have quantified volcanic fluxes of methyl halides (CH3Cl, CH3Br, and CH3I), ethyl halides (C2H5Cl, C2H5Br, and C2H5I), and higher chlorinated methanes (CH2Cl2, CHCl3, and CCl4). About every eight months over a 2‐year period (July 2001 to July 2003), gas samples were collected and analyzed from high‐temperature fumaroles (472°C–776°C) at the Nicaraguan subduction zone volcano Momotombo. Using a simultaneous record of trace and main compounds in fumarolic gases as well as SO2 fluxes of the plume, we were able to calculate halo(hydro)carbon fluxes for Momotombo and extrapolate our results to estimate halo(hydro)carbon fluxes for the whole Quaternary Nicaraguan volcanic arc and, in addition, for all volcanoes globally. The most abundant halohydrocarbon was CH3Cl with concentrations up to 19 ppmv. Further major halo(hydro)carbons were CH3Br, CH3I, CH2Cl2, CHCl3, CCl4, C2H5Cl, C2H5Br, C2H5I, and C2H3Cl with an average concentration of 0.20 to 720 ppbv. Estimated mean halo(hydro)carbon fluxes from Momotombo were in the range of 630–5000 g/yr for methyl halides, 49–260 g/yr for ethyl halides, and 2.4–24 g/yr for higher chlorinated methanes. When the results for Momotombo are scaled up to SO2 fluxes of the Nicaraguan volcanic transect, fluxes of 1.7 × 105 g/yr CH3Cl and 82 g/yr CCl4 are attained for Nicaragua. Scaled up to the estimated global SO2 flux, this translates to hypothetical global fluxes of 5.6 × 106 g/yr CH3Cl and 2.7 × 103 g/yr CCl4. These volcanic fluxes are negligible compared to global anthropogenic and natural emissions of about 3 × 1012 g/yr CH3Cl and 2 × 1010 g/yr CCl4.

MnOx/ZrO2 catalysts for the total oxidation of methane and chloromethane

Zirconia-supported manganese oxide catalysts prepared by wet impregnation and precipitation and calcined at 600 and 800°C, respectively, in air were characterized by powder X-ray diffraction (XRD), textural investigations, temperature programmed reduction (TPR), temperature programmed oxygen desorption (TPD-O2) and X-ray photoelectron spectroscopy (XPS) measurements. The catalytic activity was tested for the total oxidation of methane and chloromethane. The characterization studies showed clearly that both preparation methods result in samples with different supported MnOx phases. Compared with the wet impregnation method higher amounts of nonstoichiometrically disperse MnOx species were formed using precipitation method. The catalytic activity of the MnOx/ZrO2 catalysts for the total oxidation of methane is influenced by the dispersity of the catalytically active MnOx phase. In contrast to the methane oxidation the support zirconia itself indicates a high catalytic activity for the chloromethane conversion. Moreover, the total oxidation of chloromethane is connected with a catalyst deactivation and the formation of small amounts of higher chlorinated methanes as by-products at low reaction temperatures and chlorine. Nonstoichiometric surface basic chlorides (MnOyClz, ZrOyClz) are considered as the catalytically active phases for the total oxidation of chloromethane.

MnOx/ZrO2 catalysts for the total oxidation of methane and chloromethane

Zirconia-supported manganese oxide catalysts prepared by wet impregnation and precipitation and calcined at 600 and 800 °C, respectively, in air were characterized by powder X-ray diffraction (XRD), textural investigations, temperature programmed reduction (TPR), temperature programmed oxygen desorption (TPD-O 2 ) and X-ray photoelectron spectroscopy (XPS) measurements. The catalytic activity was tested for the total oxidation of methane and chloromethane. The characterization studies showed clearly that both preparation methods result in samples with different supported MnO x phases. Compared with the wet impregnation method higher amounts of nonstoichiometrically disperse MnO x species were formed using precipitation method. The catalytic activity of the MnO x /ZrO 2 catalysts for the total oxidation of methane is influenced by the dispersity of the catalytically active MnO x phase. In contrast to the methane oxidation the support zirconia itself indicates a high catalytic activity for the chloromethane conversion. Moreover, the total oxidation of chloromethane is connected with a catalyst deactivation and the formation of small amounts of higher chlorinated methanes as by-products at low reaction temperatures and chlorine. Nonstoichiometric surface basic chlorides (MnO y Cl z , ZrO y Cl z ) are considered as the catalytically active phases for the total oxidation of chloromethane.

침투성 반응벽체를 위한 고활성 영가금속 개발

The dechlorination of chlorinated methanes by iron powder and palladium coated iron (Pd/Fe) was studied in batch experiments. Iron powder dechlorinated carbon tetrachloride (CT) with a half-life of 4 days. Three chloromethane was found as major product and less chlorinated daughters. Mass balance found was to be about 93-99%. Pd/Fe showed very enhanced reactivity for CT in comparing with plain iron. The major dechlorination products of CT were also less chlorinated methanes with Pd/Fe. Pd/Fe also degrade the produced less chlorinated compounds. Sequential reactions were occurred on Pd/Fe. As the Pd/Fe content increased, the reaction rate was increased linearly.

One-Electron Reduction of Substituted Chlorinated Methanes As Determined from ab Initio Electronic Structure Theory

Substituted chloromethyl radicals and anions are potential intermediates in the reduction of substituted chlorinated methanes (CHxCl3-xL, with L- = F-, OH-, SH-, NO3-, HCO3- and x = 0−3). Thermochemical properties, (298.15 K), S°(298.15 K,1 bar), and ΔGS(298.15 K, 1 bar), were calculated by using ab initio electronic structure methods for the substituted chloromethyl radicals and anions: CHyCl2-yL• and CHyCl2-yL-, for y = 0−2. In addition, thermochemical properties were calculated for the aldehyde, ClHCO, and the gem-chlorohydrin anions, CCl3O-, CHCl2O-, and CH2ClO-. The thermochemical properties of these additional compounds were calculated because the nitrate-substituted compounds, CHyCl2-y(NO3)• and CHyCl2-y(NO3)-, were not stable, with all levels of ab initio theory leading to highly dissociated complexes. On the basis of these thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the substituted chlorinated methanes were predicted. In almost all of the cases, the thermodynamically most favorable pathway resulted in loss of Cl-. The exception was for the reduction of the nitrate-substituted chlorinated methanes CHxCl3-x(NO3). On reduction, these compounds were shown to readily decompose into a Cl- anion, NO2• gas, and an aldehyde. In addition, the results of this study suggest that a higher degree of chlorination corresponds to a more favorable reduction. Relative to the nonsubstituted chlorinated methanes, the thermodynamic results suggest the CHxCl3-xF, CHxCl3-xOH, and CHxCl3-x(HCO3) compounds are moderately more difficult to reduce, the CHxCl3-xSH compounds are moderately less difficult to reduce, and the CHxCl3-x(NO3) compounds are substantially more favorable to reduce. These results demonstrate that ab initio electronic structure methods can be used to calculate the reduction potentials of organic compounds to help identify the potentially important environmental degradation reactions.