Destruction Of Chlorofluorocarbons Research Articles

Impact of cosmic rays on stratospheric chlorine chemistry and ozone depletion.

Dissociation induced by cosmic rays of chlorofluorocarbons (CFC) and HCl on the surfaces of polar stratospheric clouds (PSC) has been suggested as playing a significant role in causing the ozone hole. However, observed stratospheric CFC distributions are inconsistent with a destruction of CFC on PSC surfaces and no significant correlation exists between ozone levels and cosmic-ray activity inside the polar regions. Model simulations indicate that this mechanism can have only a limited impact on chemical ozone loss and thus on the recovery of stratospheric ozone.

Combustion of methane-oxygen and methane-oxygen-CFC mixtures initiated by a high-current slipping surface discharge

Results are presented from experimental studies of the destruction of chlorofluorocarbon (CF2Cl2) molecules in a methane-oxygen (air) gas mixture whose combustion is initiated by a high-current slipping surface discharge. It is found that a three-component CH4+O2(air)+CF2Cl2 gas mixture (even with a considerable amount of the third component) demonstrates properties of explosive combustion involving chain reactions that are typical of two-component CH4+O2 mixtures. Experiments show the high degree of destruction (almost complete decomposition) of chlorofluorocarbons contained in the mixture during one combustion event. The combustion dynamics is studied. It is shown that the combustion initiated by a slipping surface discharge has a number of characteristic features that make it impossible to identify the combustion dynamics with the formation of a combustion or detonation wave. The features of the effects observed can be related to intense UV radiation produced by a pulsed high-current surface discharge.

Decomposition of Dichlorodifluoromethane by Adding Hydrogen in a Cold Plasma System

The destruction of chlorofluorocarbons (CFCs) has drawn great attention because of its well-known depletion of the ozone layer at the stratosphere. Application of RF plasma for the decomposition and conversion of dichlorodifluoromethane (CFC-12 or CCl2F2) is demonstrated. The decomposition efficiency (ηCFC-12) and the fraction of total carbon input converted into CH4 and C2H2 (FCH4+C2H2) in H2 and Ar mixtures have been investigated as a function of input power wattage, H2/CFC-12 ratio, operational pressure, and CFC-12 feeding concentration by using response surface methodology and model sensitivity analysis. The results showed that the ηCFC-12 is over 94% and the FCH4+C2H2 is over 80% under the condition of 100 W of input power wattage, 7.0 of H2/CFC-12 ratio, 15 Torr of operational pressure, and 7.6% of CFC-12 feeding concentration. In addition, the result of sensitivity analysis indicated that both the ηCFC-12 and the FCH4+C2H2 are more sensitive to CFC-12 feeding concentration and input power wattage. Experimental results showed that CFC-12 could be converted into CH4 and C2H2 up to 80% of conversion in a hydrogen-based RF plasma system.

The destruction of chlorofluorocarbons during ChemChar gasification

Due to the hazardous implications of releasing CFCs into the environment, studies on their thermal destruction are necessary. The use of incineration to destroy these compounds, while effective, have produced polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/PCDF) while releasing large amounts of corrosive HCl and HF. The ChemChar gasification process was evaluated for its ability to destroy two CFCs, l,l,2‐trichloro‐l,2,2‐trifluoroethane (CFC‐113) and dichlorodifluoromethane (CFC‐13). It was found that DRE values of > 99.9998 % are obtained for the destruction of l,l,2‐trichloro‐l,2,2‐trifluoroethane while not producing any PCDD/PCDF. Additionally, the chloride (as the potassium salt) and fluoride (as carbon‐fluoride) that result from the destruction of both CFCs are retained in the gasification system. This study illustrates that the ChemChar gasification process holds significant promise as an alternative to incineration for the safe and complete destruction of CFCs.

Destruction of Chlorofluorocarbons in a Cement Kiln

One of the thermal oxidation technologies recommended by the United Nations Environment Programme (UNEP) is destruction of chlorofluorocarbons (CFCs) in a cement kiln. The destruction of CFC12, CFC11 and CFC113 was studied in a cement kiln plant in actual commercial operation. CFCs were completely destroyed in the kiln under normal operating conditions. Hydrogen fluoride and hydrogen chloride generated by CFC decomposition were absorbed by cement materials. No formation of toxic ha-logenated organic compounds, such as polychlorinated dibenzo-p-dioxins or dibenzofurans (PCDDs/PCDFs), was observed in the CFC incineration.

Feasibility Study for the Potential Use of Biocatalytic Systems to Destroy Chlorofluorocarbons (CFCs)

ABSTRACTIn this review, we present the various microbial enzymatic systems involved in chlorocarbon biodegradation and evaluate their potential use as biocatalysts for the destruction of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons. Based on our present knowledge of the microbial metabolism of halogenated organic compounds, both anaerobic and aerobic processes could theoretically be used for the destruction of CFCs. The anaerobic processes result in the reductive dehalogenation of halogenated compounds. We describe the biological systems that were found to be involved in the reductive dehalogenation of halogenated hydrocarbons, present a number of hypotheses that have been proposed to explain this phenomenon, and discuss the potential use of these systems for the destruction of CFCs. The aerobic processes are based on the capacity of several large-spectrum activity mono- and dioxygenases that catalyze the initial oxidative step of aliphatic as well as aromatic compounds. In this case, the halogenated alkenes are converted to alkene epoxides that are quite unstable and break down to products that are readily metabolizable by other microorganisms. We discuss the potential use of this type of reaction for the destruction of CFCs and present approaches using genetically engineered microorganisms to more efficiently degrade these compounds.

Interconversion of chlorofluorocarbons in plasmas

Chlorofluorocarbons undergo interconversion during destruction in an argon arc plasma, so that, for example, in the exhaust gas from destruction of CCl2F2, CClF3 is found to be the major residual ozone depleting substance: as electron capture detectors are 104 times less sensitive for CClF3, compared with CCl2F2, although these gases have the same ozone depleting potential, analysis of exhaust from destruction of chlorofluorocarbons is therefore not a trivial matter of determining only the level of input chlorofluorocarbon remaining.

Occupational implications of the chlorofluorocarbon ban in Sweden

Limitations on the use of full halogenated chlorofluorocarbons (CFCs) may create occupational environmental problems. These are currently largely unknown, because the toxicology of most CFC substitutes is unknown. Therefore, toxicity testing of CFC substitutes is necessary, and this can best be done before their use commences. Destruction of CFC and materials containing CFC could generate new chemical compounds, especially during incineration. In addition, problems with higher noise and vibration levels may occur when CFC substitutes are employed, and we should keep in mind that occupational environment problems could also develop when new routines are introduced for transporting, storing, and handling new materials.

Incineration of CFC-12 by Burner Methods

Abstract A method of incinerating dichlorodifluoromethane (CFC-12) in the premised and diffusion flames has been developed. In the case of premixed CFC-12/methane/air flames, the burning velocity decreases with addition of CFC-12, but the amount of unreacted CFC-12 in Ihe burned gas is lower than the detection limit of the gas-chromatograph for molar ratios of CFC-12/methane smaller than around 0.2 when methane/air ratio is stoichiometric. The degree of destruction of CFC-12 decreases with increase of the CFC-12/methane ratio. No soot formation is observed in the range examined for the premixed flame experiments. On the other hand, in the case of CFC-12/methane diffusion flames in air, a large amount of soot formation is observed, although CFC-12 is also destructed almost completely in the range examined. These results indicate that the incineration melhod is useful and practical for the destruction of chloro-fluorocarbons.