Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing organic compound
Patent
1997-11-04
2000-05-30
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing organic compound
205459, 205460, 205462, C25B 300, C25B 306, C25B 308
Patent
active
060687568
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the reduction of chlorofluorocarbons and production of derivatives thereof in an electrolytic cell, and the electrolytic cell for carrying out said reduction.
The invention also relates to a process for removing the by-products formed within said electrolytic cell which are of no commercial interest or whose utilization is not required.
BACKGROUND OF THE INVENTION
The biological and environmental importance of the ozone layer in acting as a protective filter of UV solar radiation is known. According to James Andersen [I. N. Levine, Fisico-quimica, McGraw-Hill, Bogota, 1981], if the amount of stratospheric ozone were to be reduced by only 10% the consequences would be extremely serious for plants and animals.
There have been shown to exist chemical species which destroy the ozone catalytically, such as chlorine atoms, hydrogen atoms, hydroxyl radicals, nitrogen monoxide and bromine atoms. In the case of chlorine atoms, and in the presence of sufficient free oxygen atoms, the decomposition takes place according to the following reactions:
In the presence of few free oxygen atoms, as is the case of the stratosphere over the Antarctic continent, the mechanism of decomposition is as follows:
The chlorofluorocarbons, CFCs or freons, especially those with long lives such as trichlorofluoromethane (CFC 10 11), dichlorodifluoromethane (CFC 12) and 1,1,2-trichloro-1,2,2-trifluorethane (CFC 113), are the ones mainly responsible for destruction of the stratospheric ozone layer [M. J. Molins & F. S. Rowland, Nature, 249 (1974) 810].
When these chlorofluorocarbons reach the stratosphere, and despite their stability under ordinary conditions, they undergo photolysis due to the action of UV radiation, with the consequent release of chlorine atomic radicals, which act as catalysts in breakdown of the ozone into oxygen in accordance with the above reactions.
The atoms of chlorine are not destroyed following the reaction, but recover and accumulate with any subsequent supply, thereby increasing their potential for destruction of the stratospheric ozone.
Moreover, the CFCs also contribute significantly to the greenhouse effect which threatens serious climatic change within only a few decades.
In 1977 the US government prohibited the use of CFCs as aerosol propellants. In 1987 the Montreal Protocol revealed the intention of most world governments to prohibit the production, distribution and emission into the atmosphere of CFCs [The Montreal Protocol. A Briefing Book, Alliance for Responsible CFC Policy, Rosslyn, Va., 1987].
Pursuant to that objective, intense research work has been carried out into obtaining substitutes for these compounds, and this has led, for example, to the compound known as HFC 134a (CF.sub.3 --CH.sub.2 F), which is non-chlorinated.
Furthermore, equipment has been developed for the recovery and recycling of CFCs, with good results [Primera Red de Reciclaje de los CFC, Quimica 2000, 46 (1990) 16]. Preventing the emission of CFCs into the atmosphere nevertheless calls for their destruction, given that their warehousing and recycling only postpones the problem and residual emissions nearly always exist. In any case, no solution has yet been found for the definitive destruction of these hazardous pollutants.
From the chemical point of view, the CFCs are capable of forming hydrogen acids by the action of water on steel receptacles, with consequent corrosion of same [MATHESON, Gas Data Book, 6th edition, 1980, pp. 671-683].
Processes based on the destruction of CFCs, such as high-temperature incineration, molecular breakdown by plasma, thermocatalytic destruction, photochemical reactions and supercritical water, are -too expensive and/or present technical or environmental problems.
Furthermore, many attempts have been made to destroy CFCs by chemical oxidation, but these have not brought acceptable results.
The destruction of CFCs by reduction has not been so widely studied. Attempts at reduction by hydrogen have been made on metallic catalysts supported in oxid
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Casado Gimenez Juan
Julia Pere-Lluis Cabot
Gorgos Kathryn
Sociedad Espanola de Carburos Metalicos S.A.
Wong Edna
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