Following the end of the Second World War, chlorofluorocarbons (organic compounds that include carbon, chlorine and fluorine, hereinafter “CFCs”, as well as those chlorofluorocarbon compounds having at least one hydrogen present, hereinafter “HCFCs”) came into popular use as refrigerators replaced the traditional ice boxes. Refrigerants are capable of removing heat by cooling a space below the ambient temperature, and are typically used in a heat cycle, wherein the refrigerant undergoes a reversible phase change from a gas to a liquid, during which time heat is removed from a space. Thus, in addition to use in refrigerators, refrigerants also find uses in residential and business air conditioners, as well as in automobile air conditioning systems. Refrigerants have other uses as well, including use as foam blowing agents and in the pharmaceutical industry for asthma inhalers
Studies, however, have linked CFCs to atmospheric ozone depletion. As a result, the Montreal Protocol (initially entered into force in 1989, and subsequently revised multiple times) mandated that CFCs no longer be used as refrigerants and their use was phased out during the period of 1987 to 1997. The use of chlorofluorocarbons as refrigerants has gradually been replaced by the use of fluorocarbons, including perfluorocarbons (FCs), hydrofluorocarbons (HFCs), and hydrochlorofluorocarbons (HCFCs). While manufacturing of chlorofluorocarbons (CFCs) has essentially ceased in view of the Montreal Protocol, existing supplies continue to have limited commercial value, for instance as inhalers in the health field. Because CFCs, HCFCs, FCs and HFCs are often present as azeotropic mixtures, each of the components of the mixture may have value, particularly if CFCs can be effectively separated from the other components. This would allow for compounds to be recycled, or for compounds to be more effectively destroyed or converted for disposal.
The fluorocarbon refrigerants currently in use (i.e., HCFCs, FCs and HFCs) exhibit chemical stability, non-flammability, chemical inertness, are safe to health, and do not deplete ozone from the atmosphere. The refrigerants have physical characteristics such as low melting points and boiling points appropriate for refrigerant use, low vapor heat capacity, low viscosity, high thermal conductivity, and good oil solubility.
Chlorofluorocarbons and fluorocarbons are conventionally referred to by a numbering convention wherein the rightmost digit denotes the number of fluorine atoms; the “tens” digit denotes one more than the number of hydrogen atoms; the “hundreds” digit (if present) denotes the number of carbon atoms less one (thus there may be no digit for this when the compound is a methyl halide). Further, although most of the refrigerant compounds are alkanes, if the compound contains any links of unsaturation, the number of double bonds can be indicated in numbering conversion as the “thousands” digit. There may also be a suffix, “a”, “b”, “c”, to indicate isomers. Thus, HFC-134a has 4 fluorine atoms, 2 hydrogen atoms and 2 carbon atoms. The “a” suffix indicate that the F atoms are not equally distributed, but rather the compound is 1,1,1,2-tetrafluoroethane. In contrast, in referring to HFC-134, the fluorine atoms are equally distributed throughout the molecule and the compound is 1,1,2,2-tetrafluoroethane. The alkane based compounds are generally referred to as CFCs, HCFCs, FCs, and HFCs.
Because chlorofluorocarbons often form azeotropic mixtures with fluorocarbons, effective and efficient separation is frequently difficult. Therefore, in view of the current restrictions associated with chlorofluorocarbons, it has become both necessary and desirable to develop new methods to effectively and efficiently separate and purify the individual components from an azeotropic mixture. Various techniques have been developed to facilitate the separation of azeotropic mixtures, including the use of various zeolites and molecular sieves, for instance, as is described in U.S. Pat. Nos. 4,906,796; 5,087,778; 5,160,499; 5,260,496; 5,288,930; and 5,585,529. Each of the prior art techniques, however, have not been entirely satisfactory because the components of these azeotropic mixtures frequently have similar boiling points, thereby making it difficult to obtain highly pure components upon separation. In addition, the prior art zeolite/molecular sieve processes frequently require that the zeolite material or molecular sieves be changed and/or regenerated, thus requiring that the separation process be stopped for a period of time. In an exemplary prior art procedure employing zeolites and/or molecular sieves, as described in U.S. Pat. No. 5,497,627, a single stage azeotropic separation of a contaminated chlorofluorocarbon (i.e., CFC-12 contaminated with HCFC-22 and CFC-115) is processed using water as a solvent. It appears very little refrigerant is extracted and water remains with both extractants.
The process and apparatus described herein provide an apparatus that effectively and efficiently separates components for ideal mixtures (i.e., simple binary mixtures) and azeotropic mixtures (e.g., mixtures that include one or more CFC compound, in addition to at least one compounds from the group of HCFCs, HFCs, and FCs).