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Compositions and methods for cleaning vapor compression systemsRelated Patent Categories: Refrigeration, Processes, Separating Or Preventing Formation Of UndesirablesCompositions and methods for cleaning vapor compression systems description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060179852, Compositions and methods for cleaning vapor compression systems. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF INVENTION [0001] The present invention relates to non-azeotrope, azeotrope, and azeotrope-like compositions. More specifically, this invention relates non-azeotrope, azeotrope, and azeotrope-like mixtures of hydrofluorocarbons and methods of using the same for removing contaminants from vapor compression systems. BACKGROUND OF THE INVENTION [0002] There exists a need to remove contaminants from vapor compression systems and their ancillary components when these systems are manufactured and serviced. As used herein, the term "contaminants" refers to processing fluids, lubricants, particulates, sludge, and/or other materials that are used in the manufacture of these systems or generated during their use. In general, these contaminants comprise compounds such as alkylbenzenes, mineral oils, esters, polyalkyleneglycols, polyvinylethers and other compounds that are made primarily of carbon, hydrogen and oxygen. [0003] Vapor compression systems are used in a wide variety of applications such as heating and refrigeration. By compressing and expanding a heat transfer agent, such as a refrigerant, these systems are capable of absorbing and releasing heat according to the needs of a particular application. Common components of a vapor compression system include: vapor or gas compressors; liquid-cooled pumps; heat transfer equipment such as gas coolers, intercoolers, aftercoolers, heat exchangers, and economizers; vapor condensers such as reciprocating piston compressors, rotating screw compressors, centrifugal compressors, and scroll expanders; control valves and pressure-drop throttling devices such as capillaries; refrigerant-mixture separating chambers; steam-mixing chambers; connecting piping; and the like. These components are typically fabricated from copper, brass, steel, and the like, and have conventional gasket materials. [0004] Many components of a vapor compression system require lubrication to reduce friction caused by their relative physical contact and movements. These lubricants, which are compounds primarily composed of carbon, hydrogen, and oxygen, operate by coating the surfaces of component that are subjected to friction. Lubricants of a vapor compression system are typically mixed with the heat transfer agent which carries and disperses the lubricant throughout the system. However, during certain processes or procedures, it is desirable to remove these lubricants from the component surfaces, particularly during service operations. Such a need arises, for example, during the retrofitting of a chlorofluorocarbon (CFC) or hydrochlorofluorocarbon (HCFC) refrigerant-based system to a hydrofluorocarbon (HFC)-based system. There is also a need to remove processing lubricants during the manufacturing of a system. Failure to remove these types of contaminants from the system may lead to decreased efficiency or even to the failure of one or more components. [0005] In addition, a vapor compression system may require cleaning after a catastrophic event, such as a compressor blowout. This type of event can create contaminants, such as acids, sludge, and particulates, within the sealed system. Failure to remove these types of contaminants from the system may also lead to decreased efficiency or failure of one or more components. [0006] The aforementioned contaminants can typically be removed by flushing the vapor compression system with a flushing agent in which the contaminants are soluble or miscible. Generally, such flushing agents contain one or more cleaning agents (for example, solvents for various types of hydrocarbons) and a propellant that carries the cleaning agent through the vapor compression system. In some cases, the cleaning agent may also serve as the propellant. Until recently, chlorofluorocarbons (CFC's) such as tricholormethane (R-11) and dichlorofluoroethane (R-141) were used as flushing agents for such systems. Although effective, CFC's are now considered environmentally unacceptable because of their contribution to the depletion of the stratospheric ozone layer. As the use of CFC's is reduced and ultimately phased out, new flushing agents are needed that not only perform well, but also pose no danger to the ozone layer. [0007] Many environmentally acceptable flushing compositions and methods have been proposed, but their use has met with limited success. For example, terpenes and low viscosity esters are known solvents of several types of lubricants commonly used in vapor compression systems, such as polyalkylene glycols, polyol esters, polyvinyl ethers, and the like. However, many of these solvents have a boiling point above 100.degree. C. and are difficult to remove from system components once they have been introduced during cleaning. Conventional techniques for removing these high boiling solvents prolongs the flushing operation which is economically disadvantageous. In addition, solvent remnants can have a deleterious effect on the performance of the vapor compression system. [0008] One method that has been proposed to deliver a flushing composition through a vapor compression system involves the use of compressed nitrogen as the propellant. However, this method of delivery is difficult and uncertain because the amount of pressure applied by the compressed nitrogen varies. The use of pressurized nitrogen as a propellant is also expensive. As an alternative to compressed nitrogen, compressed air may be used. However, the use of compressed air brings the disadvantage that it often contains an unacceptably high amount of moisture. Once introduced, this moisture can be difficult to remove from the vapor compression system. [0009] Therefore, Applicants have recognized a need for methods, systems, and compositions that are environmentally-acceptable and which are capable of effectively and efficiently removing contaminants from vapor compression systems. DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS [0010] Certain embodiments of the present invention meet the aforementioned needs, among others, by providing novel non-azeotrope, azeotrope, and azeotrope-like compositions comprising HFC-mixtures of 1,1,1,2-tetrafluoroethane (HFC-134a) and one or more of 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,3,3-pentafluorobutane (HFC-365), and 1,1,1,2,2,3,4,5,5,5-decafluoropentane (HFC-43-10). Applicants have surprisingly discovered that when an effective amount of HFC-134a is combined with HFC-365, an azeotrope is formed, and when combined with HFC-245fa, HFC 43-10, or some combination of HFC-245fa, HFC-365, and HFC 43-10, an azeotrope-like composition is formed. Economical and efficient methods for using such compositions to remove contaminants from vapor compression systems in an environmentally acceptable manner are also provided. [0011] The term "effective amount", as used herein, refers to the amount of HFC-134a, that when combined with one or more of the other aforementioned components, results in the formation of an azeotrope or azeotrope-like composition. [0012] The term "azeotrope-like", as used herein, refers to a combination of two or more compounds that behave substantially like a single compound in so far as the vapor in substantial equilibrium with the liquid has substantially the same concentration of components present in the liquid. The term "azeotrope-like" is intended to refer to both true azeotrope compositions and to compositions which are not strictly azeotropic, but in which the concentration of components in the vapor phase of the composition are so close to the concentration of components in the equilibrium liquid phase of the composition as to make separation of the components by ordinary distillation not practically possible. In essence, the admixture distills without substantially changing its composition. This is to be contrasted with non-azeotrope (or "zeotrope") compositions wherein the liquid composition changes to a substantial degree during boiling or evaporation. [0013] Azeotropes-like compositions according to the present invention include absolute azeotropes (compositions in which azeotropic conditions are satisfied over all values of temperature (up to the critical stage)) or limited azeotropes (compositions in which azeotropic conditions are satisfied only in a certain temperature range). Azeotropes-like compositions according to the present invention also include homoazeotropes, wherein the composition exists in a single liquid phase, or heteroazeotropes, wherein the composition exists as two or more liquid phases. Moreover, azeotrope-like compositions according to the present invention can be binary, ternary, quaternary, or quinary azeotropes depending on whether the composition is composed of 2, 3, 4, or 5 compounds, respectively. [0014] The compounds HFC-245fa, HFC-365, and HFC-43-10 can be used as flushing agents. However, when any of these compounds are used in a flushing apparatus such as a flushing gun, or the like, a propellant may also be required. Applicants have discovered that HFC-134a can serve as such a propellant. Moreover, as stated above, applicants have discovered that certain azeotrope-like compositions are formed by mixing an effective amount of HFC-134a with HFC-245fa, HFC-365, HFC 43-10, or some combination thereof. The azeotrope-like nature of these compositions is useful when the composition is utilized as a flushing agent, as a heat transfer agent, as a blowing agent for foams, or as an aerosols because it allows for uniform condensation and vaporization to occur at a single temperature. For example, in closed-loop systems such as flushing machines, an azeotrope-like flushing composition can be recycled because of its constant composition ratio in both liquid and vapor states. However, it is understood that azeotrope-like compositions according to the present invention may also be used in open-loop systems, such as flush guns, although non-azeotrope compositions are preferred. [0015] Applicants have discovered that the preferred azeotrope-like compositions of the present invention have a number of attributes or properties that render them particularly effective as flushing agents for cleaning vapor compression systems. Many contaminants, including lubricants, that are commonly found in vapor compression systems are adequately miscible or soluble in the preferred azeotrope-like compositions of the present invention. The term "adequately miscible", as used herein, refers to the azeotrope-like composition's ability to interact with a contaminant to form a solution, emulsion, suspension, or mixture under normal cleaning conditions in such a way that the contaminant can be effectively removed from the surface needing to be cleaned. Examples of such lubricants include, but are not limited to, mineral oils, alkylbenzenes, polyvinylethers, polyalkylene glycols, and polyol ester oils. [0016] One advantage of the preferred azeotrope-like compositions according to the present invention is that it is possible to substantially remove these compositions from the treated surface, preferably with relatively little effort or complication. For example, the preferred azeotrope-like compositions evaporate readily using conventional techniques known in the art such as flushing the system with an inert gas, pulling a vacuum on the system, and/or heating the system. Factors that affect evaporation include vapor pressure, the amount of heat that is applied, the heat conductivity of the liquid, the specific heat of the liquid, the latent heat of vaporization, surface tension, molecular weight, the rate at which the vapor is removed. The most appropriate method for removing the flushing agent for any given application is dependent upon the characteristics of the application involved and one skilled in the art could readily determine which method would be the most appropriate for each such application. [0017] One advantage of the present compositions is that each of HFC-245fa, HFC-134a, and HFC-43-10 are nonflammable as defined by ASTME681-94, and therefore azeotrope-like compositions made from mixtures of these materials are also non-flammable. Additionally, other azeotrope-like composition according to the present invention, such as certain azeotrope-like mixtures of HFC-365 and HFC134a, may also be non-flammable. Generally, non-flammable mixtures of the present invention are preferred because they are less dangerous and therefore easier to handle. How, it is understood that mixtures according to the present invention may also be flammable, and that in certain application, the flammability of these mixtures may be advantageous. [0018] The preferred azeotrope-like compositions of the present invention are generally compatible with the materials of vapor compression systems, including metals and sealants. [0019] The preferred azeotrope-like compositions of the present invention are environmentally acceptable and do not to contribute to the depletion of the earth's stratospheric ozone layer. [0020] Data is presented that demonstrates the existence of binary azeotrope-like compositions. Non-flammable, substantially constant boiling compositions can also be formed using ternary compositions that comprise HFC-134a and two of the other components. However, it should be understood that the present invention also provides compositions that may also include additional components so as to form new azeotrope-like compositions. Any such compositions are considered to be within the scope of the present invention provided that the compositions are essentially azeotrope-like and contain all of the essential components described herein. [0021] Preferred azeotrope-like compositions of the present invention include: suitable mixtures of HFC-245fa and HFC-134a having from about 1 to about 99 weight percent HFC-134a and from about 99 to about 1 weight percent HFC-245fa; suitable mixtures of HFC-134a and HFC-365 having from about 60 to about 99 weight percent HFC-134a and from about 1 to about 40 weight percent HFC-365; and suitable mixtures of HFC-134a and HFC-43-10 having from about 45 to about 99 weight percent HFC-134a and from about 1 to about 55 weight percent HFC43-10. Continue reading about Compositions and methods for cleaning vapor compression systems... 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