Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic oxygen compound
Reexamination Certificate
2002-08-29
2004-01-13
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic oxygen compound
C252S068000
Reexamination Certificate
active
06677284
ABSTRACT:
FIELD OF INVENTION
The present invention relates to fluid compositions for compression refrigeration systems such as heat pumps, refrigerating compressors, and air conditioning compressors. The refrigerant described for these systems is an ammonia based refrigerant. The lubricants are based on a hydrocarbon lubricant such as mineral oil, hydrogenated mineral oil or polyalphaolefin.
BACKGROUND OF INVENTION
Ammonia has long served as a refrigerant and continues to be an important refrigerant. Ammonia has been found to have no effect on the depletion of the ozone layer and, equally as important, ammonia does not contribute to the greenhouse effect. Ammonia has many attractive advantages such as being a highly efficient refrigerant at a relatively low cost. It also has a distinctive and easily detected odor and therefore any leaks can be quickly identified before large losses of refrigerant have occurred. The major disadvantages of using ammonia as a refrigerant are its toxicity and to a certain extent, its flammability above certain concentrations.
U.S. Pat. No. 5,595,678 to Glenn D. Short et al. teaches the use of polyalkylene glycol of the formula Z-[(CH
2
—CH(R
1
)—O)
n
—(CH
2
—CH(R
1
)—O—)
m
]
p
—H as the lubricant in various fluid compositions for refrigeration including ammonia, chlorofluorocarbon, hydrochlorofluorocarbon and hydrofluorocarbon refrigerants. This lubricant had benefits over mineral oil lubricants in its solubility in ammonia and benefits over more conventional polyether polyols that lacked the Z group described by Short. The more conventional polyethers suffered from low thermal stability without additives.
SUMMARY OF THE INVENTION
The use of a polyether with an alkyl aromatic fragment in a refrigeration fluid having a paraffinic lubricant within an ammonia environment controls elastomer seal swell and conditions the elastomeric seals to maintain their approximate volume and modulus. This prevents the hardening and/or shrinkage of the seals (elastomers). Paraffinic lubricants have many desirable properties in relation to mineral oil lubricants high in unsaturated hydrocarbon content for ammonia environments (including improved inertness to chemical reactions and thermal degradation). A shortcoming of paraffinic lubricants low in unsaturated hydrocarbon content is their adverse effect on seal volume and hardness. For the purposes of this specification, unsaturated hydrocarbon content will refer to aromatic components, cyclic olefins and acyclic olefins. Lubricants having high concentrations of aryl and alkaryl groups such as benzene and naphthalene have been used with ammonia environments due to their good compatibility with seals (retaining modulus and volume of seals after continuous use). The combination of paraffinic lubricants with a small amount of a polyether with an alkyl aromatic fragment offers better resistance to chemical and thermal degradation than mineral oils with high aromatic content.
The most significant drawback to converting from a lubricant high in aryl and alkaryl content to paraffinic lubricants low in aryl and alkaryl content for ammonia environments has been the non-quantifiable potential for seal failure. The problem in quantifying the potential is due to the wide variety of elastomers and elastomer blends used in the different seals in an ammonia refrigeration system. Some of these seals are more tolerant of hardening and shrinkage and don't leak after the substitution. Some seals fail immediately after substitution while others fail several months after the substitution of a different lubricant.
DETAILED DESCRIPTION OF INVENTION
It would be desirable to have an additive for ammonia based refrigeration fluids that could increase the seal swell and reduce seal hardening in the presence of a hydrocarbon lubricant. Seal shrinkage and seal hardening are often seen when converting an ammonia system from a mineral oil lubricant high in benzene and naphthalene (aryl and alkaryl) content to a mineral oil, hydrotreated mineral oil, or polyalphaolefin oil low in aryl and alkaryl content.
Ammonia refrigerants are well known commercially. It is a very energy efficient refrigerant and even though ammonia is hazardous when present in high concentrations, it is considered rather benign at low concentrations due to its occurrence in normal biological processes. It is also commercially available at reasonable prices and has little long term disposal or contamination problems. Ammonia refrigerant will generally refer to refrigerants that are at least 90 weight percent ammonia based on fluids that are active refrigerant and excluding contaminants and additives that have little or no refrigerant effect under the operating conditions. The refrigerant also does not include the lubricant although the working fluid would include both the refrigerant and the lubricant, to the extent both are present in any portion of the refrigeration system.
The lubricant refers to an oil that provides lubrication to the moving parts of the refrigeration system and may include additives that are dissolved in the oil such as wear reduction agents (antiwear additives), antioxidants, etc. Desirably the lubricant will be an aliphatic or cycloaliphatic oil with less than 10, more desirably less than 5 and preferably less than 1 weight percent of aryl and alkaryl molecules. Aryl and alkaryl molecules will be defined to be compounds having one or more aromatic rings, either as individual rings or as fused rings such as benzene, substituted benzenes, naphthalene, substituted naphthalenes, anthracene etc. Desirably these lubricants would have less than 10, more desirably less than 5 mole percent, and preferably less than 1 mole percent of compounds with unsaturated carbon to carbon double bonds, i.e. they would be relatively free of unsaturation They can specifically include mineral oils with less than the specified amounts of aryl and alkaryl compounds, hydrotreated mineral oils with less than the specified amounts of aryl and alkaryls, hydrocracked mineral oils, and polyalphaolefins. Desirably these aliphatic or cycloaliphatic lubricants would have viscosities at 40° C. of from about 5 or 20 to about 200 cSt and preferably from about 5 or 20 to about 100 or 150 cSt. These aliphatic oils have better thermal and chemical stability than oils having higher concentrations of unsaturation and/or aryl groups.
The term polyalphaolefins (PAO) is used to define the polymers derived from polymerizing alpha olefin monomers and these polymers are conventionally used as lubricants and lubricant additives. The polyalphaolefin has similar saturated chains with good thermal stability to the aliphatic mineral oils low in unsaturation. These polyolefins are polymers from olefins having unsaturation between their alpha and beta carbon atoms before the polymerization reaction. The polymerization and any subsequent treatments (hydrogenation) convert the unsaturated carbons to saturated carbons. The use of enough olefins of sufficient length and the polymerization process provides many alkyl branches of 2 to 20 carbon atoms that prevent crystallization of the polyolefins when used as lubricants. Polyalphaolefin is not used in this application to describe polymeric polyolefins that are solids at room temperature and are used as plastics.
Another class of substantially aliphatic oils is the hydrotreated or hydrocracked oils where a hydrogenation procedure has been used to eliminate the majority of unsaturation. In the case of hydrocracked oils, hydrogenation is used to reduce the number average molecular weight of the oils along with converting any unsaturation to saturated carbon to carbon bonds. These oils can be identified by the low unsaturation content. In the case of hydrotreated oils, the oil is treated by a hydrogenation process to remove aliphatic and optionally aromatic unsaturation. Hydrotreated and hydrocracked are two forms of hydrogenation.
The mineral oils high in benzene and naphthalene (aryl and alkaryl) content generally have poor thermal and chemical resistance and the
Li Hsinheng
Rajewski Thomas
Tolfa John C.
Esposito Michael F.
Howard Jacqueline V.
Laferty Samuel B.
The Lubrizol Corporation
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