US 2824061 A
Description (OCR text may contain errors)
United States Patent METHOD OF OPERATING A REFRIGERATION SYSTEM USlNG A CHLORINE CONTAINING 'HALO-ALKANE AS A REFRIGERANT James R. Davidson, Iselin, and William Elena, Union,
N. J assignors to Esso Research and Engineering Company, a corporation of Delaware NoDrawing. ApplicationDecember 1, 1953 Serial No. 395,600
6 Claims. (Cl. 252-325) The present invention relates to improved oil compositions for use in compression-type mechanical refrigeration systems. It particularly relates to such compositions having improved stability and compatability with halo-alkane refrigerants used in enclosed compressor-type refrigeration systems to lubricate the moving parts thereof.
It has now been found and is the subject of this invention that lubricating oils used in. conjunction with halo-alkane refrigerants in refrigeration systems are improved in stability and life by the addition of relatively small amounts of oil-soluble alkali metal salts of phos phoric acid esters.
Self-contained compressor refrigeration systems such as mechanical refrigerators, air conditioning units, etc. include a compression-expansion system in which a gaseous refrigerant is compressed and reduced to a liquid by cooling at a relatively high temperature level. The liquid is then passed through an expansion valve where its pressure is reduced and the liquid evaporates to absorb its latent heat and the heat from the medium to be cooled. Alternate cycles of compression and expansion are carried out. The system is enclosed and must therefore contain a lubricating oil to lubricate moving parts of the system, such as the compressor, that are subject to frictional contact. The oil and refrigerant form a mutually soluble composition in the high temperature Zone, the refrigerant being the predominant component.
The lubricating oil to be used in such systems should have a number of special characteristics that enable it to lubricate effectively for a period of many years without being replaced. It should have a low pour point so that it will flow freely at extremely low temperatures. It must have a low fioc point, i. e., a low temperature at which flocculent precipitation occurs in a mixture of the lubricant and refrigerant. It should also be stable against sludge formation or the formation of other undesirable bodies that will lead to clogging of orifices and deposition of solids in the system.
Refined mineral oil base stocks, certain synthetic oils such as olefin polymers, etc., are useful lubricants for such systems because of their excellent oiliness characteristics, low pour points, and low fioc points, particularly when suitable additives are employed. However, such base stocks tend to deteriorate in the presence of conventional halo-alkane refrigerants, particularly those containing chlorine. It appears that the oil and refrigerant undergo a reaction, aided by the catalytic action of iron or other metals in the system, to form hydrogen chloride. The acid in turn evidently degrades the oil to form sludge. It has been noted for example that the compressor discharge valve, which is the highest temperature point in the compression system, becomes coated With a hard carbonaceous material which can eventually cause breakage of the valve. The used Oil also eventually becomes discolored.
The reasons for these difiiculties are: not entirely understood. However, the mechanisms are quite different from those encountered in conventional lubrication wherein the lubricating oil is in contact with airfmoisture and metal which results in oxidation of the oil and corrosion of metal parts. This difference is emphasized by the fact that conventional motor oil 'antioxidant and related additives, such as for example metal naphthenates, phenols, amines, various metal deactivators, etc., do not prevent degradation of refrigeration oils. Indeed, conventional additives frequently aggravate this difficulty in refrigeration systems. As an example, aromatic amines, which are known lubricant antioxidant additives, 'are quite effective for reducing lioc points of refrigerating oils when used in small con centrations. However, these same additives promote color degradation and sludge formation in refrigerating oils when used in the relatively large amounts taught to be effective for retarding oxidation effects in conventional motor oils and the like. It is seen that an additive designed to improve the stability of refrigerator oils must have special qualifications to meet unique problems. Furthermore, refrigeration oil additives should be soluble in the oil base stock over a wide range of temperature conditions and should not impair the floc point of the oil.
in accordance with the present invention, it has been found that alkali metal salts of phosphoric acid hydrocarbon esters are effective additives for refrigerating oils used in conjunction with halo-alkane refrigerants. Such compositions have greatly enhanced stability against deterioration and sludge formation, low pour points and other desirable characteristics required of such oils. These additives containing suitable oil-solubilizinghydrocarbon substituent groups are soluble over a wide range of temperatures.
Although various metal ester phosphates have been used heretofore as detergent additives, corrosion inhibitors, etc., for conventional motor oils and the like, they have been found to be inducers of thermal decomposition and carbon formation for such uses. It is therefore surprising that m the alkali metal salts reduce discoloration and sludge formation in refrigeration'systems. It is not desired to be bound by theoretical considera tions, but it is believed in the instant case that these salts may act as buffers in ameliorating the harmful effects of acidic bodies that are formed and cause further degradation of the oil and/or refrigerant. Regardless of the mechanism involved, the presence of haloalkanes in such systems introduces lubrication problems not encountered in other conventional systems not containing such halo-alkanes in large concentrations, and the addition agents of the present invention minimize such difficulties.
The present invention will be clearly illustrated by reference to the following examples:
Example I .---Preparation of alkali metal octadecenyl phosphates This product was prepared by heating together 80.4 g. (0.3 mol) of Ocenol (commercial oleyl alcoholC H OI-I) and 14.2 g. (0.1 mol) of P 0 for about one hour at C. The reaction mixture was cooled, and then 12 g. (0.3 mol) of NaOH and 100 g. of water were added with stirring. 100 ml. of ethyl alcohol were added to the resulting mixture, to precipitate an insoluble material. The precipitate was removed by filtration. The filtrate was diluted with water and extracted with ether. The ether extract was dried over sodium sulfate, and the ether was removed on a steam bath.
The residue was finally dried in a vacuum oven at 100 C,
The dry product consisted of an amber-colored viscous, soft resin, having an acid neutralization number of about 23 mg. KOH per gram. It was substantially a mixture of equal portions of mono-sodium di(octadecenyl) phosphate and di-sodium octadecenyl phosphate. A small amount of acid derivatives was also present.
Example II.Testing refrigeration compositions Anacid-treated Coastal oil distillate having an S. U. S. viscosity at 210 F. of about 55 had added to it 2% by weight of the product of Example I. A small amount of undissolved material was settled out of the blend. This blend and a portion of the oil base stock per se were submitted to various tests and inspections, the
1 In presence of iron wire as catalyst.
The oil blend containing the sodium alkenyl phosphates had excellent pour characteristics and was much more stable than the uninhibited oil.
Each of the above oils was subjected to a sealed-tube stability test carried out as follows: A mixture of 1 part Freon-l2 (dichlorodifluoromethane) and 2 parts oil was introduced into a heavy glass tube containing iron wire catalyst, and the tube was sealed. The sealed tube was then stored at a temperature of about 350 F. The tube was periodically inspected in front of a standard light to determine the extent of discoloration and sludge formation. The oil life is designated as the number of days under these storage conditions that the oil will transmit light. This accelerated test has been found to correlate well with full-scale operations in compression refrigeration systems.
It was found that the mixture of Freon-l2 and oil base stock per se discolored rapidly, formed sludge in the tube and on the wire and would not transmit light after 27 days storage. The mixture containing the inhibitor of the present invention was still clear and transmitted light after 95 days storage at which time the test was discontinued. There was no evidence of sludge formation and no visible color degradation of the oil after this time.
The preferred alkali metal salts of phosphoric acid esters added to the oils of the present invention may be illustrated by the formula wherein the X groups are selected from the class con sisting of hydrogen, alkali metals, such as sodium, potas sium and lithium, preferably sodium, and hydrocarbon radicals, and wherein at least one X group is an alkali metal and at least one X group is a hydrocarbon radical; preferably all of the X groups are metal and hydrocarbon.
Since the alkali metal phosphates are relatively dithcultly soluble in most lubricating oils, the hydrocarbon groups are sufficiently high in molecular weight to inrpart the desired degree of oil solubility to the compound at the extremely low temperature prevailing in certain portions of the refrigeration systems. Therefore, the
,4 metal phosphate esters desirably contain a total of at least carbon atoms, preferably above carbon atoms, in the hydrocarbon groups.
Suitable hydrocarbon groups include alkyl, alkenyl, cycloalkyl, alkaryl, aralkyl and related groups, the aliphatic members being preferred. Individual groups may have in the range of about 6 to 30, preferably 12 to 24, carbon atoms. The phosphates are readily prepared by conventional procedures, such as by reacting an ester acid phosphate with an alkali metal hydroxide, by reacting an alcohol or phenol with P 0 and sodium hydroxide, etc.
Suitable specific metal salts that may be used include sodium dodecyl phosphate, sodium decyl acid phosphate,
dipotassium oleyl phosphate, sodium di(buty1cyclohexyl) phosphate, disodium cetyl phosphate, sodium di(cetylphenyl) phosphate, sodium naphthenyl phosphate, potassium di(C -C wax) phosphate, disodium olylcyclohexyl phosphate, their mixtures, and the like.
The amount of the phosphate added to the oil base stock to form the refrigerating oil will depend on such considerations as potency and solubility of the additive, and the relative instability of the refrigerant and oil base stock. Amounts in the range of about 0.05 to 5.0% by weight based on the oil, will generally suffice, with preferred amounts being about 0.1 to 2% by weight. The alkali metal salts are generally difficult to dissolve in mineral oils in amounts above about 1 to 2% unless large hydrocarbon solubilizing groups are present. Thus a total of about to carbon atoms may be needed in the phosphate hydrocarbon radicals if relatively large amounts of the additive are to be used.
The oil base stocks useful for refrigerating oils are preferably derived from various paraflinic, naphthenic and mixed-base crude mineral oils, but naphthenic-type distillates, such as Coastals, are preferred. The base stock may be refined by conventional procedures such as by dewaxing, solvent extraction, acid treating, clay contacting, etc. Other suitable lubricating oils include synthetic oils such as polymerized olefins, e. g., polyisobutylenes, and the like. Essentially hydrocarbon oils are preferred. Oils having S. U. S. viscosities at 210 F. in the range of about 30 to 160, preferably below 100, and pour points below -l5 F., especially below 25 F. are preferred.
1 Floc points of below 25 F. are also preferred.
In addition to the additives of the present invention, other characteristic improving additives may be added to the oil base. These include pour point depressors, such as wax-naphthalene condensation products, maleate ester copolymers, fumarate ester copolymers, etc.; floc point reducers such as phenol amine compounds, etc.
Suitable refrigerants used in the compression systems in conjunction with the above lubricating oils include the halogenated substituted alkanes, particularly of the lower alkanes such as methane. Specific types include chloroalkanes, chloro-fiuoro-alkanes and the like. Specific refrigerants include dichlorodifiuoromethane, methyl chloride, methylene chloride monofluorotrichloromethane, dichloromonofluoromethane, etc. The present invention applies particularly to the chlorine-containing halo-alkanes because these materials are generally less stable than those containing only fluorine, such as fluoroform.
The refrigerant-oil composition of the present invention will contain a major portion of the refrigerant and a minor proportion, usually below about 10 weight percent, of the inhibited oil. In actual operation, once the desired amount of refrigerant and inhibited oil have been sealed into the unit, the solution of compressed liquid refrigerant and usually no more than 27% of oil, based on the refrigerant, will be carried through the compressor discharge valve (the high temperature point) into the condensing, expansion and evaporation zones. The evaporation zone will usually contain an oil separator that returns the oil to the compression zone by a different route to that followed by the vaporized refrigerant. Methods of operating such refrigeration systems are well known to the art and will not be described in detail herein.
What is claimed is:
1. In the method of operating a sealed mechanical compression-expansion-type refrigeration system using a chlofine-containing halo-alkane as a refrigerant and an essentially hydrocarbon lubricating oil for lubricating the internal moving parts thereof subject to friction, and wherein said refrigerant and oil come into contact with one another resulting in the formation of sludge and other degradation products, the improvement in accordance with which the formation of sludge and other degradation products is reduced which comprises lubricating said refrigeration system with a lubricating oil composition comprising a mineral lubricating oil base stock having an S. U. S. viscosity at 210 F. in the range of about 30 to 160 and a pour point below about 25 F. containing dissolved therein in the range of about 0.05 to 5% by weight of an alkali metal salt of a phosphoric acid ester containing at least 10 carbon atoms.
2. A method as in claim 1 wherein said alkali metal is sodium.
3. A method as in claim 2 wherein said salt is a sodium aliphatic ester phosphate.
4. A method as in claim 3 wherein the aliphatic groups in said phosphate are alkenyl radicals having in the range of l2-24 carbon atoms.
5. A method as in claim 4 wherein said refrigerant is dichlorodifiuoromethane.
6. A method as in claim 5 wherein said lubricating oil in said system is used in an amount below about 10 weight based on the amount of refrigerant therein.
The Refrigerating Data Book, 5th ed. 1953, Amer. Society of Refrig. Eng., pages 189-196.