US3375197A

US3375197A - Refrigeration system lubrication

Info

Publication number: US3375197A
Application number: US386401A
Authority: US
Inventors: Hans O Spauschus; Dietrich F Huttenlocher
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1964-07-30
Filing date: 1964-07-30
Publication date: 1968-03-26
Anticipated expiration: 1985-03-26

Description

Uite

3,375,197 Patented Mar. 26, 1968 ice The present invention relates to the lubrication of refrigeration systems of the closed hermetically sealed compression type including dichlorodifiuorom'ethane as a refrigerant and a mineral oil as a lubricant and is particularly concerned with such a system including an additive for the lubricant which is effective to inhibit reactions between the refrigerant and the oil.

In hermetically sealed refrigeration systems, in which the oil and refrigerant are in direct heat exchange relationship with each other, the maximum operating temperature of the refrigeration compressor is often limited by the chemical instability of the oil-refrigerant mixture. A refrigerant commonly used in hermetically sealed systems is dichlorodifluoromethane (R12) while various petroleum oils are employed as lubricants. When tested independently, both the refrigerant and the oil are stable for the expected operating life of the equipment at temperatures well above those which are normally attained in actual operation. However, it has been known for some years that when mixed the refrigerant R12 and petroleum oils react at moderately elevated temperatures and that the reaction may result in the formation of carbon or coke deposits. It is also known that the rate of reaction is accelerated in the presence of iron or steel and that steel valve plates are particularly susceptible to coking at elevated temperatures. Since the refrigerant R12 is soluble in petroleum oils and since the solution comes in direct contact with various components of the compressor which are made from steel, it is highly desirable to provide means for preventing or reducing the R12-mineral oil reaction. Various attempts to improve the stability of the R12-oil working fluids at elevated temperatures have included the use of highly refined mineral oils free of activating impurities which might accelerate or initiate the R12-oil reaction, and the use of various additives of the type found to be useful in improving the stability or lubricity of lubricants in fields outside the refrigeration field. However, such additives have not been found to be particularly effective in inhibiting or preventing the R12- oil reaction. In fact, it has been found that some well known oil additives when added to a highly refined mineral oil lubricant may actually lower the critical reaction temperature at which the R12-oil reaction takes place.

The present invention is based on the discovery that a certain class of additives previously used as lubricity additives for lubricating oils in other lubricating applications such as automobile engines but which have not heretofore been considered or contemplated as possible solutions to the R12-oil reaction in refrigeration systems are,

in fact, particularly effective in providing a R12-oil work- 5 ing fluid for refrigerating systems having high temperatures.

More specifically, in accordance with the present invention there is incorporated into the oil employed to lubricate the refrigeration compressor, a refrigerant-oil reaction inhibiting amounts of a metallodithiophosphate compound of the formula in which M represents a divalent metal, preferably zinc, cadmium or nickel and R represents the same or different alkyl, aryl, alkaryl or aralkyl radicals containing at least 3 carbon atoms and preferably radicals containing 6 or more carbon atoms. In general, it has been found that the improved results described herein can be obtained when the additive concentration is from 0.01 to 3 percent, preferably 0.02 to 1 percent, based on the weight of the oil.

As stated hereinbefore, it has been previously proposed to add metallodithiophosphates to various lubricating compositions for the purpose of improving their heat stability oxidation resistance and lubricity properties and it has been thought that the thermal decomposition of such additives at elevated temperatures results in an in situ deposition of solid lubricating layers on the lubricated surfaces. Chemical studies of the effect of the zinc dithiophosphates on the R12-oil reaction have now indicated that such additives apparently react with iron and steel surfaces and in effect produce a coating thereon which inhibits the catalytic or accelerating effect of such surfaces on the R12-oil reaction.

In order to demonstrate the effectiveness of such metallodithiophosphates in inhibiting the R12-oil reaction, sealed tubes were prepared containing compressor valve steel, R12 refrigerant and mineral oil plus various amounts of various additives. The sealed tubes were heated for various times at 175 C. and the contents of the tubes were then analyzed for R12 decomposition which is known (H. O. Spauschus and G. C. Doderer, ASHRAE Journal, 3, No. 2. 65, 1961) to involve the formation of monochlorodifluoromethane (R22) in accordance with the following type of reaction:

fied R12, 1 ml. of the specified refrigeration lubricant oil, with or without additive, and 0.05 gram of valve steel.

Percent Additive and R Time, lemp., Percent Test No Oil in R-Zn P Days Color R12 Reacted Z-29 P 14 No Change 0.06 +1% TCP 14 175 Slight Change.-. 1.1

P 14 175 No Ohange 0. 003 14 175 do 0.002 14 175 .do .01

14 175 Black 1.2 14 175 No Change. .01 butyL 14 175 ..do 0.002 0.1% Propyl 14 175 ..do O. 002 4A1 N2 14 175 Yellow 0. 15

N2... 0.1% Octyl 14 175 No Change 0.008 N2. 0.3% Octyl 14 175 do 0.007 N2. 0.1% Substituted Pheny1 14 175 do 0. 004 N2 8 175 Dark Brown 1. 63 4-5 N2 0.1% Octyl 175 No Change. 0.011

In the above tests, oil P was a highly refined waterwhite mineral oil of the parafinic type with a viscosity of 100 Saybolt Universal seconds at 100 F. This oil is not suitableas a compressor lubricant without addition of extreme pressure agents such as tricresylphosphate (TCP). Oil N1 was a moderately refined mapthenic pale oil from Gulf Coast crudes, de-waxed for low temperature refrigeration use and with a viscosity of 200 Saybolt Universal seconds at 100 F. Oil N2 was a medium refined napthenic oil recovered from Gulf Coast crudes and with a viscosity of 150 Saybolt Universal seconds at 100 F. The substituted phenyl dithiophosphate was a proprietary Zinc dithiophosphate containing hydrocarbon substituted phenyl groups.

From a review of these test results, it will be seen that the R12-oil reaction is effectively inhibited by the presence of relatively small additions of the metal dithiophosphates. Somewhat larger amounts can, of course, also be used to effectively prevent or inhibit the formation of coke deposits on various portions of the compressor and particularly the valve and valve areas.

Accelerated life tests on refrigerating systems containing various Zinc dithiophosphate additives have indicated that the additive is consumed in a fairly short time under accelerated life test conditions. For example, an oil sample removed after thirty days of testing at 120 C. motor winding temperature contained only about of the initial additive concentration, but even at this low residual additive level reaction with the R12-oil was inhibited. In units operated at 140160 C., zinc analysis has indicated that no additive remained after thirty days although the R12-oil reaction was still at a substantially lower level than when no additive was present.,A1th0ugh the unit tests have indicated that the additive is consumed at elevated temperatures, results have been shown that in all cases a permanent improvement has been effected insofar as coke formation is concerned. In other words, it appears that the additive, while consumed, reacts with the steel surfaces thereby altering their chemical activity.

In systems in which the compressor may operate at relatively high temperatures, it has been found that best results are obtained when the R group contains at least 6 carbon atoms as for example when R is an aryl or a higher alkyl radical. Accelerated life tests on compressors employing different additives have indicated that dithiophosphates containing lower alkyl radicals, as for example the isobutyl and propyl radicals, may produce varnish-like deposit on the valves and valve plates resulting from the thermal decomposition of the metallo dithiophosphate additive. However, additives in which the R group contains at least 6 carbon atoms and particularly higher alkyl radicals, such as represented by zinc dioctyldithiophosphate, do not produce any varnish-like deposits on the valve and valve plate surfaces. For example, after six months operation in a compressor operat-. ing under load conditions producing a temperature of 180- 200 F. in the discharge line, one inch from the case, an oil including .1% zinc dioctyldithiophosphate as an additive exhibited no deposits on the valves and no change in its operating temperatures. In addition, the used lubricant was found to contain about /3 of the initial additive and a sample of the lubricant subjected to the same sealed tube test employed in obtaining the results set forth in above table after heating for 14 days at 175 C. indicated only a 0.001% reaction of the R12.

Extensive high temperature coking tests on a number of different hermetic compressor have shown that zinc dithiophosphate additives will extend the compressor life at least three fold as compared with oils not containing such additives.

While the invention has been described with particularity in connection with certain specific metal dithiophosphates, it is obvious that it is not limited thereto and that various modifications can be made without departing from the spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In the method of operating a refrigeration system of the hermetically sealed, compression type employing dichlorodifluorornethane as a refrigerant and a mineral oil lubricant in contact with said refrigerant, the improvement which comprises lubricating said refrigeration system with a mineral oil lubricant having dissolved therein from 0.01 to 3 percent by weight of a compound of the formula in which M represents a metal selected from the group consisting of zinc, cadmium and nickel and R represents the same or different hydrocarbon radicals selected from the group consisting of alkyl, aryl, alkaryl and aralkyl radicals containing at least 3 carbon atoms, said compound being effective to inhibit reaction between said oil and said refrigerant in the presence of steel.

2. In the method of operating a refrigeration system of the hermetically sealed, compression type employing dichlorodifluoromethane as the refrigerant and a mineral oil lubricant in contact with said refrigerant, the improvement which comprises lubricating said refrigeration system with a mineral oil lubricant having dissolved therein from 0.01 to 3 percent by weight of a compound of the formula in which M represent a metal selected from the group consisting of zinc, cadmium and nickel and R represents a hydrocarbon radical selected from the group consisting of alkyl, aryl, alkaryl and aralkyl radicals containing at least 6 carbon atoms, said compound being effective to inhibit reaction between said oil and said refrigerant in the presence of steel.

3. In the operation of a refrigeration system of the hermetically sealed, compression type employing dichlorodifluoromethane as the refrigerant, and a mineral oil lubricant in contact with said refrigerant the improvement which comprises lubricating said refrigeration system with a mineral oil lubricant having dissolved therein from 0.01 to 3 percent by weight of a compound of the formula in which R represents an alkyl radical containing at least 3 carbon atoms, said compound being effective to inhibit reaction between said oil and said refrigerant in the presence of steel.

4. The operation of a refrigeration system as defined in claim 3 in which R is an octyl radical.

5. The operation of a refrigeration system as defined in claim 2 in which R is an alkaryl radical.

References Cited UNITED STATES PATENTS 2,734,865 2/1956 Peeso et al. 252400 2,824,061 2/1958 Davidson et al. 62114 3,037,932 6/1962 Barker 252l 5 X LEON D. ROSDOL, Primary Examiner.

J. D. WELSH, Assistant Examiner.

Claims

1. IN THE METHOD OF OPERATING A REFRIGERATION SYSTEM OF THE HERMETICALLY SEALED, COMPRESSION TYPE EMPLOYING DICHLORODIFLUOROMETHANE AS A REFRIGERANT AND A MINERAL OIL LUBRICANT IN CONTACT WITH SAID REFRIGERANT, THE IMPROVEMENT WHICH COMPRISES LUBRICATING SAID REFRIGERATION SYSTEM WITH A MINERAL OIL LUBRICANT HAVING DISSOLVED THEREIN FROM 0.01 TO 3 PERCENT BY WEIGHT OF A COMPOUND OF THE FORMULA