REFRIGERATION HEAT PUMP, AND HEAT ENGINE APPARATUS
United States Patent 3733850
An apparatus capable of being employed as a refrigeration, heat pump, or heat engine containing a halogenated alkane working fluid and a lubricant combination of alkylbenzenes containing from 10 to 25 carbon atoms in the alkyl groups and from about 2 to about 50 percent by weight of polyisobutylene having a viscosity in the range of about 3,000 to about 1,000,000 SUS at 100°F.
Application Number:
05/213174
Publication Date:
05/22/1973
Filing Date:
12/28/1971
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Export Citation:
Assignee:
Chevron Research Company (San Francisco, CA)
Primary Class:
Other Classes:
585/455, 62/502, 585/2, 585/10
International Classes:
C10M111/04; C10M171/00; F25B31/00; C10M111/00; F25B43/02
Field of Search:
62/468,469,502 252/68,59
Primary Examiner:
Perlin, Meyer
Parent Case Data:
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of copending application Ser. No. 3,523, filed Jan. 16, 1970 now U.S. Pat. No. 3,642,634.
Claims:
I claim
1. An apparatus of the type including compressor, condenser, evaporator, and in contact with the moving parts of said apparatus, a working fluid comprising halogenated alkanes and a lubricating oil consisting essentially of alkylbenzene having one or more side chains of one to 25 carbon atoms and containing a total of from 10 to 25 carbon atoms in the alkyl groups and from about 2 to about 50 percent by weight of polyisobutylene having a viscosity in the range of from about 3,000 to about 1,000,000 SUS at 100°F.
2. The apparatus in accordance with claim 1 which is a refrigeration apparatus.
3. The apparatus in accordance with claim 1 which is a heat engine apparatus.
1. An apparatus of the type including compressor, condenser, evaporator, and in contact with the moving parts of said apparatus, a working fluid comprising halogenated alkanes and a lubricating oil consisting essentially of alkylbenzene having one or more side chains of one to 25 carbon atoms and containing a total of from 10 to 25 carbon atoms in the alkyl groups and from about 2 to about 50 percent by weight of polyisobutylene having a viscosity in the range of from about 3,000 to about 1,000,000 SUS at 100°F.
2. The apparatus in accordance with claim 1 which is a refrigeration apparatus.
3. The apparatus in accordance with claim 1 which is a heat engine apparatus.
Description:
BACKGROUND OF THE INVENTION
This invention relates to apparatuses of the refrigeration, heat pump or heat engine type including compressor, condenser, evaporator and, in contact with the moving parts of said apparatus, a working fluid comprising halogenated alkanes and a lubricant combination of alkylbenzenes and polyisobutylene. For those knowledgeable in the art, it is well known that these apparatuses are variations in the operation of the same cyclic system.
When applied to refrigeration or heat pumps, work is added to the system through a motor-driven compressor which compresses the working fluid before it is condensed. Heat from the system at this point may be employed for heating purposes. The system is then operating as a heat pump. The condensed working fluid is partly or completely vaporized in the evaporator. The head added to the system at this point or extracted from the surroundings causes cooling (refrigeration of the heat source). In heat pumps the heat source is usually outside air, whereas in refrigeration systems it is normally a relatively confined space to be cooled.
When the system is operated as a heat engine, useful work is delivered by the system. Heat is added to the evaporator from, for instance, hot gases obtained from combustion of a suitable fuel. This results in evaporation and expansion of the working fluid which drives a compressor. The working fluid is then condensed to complete the cycle. The useful work can, in turn, be used in driving other devices. This type of heat engine is of particular importance because of its possible adaptation to anti-pollution automobile engines employing external combustion.
The same working fluids and the same lubricants are used in all three types of the above-described apparatus.
Heat engine, heat pump, and refrigeration lubricants for use in hermetic unit designs are usually sealed in the motor-compressor unit housing and are not replaceable. They are thus required to perform under relatively severe conditions of temperature change for the life of the unit, which is generally a period of several years of intermittent daily service. The lubricant is in contact with the working fluid or refrigerant and in addition to lubricating the compressor, it serves as a seal between the low-pressure and high-pressure sides of the system. As the working fluid or refrigerant flows from the compressor through the condenser and evaporator and back to the intake side of the compressor, it carries some of the lubricant with it. Thus, while the lubricant is required only at the compressor, it circulates throughout the system. In addition, the lubricant for the centrifugal compressor unit design, although replaceable, must be stable toward oxidation which commonly occurs due to air leakage around the drive shaft in order to avoid need for frequent oil changes.
The service of lubricating a heat engine, heat pump or refrigerator compressor and motor subjects the lubricant or oil to conditions not encountered in other types of service. These special unique conditions include: (1) rapid swings in temperature from about -100° to +400°F; (2) contact with working fluids or refrigerants, generally fluorinated, chlorinated methanes of the Freon types; (3) ability to serve as a pressure seal in the compressor; and (4) contact with electric motor windings. Because of these unusual conditions important properties of the oil are viscosity, viscosity index, mutual solubility with working fluids or refrigerants, pour point, volatility, wear characteristics, high temperature stability, resistance to chemical reaction with working fluids or refrigerants, and corrosivity to metals.
The viscosity of the oil-working fluid mixture is a factor in determining the effectiveness of the seal between the high-pressure and low-pressure sides of the system; and because of the wide variation in temperatures throughout the system, the viscosity index of the oil is important. An oil should be chosen with a viscosity as low as is possible, consistent with effective sealing with the working fluid or refrigerant used for the entire range of temperatures and pressures encountered. Various viscosity grades of refrigerator heat engine or heat pump lubricants are supplied to provide optimum service for different types of equipment and working fluids. The viscosity index should be high because of the very large changes in temperature encountered by the oil.
The oil and working fluid or refrigerant may be completely miscible at all temperatures and pressures encountered in the refrigeration or heat engine cycle, or they may separate into two phases at certain pressures and temperatures encountered. One of the phases will be rich in working fluid or refrigerant and of low viscosity, while the other is rich in oil and higher in viscosity. Under conditions of higher temperature in the cycle, the mutual solubility increases so that often in regions of low temperature, such as the evaporator, two phases exist; while at high temperature regions, a single phase exits. It is necessary that in cases where phase separation occurs, the resulting liquid phases are capable of flowing readily at the existing temperatures.
The pour point of the lubricant must be low in order that the oil will flow at the lowest temperatures encountered. This is particularly true in the case of lubricants prepared from paraffinic waxy oils which must be dewaxed to a sufficiently low pour point.
The oil must have a low vapor pressure at 400°F.
Since the motor compressor system is normally sealed, the oil must prevent wear of the moving parts as the life of the equipment is dependent on the wear rate.
The lubricant must be stable at the highest temperatures reached in the system and nonreactive with the working fluid or refrigerant in the presence of metals it contacts which may act as catalysts. The lubricant-refrigerant mixture also must not corrode metals such as iron, aluminum or copper which may be present.
Generally, refrigeration and heat engine oils are based upon hydrocarbon oils obtained from petroleum and highly refined. They may be derived from naphthenic or paraffinic crudes, and each type has advantages and disadvantages. The petroleum-derived oils must be dewaxed to yield a low pour point oil. They must be highly refined to eliminate components which can react with chlorine-containing refrigerants to liberate hydrogen chloride.
Alkylbenzenes have been suggested as lubricants for refrigeration equipment. U.S. Pat. No. 3,092,981 teaches the use of alkylbenzenes or blends of alkylbenzenes with conventional oil for the lubrication of refrigeration compressors. The alkylbenzenes are superior to conventional oils in compatibility with the refrigerant and in thermal stability. However, a practical disadvantage of alkylbenzenes is the low viscosity of those which are actually available, that is, the alkylbenzenes containing up to about 25 carbon atoms in the alkyl chain. Refrigeration oils are classified on the basis of the viscosity of 100°F, and grades having nominal viscosities of 80, 100, 150, 200, 300 and 500 SUS (Saybolt Universal Seconds) are provided. In addition to these grades, heat engine oils also include grades having higher viscosities such as 750, 1,000, 1,500 SUS. Most refrigeration and heat engine equipment requires the grades covering the range from 150 to 500 SUS. Alkylbenzenes with alkyl side chains containing from 18 to 25 carbon atoms generally have viscosities in the range of about 60 to 120 SUS and thus are of too low viscosity to be generally useful.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an apparatus of the refrigeration, heat pump or heat engine type including compressor, condenser, evaporator, and in contact with the moving parts of said apparatus a halogenated alkane working fluid and a lubricating oil consisting essentially of alkylbenzene having one or more side chains of one to 25 carbon atoms and containing a total of from 10 to 25 carbon atoms in the alkyl groups and from about 2 to about 50 percent by weight of polyisobutylene having a viscosity in the range of from about 3,000 to about 1,000,000 SUS at 100°F.
The lubricating oil compositions of this invention are readily obtainable and free of shortcomings associated with the lubricants of the prior art. These lubricants are readily prepared by blending relatively low molecular weight alkylbenzenes with highly viscous polymers of isobutylene. The alkylbenzenes, which are generally available, may contain from one to 25 carbon atoms in each of the alkyl groups and may contain more than one alkyl side chain with a total of from 10 to 25 carbon atoms in the alkyl groups. Usually, except for methyl radicals, there will not be more than two alkyl groups in the molecule.
The working fluids for use in this invention are the halogenated alkanes, preferably having one or two carbon atoms, containing fluorine, and commonly called "Freons" (DuPont reg. TM). Typical working fluids include trifluorochloromethane, hexafluoroethane, trifluorobromomethane, difluoromonochloromethane, difluorodichloromethane, 1,1,2,2-tetrafluorotetrachloroethane, dichlorofluoromethane, trichlorofluoromethane, 1,1,2-trifluorotrichloroethane, etc.
For use in a refrigeration apparatus the low boiling "Freons" are preferred as working fluids or refrigerants. These include, for example, difluoromonochloromethane, dichlorofluoromethane, and trichlorofluoromethane. On the other hand, working fluids of high boiling point are preferred for use in heat engine. These include: sym-tetrafluorodibromoethane, 1,1,2-trifluorotrichloroethane, and 1,2-difluorotetrachloroethane. In general the higher boiling "Freon" compounds are less thermally stable than the lower boiling ones. (Ref. DuPont Technical Bulletin, B-2, "Freon Fluorocarbons.")
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The isobutylene polymer is added to the alkylbenzene to increase the viscosity in the range required for a refrigerator or heat engine lubricant. It should have a viscosity at 100°F of from 3,000 SUS to 1,000,000 SUS. The concentration required depends on the viscosities of the alkylbenzene and the isobutylene polymer and is generally in the range of 2 to 50 percent of the total.
The alkylbenzene used in preparing this refrigeration or heat engine lubricant has alkyl groups containing a total of from 10 to 20 carbon atoms, and these may have either a branched chain or a straight chain configuration. Such compounds may be prepared by various well known methods, but it is preferred to alkylate benzene with an olefin or with an alkyl halide in the presence of an appropriate catalyst, such as hydrogen fluoride or aluminum chloride. The alkylbenzene should be essentially free of normal paraffins or other waxy-like materials which will raise the pour point. While alkylbenzenes prepared from straight chain olefins derived by cracking paraffin wax are not excluded, those having branched alkyl side chains are preferred. (Thus, the alkyl groups should be derived preferably from polypropylene or polybutylene.)
The polymerized isobutylene used in these refrigeration or heat engine lubricants is prepared in the usual way by the catalytic polymerization of isobutene. A wide range of molecular weights is available, but only those polymers having a viscosity of 3,000 SUS to 1,000,000 SUS at 100°F are useful in this formulation. Preferably, the polymerized isobutylene has a viscosity in the range of 40,000 SUS to 150,000 SUS at 100°F.
The lubricants of the invention may contain additives of the types conventionally used. These include foam inhibitors, such as silicone polymers; metal deactivators, such as alizarine, quinizarine, Schiff bases, alkyl sulfides, zinc dithiocarbamates, and mercaptobenzothiazole; oxidation inhibitors, such as dibutyl-p-cresol; and scavengers for hydrogen chloride, such as epoxides.
The following examples illustrate the refrigeration and heat engine lubricating oils according to the present invention. These examples are in no manner intended to limit the invention described. Unless otherwise indicated, percentages are on a weight basis.
A number of compositions were prepared and subjected to tests to determine their value as refrigerator and heat engine lubricants. Three different alkylbenzenes blended with an isobutylene polymer to prepare lubricants of the 300 viscosity grade (nominal 300 SUS at 100°F). The isobutylene polymer had a molecular weight of 1,400 (number average) and a viscosity at 100°F of 123,000 SUS. A description of the blends follows:
Oil A
The alkylbenzene used was prepared by alkylating benzene with a propylene polymer blend in which 80 percent of the material fell in the rang of 15 to 19 carbon atoms. The resulting alkylbenzene had a molecular weight of 320. A blend was prepared consisting of 78.4 percent of this material and 21,6 percent of the polybutene.
Oil B
The alkylbenzene used was prepared by alkylating benzene with a propylene polymer blend having from 15 to 23 carbon atoms. The molecular weight of the product was 328. A blend of 85.5 percent of the alkylbenzene and 14.5 percent of the polybutene was prepared.
Oil C
The alkylbenzene was prepared by alkylating benzene with a propylene polymer of which 82 percent fell in the range of 12 to 15 carbon atoms. The resulting alkylbenzene had a molecular weight of 263. A blend of 69.4 percent of this material and 30.6 percent of the polybutene was prepared.
The above oil blends conforming to the invention were compared with the alkylbenzene used in Oil B but without the addition of any butylene polymer. This is referred to as Oil D. The blends were also compared with a commercial conventional refrigerator lubricant which was of the highly refined naphthenic type derived from petroleum. This is referred to as Oil E. The data on all five refrigerator lubricants are presented in Table I. ##SPC1##
The oils conforming to the invention have higher viscosity indexes than either Oils D or E, which represent prior art lubricants. The oils of the invention are also superior in high temperature stability, as measured by the Elsey test procedure, and are superior in wear characteristics, as demonstrated by the Shell Four-Ball Wear Test.
Refrigerator and heat engine oils conforming to the invention and in the viscosity range of the nominal 150 and 500 grades were prepared. These oil blends were prepared from the same alkylbenzenes and polybutene used in Oils A, B and C. The compositions of these oils are as follows:
Oil F -- 89 percent alkylbenzene of Oil A and 11 percent polybutene.
Oil G -- 96 percent alkylbenzene of Oil B and 4 percent polybutene.
Oil H -- 80 percent alkylbenzene of Oil C and 20 percent polybutene.
Oil I -- 71 percent alkylbenzene of Oil A and 29 percent polybutene.
Oil J -- 78 percent alkylbenzene of Oil B and 22 percent polybutene.
Oil K -- 64 percent alkylbenzene of Oil C and 36 percent polybutene.
The test data obtained on these oils are listed in Table II. ##SPC2##
The effect of the molecular weight and viscosity of the polymerized isobutylene was investigated. The same alkylbenzenes were used as in the previous experiments. Chevron Polybutene 32 was replaced by a polyisobutylene of lower viscosity and by one of higher viscosity. These isobutylene polymers are marketed by Chevron Chemical Company under the names Polybutene 24 and Polybutene 128. Polybutene 24 has a molecular weight (number average) of 950 and a viscosity at 100°F of 40,000 SUS. Polybutene 128 has a molecular weight (number average) of 2,700 and a viscosity at 100°F of 890,000 SUS.
The following oils were prepared from the alkylbenzenes and Polybutene 24 and Polybutene 128:
Oil L -- 74 percent alkylbenzene of Oil A and 26 percent Polybutene 24.
Oil M -- 82.1 percent alkylbenzene of Oil A and 17.9 percent Polybutene 128.
Oil N -- 82.1 percent alkylbenzene of Oil B and 17.9 percent Polybutene 24.
Oil -- 89 percent alkylbenzene of Oil B and 11 percent Polybutene 128.
Oil P 63.6 percent alkylbenzene of Oil C and 36.4 percent Polybutene 24.
Oil Q -- 76.3 percent alkylbenzene of Oil C and 23.7 percent Polybutene 128.
The test data obtained on these oils are listed in Table III. ##SPC3##
Oils of the invention were prepared from alkylbenzenes having linear alkyl groups derived from paraffin. These alkylbenzenes were blended with Polybutene 32 to yield the following oils:
Oil R
An alkylbenzene being essentially monoalkyl and containing from 11 to 14 carbon atoms with an average molecular weight of 255 was blended with polybutene so that the blend contained 58.5 percent alkylbenzene and 41.5 percent Polybutene 32.
Oil S
An alkylbenzene similar to that used in Oil R but containing from 10 to 13 carbon atoms and having an average molecular weight of 236 was blended so that the final oil contained 56.5 percent alkylbenzene and 43.5 percent Polybutene 32.
Oil T
An alkylbenzene similar to that used in Oil R but containing from 10 to 15 carbon atoms and having an average molecular weight of 259 was blended so that the final oil contained 59 percent alkylbenzene and 41 percent Polybutene 32.
The test data obtained on these oils are listed in Table IV. ##SPC4##
A lubricant according to the invention was tested for friction reducing properties in a tribometer. This is a device in which a cast iron pad slides over a cast iron disk, and the apparatus was operated at a temperature of 250°F and at sliding velocities similar to those encountered in refrigerant and heat engine compressors. Static friction (zero velocity) is important in a compressor because of the reciprocating nature of piston travel.
The lubricant used was a blend of 74 percent of alkylbenzene similar to that used in Oil A and 26 percent Polybutene 24. It had a viscosity at 100°F of 286 SUS and was designated RO 300. The friction characteristics of this lubricant as indicated by Coefficient of Friction (ratio of horizontal force to the vertical force) are compared in Table V with the petroleum-derived lubricant, Oil E. ##SPC5##
The data show that the lubricant of the invention has a decidedly lower coefficient of friction and is superior to conventional petroleum-based lubricants in friction-reducing properties in the critical region of low sliding velocities. This correlates with the low wear resulting in the Shell Four-Ball Wear Test illustrated in Table I. These desirable lubricity properties are surprising since synthetic oil refrigerator lubricants have previously been poor compared to conventional mineral oil compositions.
The oxidation stability of the lubricant according to the invention was also tested using the method outlined in ASTM D 1934 both with and without copper catalyst. In this method the test material is contacted with air for a period of 96 hours at 115°C. Changes in Gardner color, neutralization number (mg KOH/g) ##SPC6##
In the above table, RO 300 is illustrative of the lubricant compositions of the invention. Oil E, as previously mentioned, is a standard petroleum base oil used for comparison.
The above tests show that the heat engine and refrigeration lubricant compositions of the invention have particularly desirable oxidation resisting properties. As indicated by the color test, very little change occurs with the alkylbenzene and polyisobutylene composition of RO 300 whereas the standard petroleum base Oil E gives a substantially increased darkening in color, even more so in the presence of copper. Also the above tests show that the neutralization number of both oils is practically nil.
The solubility of lubricant RO 300 was determined in both Freon 12 (dichlorodifluoromethane) and Freon 22 (monochlorodifluoromethane). At all temperatures up to 200°F, two phases existed; one essentially Freon rich and the other oil rich. The oil rich phase was found to consist predominantly of polybutene with a low concentration of the alkylbenzene which remained dissolved in the Freon. Surprisingly, the presence of the separate phase of the viscous polybutene does not interfere with the operation of refrigerating or heat engine equipment.
Additional tests were carried out to illustrate the effectiveness of the lubricant combination of alkylbenzenes and polyisobutylene in a heat engine apparatus. Such applications involve maximum oil temperatures in the range of about 350°-375°F or 177°-191°C. A modification of the Elsey test method (previously described) was employed. In this modification the higher boiling, but less thermally stable, R 113 (CCl 2 F-CClF 2 ) was used as a working fluid in place of the lower boiling, more thermally stable, R 12 (CCl 2 F 2 ). The working fluid-lubricant ratio was 95/5 on a weight basis. Tests were carried out at 177°C and at 200°C.
Two lubricant compositions were tested. The first test lubricant, similar to Oil O, was prepared from 87 percent by weight of alkylbenzene and 13 percent by weight polyisobutylene. The alkylbenzene portion of the lubricant was a fraction having a viscosity of 126 SUS at 100°F and was essentially the same as the alkylbenzene described in Oil B. The polyisobutylene portion of the lubricant had a viscosity of about 890,000 SUS at 100°F. The resulting blend had a viscosity of 482 SUS at 100°F and is identified as Oil U.
The second lubricant test composition was prepared from the same alkylbenzene and polyisobutylene but in a weight ratio of 75/25 respectively. The resulting blend had a viscosity of 1447 SUS at 100°F, and is identified as Oil V.
These tests were carried out in the presence of iron and aluminum, metals commonly used in the construction of heat engines. ##SPC7##
The test results show that the lubricant in combination with the halogenated alkane working fluid had satisfactory stability in the presence of aluminum to function in a typical heat engine.
While the character of this invention has been described in detail with numerous examples, this has been done by way of illustration only and without limitation of the invention. It will be apparent to those skilled in the art that modifications and variations of the illustrative examples may be made in the practice of the invention within the scope of the following claims.
This invention relates to apparatuses of the refrigeration, heat pump or heat engine type including compressor, condenser, evaporator and, in contact with the moving parts of said apparatus, a working fluid comprising halogenated alkanes and a lubricant combination of alkylbenzenes and polyisobutylene. For those knowledgeable in the art, it is well known that these apparatuses are variations in the operation of the same cyclic system.
When applied to refrigeration or heat pumps, work is added to the system through a motor-driven compressor which compresses the working fluid before it is condensed. Heat from the system at this point may be employed for heating purposes. The system is then operating as a heat pump. The condensed working fluid is partly or completely vaporized in the evaporator. The head added to the system at this point or extracted from the surroundings causes cooling (refrigeration of the heat source). In heat pumps the heat source is usually outside air, whereas in refrigeration systems it is normally a relatively confined space to be cooled.
When the system is operated as a heat engine, useful work is delivered by the system. Heat is added to the evaporator from, for instance, hot gases obtained from combustion of a suitable fuel. This results in evaporation and expansion of the working fluid which drives a compressor. The working fluid is then condensed to complete the cycle. The useful work can, in turn, be used in driving other devices. This type of heat engine is of particular importance because of its possible adaptation to anti-pollution automobile engines employing external combustion.
The same working fluids and the same lubricants are used in all three types of the above-described apparatus.
Heat engine, heat pump, and refrigeration lubricants for use in hermetic unit designs are usually sealed in the motor-compressor unit housing and are not replaceable. They are thus required to perform under relatively severe conditions of temperature change for the life of the unit, which is generally a period of several years of intermittent daily service. The lubricant is in contact with the working fluid or refrigerant and in addition to lubricating the compressor, it serves as a seal between the low-pressure and high-pressure sides of the system. As the working fluid or refrigerant flows from the compressor through the condenser and evaporator and back to the intake side of the compressor, it carries some of the lubricant with it. Thus, while the lubricant is required only at the compressor, it circulates throughout the system. In addition, the lubricant for the centrifugal compressor unit design, although replaceable, must be stable toward oxidation which commonly occurs due to air leakage around the drive shaft in order to avoid need for frequent oil changes.
The service of lubricating a heat engine, heat pump or refrigerator compressor and motor subjects the lubricant or oil to conditions not encountered in other types of service. These special unique conditions include: (1) rapid swings in temperature from about -100° to +400°F; (2) contact with working fluids or refrigerants, generally fluorinated, chlorinated methanes of the Freon types; (3) ability to serve as a pressure seal in the compressor; and (4) contact with electric motor windings. Because of these unusual conditions important properties of the oil are viscosity, viscosity index, mutual solubility with working fluids or refrigerants, pour point, volatility, wear characteristics, high temperature stability, resistance to chemical reaction with working fluids or refrigerants, and corrosivity to metals.
The viscosity of the oil-working fluid mixture is a factor in determining the effectiveness of the seal between the high-pressure and low-pressure sides of the system; and because of the wide variation in temperatures throughout the system, the viscosity index of the oil is important. An oil should be chosen with a viscosity as low as is possible, consistent with effective sealing with the working fluid or refrigerant used for the entire range of temperatures and pressures encountered. Various viscosity grades of refrigerator heat engine or heat pump lubricants are supplied to provide optimum service for different types of equipment and working fluids. The viscosity index should be high because of the very large changes in temperature encountered by the oil.
The oil and working fluid or refrigerant may be completely miscible at all temperatures and pressures encountered in the refrigeration or heat engine cycle, or they may separate into two phases at certain pressures and temperatures encountered. One of the phases will be rich in working fluid or refrigerant and of low viscosity, while the other is rich in oil and higher in viscosity. Under conditions of higher temperature in the cycle, the mutual solubility increases so that often in regions of low temperature, such as the evaporator, two phases exist; while at high temperature regions, a single phase exits. It is necessary that in cases where phase separation occurs, the resulting liquid phases are capable of flowing readily at the existing temperatures.
The pour point of the lubricant must be low in order that the oil will flow at the lowest temperatures encountered. This is particularly true in the case of lubricants prepared from paraffinic waxy oils which must be dewaxed to a sufficiently low pour point.
The oil must have a low vapor pressure at 400°F.
Since the motor compressor system is normally sealed, the oil must prevent wear of the moving parts as the life of the equipment is dependent on the wear rate.
The lubricant must be stable at the highest temperatures reached in the system and nonreactive with the working fluid or refrigerant in the presence of metals it contacts which may act as catalysts. The lubricant-refrigerant mixture also must not corrode metals such as iron, aluminum or copper which may be present.
Generally, refrigeration and heat engine oils are based upon hydrocarbon oils obtained from petroleum and highly refined. They may be derived from naphthenic or paraffinic crudes, and each type has advantages and disadvantages. The petroleum-derived oils must be dewaxed to yield a low pour point oil. They must be highly refined to eliminate components which can react with chlorine-containing refrigerants to liberate hydrogen chloride.
Alkylbenzenes have been suggested as lubricants for refrigeration equipment. U.S. Pat. No. 3,092,981 teaches the use of alkylbenzenes or blends of alkylbenzenes with conventional oil for the lubrication of refrigeration compressors. The alkylbenzenes are superior to conventional oils in compatibility with the refrigerant and in thermal stability. However, a practical disadvantage of alkylbenzenes is the low viscosity of those which are actually available, that is, the alkylbenzenes containing up to about 25 carbon atoms in the alkyl chain. Refrigeration oils are classified on the basis of the viscosity of 100°F, and grades having nominal viscosities of 80, 100, 150, 200, 300 and 500 SUS (Saybolt Universal Seconds) are provided. In addition to these grades, heat engine oils also include grades having higher viscosities such as 750, 1,000, 1,500 SUS. Most refrigeration and heat engine equipment requires the grades covering the range from 150 to 500 SUS. Alkylbenzenes with alkyl side chains containing from 18 to 25 carbon atoms generally have viscosities in the range of about 60 to 120 SUS and thus are of too low viscosity to be generally useful.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an apparatus of the refrigeration, heat pump or heat engine type including compressor, condenser, evaporator, and in contact with the moving parts of said apparatus a halogenated alkane working fluid and a lubricating oil consisting essentially of alkylbenzene having one or more side chains of one to 25 carbon atoms and containing a total of from 10 to 25 carbon atoms in the alkyl groups and from about 2 to about 50 percent by weight of polyisobutylene having a viscosity in the range of from about 3,000 to about 1,000,000 SUS at 100°F.
The lubricating oil compositions of this invention are readily obtainable and free of shortcomings associated with the lubricants of the prior art. These lubricants are readily prepared by blending relatively low molecular weight alkylbenzenes with highly viscous polymers of isobutylene. The alkylbenzenes, which are generally available, may contain from one to 25 carbon atoms in each of the alkyl groups and may contain more than one alkyl side chain with a total of from 10 to 25 carbon atoms in the alkyl groups. Usually, except for methyl radicals, there will not be more than two alkyl groups in the molecule.
The working fluids for use in this invention are the halogenated alkanes, preferably having one or two carbon atoms, containing fluorine, and commonly called "Freons" (DuPont reg. TM). Typical working fluids include trifluorochloromethane, hexafluoroethane, trifluorobromomethane, difluoromonochloromethane, difluorodichloromethane, 1,1,2,2-tetrafluorotetrachloroethane, dichlorofluoromethane, trichlorofluoromethane, 1,1,2-trifluorotrichloroethane, etc.
For use in a refrigeration apparatus the low boiling "Freons" are preferred as working fluids or refrigerants. These include, for example, difluoromonochloromethane, dichlorofluoromethane, and trichlorofluoromethane. On the other hand, working fluids of high boiling point are preferred for use in heat engine. These include: sym-tetrafluorodibromoethane, 1,1,2-trifluorotrichloroethane, and 1,2-difluorotetrachloroethane. In general the higher boiling "Freon" compounds are less thermally stable than the lower boiling ones. (Ref. DuPont Technical Bulletin, B-2, "Freon Fluorocarbons.")
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The isobutylene polymer is added to the alkylbenzene to increase the viscosity in the range required for a refrigerator or heat engine lubricant. It should have a viscosity at 100°F of from 3,000 SUS to 1,000,000 SUS. The concentration required depends on the viscosities of the alkylbenzene and the isobutylene polymer and is generally in the range of 2 to 50 percent of the total.
The alkylbenzene used in preparing this refrigeration or heat engine lubricant has alkyl groups containing a total of from 10 to 20 carbon atoms, and these may have either a branched chain or a straight chain configuration. Such compounds may be prepared by various well known methods, but it is preferred to alkylate benzene with an olefin or with an alkyl halide in the presence of an appropriate catalyst, such as hydrogen fluoride or aluminum chloride. The alkylbenzene should be essentially free of normal paraffins or other waxy-like materials which will raise the pour point. While alkylbenzenes prepared from straight chain olefins derived by cracking paraffin wax are not excluded, those having branched alkyl side chains are preferred. (Thus, the alkyl groups should be derived preferably from polypropylene or polybutylene.)
The polymerized isobutylene used in these refrigeration or heat engine lubricants is prepared in the usual way by the catalytic polymerization of isobutene. A wide range of molecular weights is available, but only those polymers having a viscosity of 3,000 SUS to 1,000,000 SUS at 100°F are useful in this formulation. Preferably, the polymerized isobutylene has a viscosity in the range of 40,000 SUS to 150,000 SUS at 100°F.
The lubricants of the invention may contain additives of the types conventionally used. These include foam inhibitors, such as silicone polymers; metal deactivators, such as alizarine, quinizarine, Schiff bases, alkyl sulfides, zinc dithiocarbamates, and mercaptobenzothiazole; oxidation inhibitors, such as dibutyl-p-cresol; and scavengers for hydrogen chloride, such as epoxides.
The following examples illustrate the refrigeration and heat engine lubricating oils according to the present invention. These examples are in no manner intended to limit the invention described. Unless otherwise indicated, percentages are on a weight basis.
A number of compositions were prepared and subjected to tests to determine their value as refrigerator and heat engine lubricants. Three different alkylbenzenes blended with an isobutylene polymer to prepare lubricants of the 300 viscosity grade (nominal 300 SUS at 100°F). The isobutylene polymer had a molecular weight of 1,400 (number average) and a viscosity at 100°F of 123,000 SUS. A description of the blends follows:
Oil A
The alkylbenzene used was prepared by alkylating benzene with a propylene polymer blend in which 80 percent of the material fell in the rang of 15 to 19 carbon atoms. The resulting alkylbenzene had a molecular weight of 320. A blend was prepared consisting of 78.4 percent of this material and 21,6 percent of the polybutene.
Oil B
The alkylbenzene used was prepared by alkylating benzene with a propylene polymer blend having from 15 to 23 carbon atoms. The molecular weight of the product was 328. A blend of 85.5 percent of the alkylbenzene and 14.5 percent of the polybutene was prepared.
Oil C
The alkylbenzene was prepared by alkylating benzene with a propylene polymer of which 82 percent fell in the range of 12 to 15 carbon atoms. The resulting alkylbenzene had a molecular weight of 263. A blend of 69.4 percent of this material and 30.6 percent of the polybutene was prepared.
The above oil blends conforming to the invention were compared with the alkylbenzene used in Oil B but without the addition of any butylene polymer. This is referred to as Oil D. The blends were also compared with a commercial conventional refrigerator lubricant which was of the highly refined naphthenic type derived from petroleum. This is referred to as Oil E. The data on all five refrigerator lubricants are presented in Table I. ##SPC1##
The oils conforming to the invention have higher viscosity indexes than either Oils D or E, which represent prior art lubricants. The oils of the invention are also superior in high temperature stability, as measured by the Elsey test procedure, and are superior in wear characteristics, as demonstrated by the Shell Four-Ball Wear Test.
Refrigerator and heat engine oils conforming to the invention and in the viscosity range of the nominal 150 and 500 grades were prepared. These oil blends were prepared from the same alkylbenzenes and polybutene used in Oils A, B and C. The compositions of these oils are as follows:
Oil F -- 89 percent alkylbenzene of Oil A and 11 percent polybutene.
Oil G -- 96 percent alkylbenzene of Oil B and 4 percent polybutene.
Oil H -- 80 percent alkylbenzene of Oil C and 20 percent polybutene.
Oil I -- 71 percent alkylbenzene of Oil A and 29 percent polybutene.
Oil J -- 78 percent alkylbenzene of Oil B and 22 percent polybutene.
Oil K -- 64 percent alkylbenzene of Oil C and 36 percent polybutene.
The test data obtained on these oils are listed in Table II. ##SPC2##
The effect of the molecular weight and viscosity of the polymerized isobutylene was investigated. The same alkylbenzenes were used as in the previous experiments. Chevron Polybutene 32 was replaced by a polyisobutylene of lower viscosity and by one of higher viscosity. These isobutylene polymers are marketed by Chevron Chemical Company under the names Polybutene 24 and Polybutene 128. Polybutene 24 has a molecular weight (number average) of 950 and a viscosity at 100°F of 40,000 SUS. Polybutene 128 has a molecular weight (number average) of 2,700 and a viscosity at 100°F of 890,000 SUS.
The following oils were prepared from the alkylbenzenes and Polybutene 24 and Polybutene 128:
Oil L -- 74 percent alkylbenzene of Oil A and 26 percent Polybutene 24.
Oil M -- 82.1 percent alkylbenzene of Oil A and 17.9 percent Polybutene 128.
Oil N -- 82.1 percent alkylbenzene of Oil B and 17.9 percent Polybutene 24.
Oil -- 89 percent alkylbenzene of Oil B and 11 percent Polybutene 128.
Oil P 63.6 percent alkylbenzene of Oil C and 36.4 percent Polybutene 24.
Oil Q -- 76.3 percent alkylbenzene of Oil C and 23.7 percent Polybutene 128.
The test data obtained on these oils are listed in Table III. ##SPC3##
Oils of the invention were prepared from alkylbenzenes having linear alkyl groups derived from paraffin. These alkylbenzenes were blended with Polybutene 32 to yield the following oils:
Oil R
An alkylbenzene being essentially monoalkyl and containing from 11 to 14 carbon atoms with an average molecular weight of 255 was blended with polybutene so that the blend contained 58.5 percent alkylbenzene and 41.5 percent Polybutene 32.
Oil S
An alkylbenzene similar to that used in Oil R but containing from 10 to 13 carbon atoms and having an average molecular weight of 236 was blended so that the final oil contained 56.5 percent alkylbenzene and 43.5 percent Polybutene 32.
Oil T
An alkylbenzene similar to that used in Oil R but containing from 10 to 15 carbon atoms and having an average molecular weight of 259 was blended so that the final oil contained 59 percent alkylbenzene and 41 percent Polybutene 32.
The test data obtained on these oils are listed in Table IV. ##SPC4##
A lubricant according to the invention was tested for friction reducing properties in a tribometer. This is a device in which a cast iron pad slides over a cast iron disk, and the apparatus was operated at a temperature of 250°F and at sliding velocities similar to those encountered in refrigerant and heat engine compressors. Static friction (zero velocity) is important in a compressor because of the reciprocating nature of piston travel.
The lubricant used was a blend of 74 percent of alkylbenzene similar to that used in Oil A and 26 percent Polybutene 24. It had a viscosity at 100°F of 286 SUS and was designated RO 300. The friction characteristics of this lubricant as indicated by Coefficient of Friction (ratio of horizontal force to the vertical force) are compared in Table V with the petroleum-derived lubricant, Oil E. ##SPC5##
The data show that the lubricant of the invention has a decidedly lower coefficient of friction and is superior to conventional petroleum-based lubricants in friction-reducing properties in the critical region of low sliding velocities. This correlates with the low wear resulting in the Shell Four-Ball Wear Test illustrated in Table I. These desirable lubricity properties are surprising since synthetic oil refrigerator lubricants have previously been poor compared to conventional mineral oil compositions.
The oxidation stability of the lubricant according to the invention was also tested using the method outlined in ASTM D 1934 both with and without copper catalyst. In this method the test material is contacted with air for a period of 96 hours at 115°C. Changes in Gardner color, neutralization number (mg KOH/g) ##SPC6##
In the above table, RO 300 is illustrative of the lubricant compositions of the invention. Oil E, as previously mentioned, is a standard petroleum base oil used for comparison.
The above tests show that the heat engine and refrigeration lubricant compositions of the invention have particularly desirable oxidation resisting properties. As indicated by the color test, very little change occurs with the alkylbenzene and polyisobutylene composition of RO 300 whereas the standard petroleum base Oil E gives a substantially increased darkening in color, even more so in the presence of copper. Also the above tests show that the neutralization number of both oils is practically nil.
The solubility of lubricant RO 300 was determined in both Freon 12 (dichlorodifluoromethane) and Freon 22 (monochlorodifluoromethane). At all temperatures up to 200°F, two phases existed; one essentially Freon rich and the other oil rich. The oil rich phase was found to consist predominantly of polybutene with a low concentration of the alkylbenzene which remained dissolved in the Freon. Surprisingly, the presence of the separate phase of the viscous polybutene does not interfere with the operation of refrigerating or heat engine equipment.
Additional tests were carried out to illustrate the effectiveness of the lubricant combination of alkylbenzenes and polyisobutylene in a heat engine apparatus. Such applications involve maximum oil temperatures in the range of about 350°-375°F or 177°-191°C. A modification of the Elsey test method (previously described) was employed. In this modification the higher boiling, but less thermally stable, R 113 (CCl 2 F-CClF 2 ) was used as a working fluid in place of the lower boiling, more thermally stable, R 12 (CCl 2 F 2 ). The working fluid-lubricant ratio was 95/5 on a weight basis. Tests were carried out at 177°C and at 200°C.
Two lubricant compositions were tested. The first test lubricant, similar to Oil O, was prepared from 87 percent by weight of alkylbenzene and 13 percent by weight polyisobutylene. The alkylbenzene portion of the lubricant was a fraction having a viscosity of 126 SUS at 100°F and was essentially the same as the alkylbenzene described in Oil B. The polyisobutylene portion of the lubricant had a viscosity of about 890,000 SUS at 100°F. The resulting blend had a viscosity of 482 SUS at 100°F and is identified as Oil U.
The second lubricant test composition was prepared from the same alkylbenzene and polyisobutylene but in a weight ratio of 75/25 respectively. The resulting blend had a viscosity of 1447 SUS at 100°F, and is identified as Oil V.
These tests were carried out in the presence of iron and aluminum, metals commonly used in the construction of heat engines. ##SPC7##
The test results show that the lubricant in combination with the halogenated alkane working fluid had satisfactory stability in the presence of aluminum to function in a typical heat engine.
While the character of this invention has been described in detail with numerous examples, this has been done by way of illustration only and without limitation of the invention. It will be apparent to those skilled in the art that modifications and variations of the illustrative examples may be made in the practice of the invention within the scope of the following claims.