Nitrous oxide compositions
This invention relates to compositions that include nitrous oxide and at least one of trifluoromethane, difluoromethane, tetrafluoroethane, pentafluoroethane, perfluoroethane or ethane. These compositions are useful as refrigerants, cleaning agents, expansion agents for polyolefins and polyurethanes, refrigerants, aerosol propellants, heat transfer media, electronic gases, plasma etchants, gaseous dielectrics, fire extinguishing agents, power cycle working fluids, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, and displacement drying agents.
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This invention relates to compositions that contain nitrous oxide and at least one compound selected from the group consisting of trifluoromethane, difluoromethane, tetrafluoroethane, pentafluoroethane, perfluoroethane and ethane. These compositions are useful as refrigerants, cleaning agents, expansion agents for polyolefins and polyurethanes, refrigerants, aerosol propellants, heat transfer media, electronic gases, plasma etchants, gaseous dielectrics, fire extinguishing agents, power cycle working fluids, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, and displacement drying agents.
BACKGROUND OF THE INVENTIONFluorinated hydrocarbons have many uses, one of which is as a refrigerant. Such refrigerants include dichlorodifluoromethane (CFC-12) and chlorodifluoromethane (HCFC-22).
In recent years it has been pointed out that certain kinds of fluorinated hydrocarbon refrigerants released into the atmosphere may adversely affect the stratospheric ozone layer. Although this proposition has not yet been completely established, there is a movement toward the control of the use and the production of certain chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) under an international agreement.
Accordingly, there is a demand for the development of refrigerants that have a lower ozone depletion potential than existing refrigerants while still achieving an acceptable performance in refrigeration applications. Hydrofluorocarbons (HFCs) have been suggested as replacements for CFCs and HCFCs since HFCs have no chlorine and therefore have zero ozone depletion potential.
In refrigeration applications, a refrigerant is often lost during operation through leaks in shaft seals, hose connections, soldered joints and broken lines. In addition, the refrigerant may be released to the atmosphere during maintenance procedures on refrigeration equipment. If the refrigerant is not a pure component or an azeotropic or azeotrope-like composition, the refrigerant composition may change when leaked or discharged to the atmosphere from the refrigeration equipment, which may cause the refrigerant to become flammable or to have poor refrigeration performance.
Accordingly, it is desirable to use as a refrigerant a single fluorinated hydrocarbon or an azeotropic or azeotrope-like composition that includes at least one fluorinated hydrocarbon.
Refrigerant compositions of the invention which are non-azeotropic, i.e., zeotropic may also be useful in vapor compression systems. See Didion, The Role of Refrigerant Mixtures as Alternatives, Proceedings of ASHRAE CFC Technology Conference, Gaithersburg, Md., 1989. Non-azeotropic mixtures can boil over a wide temperature range under constant pressure conditions and create a temperature glide in the evaporator and in the condenser. This temperature glide can reduce the energy required to operate the system by taking advantage of the Lorenz cycle. The preferred method involves the use of counter current flow evaporator and/or condenser heat exchangers in which the refrigerant and the heat transfer fluid flow countercurrently. This method decreases the temperature difference between the evaporating and condensing refrigerant but maintains a high enough temperature difference between the refrigerant and external heat transfer fluid to effectively transfer heat. Another benefit of this type of system is that pressure differences are also minimized. This can result in an improvement in energy efficiency and/or capacity versus conventional systems.
Azeotropic, azeotrope-like, or zeotropic compositions that include a fluorinated hydrocarbon are also useful as blowing agents in the manufacture of closed-cell polyurethane, phenolic and thermoplastic foams, as propellants in aerosols, as heat transfer media, electronic gases, plasma etchants, gaseous dielectrics, fire extinguishing agents, power cycle working fluids such as for heat pumps, inert media for polymerization reactions, fluids for removing particulates from metal surfaces, as carrier fluids that may be used, for example, to place a fine film of lubricant on metal parts, as buffing abrasive agents to remove buffing abrasive compounds from polished surfaces such as metal, as displacement drying agents for removing water, such as from jewelry or metal parts, as resist developers in conventional circuit manufacturing techniques including chlorine-type developing agents, or as strippers for photoresists when used with, for example, a chlorohydrocarbon such as 1,1,1-trichloroethane or trichloroethylene.
A farther utility for the nitrous oxide compositions of the present invention is a process for etching a thin film device comprising the steps of:
a) contacting said device with at least one nitrous oxide composition; and
b) forming a plasma from said composition during said contacting whereby said device is etched.
At least one oxygen-containing additive gas such as O.sub.2, O.sub.3, CO, CO.sub.2, NO, and NO.sub.2 is optionally employed in concert with the nitrous oxide compositions of the present invention for plasma etching of thin film devices. Of the oxygen-containing additive gases, O.sub.2 is the most preferred.
At least one secondary additive gas is optionally employed in concert with the nitrous oxide compositions of the present invention for plasma etching of thin film devices. These secondary additive gases include fluorinated gases such as CF.sub.4, CH.sub.2 F.sub.2, CH.sub.3 F, CF.sub.3 --CF.sub.3, CF.sub.3 --CF.sub.2 H, CF.sub.3 --CH.sub.2 F, CF.sub.2 H--CF.sub.2 H, CF.sub.2 H--CFH.sub.2, CH.sub.3 --CF.sub.2 H, CH.sub.2 F--CH.sub.2 F, C.sub.3 F.sub.8, NF.sub.3, SF.sub.6, and well as ion-producing inert gases such as helium, neon, and argon.
A common reactor for carrying out the plasma etching utility of the nitrous oxide compositions of the present invention is a capacitively-coupled parallel-plate plasma processing reactor. Such reactors are widely used and well known in the semiconductor industry. A representative example of such a reactor system is described by Hargis, et. al., in a paper titled "The Gaseous Electronics Conference Radio-Frequency Reference Cell: A Defined Parallel-Plate Radio-Frequency System For Experimental and Theoretical Studies of Plasma-Processing Discharges" in the Review of Scientific Instruments, volume 65, 1994, page 140. Such a reactor is useful for precision etching of thin films of silicon; dielectric materials such as silicon dioxide, silicon nitride, silicon oxynitride, and doped dielectric oxides such as phosphosilicate glass, borophosphosilicate glass and other dielectric materials; conductive materials such as tungsten, molybdenum, titanium, tantalum and suicides of these materials as found on thin film devices, such as semiconductor wafers and flat panel displays; micro-mechanical devices; and similar structures employing semiconductor fabrication technology.
The plasma etching utility of the nitrous oxide compositions of the present invention is not restricted to the aforementioned reactor configuration, and can be employed in other systems useful for plasma activation of gaseous reactant species. Such systems include diode parallel-plate systems using either radio-frequency power (commonly at 13.56 MHz) or audio-frequency power (commonly in the range 100-400 Hz), or a combination of the previous two in systems commonly referred to as triode systems. In addition, the power can be alternatively applied by inductive rather than capacitive means, using a variety of planar and loop antennas known in the art; some such systems include helicon or helical resonator configurations, with other types of coupling also applicable. Additionally, microwave frequency excitation (commonly at 2.45 GHz) can also be used. A variety of configurations may be used, including but not limited to the configurations commonly referred to as electron cyclotron resonance (ECR) systems.
SUMMARY OF THE INVENTIONThe present invention relates to the discovery of compositions that containing nitrous oxide and at least one compound selected from the group consisting of trifluoromethane, difluoromethane, tetrafluoroethane, pentafluoroethane, perfluoroethane or ethane.
Specifically, the present invention relates to the discovery of compositions of trifluoromethane (HFC-23) and nitrous oxide (N.sub.2 O); N.sub.2 O and ethane; HFC-23, perfluoroethane (FC-116) and N.sub.2 O; difluoromethane (HFC-32), pentafluoroethane (HFC-125) and N.sub.2 O; HFC-32, HFC-125, N.sub.2 O and ethane; HFC-32, HFC-125, 1,1,1,2-tetrafluoroethane (HFC-134a) and N.sub.2 O. These compositions are useful as refrigerants, cleaning agents, expansion agents for polyolefins and polyurethanes, refrigerants, aerosol propellants, heat transfer media, electronic gases, plasma etchants, gaseous dielectrics, fire extinguishing agents, power cycle working fluids, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, and displacement drying agents.
Further, the invention relates to the discovery of binary and ternary azeotropic or azeotrope-like compositions comprising effective amounts of HFC-23 and N.sub.2 O; N.sub.2 O and ethane; HFC-23, FC-116 and N.sub.2 O; HFC-32, HFC-125 and N.sub.2 O to form an azeotropic or azeotrope-like composition.
Further, the invention relates to the discovery of quarternary zeotropic compositions comprising effective amounts of HFC-32, HFC-125, N.sub.2 O and ethane; and HFC-32, HFC-125, HFC-134a and N.sub.2 O to form a non-azeotrope or zeotropic composition.
DETAILED DESCRIPTIONThe present invention relates to the discovery of compositions that include nitrous oxide and at least one of trifluoromethane, difluoromethane, tetrafluoroethane, pentafluoroethane, perfluoroethane or ethane.
Specifically, the present invention relates to compositions of HFC-23 and N.sub.2 O; N.sub.2 O and ethane; HFC-23, FC-116 and N.sub.2 O; HFC-32, HFC-125 and N.sub.2 O; HFC-32, HFC-125, N.sub.2 O and ethane; HFC-32, HFC-125, HFC-134a and N.sub.2 O.
The present invention also relates to the discovery of azeotropic or azeotrope-like compositions of effective amounts of HFC-23 and N.sub.2 O; N.sub.2 O and ethane; HFC-23, FC-116 and N.sub.2 O; HFC-32, HFC-125 and N.sub.2 O to form an azeotropic or azeotrope-like composition.
The present invention also relates to the discovery of zeotropic compositions of effective amounts of HFC-32, HFC-125, N.sub.2 O and ethane; and HFC-32, HFC-125, HFC-134a and N.sub.2 O.
By "azeotropic" composition is meant a constant boiling liquid admixture of two or more substances that behaves as a single substance. One way to characterize an azeotropic composition is that the vapor produced by partial evaporation or distillation of the liquid has the same composition as the liquid from which it was evaporated or distilled, that is, the admixture distills/refluxes without compositional change. Constant boiling compositions are characterized as azeotropic because they exhibit either a maximum or minimum boiling point, as compared with that of the non-azeotropic mixtures of the same components.
By "azeotrope-like" composition is meant a constant boiling, or substantially constant boiling, liquid admixture of two or more substances that behaves as a single substance. One way to characterize an azeotrope-like composition is that the vapor produced by partial evaporation or distillation of the liquid has substantially the same composition as the liquid from which it was evaporated or distilled, that is, the admixture distills/refluxes without substantial composition change.
It is recognized in the art that a composition is azeotrope-like if, after 50 weight percent of the composition is removed such as by evaporation or boiling off, the difference in vapor pressure between the original composition and the composition remaining after 50 weight percent of the original composition has been removed is about 10 percent or less, when measured in absolute units. By absolute units, it is meant measurements of pressure and, for example, psia, atmospheres, bars, torr, dynes per square centimeter, millimeters of mercury, inches of water and other equivalent terms well known in the art. If an azeotrope is present, there is no difference in vapor pressure between the original composition and the composition remaining after 50 weight percent of the original composition has been removed.
Therefore, included in this invention are compositions of effective amounts of HFC-23 and N.sub.2 O; N.sub.2 O and ethane; HFC-23, FC-116 and N.sub.2 O; HFC-32, HFC-125 and N.sub.2 O such that after 50 weight percent of an original composition is evaporated or boiled off to produce a remaining composition, the difference in the vapor pressure between the original composition and the remaining composition is 10 percent or less.
For compositions that are azeotropic, there is usually some range of compositions around the azeotrope that, for a maximum boiling azeotrope, have boiling points at a particular pressure higher than the pure components of the composition at that pressure and have vapor pressures lower at a particular temperature than the pure components of the composition at that temperature, and that, for a minimum boiling azeotrope, have boiling points at a particular pressure lower than the pure components of the composition at that pressure and have vapor pressures higher at a particular temperature than the pure components of the composition at that temperature. Boiling temperatures and vapor pressures above or below that of the pure components are caused by unexpected intermolecular forces between and among the molecules of the compositions, which can be a combination of repulsive and attractive forces such as van der Waals forces and hydrogen bonding.
The range of compositions that have a maximum or minimum boiling point at a particular pressure, or a maximum or minimum vapor pressure at a particular temperature, may or may not be coextensive with the range of compositions that are substantially constant boiling. In those cases where the range of compositions that have maximum or minimum boiling temperatures at a particular pressure, or maximum or minimum vapor pressures at a particular temperature, are broader than the range of compositions that are substantially constant boiling according to the change in vapor pressure of the composition when 50 weight percent is evaporated, the unexpected intermolecular forces are nonetheless believed important in that the refrigerant compositions having those forces that are not substantially constant boiling may exhibit unexpected increases in the capacity or efficiency versus the components of the refrigerant composition.
By "zeotropic" composition is meant a non-constant boiling liquid admixture of two or more substances. Non-azeotropic mixtures can boil over a wide temperature range under constant pressure conditions and create a temperature glide in the evaporator and in the condenser. This temperature glide can reduce the energy requited to operate the system by taking advantage of the Lorenz cycle. The preferred method involves the use of counter current flow evaporator and/or condenser heat exchangers in which the refrigerant and the heat transfer fluid flow countercurrently. This method decreases the temperature difference between the evaporating and condensing refrigerant but maintains a high enough temperature difference between the refrigerant and external heat transfer fluid to effectively transfer heat. Another benefit of this type of system is that pressure differences are also minimized. This can result in an improvement in energy efficiency and/or capacity versus conventional systems.
It is recognized in the art that a composition is zeotropic if, after 50 weight percent of the composition is removed such as by evaporation or boiling off, the difference in vapor pressure between the original composition and the composition remaining after 50 weight percent of the original composition has been removed is greater than 10 percent, when measured in absolute units. By absolute units, it is meant measurements of pressure and, for example, psia, atmospheres, bars, torr, dynes per square centimeter, millimeters of mercury, inches of water and other equivalent terms well known in the art.
It is also recognized in the art that a composition is zeotropic if the temperature glide in the evaporator and/or condenser is greater than about 3.degree. C.
Therefore, included in this invention are compositions of effective amounts of HFC-32, HFC-125, N.sub.2 O and ethane; HFC-32, HFC-125, HFC-134a and N.sub.2 O to form a zeotropic mixture. Addition of N.sub.2 O to a ternary mixture such as HFC-32/HFC-125/HFC-134a results in a more linear temperature glide profile and thereby provides more effective utilization of heat transfer surfaces.
The components of the compositions of this invention have the following vapor pressures at the temperature specified.
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25.degree. C.
-30.degree. C.
Components Psia kPa Psia kPa
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HFC-23 665.5 4588 148.0
1020
HFC-32 246.7 1701 40.4 279
FC-116 453.9 3130 109.8
757
HFC-125 199.1 1373 32.9 227
HFC-134a 98.3 677 12.2 84
N.sub.2 O 769.7 5307 189.4
1306
Ethane 566.3 3905 152.9
1054
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Substantially constant boiling, azeotropic or azeotrope-like compositions of this invention comprise the following at the temperature specified:
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Weight Ranges
Preferred Ranges
Components
T.degree. C.
(wt. %/wt. %)
(wt. %/wt. %)
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23/N.sub.2 O
-30 1-99/1-99 10-99/1-90
N.sub.2 O/Ethane
-30 1-99/1-99 40-99/1-60
23/116/N.sub.2 O
25 1-98/1-79/1-98
1-70/10-80/1-60
32/125/N.sub.2 O
25 15-84/15-84/1-5
15-60/30-84/1-5
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Substantially constant boiling zeotropic compositions of this invention comprise the following at the temperature specified:
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Weight Ranges Preferred Ranges
Components T.degree. C.
(wt. %/wt. %) (wt. %/wt. %)
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32/125/N.sub.2 O/ethane
-30 5-40/30-90/1-20/1-10
10-30/40-80/
1-10/1-5
32/125/134a/N.sub.2 O
-30 5-50/10-60/20-70/1-20
20-40/10-30/
30-50/1-15
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For purposes of this invention, "effective amount" is defined as the amount of each component of the inventive compositions which, when combined, results in the formation of an azeotropic or azeotrope-like composition. This definition includes the amounts of each component, which amounts may vary depending on the pressure applied to the composition so long as the azeotropic or azeotrope-like compositions continue to exist at the different pressures, but with possible different boiling points.
Therefore, effective amount includes the amounts, such as may be expressed in weight percentages, of each component of the compositions of the instant invention which form azeotropic or azeotrope-like compositions at temperatures or pressures other than as described herein.
For the purposes of this discussion, azeotropic or constant-boiling is intended to mean also essentially azeotropic or essentially-constant boiling. In other words, included within the meaning of these terms are not only the true azeotropes described above, but also other compositions containing the same components in different proportions, which are true azeotropes at other temperatures and pressures, as well as those equivalent compositions which are part of the same azeotropic system and are azeotrope-like in their properties. As is well recognized in this art, there is a range of compositions which contain the same components as the azeotrope, which will not only exhibit essentially equivalent properties for refrigeration and other applications, but which will also exhibit essentially equivalent properties to the true azeotropic composition in terms of constant boiling characteristics or tendency not to segregate or fractionate on boiling.
It is possible to characterize, in effect, a constant boiling admixture which may appear under many guises, depending upon the conditions chosen, by any of several criteria:
The composition can be defined as an azeotrope of A, B, C (and D . . . ) since the very term "azeotrope" is at once both definitive and limitative, and requires that effective amounts of A, B, C (and D . . . ) for this unique composition of matter which is a constant boiling composition.
It is well known by those skilled in the art, that, at different pressures, the composition of a given azeotrope will vary at least to some degree, and changes in pressure will also change, at least to some degree, the boiling point temperature. Thus, an azeotrope of A, B, C (and D . . . ) represents a unique type of relationship but with a variable composition which depends on temperature and/or pressure. Therefore, compositional ranges, rather than fixed compositions, are often used to define azeotropes.
The composition can be defined as a particular weight percent relationship or mole percent relationship of A, B, C (and D . . . ), while recognizing that such specific values point out only one particular relationship and that in actuality, a series of such relationships, represented by A, B, C (and D . . . ) actually exist for a given azeotrope, varied by the influence of pressure.
An azeotrope of A, B, C (and D . . . ) can be characterized by defining the compositions as an azeotrope characterized by a boiling point at a given pressure, thus giving identifying characteristics without unduly limiting the scope of the invention by a specific numerical composition, which is limited by and is only as accurate as the analytical equipment available.
The azeotrope or azeotrope-like compositions of the present invention can be prepared by any convenient method including mixing or combining the desired amounts. A preferred method is to weigh the desired component amounts and thereafter combine them in an appropriate container.
For the purposes of this discussion, zeotropic is intended to mean also essentially non-azeotropic or not constant boiling. The zeotropic compositions of the present invention can be prepared by any convenient method including mixing or combining the desired amounts. A preferred method is to weigh the desired component amounts and thereafter combine them in an appropriate container.
Specific examples illustrating the invention are given below. Unless otherwise stated therein, all percentages are by weight. It is to be understood that these examples are merely illustrative and in no way are to be interpreted as limiting the scope of the invention.
EXAMPLE 1 Phase StudyA phase study shows the following composition is azeotropic. The temperature is specified below.
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Vapor Pressure
Composition
T(.degree. C.)
Weight Percents
psia kPa
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23/N.sub.2 O
-30 15.3/84.7 192.8
1329
N.sub.2 O/Ethane
-30 75.1/24.9 213.2
1470
23/116/N.sub.2 O
25 15.1/33.9/51.0
826.9
5701
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EXAMPLE 2
Impact of Vapor Leakage on Vapor Pressure
A vessel is charged with an initial liquid composition. The liquid, and the vapor above the liquid, are allowed to come to equilibrium, and the vapor pressure in the vessel is measured. Vapor is allowed to leak from the vessel, while the temperature is held constant at the specified temperature until 50 weight percent of the initial charge is removed, at which time the vapor pressure of the composition remaining in the vessel is measured. The results are summarized below.
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0% change
Refrigerant
0 wt % evaporated
50 wt % evaporated
in vapor
Composition
psia kPa psia kPa pressure
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23/N.sub.2 O (-30.degree. C.)
1/99 190.0 1310 189.9 1309 0.1
10/90 192.5 1327 192.4 1327 0.0
15.3/84.7
192.8 1329 192.8 1329 0.0
30/70 191.1 1318 190.4 1313 0.4
50/50 184.2 1270 181.7 1253 1.4
70/30 172.8 1280 169.4 1168 2.0
90/10 157.6 1087 155.8 1074 1.1
99/1 149.9 1034 149.7 1032 0.1
N.sub.2 O/ethane (-30.degree. C.)
1/99 156.3 1078 155.6 1073 0.4
20/80 178.7 1232 171.3 1181 4.1
40/60 197.5 1362 191.2 1318 3.2
60/40 209.8 1447 208.1 1435 0.8
75.1/24.9
213.2 1470 213.2 1470 0.0
90/10 207.7 1432 205.6 1418 1.0
99/1 193.9 1337 192.9 1330 0.5
23/116/N.sub.2 O (25.degree. C.)
15.1/33.9/51.0
826.9 5701 826.9 5701 0.0
1/1/98 775.0 5343 772.8 5328 0.3
1/98/1 501.7 3459 466.1 3214 7.1
98/1/1 672.8 4639 669.9 4619 0.4
42/50/8 768.6 5299 763.7 5266 0.6
46/54/1 744.4 5132 741.4 5112 0.4
20/40/40 823.9 5681 822.7 5672 0.1
40/20/40 809.5 5581 802.9 5536 0.8
40/40/20 797.0 5495 793.3 5470 0.5
80/10/10 729.7 5031 713.4 4919 2.2
10/80/10 721.8 4977 647.8 4466 10.3
10/79/11 729.2 5028 658.5 4540 9.7
10/10/80 806.9 5563 800.0 5516 0.9
32/125/N.sub.2 O (25.degree. C.)
27/70/3 260.9 1799 240.8 1660 7.7
29/70/1 242.2 1670 234.3 1615 3.3
26/70/4 270.1 1862 244.2 1684 9.6
50/49/1 249.9 1723 243.5 1679 2.6
50/45/5 284.5 1962 256.7 1770 9.8
15/84/1 232.1 1600 223.3 1540 3.8
15/82/3 253.4 1747 231.7 1598 8.6
80/19/1 253.0 1744 247.5 1706 2.2
80/15/5 283.5 1955 257.8 1777 9.1
84/15/1 253.0 1744 247.6 1707 2.1
32/125/N.sub.2 O/ethane (25.degree. C.)
22/75/2/1
275.6 1900 238.1 1642 13.6
5/80/10/5
416.0 2868 309.5 2134 25.6
40/30/20/10
544.5 3754 435.3 3001 20.1
40/50/9/1
342.0 2358 276.0 1903 19.3
5/90/3/2 296.2 2042 234.1 1614 21.0
14/80/1/5
348.4 2402 255.8 1764 26.6
15/60/20/5
491.6 3389 384.0 2648 21.9
HFC-32/HFC-125/HFC-134a/N.sub.2 O (25.degree. C.)
32/18/42/8
259.9 1792 188.7 1301 37.7
5/30/60/5
193.9 1337 136.0 938 29.9
50/20/22/8
285.1 1966 228.8 1578 19.7
30/10/50/10
267.2 1842 179.9 1240 32.7
10/60/29/1
192.2 1325 172.2 1187 10.4
20/50/20/10
298.2 2056 226.4 1560 24.1
9/20/70/1
148.4 1023 124.4 858 16.2
10/30/40/20
352.5 2430 220.6 1521 37.4
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The results of this Example show that these compositions are azeotropic or azeotrope-like because when 50 wt. % of an original composition is removed, the vapor pressure of the remaining composition is within about 10% of the vapor pressure of the original composition except for 32/125/N.sub.2 O/ethane and 32/125/134a/N.sub.2 O which are zeotropic.
EXAMPLE 3 Impact of Vapor Leakage at 25.degree. C.A leak test is performed on compositions of 23 and N.sub.2 O, at the temperature of 25.degree. C. The results are summarized below.
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Refrigerant
0 wt % evaporated
50 wt % evaporated
0% change in
Composition
psia kPa psia kPa vapor pressure
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23/N.sub.2 O
1/99 772.1 5323 771.4 5319 0.1
10/90 785.5 5416 784.2 5407 0.2
24.1/75.9
791.5 5457 791.5 5457 0.0
4O/60 785.4 5415 783.6 5403 0.2
60/40 762.0 5254 755.8 5211 0.8
80/20 721.6 4975 714.5 4926 1.0
99/1 668.6 4610 668.0 4606 0.1
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These results show that compositions of HFC-23 and N.sub.2 O are azeotropic or azeotrope-like at different temperatures, but that the weight percents of the components vary as the temperature is changed.
EXAMPLE 4 13B1 Alternative Refrigerant PerformanceThe following table shows the performance of various refrigerants in an ideal vapor compression cycle. The data are based on the following conditions.
Condenser=100.degree. F. (37.8.degree. C.)
Evaporator=-40.degree. F. (-40.0.degree. C.)
Subcooled=15.degree. F. (8.3.degree. C.)
Return Gas=-10.degree. F. (-23.3.degree. C.)
Clearance Volume=3%
Efficiency=70%
The refrigeration capacity is based on a compressor with a fixed displacement of 3.5 cubic feet per minute and 70% volumetric efficiency. Capacity is intended to mean the change in enthalpy of the refrigerant in the evaporator per pound of refrigerant circulated, i.e. the heat removed by the refrigerant in the evaporator per time. Coefficient of performance (COP) is intended to mean the ratio of the capacity to compressor work. It is a measure of refrigerant energy efficiency.
TABLE 1
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Compressor
Compressor Capacity
Discharge Discharge Btu/
Temp (.degree. F., .degree. C.)
Psia kPa COP min kW
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13B1 207 97 314 2165 1.75 70.5 1.2
HFC-32/HFC-125
269 131 335 2310 1.90 72.1 1.3
(50/50 wt %)
HFC-32/HFC-
231 111 349 2406 1.82 67.8 1.2
125/N.sub.2 O
(27/70/3 wt %)
HFC-32/HFC-
223 106 355 2448 1.76 64.1 1.1
125/N.sub.2 O/Ethane
(22/75/2/1 wt %)
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The data in Table 1 show that the HFC-32/HFC-125/N.sub.2 O composition and the HFC-32/HFC-125/N.sub.2 O/ethane composition provide a compressor discharge temperature closer to 13B1 (bromotrifluoromethane) than HFC-32/HFC-125. The discharge temperature can be effectively lowered while improving energy efficiency (COP) versus 13B1.
EXAMPLE 5 R-503 AlternativeCondenser=-26.degree. F. (-32.degree. C.)
Evaporator=-112.degree. F. (-80.degree. C.)
No Subcool
Superheated=54.degree. F. (30.degree. C.)
Clearance Volume=3%
Efficiency=70%
TABLE 2
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Compressor
Compressor
Discharge Discharge
Capacity
Temp
(.degree. F., .degree. C.)
Psia
kPa
COP
Btu/min
kW
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R-503 139 59.4 159
1096
2.62
75 1.3
HFC-23/HFC-116
107 41.7 161
1110
2.53
70 1.2
(46/54 wt %)
HFC-23/HFC-116/N.sub.2 O
(38/52/10 wt %)
118 47.8 183
1262
2.55
82 1.4
(42/50/8 wt %)
120 48.9 178
1227
2.54
79 1.4
HFC-23/N.sub.2 O
244 118 177
1220
2.67
91 1.6
(15.3/84/7 wt %)
N.sub.2 O/Ethane
202 94.4 119
1373
2.65
107 1.9
(75.1/24.9 wt %)
__________________________________________________________________________
The data in Table 2 show that addition of N.sub.2 O to HFC-23/HFC-116 compositions significantly increases capacity and provides better efficiency than HFC-23 and HFC-116 while maintaining compressor discharge temperature below R-503. R-503 is an azeotropic mix of 40 wt % HFC-23 and 60 wt % R-13 (chlorotrifluoromethane).
EXAMPLE 6 High Pressure HCFC-22 Alternative Refrigerant PerformanceThe following table shows the performance of refrigerants of the present invention in a high efficiency vapor compression system. The data show system performance using cross-flow and countercurrent-flow heat exchangers with a zeotropic mixture of the present invention containing 32 weight percent HFC-32, 18 weight percent HFC-125, 42 weight percent HFC-134a and 8 weight percent nitrous oxide (N.sub.2 O). The N.sub.2 O containing zeotropic mixture is compared to a leading high pressure HCFC-22 alternative, an azeotropic mixture of 50 weight percent HFC-32 and 50 weight percent HFC-125.
For the test conditions, all heat exchangers have equal UA, equal air flows, and 5 psia pressure drop. Initial conditions for the condenser and evaporator are 47.8.degree. C. (118.degree. F.) and 8.9.degree. C. (48.degree. F.) respectively. For a countercurrent flow system, the condenser temperature is effectively reduced by 0.5.degree. C. and the evaporator temperature is effectively increased by 1.6.degree. C. when operating with the zeotropic mixture. Other system conditions include no subcool, no superheat, and a fixed compressor displacement of 0.1 m.sup.3 /min.
Results for HFC-32/HFC-125 using typical cross-flow heat exchangers and HFC-32/HFC-125/HFC-134a/N.sub.2 O using cross-flow and counter-flow heat exchangers are shown in Table 3.
TABLE 3
______________________________________
HFC-32/ HFC-32/HFC-125/
HFC-125 HFC-134a/N.sub.2 O
(50/50 wt %)
(32/18/42/8 wt %)
Cross-flow
Cross-flow
Counter-flow
______________________________________
Discharge temperature (.degree. C.)
77.3 85.6 83.5
Condenser average
47.8 47.8 47.3
temperature (.degree. C.)
Condenser pressure (kPa)
2925 2700 2670
Liquid temperature (.degree. C.)
47.8 42.8 42.3
Evaporator average temp.
8.9 8.9 10.5
(.degree. C.)
Evaporator pressure (kPa)
1065 879 926
Suction temperature
8.9 12.9 14.6
Condenser delta T (.degree. C.)
0.10 10.7 10.8
Evaporator delta T (.degree. C.)
0.04 9.1 9.3
Cooling Load, W
8770 8033 8607
Isentropic COP 4.99 5.03 5.40
______________________________________
The data in Table 3 show that taking advantage of the increased temperature glide (Delta T) of the zeotropic N.sub.2 O mixture with countercurrent-flow heat exchangers significantly increases system efficiency (COP) while providing equivalent capacity (within 2%) versus HFC-32/HFC-125. Evaporator and condenser pressures are also significantly reduced versus HFC-32/HFC-125.
ADDITIONAL COMPOUNDSOther components, such as aliphatic hydrocarbons having a boiling point of -100 to +60.degree. C., hydrofluorocarbonalkanes having a boiling point of -100 to +60.degree. C., hydrofluoropropanes having aboiling point of between -100 to +60.degree. C., hydrocarbon ethers having a boiling point between -100 to +60.degree. C., hydrochlorofluorocarbons having a boiling point between -100 to +60.degree. C., hydrofluorocarbons having a boiling point of -100 to +60.degree. C., hydrochlorocarbons having a boiling point between -100 to +60.degree. C., chlorocarbons, inorganics and perfluorinated compounds, can be added to the azeotropic, azeotrope-like, zeotropic compositions described above without substantially changing the properties thereof.
Additives such as lubricants, surfactants, corrosion inhibitors, stabilizers, dyes and other appropriate materials may be added to the novel compositions of the invention for a variety of purposes provides they do not have an adverse influence on the composition for its intended application. Preferred lubricants include esters having a molecular weight greater than 250.
Claims
1. An azeotrope-like composition consisting essentially of from 40 to about 99 weight percent nitrous oxide and from about 1 to 60 weight percent trifluoromethane (HFC-23), said composition having a vapor pressure of from about 762 psia (5254 kPa) to about 791.5 psia (5457 kPa) at a temperature of about 25.degree. C.
2. An azeotropic composition consisting essentially of about 84.7 weight percent nitrous oxide and about 15.3 weight percent trifluoromethane (HFC-23), wherein when the temperature has been adjusted to about -30.degree. C., said composition has a vapor pressure of about 192.8 psia (1329 kPa).
3. An azeotropic composition consisting essentially of about 75.9 weight percent nitrous oxide and about 24.1 weight percent trifluoromethane (HFC-23) wherein when the temperature has been adjusted to about 25.degree. C., said composition has a vapor pressure of about 791.5 psia (5457 kPa).
4. A process for cooling a body, comprising evaporating the composition of claims 1, 2, or 3 in the vicinity of the body to be cooled.
5. A process for producing refrigeration, comprising condensing a composition of any of claims 3 and thereafter evaporating said composition in the vicinity of the body to be cooled.
| 3723318 | March 1973 | Butler |
| 3812040 | May 1974 | Borchardt |
| 5766503 | June 16, 1998 | Shiflett et al. |
| 5-259128 | October 1993 | JPX |
| 94/01512 | January 1994 | WOX |
- Chemical Abstracts, 77:50685, "Predicting critical temperature of azeotropes", Li, 1972. David A. Didion and Donald B. Bivens, Role of Refrigerant Mixtures As Alternatives to CFCs, ASHRAE CFC Technology Conference, Gaithersburg, MD in 1989, May, 1990. R. L. Powell, Extending the Range, International Conference Proceedings, CFCs, The Day After, Joint Meeting of IIR Commissions B1, B2, E1 and E2, Padova, Italy, 11-19, Sep. 21-23, 1994.
Type: Grant
Filed: Mar 19, 1998
Date of Patent: Dec 5, 2000
Assignee: E. I du Pont de Nemours and Company. (Wilmington, DE)
Inventors: Barbara Haviland Minor (Elkton, MD), Donald Bernard Bivens (Kennett Square, PA), Clifford Keith Rice (Clinton, TN), James Richard Sand (Oak Ridge, TN)
Primary Examiner: Christine Skane
Attorney: Mark A. Edwards
Application Number: 9/44,303
International Classification: C09K 504;
