WO1995004787A1

WO1995004787A1 - Mixture refrigerants

Info

Publication number: WO1995004787A1
Application number: PCT/US1994/009047
Authority: WO
Inventors: Mikhail Boyarsky; Richard Stevenson; Boris V. Yudin; Oleg N. Podcherniaev
Original assignee: Intermagnetics General Corporation
Priority date: 1993-08-10
Filing date: 1994-08-10
Publication date: 1995-02-16

Abstract

A mixed refrigerant for use as a drop-in replacement for CFC refrigerants which include a first flame-retardant refrigerant constituent selected from a first group of low nominal boiling point refrigerants, a second component comprising at least one flame-retardant refrigerant constituent selected from a group of higher nominal boiling point refrigerants, and a third component comprising at least one hydrocarbon selected from a restricted group of hydrocarbons.

Description

MIXTURE REFRIGERANTS

BACKGROUND OF THE INVENTION

This invention relates to mixed refrigerants (MR), and more particularly to a mixed refrigerant for use as a replacement of an existing chlorofluorocarbon refrigerant.

Chloronated fluorocarbon refrigerants (CFC) have been implicated in causing environmental damage. Specifically, these gases which are very inert, are released from the refrigeration systems at ground level and diffused into the upper atmosphere. Because of their inertness, the gases are able to survive without decomposition until they reach the stratosphere where they are broken down by ultraviolet radiation, releasing chlorine atoms which break down the stratospheric ozone layer. There has recently been

considerable concern about reductions in stratospheric ozone levels and this has led to bans on certain CFC's such as R-12, R-11, and others.

In automobile air conditioning systems, typically R-12 has been utilized. As such has been banned for future use after a given phase-out period, alternatives have been considered. At present, the best known new refrigerant for replacement of R-12 for automobile air conditioning use has been considered R-134A. While this material comprised of C₂H₂F₄ is ozone safe, it will not work in most existing automobile air conditioning systems using R-12 without expensive retro-fitting. Various automobile manufacturers are already installing new equipment in new automobiles scheduled for future sales which will accommodate the R-134A refrigerant. However, for the many existing automobiles, the imposition of the restrictions on R-12 will require such retro-fitting. Knowledgeable estimates predict a costly conversion requirement to convert the air conditioning systems to make it compatible with R-134A.

Considerable efforts are being made to provide a drop-in replacement for R-12 in order to permit utilization of existing automobile air conditioning systems without unnecessary expensive retro-fitting. One type of

refrigerant that has been given considerable attention are the hydrocarbons and, especially, propane. While propane has many useful thermodynamic properties which could perhaps serve as a replacement for R-12, unfortunately, its

flammability prohibits its direct use. Proposals have therefore been to combine various hydrocarbons with other ingredients in order to provide an adequate mixture for replacement of R-12.

From a theoretical viewpoint, a preferable mixture would have at least 70% hydrocarbons, with the other 30% being flame-retardant fluorocarbons. Tests have shown that such mixtures provide excellent thermodynamic properties for replacement of R-12, as well as other refrigerants which are being banned. While these mixtures will not ignite, and are therefore in practice non-flammable, numerous standards exist for flammability testing and in order to meet some of the most restrictive flammability standards, it may be necessary to increase the amount of flame-retardant components in a mixture even though it sacrifices the thermodynamic properties.

Furthermore, in designing a specific mixture,

additional factors and constraints must be taken into consideration. Specifically, there are environmental safety conditions which must be met including sufficiently low ozone depletion potential, as well as sufficiently low global warming potential. Furthermore, the ultimate result should be of low toxicity.

There also exist additional constraints which must be met including material compatibility so that the resulting refrigerant will not deteriorate the material from which the system are constructed. As to the developing "drop in" refrigerant, one of the most important parameters is hose penetration. Oil compatibility is also a severe problem since the oil must be a part of the air conditioning system and the gas mixture must be able to accommodate oils that are already on the market, including certain synthetic akylbenzenes and esters.

The mixed refrigerant must also be compatible with the particular equipment that is being utilized within the refrigerating system. A system based on the new mixed refrigerant should have the same pressure values as the refrigerant being replaced both at the condensor (high pressure) and at the evaporator (low pressure). There also exist the performance requirement so that the mixture must have its thermodynamic characteristics closely match those of the refrigerant being replaced and must have a coefficient of performance sufficiently high to provide efficient results with the system being utilized.

Finally, there are commercial aspects, namely the components of the mixture should be relatively cheap and available on the market.

Unfortunately, in designing mixtures to meet some of these constraints, sacrifices must be made. For example, while hydrocarbons provide excellent oil compatibility, they are of high flammability. On the other hand, fluorocarbons are generally of flame-retardant capabilities, however, they present problems with oil compatibility. Each of these has its own unique ozone depletion potential and global warming potential, and generally, it is required that the ozone and global problem should not be worse than the levels which may be acceptable according to the current government

regulations. Furthermore, when using hydrocarbons, there is a problem that the hydrocarbon in its vapor and liquid phase should be approximately equal so that there will be a reduced problem of flammability, should there be leakage.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a refrigerant which can serve as a replacement for an existing CFC refrigerant of the type subject to government restrictions because of environmental problems.

A further object of the present invention is to provide a specific group of replacements for a R-12 refrigerant, typically utilized in automobile air conditioning systems.

Yet, another object of the present invention is to provide a mixed refrigerant which can replace an existing CFC refrigerant and which provides environmental safety, material compatibility, oil compatibility, equipment compatibility, non-flammability, non-toxicity, a high coefficient of performance and has sufficiently reasonable commercial costs.

These and other objects, features and advantages of the invention will, in part, be pointed out with particularity, and will, in part, become obvious from the following detailed description of the invention, taken in conjunction with the accompanying drawings, which form an integral part thereof. BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures;

Figs, 1-7 show thermodynamic curves of temperature versus enthalpy for 7 mixed refrigerants in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides for a mixed refrigerant which can serve as replacement for CFC refrigerants and, specifically, is useful for replacement of the R-12

refrigerant. The present invention recognizes that there are numerous constraints that must be addressed and that no single component provides an adequate coverage to meet all of the constraints. Specifically, these constraints include the environmental safety constraints which include the ozone depletion potential, global warming potential, and low toxicity. Also to be addressed are the material

compatibility aspects of the mixture such that it should not deteriorate the other components of the system. The mixed refrigerant should not leak through seals and hoses of the system. Oil compatibility is of major significance since the material must be able to work with existing oils in the equipment. Equipment compatibility is another problem which must be met by the gas mixture. A serious problem is the flammability problem. Although there exist numerous flammability tests, and while some of the tests can be met with a minimal amount of non-flammable components, others tests are more stringent and require higher degrees of nonflammable components. Finally, the co-efficient of

performance of the ultimate product must be such that the thermodynamic characteristics of the ultimate gas mixture must meet those of the refrigerants being replaced and it must operate efficiently. Of course, the commercial aspects are such that the components of the mixture should be relatively reasonable in cost and available on the market.

Based upon the foregoing, the present invention has recognized that there are only a limited number of

components from which replacements can be chosen when utilizing hydrocarbons and flame-retardant components.

Beginning with the basic gas to be replaced, by way of example R-12, it is noted that the nominal normal boiling point of R-12 is at 243.4K. In order to provide a mixed refrigerant replacement, a limited number of flame-retardant components having a nominal boiling point lower than this boiling point can be used and a limited number of flame- retardant refrigerants having a greater nominal boiling point than this can be utilized without deviating

excessively from the thermodynamic results. Likewise, there are a limited number of hydrocarbon components below and above this boiling point which can be utilized. More particularly, it has been found that of the available gases having a lower nominal boiling point than the nominal boiling point of the R-12 refrigerant, those flame-retardant components that can be utilized which can meet the numerous constraints indicated above include SF-6, R-125 (C₂HF₅), R-22 (CHClF₂), and R-218 (C₃F₈).

Of the flame-retardant components having a higher nominal boiling point than R-12 which can be utilized there exist R-134A (C₂H₂F₄), R-124 (C₂HClF₄), RC-318 (C₄F₈), and R-123 (C₂HCl₂F₃).

Of the hydrocarbons that can be used, the two

hydrocarbons having lower nominal boiling points than the R-12 include propylene (C₃H₆) and propane (C₃H₈). Of the hydrocarbon components having a higher nominal boiling point than the R-12 which can be utilized include isobutane

(iC₄H₁₀) and normal butane (nC₄H₁₀). Also, non-saturated derivatives of these hydrocarbons may be used, like

butadiene, butene, etc., and such are included in the definition of the hydrocarbons, herein.

Substances which are the isomers of the flame retardant components (like R-134, R-123a, etc.) or isomers of the hydrocarbons described herein, may also be used as

components and such are herein included in the recitation of each of the individual components.

It should be appreciated that the actual boiling point temperature of a component depends on its purity and accordingly, may vary slightly. However, the boiling points herein described and listed hereafter in Table 1 are the nominal boiling points for each of the components.

The method of combining these various ingredients, however, is not readily apparent in order to provide all of the constraints. Each of these components, while they may be adequate in certain regards, they fail in other parts. By way of example, it is noted that R-134A, while providing zero ozone depletion potential and acceptable global warming potential has bad thermodynamic efficiency problems and presents oil compatibility problems. R-22, while likewise providing fairly good global warming potential will have to be phased out after a limited number of years due to high ozone depletion potential and must only be used in limited proportions at the present time. R-123 has acceptable ozone depletion potential and good global warming potential, but is slightly toxic. R-124 has acceptable ozone depletion potential and good global warming potential, but has poor material compatibility. R-125 has excellent ozone depletion potential, fairly good global warming potential, but is expensive and is only in limited availability. The

hydrocarbons, of course, provide excellent thermodynamic characteristics, but are highly flammable, although they do provide excellent oil compatibility.

Accordingly, it is apparent that the necessary balance between the yarious components is such that the ultimate results must provide a satisfactory compromise for all of the constraints and, of course, provide the necessary thermodynamic requirements for the refrigerant that is being replaced, in this case, R-12.

Because of its placement close to the nominal boiling point of R-12, although R-134A has a higher nominal boiling point, in forming a mixture, R-134A is to be included with those having a lower nominal boiling point than R-12.

Applicant has found that it is possible to produce an excellent drop-in replacement for a banned refrigerant and, specifically, for R-12, comprising the following

composition. A first component includes at least one flame-retardant refrigerant constituent selected from the group of low nominal boiling point flame-retardants including SF-6, R-125, R-22, R-218, R-134A, and mixtures thereof. A second component including at least one flame-retardant refrigerant constituent selected from the group consisting of high nominal boiling point flame-retardants including R-124, RC- 318, R-123, and mixtures thereof. A third component including at least one hydrocarbon constituent selected from the group consisting of propylene, propane, i-butane, n-butane, and mixtures thereof.

In addition to the above selection of components, in order to meet the most stringent of flammability tests and, at the same time, provide adequate oil compatibility, there must be between 15 and 30 mole percent of the hydrocarbon components, and between 70 and 85 mole percent of the flame-retardant refrigerant components. However, in addition to the above constraints, applicant has found that to fulfill all of the required constraints there should be at least two fluorocarbon components having adjacent nominal boiling point temperatures in a row, or two hydrocarbons having adjacent nominal boiling point temperatures in a row.

Accordingly, if only one hydrocarbon constituent is selected for the gas mixture, there must be at least two flame-retardant refrigerant constituents having nominal boiling point temperatures greater than or less than the nominal boiling point temperature of the hydrocarbon. On the other hand, if there are more than one hydrocarbon constituent in the final mixture, then either there are no flame-retardant refrigerant constituents having nominal boiling point temperatures between those of the two hydrocarbon

constituents, or there must be at least two flame-retardant refrigerant constituents having nominal boiling point temperatures between those of the two hydrocarbon

constituents.

It has also been found that i-pentane and n-pentane has a boiling point which is too far removed from that of R-12 to be of use as a major component in the final mixture, nevertheless, the presence of i-pentane or n-pentane in small amounts can provide an improvement in the overall efficiency of the refrigerant, particularly at extremely high ambient temperatures. Such additions up to about 5% have been shown to be effective. The presence of such i-pentane or n-pentane lowers the pressure, at a set

temperature, of the high pressure isobar without very much effecting the low pressure isobar and, hence, reducing the compression ratio and the work done by the compressor.

In determining the thermodynamic effectiveness of the mixture replacement for the existing refrigerant, the replacement should have the same or lower pressure at the high temperature of the condenser and should have a pressure at least as high if not higher, at the low temperature which is the temperature of the evaporator.

Various example mixtures that have been tried and tested using the above constraints will now be given. All the mixed refrigerants given below are examples which provide the same values of high and low pressures like that of the refrigerant R-12 being replaced.

The influence of variations in composition of various components on the thermodynamic properties is of great interest, not only in respect to the relative depletion of one component compared to another as a vessel containing the refrigerant is emptied, but also in respect to variations in composition during manufacture. For a three-component mixed refrigerant, the tolerances on compositions must be rather tight and a 3 or 5% variation in concentration of one component causes similar variations in the compositions of the other components and may well cause a significant deterioration of the thermodynamic properties. With four, five, and six components like situation is much eased, particularly if the refrigerant is made of pairs of similar components. Thus a six-component mixture might contain the propane R-22 "pair", two substances which are very similar in their effects. A design for the refrigerant might specify a molar concentration of propane at 5% and a concentration of R-22 at 15%; in practice, little difference in performance would be perceived if the propane were at a composition of 15% and the R-22 at 5%, the point is that these multi-component mixed refrigerants which have within them pairs of substances with similar boiling points can be designed so that their compositions can tolerate

considerable variation within the pair with little if any effect on the thermodynamic properties. However, such dramatic variations may have effect on some of the other constraints.

Example 1 - The first example comprises the following ingredients in the following proportions in mole

percentages:

R-22 - 32-38%

R-134A - 27-33%

i-butane - 23-27%

R-123 - 9-11%

The pressure range were 4 atmospheres for the low pressure and 24 atmospheres for the high pressure. The minimal temperature was 220K. The thermodynamic

characteristic is shown in Fig. 1 from which it can be seen that the mixture of Example 1, designated as Patent 1, provides a fairly good replacement for the R-12 refrigerant. The temperature difference of the replacement between its dew point and boiling point at the low pressure was 12.1K and at the high pressure was 7.8K. Note: Ta is the ambient temperature; Tc is the cooling temperature; Pl is the low pressure, and Ph is the high pressure.

Example 2 - The following example was provided, with the components and their mole percentages given:

R-22 - 9-11%

R-134A - 41-49%

R-124 - 18-22%

i-butane - 23-27%

The pressures were low pressure of 4 atmospheres and high pressure of 24 atmospheres, and the minimal temperature was 220K.

The thermodynamic characteristics of the results, identified as the mixture Patent 2 is shown in attached Fig. 2. The temperature difference of the replacement between its dew point and boiling point at the low pressure was 2.3K and at the high pressure was 1.8K.

Example 3 - A third example calculated from the above comprise the following components in the following mole percentages:

R-22 - 9-11%

Propane - 13-17%

R-134A - 22-27%

R-124 - 32-38%

i-butane - 13-17%

The low pressure was 4 atmospheres and the high pressure was 24 atmospheres. The minimal temperature was 220K.

The resulting characteristic is shown in Fig. 3 wherein the mixture identified as Patent 3 is compared with the basic refrigerant being replaced R-12. The temperature difference of the replacement between its dew point and boiling point at the low pressure was 6.5K and at the high pressure was 3.2K.

Example 4 - A fourth example calculated from the above comprise the following components in the following mole percentages:

R-22 - 9-11%

R-134A - 45-55%

RC-318 - 9-11%

i-butane - 22-27%

The resulting characteristics is shown in Fig. 4 wherein the mixture identified as Patent 4 is compared with the basic refrigerant being replaced R-12. The temperature difference of the replacement between its dew point and boiling point at the low pressure was 2.1K and at the high pressure was 1.7K.

Example 5 - A fifth example calculated from the above comprise the following components in the following mole percentages:

R-22 - 18-22%

Propane - 4-6%

R-134A - 35-45%

RC-318 - 18-22%

n-butane - 13-17%

The resulting characteristics is shown in Fig. 5 wherein the mixture identified as Patent 5 is compared with the basic refrigerant being replaced R-12. The temperature difference of the replacement between its dew point and boiling point at the low pressure was 5.5K and at the high pressure was 3.2K.

Example 6 - A sixth example calculated from the above comprise the following components in the following mole percentages:

Propane - 13-17%

R-134a - 35-45%

R-124 - 35-45%

n-butane - 4-6%

The low pressure was 4 atmospheres and the high pressure was 24 atmospheres. The minimal temperature was 223K.

The resulting characteristics is shown in Fig. 6, wherein the mixture identified as Patent 6 is compared with the basic refrigerant being replaced R-12. The temperature difference of the replacement between its dew point and boiling point at the low pressure was 7.3K and at the high pressure was 3.4K.

Example 7 - A seventh example calculated from the above comprise the following components in the following mole percentages:

Propane - 13-17%

R-22 - 9-11%

R-134a - 23-27%

R-124 - 35-45%

n-butane - 9-11%

The resulting characteristics is shown in Fig. 7, wherein the mixture identified as Patent 7 is compared with the basic refrigerant being replaced R-12. The temperature difference of the replacement between its dew point and boiling point at the low pressure was 8.0K and at the high pressure was 4.1K.

These temperature differences of the replacement are significant to show the efficiency of the replacements. The less the temperature difference the closer they are to azeotropes and the closer to R-12. For example, the mixture refrigerants of Examples 2 and 4 are close replicates of R- 12 with an identical cooling capacity and small temperature differences between the bubble and dew point. Nevertheless, all these examples are excellent mimics of R-12.

Other mixture refrigerants that have been generated from the above for possible replacements of R-12 are given below in Table 1, together with the nominal boiling points of the components. Although each of these may not be as desirable as the above, they each had some areas meeting more of the constraints, but provided greater compromises in certain areas. Nevertheless, they each could be utilized as a replacement, depending upon the degree of compromise that is desired on any of the constraints.

There has been disclosed heretofore the best

embodiments of the invention presently contemplated.

However, it is to be understood that various changes and modifiσations may be made hereto without departing from the spirit of the invention.

Claims

Claims:

1. A refrigerant composition comprising:

a first component comprising at least one flame-retardant constituent selected from the group consisting of:

SF6, R-22, R-218, R-134A, and mixtures thereof;

a secσnd component comprising at least one flame-retardant refrigerant constituent selected from the group consisting of:

R-124, RC-318, R-123, and mixtures thereof; a third component comprising at least one hydrocarbon constituent selected from the group consisting of:

propylene, propane, i-butane, n-butane, and mixtures thereof;

there being between 15 and 30 mole percent of hydrocarbon components and 70-85 mole percent of flame-retardant refrigerant components, and wherein if there be only one hydrocarbon constituent, there are at least two flame- retardant refrigerant constituents having nominal boiling point temperatures greater than or less than the nominal boiling point temperature of the hydrocarbon, and if there is more than one hydrocarbon constituent than either, there are no flame-retardant refrigerant constituents having nominal boiling point temperatures between those of the hydrocarbon constituents or there are at least two flame retardant refrigerant constituents having nominal boiling point temperatures between those of the hydrocarbon constituents.

2. A refrigerant composition as in claim 1, and further comprising at least 5 molar percent of i-pentane or n-pentane.

3. A refrigerant composition as in claim 1, wherein the ozone depletion potential and the global warming potential is superior to that of R-12.

4. A refrigerant composition as in claim 1, and comprising in approximate mole percentage:

R-22 - 32-38%

R-134A - 27-33%

i-butane - 23-27%

R-123 - 9-11%

5. A refrigerant composition as in claim 1, and comprising in approximate mole percentage:

R-22 - 9-11%

R-134A - 41-48%

R-124 - 18-22%

i-butane - 23-17%

6. A refrigerant composition as in claim 1, and comprising in approximate mole percentage:

R-22 - 9-11%

Propane - 13-17%

R-134A - 22-27%

R-124 - 32-38%

i-butane - 13-17%

7. A refrigerant composition as in claim 1, and comprising in approximate mole percentages:

R-22 - 9-11%

R-134a - 45-55%

RC-318 - 9-11%

i-butane - 22-27%

8. A refrigerant composition as in claim 1, and comprising in approximate mole percentages: R-22 - 18-22%

Propane - 4-6%

R-134a - 35-45%

RC-318 - 18-22%

n-butane - 13-17%

9. A refrigerant composition as in claim 1, and comprising in approximate mole percentages:

Propane - 13-17%

R-134a - 35-45%

R-124 - 35-45%

n-butane - 4-6%

10. A refrigerant composition as in claim 1, and comprising in approximate mole percentages:

Propane - 13-17%

R-22 - 9-11%

R-134a - 23-27%

R-124 - 35-45%

n-butane - 9-11%

11. A refrigerant composition as in claim 1, and comprising at least four constituents.

12. A refrigerant composition as in claim 1, and comprising at least five constituents.