WO1994004629A1

WO1994004629A1 - Substantially constant boiling mixtures of 1,1,1,2-tetrafluoroethane, dimethyl ether and isobutane

Info

Publication number: WO1994004629A1
Application number: PCT/US1993/007483
Authority: WO
Inventors: Mark Brandon Shiflett
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1992-08-21
Filing date: 1993-08-13
Publication date: 1994-03-03
Anticipated expiration: 1995-02-21

Abstract

Substantially constant boiling composition comprising 2.5-95 weight percent 1,1,1,2-tetrafluoroethane, 2.5-95 weight percent dimethyl ether and 2.5-50 weight percent isobutane.

Description

TITLE SUBSTANTIALLY CONSTANT BOILING MIXTURES OF 144 TETRAFLUOROETHANE, DIMETHYL ETHER AND ISOBUTANE

BACKGROUND OF THE INVENTION

This invention relates to substantially constant boiling compositions that are mixtures of 1,1.1.2-tetrafluoroethane, dimethyl ether and isobutane.

Recently the long-term environmental effects of chlorofluorocarbons used as refrigerants, aerosol propellants, heat transfer media, blowing agents, etc. have come under scientific scrutiny because it has been postulated that these materials, because of their high stability, are able to reach the stratosphere where under the influence of ultraviolet radiation release chlorine atoms which, in turn, undergo chemical reaction with stratospheric ozone. Reduction of the stratospheric ozone layer would increase the amount of ultraviolet radiation reaching the earth's surface. In view of the potential environmental problems associated with stratospheric ozone depletion, there is a need for materials possessing properties which make them useful substitutes for applications in which chlorofluorocarbons have been used.

There is a limit to the number of single fhiorinated hydrocarbon substances which can be candidates as environmentally safe materials. Mixtures of fhiorinated hydrocarbons with other compounds, such as hydrocarbons, might be used if the desired combination of properties could be found in a given mixture. Simple mixtures, however, create problems in design and operation of refrigeration and other equipment because of component segregation in both the vapor and liquid phases. To avoid component segregation problems, it is particularly desirable to discover new substantially constant boiling blends containing hydrofluorocarbons. Such blends should not suffer from component segregation problems. Unfortunately, it is not possible to predict the formation of constant boiling compositions, thus complicating the search for novel constant boiling compositions which possess the desired combination of properties. There is a need for substantially constant boiling compositions that have properties which make them particularly useful as refrigerants, aerosol propellants, heat transfer media, gaseous dielectrics, fire extinguishing agents, expansion agents for polyolefins and polyurethanes, and as power cycle working fluids that are potentially environmentally safe.

SUMMARY OF THE INVENTION

The present invention is directed to substantially constant boiling compositions comprising 2.5-95 weight percent, usually 19-39 weight percent, 1,1,1,2-tetrafluoroethane (HFC- 134a), 2.5-95 weight percent, usually 49-69 weight percent, dimethyl ether (DME), and 2.5-50 weight percent, usually 7-17 weight percent, isobutane that are resistant to component segregation. Preferably, the substantially constant boiling compositions comprise 24-34 weight percent 1,1,1,2-tetraf-uoroethane, 54-64 weight percent dimethyl ether, and 7-17 weight percent isobutane. A particularly preferred composition contains about 29 weight percent 1,1,1,2- tetrafluoroethane, 59 weight percent dimethyl ether, and 12 weight percent isobutane boiling at about 25° C at about 4302 torr.

The novel compositions of the present invention exhibit a higher vapor pressure than any of its three constituents. Substantially constant boiling compositions of the present invention means that their vapor pressure at 25° C does not change by more than 10% after half of the initial mixture has been allowed to evaporate. Thus, the compositions described herein resist component segregation which would seriously dimmish their usefulness in the contemplated applications. The substantially constant boiling compositions are especially useful as refrigerants, heating applications, aerosol propellants, gaseous dielectrics, fire extinguishing agents, expansion agents for polyolefins and polyurethanes and as power cycle working fluids.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The fhiorinated compounds which comprise these mixtures are identified in the industry as HFC-134a (1,1,1,2-tetrafluoroethane), DME (dimethyl ether) and isobutane (IB). A phase study on various mixtures of 1,1,1,2-tetrafluoroethane, dimethyl ether and isobutane containing widely different amounts of the constituents indicate that at constant temperature an azeotrope is formed over the temperature range studied. Further studies for the evaluation of substantially constant boiling compositions containing a wide range of proportions of the components resulted in resistance to component fractionation of the mixture so that the compositions are substantially constant boiling at constant temperature. Utilizing the particular components in the amounts described, quite unexpectedly, illustrate that at a constant temperature of 25° C the change in vapor pressure of the compositions even after 50% of the initial composition has been allowed to evaporate does not change by more than 10%. The small change in vapor pressure at constant temperature illustrates that the amount of separation and loss of one component in excess amount that would substantially change the boiling temperature of the mixture does not occur, which makes the composition suitable for the contemplated uses, especially for use as a refrigerant.

As is well recognized in this field of technology, there is a range of compositions which contain the same components as the true azeotrope, which not only will exhibit substantially equivalent properties as the true azeotrope for refrigerant and other applications, but which will also exhibit substantially equivalent properties to the true azeotropic composition in terms of constant boiling characteristics or tendency not to segregate or fractionate on boiling at other temperatures and pressures. Additives that are frequently incorporated in the mixture that can be added to the present compositions include lubricants, corrosion inhibitors, stabilizers and dyes.

In addition to refrigeration applications, the novel substantially constant boiling compositions of this invention are also useful as aerosol propellants, heat transfer media, gaseous dielectrics, fire extinguishing agents, expansion agents for polyolefins and polyurethanes, and as power cycle working fluids.

The compositions described herein can be used to produce refrigeration by condensing the constant boiling compositions and thereafter evaporating the compositions, e.g., condensate, in the vicinity of a body to be cooled. Further, these compositions described herein can also be used to produce heat by condensing the constant boiling compositions in the vicinity of a body to be heated and thereafter evaporating the compositions.

The use of substantially constant boiling compositions of this invention eliminates the problem of component fractionation and handling in system operations because these compositions behave substantially as a single substance.

The compositions of the present invention have zero ozone depletion potentials compared with Refrigerant-12, which has an ozone depletion potential of 1.0.

The following Examples further illustrate the invention wherein parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 Several mixtures of 1,1,1,2-tetrafluoroethane (boiling point

-26.5° C), dimethyl ether (boiling point -24.6° C), and isobutane (boiling point -11.7° C) were distilled wherein the still pot composition was varied and the distillate vapor compositions and temperatures were measured at atmospheric pressure. A maximum vapor pressure azeotropic composition was identified as follows:

1,1,1,2-Tetrafluoroethane = 29.3 weight percent Dimethyl Ether = 59.1 weight percent

Isobutane = 11.6 weight percent

Vapor Pressure = 4302 torr at 25° C.

EXAMPLE 2

A phase study was made on constant boiling compositions of

1,1,1,2-tetrafhιoroethane (HFC-134a), dimethyl ether (DME) and isobutane

(IB) to verify mi-dmal fractionation and change in pressure and composition during a vapor loss at 25° C. Initial Liquid (IQ), final liquid (FQ), initial vapor composition (1), final vapor composition (2), vapor pressure, and change in vapor pressure from the initial vapor pressure were all studied.

The composition containing HFC- 134a, DME, and IB was studied as shown in Table 1 to determine the effects of vapor leakage on the composition and the vapor pressure. TABLE1

The data indicate that mixtures of 1,1,1,2-tetrafluoroethane, dimethyl ether and isobutane are substantially constant boiling with only a maximum of 5.1% change in vapor pressure with 50% of the original mixture evaporated.

EXAMPLE 3 Evaluation of the refrigeration properties of the substantially constant boiling composition comprising 20 weight percent 1,1,1,2- tetrafluoroethane, 60 weight percent dimethyl ether, and 20 weight percent isobutane with the chlorofluorocarbon R-12 (CCI2F2) is shown in Table 2.

TABLE 2 COMPARISON OF REFRIGERATION PERFORMANCES OF HFC-134a/DME/IB WITH CFC-12

Weight Percentages of HFC-134a/DME/IB

CFC-12 (20/60/20^

Evaporator Temp., °F 0 0

Evaporator Pressure, psia 23.8 18.6

Condenser Temρ., °F 100 100

Condenser Pressure, psia 131.8 116.3 Compressor

Discharge, °F 117 120

Coefficient of

Performance 3.53 3.60 Capacity

Btu/min 99.8 86.4

Capacity means 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 (C.O.P.) means the ratio of the capacity to the compressor work. It is a measure of refrigerant energy efficiency.

Capacity is based on a compressor with a fixed displacement of 3.5 cubic feet per minute.

The above data show that the ternary composition provides an increase in C.O.P. (energy efficiency) when compared with the commercially successful refrigerant CFC-12.

Claims

CLAIMS:

1. Substantially constant boiling compositions comprising 2.5-95 weight percent 1,1,1,2-tetrafluoroethane, 2.5-95 weight percent dimethyl ether and 2.5-50 weight percent isobutane that are resistant to component segregation.

2. A substantially constant boiling composition of Claim 1 which comprises 19-39 weight percent 1,1,1,2-tetrafluoroethane, 49-69 weight percent dimethyl ether and 2-22 weight percent isobutane.

3. A substantially constant boiling composition of Claim 1 which comprises 24-34 weight percent 1,1,1,2-tetrafluoroethane, 54-64 weight percent dimethyl ether and 7-17 weight percent isobutane.

4. A substantially constant boiling composition of Claim 1 which comprises about 29 weight percent 1,1,1,2-tetrafluoroethane, about 59 weight percent dimethyl ether and about 12 weight percent isobutane.

5. A substantially constant boiling composition of Claim 4 having a boiling point of about 25° C at 4302 torr.

6. A process for producing refrigeration which comprises condensing the composition of Claim 1 and thereafter evaporating said composition in the vicinity of a body to be cooled.

7. A process for producing heat which comprises condensing the composition of Claim 1 in the vicinity of a body to be heated and thereafter evaporating said composition.

8. A process for producing refrigeration which comprises condensing the composition of Claim 2 and thereafter evaporating said composition in the vicinity of a body to be cooled.

9. A process for producing heat which comprises condensing the composition of Claim 2 in the vicinity of a body to be heated and thereafter evaporating said composition.