The present invention relates to gaseous mixtures that are useful as replacement or alternative refrigerants for R134a.

R134a (1, 1, 1, 2-tetrafluoroethane) is a hydrofluorocarbon which has been used since the start of the 1990s as a replacement refrigerant gas for chlorofluorocarbons or hydrochlorofluorocarbons, which have a substantial ozone depletion potential (ODP hereinbelow) and which are regulated by the Montreal protocol.

Unlike chlorofluorocarbons or hydrochlorofluorocarbons, R134a does not have a substantial ODP and has found and finds application particularly as a refrigerant for air conditioning or refrigeration.

However, R134a has a high global warming potential (GWP hereinbelow), and, following the Kyoto protocol, the European regulation has limited and will gradually limit its availability and use in air-conditioning or refrigeration plants.

The main aim of the present invention is to provide refrigerant gas mixtures that may be used as replacements or alternatives to R134a, and/or other replacement or alternative refrigerants for R134a containing HFC (hydrofluorocarbons), HFO (hydrofluoro olefins) and HFE (hydrofluoro ethers), which have a lower production cost and improved environmental impact characteristics, particularly in terms of the GWP, relative to those of R134a, together with thermodynamic properties that are suitable for their use as replacement refrigerant gases with improved characteristics in applications as air conditioning for motor vehicles, and domestic, commercial and industrial air conditioning and refrigeration.

The invention is based on the acknowledgement that the above mentioned aims may be achieved by using a gaseous mixture of non-fluorinated hydrocarbons with relative concentrations of the constituent hydrocarbons of the mixture that are within a quite limited range. Binary mixtures of hydrocarbons have already been proposed in the prior art as refrigerant gases; for example, US 1 497 615 refers to a refrigerant mixture of isobutane and of another hydrocarbon compound of lower molecular weight, with a boiling point above 45°C.

CN 101402847 describes mixtures consisting of isobutane and propane as components of a refrigerant mixture which is a replacement for R22, in which propane may be present in a concentration from 80% to 89% by weight and isobutane in a concentration from 11% to 20% by weight.

CN 1693408 describes mixtures comprising propane in an amount from 55% to 62% by weight and isobutane in an amount from 38% to 45% by weight as replacement refrigerants for R134a.

The documents Shin J. Y. et al., International Journal of Refrigeration, Vol. 20, No. 4, 1 June 1997, pages 267-275, Chang Y. S. et al, International Journal of Refrigeration, Vol. 23, No. 3, 1 May 2000, pages 232-242 and Granryd E., International Journal of Refrigeration, Vol. 24, No. 1, 1 January 2001, pages 15-24 describe refrigerant mixtures consisting of propane/isobutane in a 75/25 weight ratio.

In this respect, the present invention provides mixtures which, by virtue of a specific selection of the concentration ranges of the hydrocarbons used, make it possible to obtain thermodynamic characteristics that are particularly suitable and improved for replacing R134a.

A subject of the invention is thus the use of a gaseous mixture selected from the group consisting of:

- propane in a concentration from 71% to 79% by weight and a gas selected from the group consisting of isobutene and butene or mixtures thereof in a concentration from 21% to 29% by weight as a replacement or alternative refrigerant gas for R134a, in air- conditioning or refrigeration plants, particularly in motor vehicle air conditioning designed for the use of R 134a.

In the present description, the examples and the claims, the term "butene" includes 1- butene and cis and trans 2-butene.

The mixtures according to the invention find use both in brand new installations and in the retrofit of existing installations, requiring only the replacement of certain components since the mixtures according to the invention are flammable.

In particular, the mixtures according to the invention find application in air-conditioning systems of motor vehicles, refrigerated cabinet for supermarkets, cold stores, domestic refrigerators, centrifugal chillers, domestic, commercial and industrial air-conditioning plants, domestic, commercial and industrial chillers, air-conditioning or refrigeration plants in the process industry, refrigerated transport, chilled water dispensers, commercial ice machines, and domestic, commercial and industrial dehumidifiers.

Air-conditioning or refrigeration plants which use the mixtures according to the invention as refrigerant also fall within the scope of the invention.

Another subject of the invention is refrigerant mixtures consisting of 71% to 79% by weight of propane and 21% to 29% by weight of isobutene, butene or mixtures thereof.

Within the scope of the restricted concentration range of the constituent gases of the mixtures, preferred mixtures are those selected from the group consisting of:

- 74-79% by weight and particularly 75% by weight of propane and 21-26% by weight and particularly 25% by weight of a gas selected from the group consisting of isobutene or butene.

The mixtures proposed herein have improved characteristics relative to the use of R134a in refrigeration cycles for moderate and high temperature applications. The table which follows illustrates a number of salient characteristics relating to the thermodynamic properties of the mixtures according to the invention within the scope of the concentration ranges mentioned above, together with the salient environmental impact characteristics thereof, such as the ODP and the GWP, compared with the corresponding properties of R134a.

Table 1

As it is seen from the table given above, the mixtures used according to the invention have low glide values (difference between the boiling point and the dew point at a pressure of 1 atmosphere).

In comparison with R134a, the mixtures drastically reduce the GWP from 1300 to values generally not exceeding 3.

In addition, since the mixtures consist exclusively of hydrocarbons, they make it possible to have wide availability of low-cost raw materials.

In the attached drawings:

- Figures 1 and 2 are diagrams illustrating the pressure and temperature curves for the preferred mixtures according to the invention compared with the corresponding curves relating to R134a; the relevant numerical values are given in Tables 3 and 4.

A comparative table between R134a and the replacements that are the subject of the present invention is presented hereinbelow.

Table 2

The table describes the coefficients of performance (COP) for specific mixtures that are the subject of the invention, compared with R134a.

The coefficients of performance in heating (COPh) and in cooling (COPc) are indicated in the table.

The values were calculated for an air-conditioning plant with a thermal capacity of 6 KW in cooling, 500 We of auxiliary power and subcooling by 5°C. The excess heat was considered as additional heat to the condenser.

The indicated values are the results of a mathematical simulation based on thermodynamic data known from the literature, exploiting internationally recognized programs.

It may be observed that, in all cases, the COP of the proposed mixtures is entirely in line with that of Rl 34a.

Table 3

Propane Isobutene (75/25): P/T Table

P

T R134a P ^L mix P ^v mix

°c atm atm atm

-70 0.08 0.20 0.12

-65 0.11 0.27 0.16

-60 0.16 0.35 0.22

-55 0.22 0.46 0.30

-50 0.29 0.59 0.39

-45 0.39 0.74 0.51

-40 0.51 0.93 0.65

-35 0.65 1.15 0.83

-30 0.83 1.41 1.04

-25 1.05 1.71 1.28

-20 1.31 2.06 1.57

-15 1.62 2.46 1.91

-10 1.98 2.92 2.30

-5 2.40 3.44 2.75

0 2.89 4.02 3.27

5 3.45 4.68 3.85

10 4.09 5.41 4.50

15 4.82 6.22 5.24

20 5.64 7.12 6.06

25 6.57 8.11 6.97

30 7.60 9.20 7.98

35 8.75 10.39 9.09

40 10.03 11.69 10.32

45 11.45 13.10 11.66

50 13.01 14.63 13.12

55 14.72 16.29 14.72

60 16.60 18.08 16.45

65 18.65 20.01 18.34

70 20.89 22.09 20.38

75 23.33 24.32 22.59

80 25.99 26.71 24.98

85 28.88 29.26 27.56

90 32.02 32.00 30.35

95 35.44 34.92 33.38

100 39.20 38.02 36.68 Table 4

Propane/Butene (75/25): P/T Table

P

T R134a P ^L mix P ^v mix

°c atm atm atm

-70 0.08 0.20 0.12

-65 0.11 0.27 0.16

-60 0.16 0.36 0.22

-55 0.22 0.46 0.30

-50 0.29 0.59 0.40

-45 0.39 0.75 0.52

-40 0.51 0.94 0.66

-35 0.65 1.16 0.84

-30 0.83 1.42 1.05

-25 1.05 1.73 1.30

-20 1.31 2.08 1.60

-15 1.62 2.48 1.94

-10 1.98 2.94 2.34

-5 2.40 3.46 2.80

0 2.89 4.05 3.32

5 3.45 4.71 3.90

10 4.09 5.45 4.57

15 4.82 6.26 5.31

20 5.64 7.17 6.14

25 6.57 8.17 7.06

30 7.60 9.26 8.08

35 8.75 10.46 9.21

40 10.03 11.77 10.44

45 11.45 13.19 11.80

50 13.01 14.73 13.27

55 14.72 16.40 14.89

60 16.60 18.21 16.64

65 18.65 20.15 18.54

70 20.89 22.24 20.60

75 23.33 24.48 22.82

80 25.99 26.89 25.23

85 28.88 29.46 27.84

90 32.02 32.22 30.65

95 35.44 35.16 33.71

100 39.20 38.30 37.05