GB2298866A

GB2298866A - Refrigerant composition comprising fluoroethane

Info

Publication number: GB2298866A
Application number: GB9605070A
Authority: GB
Inventors: Stephen Forbes Pearson
Original assignee: Star Refrigeration Ltd
Current assignee: Star Refrigeration Ltd
Priority date: 1995-03-11
Filing date: 1996-03-11
Publication date: 1996-09-18
Also published as: GB9605070D0; GB9504955D0

Abstract

A refrigerant composition comprises a non-flammable amount of fluoroethane (R161). Preferred compositions comprise (percetages by weight): (i) up to 15%, preferably from 1 to 10%, of fluoroethane and either pentafluoroethane (R125) or octafluoropropane (R218); (ii) up to 30% fluoroethane, pentafluoroethane and octafluoropropane; (iii) fluoroethane and from 10 to 70% of at least one of pentafluoroethane and octafluoropropane. The composition may comprise a hydrocarbon, preferably from 2 to 10%, which may be at least one of n-propane, isopropane, n-butane or propylene.

Description

HIGH EFFICIENCY REFRIGERANT The present invention relates to a refrigerant composition, of good environmental acceptability.

Chlorofluorocarbon (CFC) gases, such as refrigerant R12 (CC12F2) and R22 (CHC1F2), have been used for many years as refrigerants and are especially used in domestic refrigerators and car air conditioning systems. However, such gases have been implicated in environmental damage. These gases, which are very inert, are released from refrigeration systems at ground level and diffuse 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 catalyse breakdown of the stratospheric ozone layer.

There has recently been considerable concern about reduction in stratospheric ozone levels and this has lead to proposed restrictions and prohibitions on certain CFCs.

A range of replacement refrigerants have been proposed and are being utilised, including hydrofluorocarbon (HFC) refrigerants, however these tend to have lower refrigeration efficiencies than CFCs.

US Patent 5 248 433 discloses the use of azeotrope like mixtures of octafluoropropane (R218) and fluoroethane (R161) as refrigerants. However, the disclosed mixtures contain at least 15wt% of fluoroethane (generally 16 to 31 weight percent) and possess the practical disadvantage of being flammable.

It is among the objects of the present invention to mitigate these problems and to provide a refrigerant composition which will not contribute to ozone depletion but will have a higher efficiency than currently available CFC, and HCFC, replacements.

According to the present invention there is provided a refrigerant composition for use in a refrigeration apparatus which contains fluoroethane (R161) in a non-flammable proportion.

A further aspect of the present invention provides a method of refrigeration (particularly vapour compression) which employs the composition as a refrigerant medium.

A still further aspect provides a refrigeration apparatus which employs the composition as a refrigerant medium.

Fluoroethane contains no chlorine atoms and therefore does not contribute to ozone depletion in the atmosphere.

In the past, fluoroethane (R161) has apparently been overlooked as a replacement refrigerant, possibly because various references (see 1, 2, 3) state that it is "toxic" or "highly toxic". However, our investigations indicate that the quoted references may be incorrect. Although, fluoroethane itself is highly flammable we have discovered that it may be mixed with other refrigerants to provide a non-flammable nontoxic refrigerant composition. A non-flammable composition is one which contains the components of the mixture in such a ratio that when the composition is mixed with air in practical proportions, for example in the event of a leak, no flammable mixture results. The assessment of flammability is not necessarily predictable but can be determined by routine experimentation (see, for example, our US Patent No. 5108637).To provide a non-flammable composition a fluoroethane (R161) content of less than 30 wt % may be required, usually less than 20% wt%, with 1 to 10 wt % preferred, and 2 to 5 wt % most preferred.

However, the upper limit for non-flammability depends upon the nature of the other components of the composition. Certain components (e.g.

octafluoropropane) if included in the composition may exert a flammability reducing effect on the overall composition. For example, in binary mixtures of fluoroethane and pentafluoroethane (R125) up to 15wt% of fluoroethane may generally be present before the mixture becomes flammable. In binary mixtures of fluoroethane and octafluoropropane (R218) the fluoroethane content is generally up to 15 to 20wt%.

In ternary mixtures of R161, R218 and R125 the fluoroethane content may be up to 30wt%. These figures are, of course, reduced if the composition includes a flammable hydrocarbon (for example, to improve miscibility or solubility of the refrigerant with mineral lubricating oil). Generally, the R161 upper limit is reduced in accordance with the amount of hydrocarbon added.

By comparison with refrigerants such as pentafluoroethane (R125) and octafluoropropane (R218), R161 has a relatively high critical temperature and is therefore more efficient as a refrigerant due to its high latent heat at operating conditions. The boiling point of R161 at atmospheric pressure is -37.2 C and its critical temperature is 102.20C, as compared to 720C for R218 and 67CC for R125. Since the boiling point of fluoroethane is close to that of octafluoropropane (R218), preferential evaporation of either of these components in the evaporator of a refrigeration apparatus is unlikely to occur to any significant extent in compositions containing these components. Constant boiling azeotropes tend to be formed relatively easily between refrigerants of different carbon number e.g. ethanes and propanes.

Preferably, the refrigerant composition additonally comprises a further fluorocarbon component selected from pentafluoroethane (R125), octafluoropropane (R218) and mixtures thereof. These fluorocarbon components possess fire retardant properties. The further fluorocarbon component is preferably present in an amount of 5 - 90 wt %, particularly 10 - 70 wt %, and especially 20 - 50 wt % of the total refrigerant composition. The pentafluoroethane (R125) is preferably present in an amount of 1 to 50wt% and particularly 5 to 50 wt % of the total composition (e.g. 10 to 40 wt %). For compositions for use as an R12 replacement, the amount of R125 is usually at the low end of this range, that is 1 to 10 wt %. When used as an R22 replacement, the composition preferably comprises 1 to 20wt% of R125.The octafluoropropane (R218) is typically present in an amount of 5 to 50 wt % (e.g. 10 - 40 wt %) .

Preferably also, the refrigerant composition further comprises a hydrocarbon component selected from propane (R290), isobutane (R600a), n-butane (R600), propylene (R1270) and mixtures thereof; most preferably propane or propylene. To provide a nonflammable composition the (flammable) hydrocarbon content is usually 1 to 20 wt %, preferably 2 to l0wt%, (particularly 1 to 6wt%), advantageously 2 to 5wt% or most preferably 3 to 5 wt %; but may also depend upon the amount of fluoroethane present.

The hydrocarbon has a principal benefit of rendering the refrigerant composition soluble in the mineral oils normally used in refrigeration apparatus, so that special oils (which are generally more expensive) are not required. Moreover, changing the oil usually involves draining and flushing the apparatus before filling with replacement oil; which is time consuming and inconvenient.

According to a second aspect of the present invention there is provided a refrigerant composition for use in a refrigeration apparatus which comprises a mixture of the following components: (i) fluoroethane (R161); (ii) a further fluorocarbon component selected from pentafluoroethane (R125) and octafluoropropane (R218) and mixtures thereof; and (iii) a hydrocarbon component; the components being in proportion such that the refrigerant composition is non flammable.

Preferably, the hydrocarbon component is selected from propane (R290) and propylene (R1270) and mixtures thereof.

Thus, the refrigerant composition has relatively high efficiency as a refrigerant. It also has low ozone depletion potential.

EXAMPLE A refrigerant composition can be prepared by admixing the following components in the following percentages by weight: (i) up to 15% R161 balance R125 (ii) up to 20% R161 (preferably up to 15%) balance R218 (iii) up to 30% R161 30% R218 balance R125 The amount of R161 is, of course, such that the composition is not flammable. If required, a hydrocarbon may be included in the composition so as to improve the solubility of the composition in mineral lubricating oil.

References 1) McLindon, M O, Didion, B. A.: CFCs: Quest for Alternatives, ASHRAE Journal, December 1987 2) Kopco, W L: Extending the Search for new Refrigerants, Int. J. Refrig., March 1990 3) Statt, T G: Ozone-safe Refrigerants, Ashrae Journal, September, 1990, p49.

Claims

1. A refrigerant composition for use in a refrigeration apparatus which contains fluoroethane (R161) in a non-flammable proportion.

2. A non-flammable composition according to claim 1 which comprises a mixture of up to l5wt% fluoroethane with pentafluoroethane (R125).

3. A non-flammable composition according to claim 2 which comprises 1 to 10wit% fluoroethane.

4. A non-flammable composition according to claim 1 which comprises a mixture of up to 15wt% fluoroethane with octafluoropropane (R218).

5. A non-flammable composition according to claim 4 which comprises 1 to 10wt% fluoroethane.

6. A non-flammable composition according to claim 1 which comprises a mixture of up to 30wt% fluoroethane (R161), pentafluoroethane (R125) and octafluoropropane (R218).

7. A non-flammable composition according to any preceding claim which further comprises a hydrocarbon.

8. A non-flammable composition according to claim 7 wherein the hydrocarbon is selected from propane, isobutane, n-butane, propylene and mixtures thereof.

9. A non-flammable composition according to claim 7 or 8 wherein the hydrocarbon content is 2 to 10wt%.

10. A non-flammable composition according to claim 1 which further comprises 10 to 70wt% of pentafluoroethane (R125), octafluoropropane (R218) or mixtures thereof.

11. A refrigeration apparatus containing arefrigerant composition of any preceding claim.