The present invention relates to quaternary refrigerant compositions, particularly for use as replacements in air conditioning and refrigeration equipment currently employing, or designed to employ, chlorodifluoromethane (R22).
BACKGROUND OF THE INVENTION
Refrigerant is the substance which is used as working fluid in a thermodynamic cycle, undergoes a phase change from liquid to vapour and produces cooling. These are used in refrigeration, air conditioning, and heat pumping systems. They absorb heat from one area, such as an air conditioned space, and reject it into another, such as outdoors, usually through evaporation and condensation, respectively. These phase changes occur both in absorption and mechanical vapour compression refrigeration systems, but they do not occur in systems operating on a gas cycle using a fluid such as air.
Before the discovery of ozone hole in early 1970s, the refrigeration and air-conditioning industry was relying heavily on chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and their azeotropics.
HCFC refrigerant namely chlorodifluoromethane (R22) is widely used for residential and commercial air conditioning, as well as commercial refrigeration and has been commonly used with a mineral oil lubricant. R22 is the subject of a phase-out schedule under the Montreal Protocol as its chlorine content make it the largest ozone depleting substance in volumetric terms. R22 is prohibited from use in new equipment in some countries. After the discovery of ozone hole, the era for alternative refrigerants has started.
Refrigerant mixtures may be used as the alternative refrigerants. Refrigerant mixtures/blends can be classified based on the number of pure components, that is,

binary/ternary/quaternary. A number of patents have suggested quaternary refrigerant compositions as replacements for R22.
U.S. Patent no. 6,526,764 discloses a refrigerant composition comprising from about 80 to about 99. 9 weight percent of a hydrofluorocarbon refrigerant and from about 20 to about 0.1 weight percent of a solubilizing agent selected from the group consisting of butane, isobutane, pentane, dimethyl ether and mixtures thereof.
U.S. Patent no. 6,363,741 discloses a refrigerant composition comprising from 20 to 30 weight percent, preferably 25 weight percent, of R-32 (difluoromethane), 10 to 20 weight percent, preferably 15 weight percent, of R-125 (pentafluoromethane), 40 to 60 weight percent, preferably 50 weight percent, of R-134a (tetrafluoroethane), and O.itivel to 14 weight percent, preferably 10 weight percent, of n-pentane.
U.S. Patent no. 9,765,250 discloses a non-azeotropic fluid mixture for air conditioning devices, comprising a mixture of 0.5-5% 2-methylpropane (isobutane, R-600a); 1-3% pentafluoroethane (R-125), 93-95% 1,1,1,2-tetrafluoroethane, (R-134a), and 2-3% difluoromethane (R-32).
U.S. Patent no. 6,783,691 discloses a nonflammable, azeotrope-like composition consisting essentially of from about 1 to about 19 weight percent difluoromethane, from about 25 to about 60 weight percent pentafluoroethane, from about 24 to about 60 weight percent 1,1,1,2-tetrafluoroethane and from about 0.5 to about 5 weight percent of a hydrocarbon selected from the group consisting of: n-butane; isobutane; n-butane and 2-methylbutane; n-butane and n-pentane; isobutane and 2-methylbutane; and isobutane and n-pentane.

U.S. Patent no. 7,837,894 discloses a nonflammable refrigerant composition based on the weight of the composition consisting of pentafluoroethane in an amount of 83-90%; 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane or a mixture thereof in an amount of 7.5-15%) by weight based on the weight of the composition; and isobutane in an amount of from 1-4% by weight based on the weight of the composition.
U.S. Patent Appl. Pub. no. 2004/0061091 discloses a refrigerant composition comprising 45-50 weight percent R-134a, 45-50 weight percent R-125, 3-5 weight percent R-32, and 1-4 weight percent of the hydrocarbon component, the hydrocarbon component comprising one or more hydrocarbons selected from Group A and one or more hydrocarbons selected from Group B, wherein the Group A hydrocarbon comprises R-290 and the Group B hydrocarbon comprises R-600a.
The above compositions have significant amount of R125 which contributes to the higher GWP of these compositions and defeats the purpose of using them as replacement for R22. There is an urgent need to develop nonflammable refrigerant compositions with lower GWP that can replace R22 and are compatible with the systems already in use for R22.
The present invention discloses quaternary refrigerant compositions as replacement for R22 comprising non chlorine containing refrigerants having low GWP and no deleterious effect on ozone layer.

OBJECT OF THE INVENTION
The object of the present invention is to provide a refrigerant composition having low GWP that can be used as a drop-in replacement for R22.
SUMMARY OF THE INVENTION
A first aspect of the present invention provides refrigerant composition comprising difluoromethane (R32); pentafluoroethane (R125); 1,1,1,2-tetrafluoroethane (R134a) and isobutane (R600a) as a drop-in replacement for R22.
A second aspect of the present invention provides a refrigerant composition comprising about 15% by weight to about 30% by weight of R32; about 1% by weight to about 10% by weight of R125; about 60% by weight to about 75% by weight of R134a and about 5% by weight to about 15% by weight of R600a as a drop-in replacement for R22.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, a refrigerant is defined as a heat transfer fluid that undergoes a phase change from liquid to gas and back again during a cycle used to transfer of heat.
Drop-in refrigerant is a refrigerant which can replace the other refrigerant without any change in the existing system.
As used herein, non-absorbable gases are the gases which cannot be compressed predominately include air.
Non-azeotropic composition is a mixture of two or more substances that behaves as a simple mixture rather than a single substance. One way to characterize a non-azeotropic composition is that the vapor produced by partial evaporation or distillation of the liquid has a substantially different composition as the liquid from

which it was evaporated or distilled, that is, the admixture distills/refluxes with substantial composition change.
The quaternary blend composition has lower molecular weight thus has large enthalpy of evaporation. The comparative data for enthalpy of evaporation is given below:

Refrigerant Temperature Liquid Phase (°C) Liquid Phase Molar Mass (kg/kmol) Vapour phase Enthalpy (Kj/Kg)
R-22 25 86.468 413.03
Composition 1 25 79.735 452.3
R-22 -25 86.468 394.9
Composition 1 -25 79.735 439.46
The refrigeration capacity is a measure of the ability of a refrigerant or heat transfer composition to produce cooling. Therefore, the higher the capacity, the greater the cooling that is produced. Cooling rate refers to the heat removed by the refrigerant in the evaporator per unit time.
Coefficient of performance (COP) is the amount of heat removed divided by the required energy input to operate the cycle. The higher the COP, the higher is the energy efficiency. COP is directly related to the energy efficiency ratio (EER) that is the efficiency rating for refrigeration or air conditioning equipment at a specific set of internal and external temperatures.
The quaternary blend composition of the present invention has higher latent heat of vaporization which helps to achieve higher COP.

Discharge temperature is a temperature of the refrigerant gas at the discharge of the compression.
Flammability is a term used to mean the ability of a composition to ignite and/or propagate a flame. Determination of whether a refrigerant compound or mixture is flammable or non-flammable can be done by testing under the conditions of ASTM-681.
Global warming potential (GWP) is an index for estimating relative global warming contribution due to atmospheric emission of a kilogram of a particular greenhouse gas compared to emission of a kilogram of carbon dioxide. GWP can be calculated for different time horizons showing the effect of atmospheric lifetime for a given gas. The GWP for the 100-year time horizon is commonly the value referenced. For mixtures, a weighted average can be calculated based on the individual GWPs for each component. The standard GWP values for R22, 32, 125 and 134a has been taken from IIPCC 5th Assessment report 2014 (AR5). The GWP of the refrigerant mixture has been derived from mass fraction and the corresponding GWP values.
Ozone depletion potential (ODP) is a number that refers to the amount of ozone depletion caused by a substance. The ODP is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11 (fluorotrichloromethane). Thus, the ODP of CFC-11 is defined to be 1.0. Other CFCs and HCFCs have ODPs that range from 0.01 to 1.0. FIFCs have zero ODP because they do not contain chlorine or other ozone depleting halogens.
A first aspect of the present invention provides a refrigerant composition comprising R32, R125, R134a and R600a as replacement of refrigerant R22.
In one embodiment of this aspect of the present invention, the refrigerant composition comprises of about 15% by weight to about 30% by weight of R32;

about 1% by weight to 10% by weight of R125; about 60% by weight to about 75% by weight of R134a and about 5% by weight to 15% by weight of R600a.
In one embodiment of this aspect of the present invention, the refrigerant composition comprises of about 15% by weight to about 30% by weight of R32; about 0.1%> by weight to 5% by weight of R125; about 60% by weight to about 75% by weight of R134a and about 5% by weight to 15% by weight of R600a.
In one another embodiment of this aspect of the present invention, the nominal quaternary refrigerant composition comprises of about 15% by weight to about 20% by weight of R32; about 1% by weight to 4% by weight of R125; about 60%) by weight to about 75% by weight of R134a and about 5% by weight to 10% by weight of R600a.
In one another embodiment of this aspect of the present invention, the nominal quaternary refrigerant composition comprises of about 15% by weight to about 20% by weight of R32; about 1% by weight to 4% by weight of R125; about 60%) by weight to about 75% by weight of R134a and about 1% by weight to 5% by weight of R600a.
In one another embodiment of this aspect of the present invention, the nominal quaternary refrigerant composition comprises of about 20% by weight to about 25% by weight of R32; about 1% by weight to 4% by weight of R125; about 60%) by weight to about 75% by weight of R134a and about 5% by weight to 10% by weight of R600a.
In one another embodiment of this aspect of the present invention, the nominal quaternary refrigerant composition comprises of about 20% by weight to about 25% by weight of R32; about 1% by weight to 4% by weight of R125; about 60%) by weight to about 75% by weight of R134a and about 1% by weight to 5% by weight of R600a.

Refrigerant compositions in accordance with this invention confer several advantages. R125 has fire suppressing characteristics. The presence of R125 suppresses the flammability of the refrigerant mixture. The higher HFC content enables more isobutane to be added to the mixture thereby improving the solubility properties of the mixture with traditional lubricants, for example mineral and alkyl benzene oils. This composition does not have HCFC so it is a ZERO ODP refrigerant.
In another embodiment of this aspect of the present invention, the refrigerant composition has GWP of less than 1300.
In another embodiment of this aspect of the present invention, the refrigerant composition additionally comprises of about less than 0.5% of non-absorbable gases.
In another embodiment of this aspect of the present invention, the refrigerant composition may contain optional components selected from the group consisting of lubricants, dyes (including Ultra Violet dyes), solubilizing agents, compatibilizers, stabilizers, tracers, perfluoropolyethers, anti-wear agents, extreme pressure agents, corrosion and oxidation inhibitors, metal surface energy reducers, metal surface deactivators, free radical scavengers, foam control agents, viscosity index improvers, pour point depressants, detergents, viscosity adjusters, and mixtures thereof. Indeed, many of these optional other components fit into one or more of these categories and may have qualities that lend themselves to achieve one or more performance characteristic.
In another embodiment of this aspect of the present invention, the refrigerant composition is a drop in replacement for R22.
In another embodiment of this aspect of the present invention, the refrigerant composition is a non-azeotropic mixture.
In another embodiment of this aspect of the present invention, the refrigerant composition can be either charged as liquid composition or full vapor composition.

In another embodiment of this aspect of the present invention, the refrigerant composition is preferably charged in liquid form.
In another embodiment of this aspect of the present invention, the refrigerant composition has lower discharge temperature compared to R22 thus the use of this composition increases life of the compressor and can be worked at outdoor conditions at higher temperatures.

Refrigerant Discharge Temperature
(°Q Liquid phase specific heat at constant volume (Cv) at 25°C (kj/kg-K)
R-22 57.5 0.69086
Composition 1 49.5 0.9657
The refrigerant composition of the present invention has higher specific heat capacity, lower discharge temperature and increased thermal efficiency.
In another embodiment of this aspect, the present invention provides a refrigeration process using the refrigerant composition of the present invention comprising the steps of:
a) Condensing the refrigerant composition;
b) Evaporating the refrigerant composition.
The quaternary blend composition of the present invention has higher volumetric refrigerating capacity as compared to R-22, thus need a smaller compressor, and less power for a given capacity.
In another embodiment of this aspect of the present invention, the refrigerant composition of present invention has lower value of viscosity that decreases pressure drop in condenser and evaporators, leading to increase in mass flow of refrigerant, increase in system capacity and increased Heat transfer coefficient (HTC).

Further, the refrigerant composition of present invention has higher thermal conductivity, higher rate of evaporation and thus higher HTC.

Refrigerant Liquid phase Viscosity at 25°C (uPa-s) Liquid Phase Thermal Conductivity at 25°C (mW/m-K)
R-22 164.39 83.479
Composition 1 146.21 86.936
The refrigerant composition of present invention has higher vapour pressure, therefore it has higher volumetric refrigerant capacity (VRC) thus require smaller compressor displacement.

Refrigerant Vapour pressure at 25°C (bars)
R-22 10.439
Composition 1 11.408
The refrigerant compositions of the present invention may be used in stationary or mobile air conditioning systems or heat exchanger systems. Preferably, the refrigerant compositions would be utilized in domestic room air conditioning systems.
The present invention thus provides an R22 replacement refrigerant compositions that are compatible with existing mineral oil and alike lubricants and do not require replacement of the expensive devices in the legacy system.
The AHRI210/240 standard uses several different temperatures to derive the "Seasonal" component of the rating. The highest ambient air temperature used in the AHRI 210/240 standard is 95F (35°C), and this may result in condensing temperatures for the refrigerant inside the condenser of between 105F and 11 OF (40°C to 43°C) because the refrigerant inside the system has to be warmer than the outside air temperature in order for the heat to move from the refrigerant to the

outside air. Conventional operation conditions for the legacy R22 systems include these standards and their conditions.
Each of the components of the cooling system is sensitive to the composition and amount of refrigerant flowing through it, and the legacy R22 systems are no exception. Large changes in refrigerant flow rate as compared to the designed flow rates will cause the amount of heat absorbed by the system to change adversely. For example, if the refrigerant absorbs too much heat from the evaporator because the expansion device cannot adequately slow down the flow rate of refrigerant, the compressor will pump too much refrigerant and overload the electric motor which could either trigger associated electrical protection circuits or permanently damage the motor. On the other hand, if the refrigerant absorbs too little heat because the expansion device cannot pass enough refrigerant, the system will lose the ability to absorb enough heat to keep the cooled area at the selected temperature.
Fortunately, legacy refrigeration systems were all designed at a time when there were far fewer refrigerants and lubricant options. This fact caused design engineers to use substantially the same refrigerant and lubrication performance criteria when specifying the expansion devices, motors, etc. that were used in these legacy systems. As a result, those systems tended to be fairly close in terms of the tolerable range of adjustments that each could employ and still achieve acceptable performance. The present invention is specifically designed to be a retrofit refrigerant for R22 systems that can be used in the legacy R22 equipment with the legacy mineral oil and alike lubricants.
The quaternary blend composition of the present invention has good chemical miscibility with hydrocarbons/mineral oil, lubricant oil which is blown out of the compressor will be carried through the system by this refrigerant easily so it can be used as less expensive drop-in substitute of R-22 without any change in the hardware.

The formulation according to the invention exhibits cooling and condensation properties that make it well suited as a retrofit for R22 refrigerants without the need to replace the expansion devices and flow valves of the existing legacy equipment. Specifically, the inventor has found that the existing flow control devices in legacy equipment for R22 refrigeration systems has the ability to deliver the correct refrigerant flow rate without affecting the continuity of the refrigerating cycle. The refrigerant formulation of the invention exhibits cooling capacities and mass flow rates that are within the flow adjustment tolerances of such equipment. Thus, the refrigerant formulation of the present invention can replace the legacy R22 refrigerant using the same lubricant and the same expansion valves with only adjustments that are within acceptable ranges of such legacy equipment.
R600a (isobutane) is commercially available.
R32 is commercially available or may be prepared by methods known in the art, such as by dechlorofluorination of methylene chloride.
R125 is commercially available or may be prepared by methods known in the art, such as dechlorofluorination of 2,2-dichloro-1,1,1-trifluoroethane as described in US Patent No. 5,399,549, incorporated herein by reference.
R134a is commercially available or may be prepared by methods know in the art, such as by the hydrogenation of 1,1-dichloro-l ,2,2,2-tetrafluoroethane (i.e., CCI2FCF3 orCFC-114a)to 1 ,1 ,1 ,2-tetrafluoroethane.
It is against this and other backgrounds, which shall be filed in a detailed manner in complete specifications, in due course, the present invention is brought out and explained in following non-limiting examples.

EXAMPLES
Example 1
The refrigerant compositions according to the invention having composition of R125:R134a:R32:R600a were prepared and tested with standard ASHRAE modeling program maintaining indoor at 27°C dry bulb temperature (DBT) and 19°C wet bulb temperature (WBT) and outdoor at 35 DBT and 24 WBT. The refrigerant compositions of the present invention are enlisted in Table 1 and the results are shown below in Table 2, Table 3 and Table 4.
Table 1

Compositions R32* R134a* R125* R600a*
Composition 1 25 65 4 6
Composition 2 16 72 4 8
Composition 3 20 70 4 6
Composition 4 22 68 4 6
Comparative Composition 2.5 93.5 1.5 2.5
*all quantities are calculated as % by weight

Table 2

Refrigerant compositions Cooling Capacity Quantity Charged Power Consumption COP ODP GW P
R22 100% 100% 100% 100% 0.05
5 1760
Composition 1 95.1 100 98.7 96.3 0 1238
Composition 2 95.5 100 101.4 94.3 0 1276
Composition 3 91.2 100 99.1 92.2 0 1276
Composition 4 95.1 100 108.1 95.1 0 1261
Table 3

Refrigerant Liquid phase Vapour Pressure Liquid phase specific heat at constant pressure (Cp) Vapour phase specific heat at constant pressure (Cp) Liquid phase
thermal
conductivity
at 25 Degree Celsius bar kj/kg-K kj/kg-K mW/m-K
Composition 1 11.408 1.6243 1.3059 86.936
R-22 10.439 1.2568 0.87237 83.479
Comparative Composition 7.589 1.4665 1.1017 80.724

Table 4

Refrigerant Vapour phase thermal conductivity Liquid
phase
viscosity Molar Mass Global Warming Potential
at 25 Degree Celsius mW/m-K uPa-s kg/kmol
Composition 1 15.002 146.21 79.735 1238.43
R-22 11.337 164.39 86.468 1810
Comparative Composition 14.365 181.75 98.045 1406.5
As depicted in Table 2, 3 and 4, the refrigerant compositions of the present invention exhibit good cooling capacity and will operate in substantially the same manner as the legacy R22 refrigerant under the same conditions. The performance factor is almost close to R22 and having ZERO ODP.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention and specific examples provided herein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of any claims and their equivalents.

We Claim:

1.A refrigerant composition comprising difluoromethane (R32); pentafluoroethane (R125); 1,1,1,2-tetrafluoroethane (R134a) and isobutane (R600a) as a drop-in replacement for R22.
2. A refrigerant composition comprising about 15% by weight to about 30% by weight of R32; about 0.1% to 1% by weight to about 05% to 10% by weight of R125; about 60% by weight to about 75% by weight of R134a and about 5% by weight to about 15% by weight of R600a as a drop-in replacement for R22.
3. A nominal quaternary refrigerant composition comprises of about 15% to 20% by weight to about 20% to 25% by weight of R32; about 1% by weight to 4% by weight of R125; about 60% by weight to about 75% by weight of R134a and about 01% to 5% by weight to 05% tol0% by weight of R600a.
4. The claim as claimed in claim 1 to 3, wherein, the refrigerant composition is a non-azeotropic mixture.

5. A refrigeration process using the refrigerant composition comprising the steps of:
c) Condensing the refrigerant composition;
d) Evaporating the refrigerant composition.