KR0143547B1 - Azeotropic Compositions of 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane - Google Patents

Abstract

New azeotropic compositions are provided that comprise 1, 1, 1,2-tetrafluoroethane and 1, 1-difluoroethane and are beneficial for heating and cooling applications.

Description

Azeotropic compositions of 1, 1, 1,2-tetrafluoromethane and 1, 1-difluoroethane

FIELD OF THE INVENTION The present invention relates to azeotrope-1ike compositions of 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane, the mixtures of which are useful as coolants for heating and cooling applications. .

Fluorocarbon based emulsions have been widely used in cooling, air conditioning and heat pumps.

Steam compression is one form of cooling.

In brief, vapor compression involves converting a coolant from a liquid state into a gaseous state through heat absorption at low pressure, and then converting the gas into a liquid state through heat removal at elevated pressures.

First, the coolant is vaporized in an evaporator that is in contact with the object to be cooled.

The pressure in the evaporator is lower than the boiling point of the object to which the boiling point of the coolant is cooled. In this way, heat is transferred from the object to the coolant to vaporize the coolant.

The vapor formed is then removed by a compressor to maintain a low pressure in the evaporator. The temperature and pressure of the steam are then increased by the addition of mechanical energy by the compressor.

The high pressure steam then passes through a condenser where it exchanges heat with the refrigerant.

Subsequent condensation removes sensible and latent heat.

The hot liquid coolant then goes to the expansion valve and is circulated again.

While the primary purpose of cooling is to remove energy at low temperatures, the primary purpose of heat pumps is to add energy at high temperatures. Heat pumps are considered to be a reverse circulation system for heating purposes because the operation of the condenser is staggered from the operation of the cooling evaporator.

Some chloro fluorocarbons have been used in a variety of cooling applications including air conditioning and heat pump applications due to their unique combination of chemical and physical properties.

Most refrigerants used in vapor compression systems are single component fluids or azeotropic mixtures.

Single component emulsions and azeotropic mixtures are characterized as constant-boiling because they exhibit isothermal and isothermal evaporation and condensation.

The use of azeotropic mixtures as coolants is described, for example, in R. C. Downing, Fluorocarbon Refrigerants Handbooks, pp 139-158, Prentice Hal 1, 1988 and US Pat. Nos. 2,101,993 and 2,641,579. Azeotropic or azeotropic compositions are preferred because they are not fractionated upon boiling or evaporation.

This property is desirable because condensed material is produced for cooling or heating in the above described vapor compression apparatus where these coolants are used, and fractionation upon evaporation and condensation if the coolant composition is not constant, i.e., azeotropic. And segregation may occur, and undesirable coolant distribution may result in improper cooling or heating.

For example, US Pat. No. 4,303,536, et al. Discloses a non-azeotropic mixture as a coolant, but has not been widely applied commercially, although the improved thermodynamic properties of the non-azeotropic coolant mixture have often been reviewed in the literature.

Such documents include T. Atwood, NARBS-The Promise and the Problem, American Society of Mechanical Engineers, WinterAnnual Hotting, paper 86-WA / HT-61, 1986, and M, O. McLinden et al. Methods for Comparing the Performance of Pure and Mixed Refrigerants in the Vapor Compression Cycle, Int. J. Refrig 10.318 (1987), for example.

Since non-azeotropic mixtures can be sorted during the cooling cycle, they require specific equipment.

This additional difficulty in changing chillers is the main reason for avoiding non-azeotropic mixtures.

This situation is further complicated by inadvertent leakage into the system during use or storage.

Mixture compositions can change system pressure and system performance.

If any component of the non-azeotropic mixture is flammable, fractionation may move the composition into the flammable zone and potentially cause adverse effects.

In the meantime, new fluorocarbon-based azeotropic mixtures have been sought to provide alternatives for cooling and heat pump applications.

As a result, environmentally acceptable fluorinated carbon-based coolants are of interest because fully halocarbonized chlorofluorocarbons cause environmental problems with the destruction of the earth's ozone layer.

Hydrofluorocarbons such as 1, 1, 1, 2-tetrafluoroethane (HFC-l34a) and 1, 1-difluoroethane (HPC -152a) have ozone depletion and global warming compared to fully halogenated It was proved by mathematical model that it did not affect so much.

This alternative should also have the properties of CFCs such as chemical stability, low toxicity, non-flammability and efficacy of use.

The last characteristic of the above is, for example, that the reduction of coolant thermodynamic performance or energy efficiency leads to an increase in the demand for electric energy, which in turn requires more fossil fuels, which can lead to secondary environmental problems. In Ning it is important.

Moreover, this ideal CFC coolant replacement does not need to significantly alter the conventional vapor compression techniques used for CFC coolants.

It is therefore an object of the invention to provide new azeotropic compositions based on 1, 1, 1,2-tetrafluoroethane and 1, 1-difluoroethane, which are beneficial for cooling and heating applications.

It is another object of the present invention to provide a new environmentally acceptable coolant for use in such applications.

Hereinafter, the present invention will be described.

The present invention relates to novel environmentally acceptable azeotropic compositions of 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane that are beneficial for heating and cooling applications. In accordance with the present invention, new azeotropic compositions have been found comprising 1, 1, 1, 2-tetrafluoroethane and 1, 1-difluoroethane.

This azeotropic composition comprises about 5 to 90 weight percent 1, 1, 1, 2-tetrafluoroethane and about 10 to 95 weight percent 1, 1-difluoroethane, and about 76 psia ± 5 psia at 20 ° C. Has a vapor pressure of.

These compositions are essentially isotropic because they exhibit a constant vapor pressure on the composition and essentially the same liquid and gas composition over the range.

In a preferred embodiment of the present invention, this isotropic composition comprises about 40-85% by weight 1, 1, 1,2-tetrafluoroethane and about 15-60% by weight 1, 1-difluoroethane , Vapor pressure of 76 psia ± 3 psia at 20 C.

Gaseous compositions containing more than about 80% by weight of 1, 1, 1, 2-tetrafluoroethane were determined to be non-flammable in the atmosphere at ambient conditions using a Bureau of Mines-style udinometer device.

The azeotropic composition of the invention consisting of HFC-152a and HFC 134a is not isolated.

They also have several advantages over dichlorodifluoromethane (CFC-12), HFC-134 and HFC-152a.

For example, this azeotropic mixture is non-combustible at more than 80% by weight of HFC-l34a, thus reducing the risk of explosion that may occur if an increase in flammable HFC-152a is used, stored or handled in the form of pure water.

Since these azeotropic mixtures also have no risk of ozone depletion and have a low atmospheric life, they neglect the effects on the global greenhouse effect.

This is in contrast to CFC-12's effect on high ozone depletion and subsequent greenhouse effects.

The energy efficiency and cooling capacity of the azeotropic composition of the present invention is superior to pure HFC-134a, and this 134a / 152a composition has significantly reduced direct and indirect effects on the greenhouse effect than pure HFC-134a.

The azeotrope compositions of the present invention can be used in most pure fluoromethane or fluoroethane fluids: ie, fluorocarbon coolants boiling at −l9 ° C. to −30 ° C. (the above ranges of fluids used as air conditioning and coolants currently used) Compared to most boiling points), all the characteristics that an ideal coolant should have, such as stability to use, non-flammability, stability to ozone depletion, negligible greenhouse effects, and desirable energy / cooling performance. To have.

In other words, when HFC-152a and HFC-134a are combined in an effective amount, a non-combustible, non-segregating, environmentally acceptable azeotropic coolant with improved thermodynamic performance is provided.

The term azeotrope-1ike as used herein means that a mixture of 1, 1, 1, 2-tetrafluoroethane and 1, 1-difluoroethane is boiled (constant boiling) or essentially constant (essentially constant boi1ing).

All compositions within the range as well as out of the range indicated in the present invention are azeotropic. From the basic principles, the thermodynamic state of a fluid is defined as four of P, T-X-Y or pressure, temperature, liquid and vapor composition respectively.

Azeotropes are a unique feature of systems of two or more components, where X and Y are the same at a given P and T.

In practice this means that the components do not separate during the phase change and are therefore beneficial for the cooling and heating applications described above.

For this review, an azeotropic composition means that the composition exhibits azeotropic properties in view of its boiling properties and is not classified upon boiling or evaporation.

As such, in such a system, the composition of the gas formed during evaporation is the same as the original liquid composition.

Thus, during boiling or evaporation, the liquid composition changes only slightly if the liquid is all converted.

This is in contrast to non-azeotropic compositions where the composition of liquids and gases changes essentially during evaporation or condensation.

If the gas and liquid phases have the same composition, then, based on theoretical thermodynamics, the boiling point curve for the composition can be seen to pass the absolute maximum or absolute minimum in this composition.

If one of the two conditions, the same liquid and gas composition or minimum or maximum boiling point, is indicated to exist, the system is an azeotrope and the other conditions must be followed.

One way of determining whether a mixture is azeotropic as meant by the present invention is to evaporate the sample under conditions that separate the mixture into individual components. If the mixture is non-azeotropic or non-azeotropic, the mixture will be classified, that is, distilled from the lowest boiling component and separated into its various components.

If the mixture is azeotropic, it will contain all the components of the mixture to obtain a first distillate that will either act as a single substance or boil together.

If the mixture is not azeotropic, that is, not part of an azeotropic system, this phenomenon cannot occur.

Another characteristic of azeotropic compositions from the foregoing is that there is a range of azeotropic compositions containing the same components in varying component ratios.

All such compositions are to be interpreted in the term azeotropic as used herein.

For example, as the boiling point of the composition varies at different pressures, the composition of a given azeotrope will change at least slightly.

As described above, the azeotropes of A and B exhibit a unique form of relationship, but their composition varies with temperature and / or pressure.

Those skilled in the art will easily understand, but the boiling point of the azeotrop has changed with pressure.

In one process embodiment of the present invention, the azeotropic composition of the present invention may be used in a cooling method comprising condensing a coolant comprising an azeotropic composition and then evaporating the coolant in the vicinity of the object being cooled.

In another process embodiment of the present invention, the azeotropic composition of the present invention may be used in a heating method using condensing a coolant in the vicinity of an object to be heated and then evaporating the coolant.

For this application, the process embodiments for cooling or heating described above will be called heat exchange applications.

The 1, 1, 1, 2-tetrafluoroethane and 1, 1-difluoroethane components constituting the novel azeotropic composition of the present invention are known materials.

They should be used with high enough purity to prevent adverse effects on the azeotropy of the system.

The composition of the present invention may include additional components to form new azeotropic compositions.

None of these compositions is construed as falling within the scope of the present invention as long as the composition is substantially azeotropic and contains all of the above essential ingredients.

The azeotropic composition of the present invention may also include components that may not constitute a new azeotropic composition.

In particular, lubricants such as those disclosed in US Pat. No. 4,755,316 can be added within the scope of the present invention.

Hereinafter, the present invention will be described according to examples.

This example shows that certain compositions of 1, 1, 1, 2-tetrafluoroethane and 1, 1-difluoroethane are azeotropic, i.e. exhibit essentially the same liquid and gas composition, and also have a constant boiling (boiling together). constant boi1ing, ie, a constant vapor pressure for the composition within this range.

A gas liquid equilibrium test was conducted by preparing a mixture of HFC-134a and HFC-152a in a container of about 150 cm 3.

A user equipped with a magnetic stirrer and a 0 to 300 psia pressure transducer with an accuracy of ± 0.2% was settled into a controlled thermostat in the range of ± 0,02 ° C.

Once the thermal equilibrium was reached, liquid and gas samples were recovered from the vessel and analyzed using standard gas chromatograph techniques, as by constant vapor pressure measurement.

This procedure was repeated in three compositions of about 25, 50 and 70 mole% HFC-134a and -20, 20 at 60 ° C in HFC-152a.

Table 1 below summarizes these test results.

According to the data in Table I, this gas (vapor) and liquid composition were determined by chromatographic analysis ± 2. It can be seen that it is essentially the same within the experimental error of 0% by weight.

Vapor pressure data measured at −20 ° C. shows minimum values for the composition, demonstrating azeotropic properties.

The vapor pressure of this mixture is essentially constant within ± 5 psia over a composition of about 5-90 wt% HFC-134a and 10-95 wt% HFC-152a, indicating that these mixtures are either constant or azeotropic.

Example 2

This example shows that the azeotropic HFC-134a / HFC-152a mixture has several advantages compared to FC-134a alone.

Under certain operating conditions, the performance of the coolant can be measured by the coefficient of performance (COP) and the capacity of the coolant.

Coefficient of Performance (COP) is a globally recognized measure that is particularly useful in indicating the relative thermodynamic efficiency of a coolant during certain heating or cooling cycles, including evaporation or condensation of the coolant.

In cooling engineering, this word represents a useful cooling ratio for the energy applied by the compressor in compressing the steam.

The capacity of the coolant represents the volumetric efficiency of the coolant.

For compressor engineers, this value represents the capacity of the compressor to pump heat for a given volume flow rate of coolant.

In other words, for a given particular compressor, the larger capacity coolant will produce greater cooling or heating power.

The azeotropic mixture of parts by weight 78/22 HFC-134a / HF0-152a was evaluated in a typical automotive air conditioning unit operated under controlled laboratory calorimeter conditions.

The compressor and condenser sections of the air conditioning cycle were kept at 100 ° F.

Thermocouples were used to measure the temperature of the airflow going to and from the condenser and at the condenser outlet and at the outlet and suction of the compressor.

The compressor was operated at a constant speed of 1188 revolutions / min as an electric motor. A watt-hour meter was used to measure the mechanical power input to the compressor.

Heat removal from the condenser was performed using quench water flowing at a flow rate measured to a cooling coil in the condenser chamber.

The capacity of this air conditioning system was measured by performing energy balance on the condenser chamber.

The vaporizer and the expansion valve of the air conditioning cycle were maintained at 100 ° F and 40% relative humidity.

Thermocouples were used to measure the temperature of the coolant leaving the carburetor and leaving the accumulator.

The coolant pressure was measured throughout the cycle using four pressure transducers located just behind the compressor inlet and exhaust lines and the condenser and accumulator.

Two sets of electric heaters in the vaporization chamber were adjusted to balance the heat removed by the vaporizer.

Three coolants, CFC-12 (dichlorodifluoromethane), HFC-134a and 78 / 22HFC-134a / HF0-152a azeotropic mixtures were tested under these conditions.

CFC-12 is a fully halogenated chlorofluorocarbon used extensively in air conditioning and cooling applications.

CFC-12 is known to destroy the earth's ozone layer.

Each test consisted of at least two consecutive experiments with a measured COP of less than 1%.

This test data is shown in Table 2 below.

The data listed in this table for Trial 1-3 show that the 78/22 HFC-134a / HF0-152a azeotropic mixture is 6.6% higher in COP than HFC-134a and the capacity is comparable to HFC-134a.

This mixture also provides a COP and capacity that is comparable to that obtained with CFC-12.

The compressor exhaust pressure for this mixture is lower than HFC-134a, which eliminates the need to design an air conditioning device to withstand the higher pressure operating pressure.

Tests 4-6 indicate more severe conditions where the air flow through the condenser is reduced, resulting in greater discharge pressure and temperature.

The HFC-134a / HF0-152a mixture not only reduced the discharge pressure but also showed a 4% improvement in HFC-134a and COP and a slight drop in capacity (2%).

Those skilled in the art according to the present invention as described above may be modified without departing from the scope of the present invention.

Claims (3)

An azeotropic composition having a vapor pressure of about 76 psia at 20 ° C. and comprising about 85-96 wt% of 1,1,1,2-tetrafluoroethane and about 5-15 wt% of 1,1-difluoroethane. Condensing the composition of claim 1 and then evaporating said composition in the vicinity of the object being cooled. A method of heating comprising condensing the composition of claim 1 in the vicinity of the object being heated and then evaporating the composition.