Substantially constant boiling blowing agent compositions of 1,1,1,2-tetrafluoroethane and dimethyl ether

Substantially constant boiling blowing agent compositions of 1,1,1,2-tetrafluoroethane and dimethyl ether.

BACKGROUND OF THE INVENTION 
This invention relates to mixtures of 1,1,1,2-tetrafluoroethane (HFC-134a) 
and dimethyl ether (DME). Such mixtures are useful as refigerants, heat 
transfer media, gaseous dielectrics, foam expansion agents, aerosol 
propellants and power cycle working fluids. These mixtures are potentially 
environmentally safe substitutes for dichlorodifluoromethane (CFC-12), 
which is a large volume commercial refrigerant. 
Closed-cell polyurethane foams are widely used for insulation purposes in 
building construction and in the manufacture of energy efficient 
electrical appliances. In the construction industry, polyurethane 
(polyisocyanurate) board stock is used in roofing and siding for its 
insulation and load-carrying capabilities. Poured and sprayed polyurethane 
foams are widely used for insulating large structures such as storage 
tanks, etc. Pour-in-place polyurethane foams are used, for example, in 
appliances such as refrigerators and freezers plus they are used in making 
refrigerated trucks and railcars. 
All of these various types of polyurethane foams require expansion agents 
(blowing agents) for their manufacture. Insulating foams depend on the use 
of halocarbon blowing agents, not only to foam the polymer, but primarily 
for their low vapor thermal conductivity, a very important characteristics 
for insulation value. Historically, polyurethane foams are made with 
CFC-11 (CFCl.sub.3) as the primary blowing agent. 
A second important type of insulating foam is phenolic foam. These foams, 
which have very attractive flammability characteristics, are generally 
made with CFC-11 and CFC-113 ( 1,1,2-trichloro-1,2,2-trifluoroethane) 
blowing agents. 
A third type of insulating foam is thermoplastic foam, primarily 
polystyrene foam. Polyolefin foams (polyethylene and polypropylene) are 
widely used in packaging. These thermoplastic foams are generally made 
with CFC-12. 
Many products designed for household, personal or industrial use are 
available as aerosol products. Typical examples of such products and ones 
in which the propellant system of the present invention can be used 
included personal products such as hair sprays, deodorants and colognes; 
household products such as waxes, polishes, pan sprays, room fresheners 
and household insecticides; industrial products such as cleaners, 
lubricants and mold release agents; and automotive products such as 
cleaners and polishers. All such products utilize the pressure of a 
propellant gas or a mixture of propellant gases (i.e., a propellant gas 
system) to expel the active ingredients from the container. For this 
purpose, most aerosols employ liquified gases which vaporize and provide 
the pressure to propel the active ingredients when the valve on the 
aerosol container is pressed open. 
An important physical property associated with the dispensing of aerosol 
products is the vapor pressure of the propellant. Vapor pressure from the 
viewpoint of this invention is the pressure exerted when a liquified 
propellant gas is in equilibrium with its vapor in a closed container, 
such as an aerosol can. Vapor pressure can be measured by connecting a 
pressure gauge to the valve on an aerosol can or gas cylinder containing 
the vapor/liquid mixture. A standard of measurement of vapor pressure in 
the U.S. aerosol industry is pounds per square inch gauge (psig) with the 
gas/liquid mixture at constant temperature, most commonly at 70.degree. F. 
(21.degree. C.). The vapor pressure of liquified gases most widely 
employed as aerosol propellants will vary over the range of about 20 to 90 
psig (138 to 621 kPa) at 70.degree. F. (21.degree. C.). The propellant 
systems of the present invention have vapor pressures in this range. 
In the early 1970s, concern began to be expressed that the stratospheric 
ozone layer (which provides protection against penetration of the earth's 
atmosphere by ultraviolet radiation) was being depleted by chlorine atoms 
introduced to the atmosphere from the release of fully halogenated 
chlorofluorocarbons. These chlorofluorocarbons are used as propellants in 
aerosols, as blowing agents for foams, as refrigerants and as 
cleaning/drying solvent systems. Because of the great chemical stability 
of fully halogenated chlorofluorocarbons, according to the ozone depletion 
theory, these compounds do not decompose the earth's atmosphere but reach 
the stratosphere where they slowly degrade liberating chlorine atoms which 
in turn react with the ozone. 
Concern reached such a level that in 1978 the U.S. Environmental Protection 
Agency (EPA) placed a ban on nonessential uses of fully halogenated 
chlorofluorocarbons as aerosol propellants. This ban resulted in a 
dramatic shift in the U.S. away from chlorofluorocarbon propellants 
(except for exempted uses) to primarily hydrocarbon propellants. However, 
since the rest of the world did not join the U.S. in this aerosol ban, the 
net result has been to shift the uses of chlorofluorocarbons in aerosols 
out of the U.S., but not to permanently reduce the world-wide total 
chlorofluorocarbon production, as sought. In fact, in the last few years 
the total amount of chlorofluorocarbons manufactured worldwide has 
exceeded the level produced in 1978 (before the U.S. ban). 
During the period of 1978-1987, much research was conducted to study the 
ozone depletion theory. Because of the complexity of atmospheric 
chemistry, many questions relating to this theory remain unanswered. 
However, assuming the theory to be valid, the health risks which would 
result from depletion of the ozone layer are significant. This, coupled 
with the fact that world-wide production of chlorofluorocarbons has 
increased, has resulted in international efforts to reduce 
chlorofluorocarbon use. Particularly, in September, 1987, the United 
Nations through its Environment Programme (UNEP) issued a tentative 
proposal calling for a 50 percent reduction in world-wide production of 
fully halogenated chlorofluorocarbons by the year 1998. This proposal was 
ratified Jan. 1, 1989 and became effective on Jul. 1, 1989. 
Because of this proposed reduction in availability of fully halogenated 
chlorofluorocarbons such as CFC-11, CFC 12 and CFC-113, alternatively more 
environmentally acceptable products are urgently needed. 
As early as the 1970s with the initial emergence of the ozone depletion 
theory, it was known that the introduction of hydrogen into previously 
fully halogenated chlorofluorocarbons markedly reduced the chemical 
stability of these compounds. Hence, these now destabilized compounds 
would be expected to degrade in the atmosphere and not reach the 
stratosphere and the ozone layer. The following Table I lists the ozone 
depletion potential for a variety of fully and partially halogenated 
halocarbons. Halocarbon Global Warming Potential data (potential for 
reflecting infrared radiation (heat) back to earth and thereby raising the 
earth's surface temperature) are also shown. 
TABLE I 
______________________________________ 
Ozone Depletion and Halocarbon Global Warming Potentials 
Halocarbon 
Ozone Depletion 
Global Warming 
Blowing Agent Potential Potential 
______________________________________ 
CFC-11 (CFCl.sub.3) 
1.0 1.0 
CFC-12 (CF.sub.2 Cl.sub.2) 
1.0 2.8 
HCFC-22 (CHF.sub.2 Cl) 
0.05 0.3 
HCFC-123 (CF.sub.3 CHCl.sub.2) 
0.02 0.02 
HCFC-124 (CF.sub.3 CHFCl) 
0.02 0.09 
HFC-134a (CF.sub.3 CH.sub.2 F) 
0 0.3 
HCFC-141b (CFCl.sub.2 CH.sub.3) 
0.1 0.09 
HCFC-142b (CF.sub.2 ClCH.sub.3) 
0.06 0.3 
HFC-152a (CHF.sub.2 CH.sub.3) 
0 0.03 
CFC-113 (CF.sub.2 Cl--CFCl.sub.2) 
0.8-0.9 1.4 
______________________________________ 
Halocarbons such as HFC-134a have zero ozone depletion potential. Dimethyl 
ether, having no halogen content, is also a zero ozone depleter. 
Although 1,1,1,2-tetrafluoroethane has utility as a refrigerant, aerosol 
propellant or foam blowing agent, an azeotrope offers the possibility of 
producing more economical nonfractionating systems with improved 
properties such as polymer and refrigerant oil solubility. 
Unfortunately, as recognized in the art, it is not possible to predict the 
formation of azeotropes. 
This fact obviously complicates the search for new azeotropes which have 
application in the field. Nevertheless, there is a constant effort in the 
art to discover new azeotropic compositions, which have desirable 
characteristics. 
SUMMARY OF THE INVENTION 
The present invention is directed to substantially constant boiling blowing 
agent compositions consisting essentially of 40-99 weight percent, usually 
40-95 weight percent, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1-60 weight 
percent, usually 5-60 weight percent, dimethyl ether (DME). Generally, the 
blowing agent compositions consist essentially of 50-99 weight percent, 
usually 70-99 weight percent, 1,1,1,2-tetrafluoroethane and 1-50 weight 
percent, usually 1-30 weight percent, dimethyl ether. Preferred blowing 
agent compositions consist essentially of 85-99 weight percent 
1,1,1,2-tetrafluoroethane and 1-15 weight percent dimethyl ether. 
Preferred blowing agent compositions nonflammable at ambient temperature 
consist essentially of 90-99 weight percent 1,1,1,2-tetrafluoroethane and 
1-10 weight percent dimethyl ether. The substantially constant boiling 
azeotropic blowing agent composition consists essentially of about 45-55 
weight percent 1,1,1,2-tetrafluoroethane and 45-55 weight percent dimethyl 
ether. The specific azeotropic composition contains 50 weight percent 
1,1,1,2-tetrafluoroethane and 50 weight percent dimethyl ether (.+-.5 
weight percent) with a boiling temperature of about -23.degree. C. at 
about atmospheric pressure. 
By substantially constant boiling composition as used in the present 
invention means the initial vapor pressure of the composition at 
25.degree. C. does not change by more than 2% after half of the initial 
mixture has been allowed to evaporate. Thus, the compositions described 
herein resist component segregation and change in vapor pressure which 
would seriously diminish their usefulness in the contemplated application. 
In addition, studies have further shown that the novel substantially 
constant boiling composition of the present invention exhibits dew and 
bubble point pressures with small pressure differentials of less than 
about 2%. As is well known in this technology, small differences between 
the dew point pressure and the bubble point pressure at the same 
temperature is a further indication of the substantially constant boiling 
or azeotrope-like behavior of the mixtures. 
Azeotropic or substantially constant boiling is intended to s mean also 
essentially azeotropic or essentially constant boiling. In other words, 
included within the meaning of these terms are not only the true azeotrope 
described above, but also other compositions containing the same 
components in different proportions, which are true azeotropes at other 
temperatures and pressures, as well as those equivalent compositions which 
are part of the same azeotropic system and are azeotrope-like in their 
properties. As is well recognized in this art, there is a range of 
compositions which contain the same components as the azeotrope, which not 
only will exhibit essentially equivalent properties for use as blowing 
agents, but which will also exhibit essentially equivalent properties to 
the true azeotropic composition in terms of constant boiling 
characteristics or tendency not to separate or fractionate on boiling. 
The substantially constant boiling compositions of the invention are useful 
as blowing agents. They have zero ozone depletion potential opposite 
CFC-12, which is rated at 1.0. The compositions of this invention are 
especially suitable as blowing agents because 1,1,1,2-tetrafluoroethane 
reduces the solvency or plasticizing effect of dimethyl ether and the 
dimethyl ether solubilizes 1,1,1,2-tetrafluoroethane in the polymer foam. 
This balancing of solubility makes 1,1,1,2-tetrafluoroethane and dimethyl 
ether particularly useful as foam blowing agents. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
Mixtures of HFC-134a and DME may be formulated such that they are 
nonflammable. Therefore, also included among the compositions of this 
invention are compositions nonflammable at ambient temperature containing 
I to 10 weight percent DME and 90 to 99 weight percent HFC-134a that are 
especially effective blowing agents. Also, compositions containing 70-99 
weight percent 1,1,1,2-tetrafluoroethane and 1-30 weight percent dimethyl 
ether are especially useful as blowing agents because they have excellent 
insulating values. 
The HFC-134a/DME azeotropic and substantially constant boiling 
azeotrope-like compositions are excellent polymer blowing agents. The 
dimethyl ether component unexpectedly solubilizes the poorly soluble 
HFC-134a in polyurethane, phenolic and polystyrene foam, resulting in 
excellent insulating foams. Once solubilized in the foam, the HFC-134a 
insulating gas does not diffuse out of the foam. 
The novel substantially constant boiling compositions of the invention were 
discovered during a phase study wherein the compositions were varied and 
vapor pressures measured. The azeotropic composition at 22.degree. C. 
occurred at the minimum point of the vapor pressure-concentration plot, 
being at 50 weight percent HFC-134a and 50 weight percent DME (.+-.5 
weight percent). The azeotrope has an atmospheric pressure boiling point 
of about -23.degree. C., compared with -26.5.degree. C. for HFC-134a and 
-24.6.degree. C. for DME. 
The language "an azeotrope composition consisting essentially of . . . " is 
intended to include mixtures which contain all the components of the 
azeotrope of this invention (in any amounts) and which, when fractionally 
distilled, would produce an azeotrope containing all the components of 
this invention in at least one fraction, alone or in combination with 
another compound, e.g., one which distills at substantially the same 
temperature as o said fraction. 
The nonflammable blowing agents of this invention (at ambient temperature) 
consist essentially of effective amounts of HFC-134a and DME within the 
range of about 90 to 99 weight percent of HFC-134a and 1 to 10 weight 
percent of DME. Usually, for purposes of the invention, the blowing agents 
will contain from about 40 to 99 weight percent of HFC-134a, the remainder 
being DME. 
As stated above, the preferred binary 1,1,1,2-tetrafluoroethane/DME 
compositions are essentially nonflammable. By nonflammable is meant a gas 
mixture which in air will not burn when subjected to a spark igniter as 
described in "Limits of Flammability of Gases and Vapors", Bulletin 503, 
H. F. Coward et al., Washington, U.S. Bureau of Mines, 1952. 
The HFC-134a/dimethyl ether azeotrope of the invention has a vapor pressure 
at 70.degree. F. (21.degree. C.) of about 58 psig (400 kPa). This pressure 
range makes the azeotrope attractive and useful as an aerosol propellant. 
The HFC-134a/dimethyl ether azeotrope has been determined to be a good 
solvent for polystyrene. Thus, the azeotrope and, more particularly, the 
nonflammable mixtures of HFC-134a and dimethyl ether are excellent blowing 
agents for polystyrene and will make it possible to solubilize HFC-134a in 
polystyrene. 
Additionally, the HFC-134a/dimethyl ether azeotrope is soluble in 
polyurethane polyols; whereas, HFC-134a alone has quite poor solubility. 
The composition of the instant invention can be prepared by any convenient 
method including mixing or combining, by suitable methods, the desired 
amounts of the components, using techniques well-known to the art. 
Without further elaboration, it is believed that one skilled in the art 
can, using the preceding description, utilize the present invention to its 
fullest extent. The following preferred specific embodiments are, 
therefore, to be construed as merely illustrative and not limitative of 
the remainder of the disclosure in any way whatsoever. 
In the foregoing and in the following Examples, all temperatures are set 
forth uncorrected in degrees Celsius and unless otherwise indicated, all 
parts and percentages are by weight.

EXAMPLE 1 
A phase study is made on 1,1,1,2-tetrafluoroethane and dimethyl ether 
wherein the composition is varied and the vapor pressures measured at a 
temperature of 22.degree. C. An azeotropic composition is obtained as 
evidenced by the minimum vapor pressure observed and is identified as 50 
weight percent 1,1,1,2-tetrafluoroethane and 50 weight percent dimethyl 
ether (.+-.5 weight percent). 
EXAMPLE 2 
Phase studies were made on the substantially constant boiling compositions 
of 1,1,1,2-tetrafluoroethane (HFC-134a) and dimethyl ether (DME) to verify 
minimal fractionation and change in vapor pressure during a vapor phase 
loss of 50% of the compositions at 25.degree. C., about room temperature. 
Initial liquid composition (IQ), final liquid composition (FQ), initial 
vapor pressure, and change in vapor pressure from initial vapor pressure 
were all studied to determine the effects of vapor pressure as illustrated 
in Table II. 
TABLE II 
______________________________________ 
Percent Wt. % Vapor Vapor 
Loss of Composition Pressure Pressure 
Sample 
Mixture HFC-134a DME (psia) Change (%) 
______________________________________ 
IQ 0 99 1 97.4 
FQ 50 98.7 1.3 97.2 0.2 
IQ 0 95 5 94.4 
FQ 50 93.7 6.3 93.6 0.8 
IQ 0 90 10 91.3 
FQ 50 87.8 12.2 90.1 1.2 
IQ 0 80 20 86.7 
FQ 50 77.3 22.7 85.8 1.0 
IQ 0 70 30 84.1 
FQ 50 67.7 32.3 83.7 0.5 
IQ 0 60 40 82.7 
FQ 50 58.7 41.3 82.7 0.0 
IQ 0 50 50 82.4 
FQ 50 49.9 50.1 82.4 0.0 
IQ 0 40 60 82.6 
FQ 50 41.0 59 82.5 0.1 
______________________________________ 
The data in Table II indicate that the mixtures of HFC-134a and DME are 
substantially constant boiling with only a maximum change of 1.2% in the 
vapor pressure at 25.degree. C. with 50% of the initial mixture 
evaporated. 
EXAMPLE 3 
The difference between the dew point and the bubble point pressures of the 
compositions of the present invention are very small when compared with 
known non-azeotropic compositions, namely (50+50) weight percent mixtures 
of pentafluoroethane (HFC-125) and 1,1,1,2-tetrafluoroethane (HFC-134a) 
and chlorodifluoromethane (HCFC-22) and 1-chloro-1,1-difluoroethane 
(HCFC-142b), respectively. The following data in Table III confirm the 
constant boiling behavior of the compositions described herein. 
TABLE III 
______________________________________ 
Pressures (psia) at 0.degree. C. 
Refrigerant Composition 
Bubble Point 
Dew Point DP* 
(Weight Percent) 
Pressure Pressure (psia) 
______________________________________ 
HFC-134a + DME 
1000 43.04 43.04 0 
991 42.69 42.48 0.21 
955 41.37 40.73 0.64 
9010 39.99 39.26 0.73 
8020 38.06 37.61 0.45 
7030 36.99 36.84 0.15 
6040 36.55 36.54 0.01 
5050 36.53 36.52 0.01 
4060 36.77 36.70 0.07 
HFC-125 + HFC-134a 
68.7 58.3 10.4 
(50 + 50) 
HCFC-22 + HCFC-142b 
44.1 31.2 12.9 
(50 + 50) 
______________________________________ 
*DP is difference in pressure between the dew point and bubble point 
pressures. 
The small difference in pressure between the dew point pressure and the 
bubble point pressure at 0.degree. C. for the mixture of HFC-134a and DME 
indicates that the compositions have insignificant fractionation and 
behave as a single compound with a substantially constant boiling point. 
EXAMPLE 4 
An aerosol room freshener was prepared with the HFC-134a/dimethyl ether 
azeotrope. The formulation and vapor pressure are shown in Table IV. 
TABLE IV 
______________________________________ 
Aerosol Room Freshener Formulation 
Ingredient Wt. % 
______________________________________ 
Perfume 2.0 
HFC-134a/Dimethyl ether (46/54) 
98.0 
Vapor Pressure at 70.degree. F., psig 
60.5 
(at 21.degree. C., kPa) 
(417) 
______________________________________ 
EXAMPLE 5 
The solubility of the HFC-134a/dimethyl ether azeotrope is determined in a 
polyurethane polyol. The azeotrope is readily soluble at 30.0 weight 
percent; whereas, HFC-134a is insoluble. The solubility data are 
summarized in Table V. 
TABLE V 
______________________________________ 
Solubility of HFC-134a/Dimethyl Ether Azeotrope in Polyol 
Wt. % 
Blowing Agent in Polyol* 
Appearance 
______________________________________ 
HFC134a 30.0 Insoluble, two phases 
HFC-134a/Dimethyl ether 
30.0 Soluble, single phase 
(46/54) 
______________________________________ 
*Stepanol .RTM. PS-2852 (Stepan Company) an aromatic polyester polyol. 
EXAMPLE 6 
The solubility of the HFC-134a/dimethyl ether azeotrope in polystyrene is 
determined by combining a piece of polystyrene (about 2.5 cm long, 0.5 cm 
wide and 0.5 cm thick) with about 50 g azeotrope. Whereas HFC-134a has 
essentially no solvency in polystyrene, the HFC-134a/dimethyl ether 
azeotrope softens and deforms the polystyrene. The data are summarized in 
Table VI. 
TABLE VI 
______________________________________ 
Solubility of HFC-134a/Dimethyl Ether 
Azeotrope in Polystyrene 
Blowing Agent Appearance of Polystyrene 
______________________________________ 
HFC-134a No effect 
HFC-134a/Dimethyl Ether (46/54) 
Polystyrene softened and 
deformed* 
______________________________________ 
*On removing the polystyrene from the azeotrope, expansion occurs from 
solubilized HFC134a. 
EXAMPLES 7-10 
The solubility of substantially constant boiling blowing agent compositions 
of HFC-134a/DME in the amounts given below was determined in a 
polyisocyanurate having an isocyanate index of 250.+-.50 and the K-factor 
of the foams was measured. 
TABLE VII 
______________________________________ 
Wt. % of Blowing 
K-factor (BTU- 
Blowing Agent Agent in Foam 
in/hr-ft.sup.2 .degree.F.) 
______________________________________ 
HFC-134a/DME (90/10) 
8.9 0.165 
HFC-134a/DME (80/20) 
7.2 0.166 
HFC-134a/DME (70/30) 
7.7 0.171 
HFC-134a/DME (50/50) 
6.0 0.174 
______________________________________ 
These examples show that the insulating value (K-factor) is substantially 
independent of the quantity of dimethyl ether in the blowing agent 
compositions. A polyurethane foam made with an equivalent amount of a 
CFC-11 blowing agent content (about 10.3 weight percent) would have a 
K-factor of about 0.14. 
EXAMPLE 11 
The quantity of HFC-134a required in the vapor space above blends of 
HFC-134a and dimethyl ether for nonflammability is determined. The test 
conditions and results are summarized in Table VIII 
TABLE VIII 
______________________________________ 
Nonflammable Blend of HFC-134a/Dimethyl Ether 
Ignition Source: 3-mil copper exploding wire (110 volts) 
Temperature: 80.degree. C. 
150.degree. C. 
______________________________________ 
Quantity of HFC-134a required 
greater than 
greater than 
for nonflammability* 
91.% 98.% 
______________________________________ 
*In HFC134a/dimethyl ether vapor mixtures in air. 
Data in Table VIII indicate an effect of test temperature on the amount of 
HFCo 134a required for nonflammability. This indicates that a 
concentration of dimethyl ether higher than 9% could be present in a 
nonflammable composition at ambient temperature (about 25.degree. C.). 
The preceding Examples can be repeated with similar success by substituting 
the generically or specifically described reactants and/or operating 
conditions of this invention for those used in the preceding Examples. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics, spirit and scope thereof, can make various 
changes and modifications of the invention to adapt it to various usages 
and conditions.