Note: Descriptions are shown in the official language in which they were submitted.
~ WO94/21745 21~ 7 7 81 PCT~S94/02~
AzEorRopE-LIKE C~MPOSI~I~NS ~F
l,l,l,Z,3,3,3-1~EPTAFLUOXOPRO~ANE
AND 1,l-DIFLUOROET~ E
CROSS-R~.~R~CE TO R~T.~l'ED APPLICATION
This application is a continuation-in-part of my prior
co-pending patent application Serial No. 07/858,240 filed
March 26, l9g2.
B~CK~ROUND OF TH~ lNV~NTION
Field of the Inven~ion:
l'he present invention relates to azeotrope-like
compositions of l,l,l,2,3,3,3-heptafluoropropane and
l,l-difluoroethane. These mixtures have no efect on
stratospheric ozone and are useful as refrigerants for
heating and cooling applications. l'hese mixtures may also be
employed as aerosol propellants, heat transfer media, fire
suppression agents, gaseous dielectrics or blowing agents for
plastic foams.
Description of the Prior Art:
A number of chlorofluorocarbons (CFCs) have gained
widespread use in refrigeration applications owing to ~heir
unique combination of physical and chemical properties.
However, due to their implication in the destruction of
stratospheric ozone, the production and use of CFCs is
currently ~eing severely restricted, and the use of these
agents will be completely banned in the near future. This
will require the replacement of these agents by refrigerants
containing neither chlorine nor bromine and which have no
effect on stratospheric ozone. One such zero ozone depleting
compound which has been proposed is l,l-difluoroethane,
(refrigerant Rl52a), which has been shown to provide 4 to 10%
WO94/21745 PCT~S94/02~ ~
2ls7~8l _
increases in efficiency compared to dichlorodifluoromet}lane
(rerigerant R12), as discussed in Kuijpers, et al., in
"CFCs: Time of Transition," ASHRAE, Atlanta,~Ga, 1989, p.
175. A major drawback of this compound however is its lligh
fla~nability.
The use of azeotropic mixtures as refrigerants is know
in the art, and is discussed for example in R.C. ~owning,
"Fluorocarbon Refrigerants Handbook," Prentice-Hall, 1988 and
R.J. ~ossat, "Principles of Refrigeration," 2nd edition,
Wiley, 1981. Azeotropic or azeotrope-like compositions do
not fractionate upon boiling or evaporation. This behavior
is desirable when employing vapor compression equipment for
refrigeration, since no fractionation will occur UpOII
evaporation and condensation. Such fractionation can result
in undesirable refrigerant distribution and also adversely
affect the cooling or heating ability of the system.
Non-azeotropic refrigerant mixtures (NARMs) are known in
the art, see, e.g., U.S. Patent 4,303,536, but have not found
widespread use. Since the NARMs fractionate during the
refrigeration cycle, their use may require certain equipIllent
changes.
The art is continually seeking new fluorocarbon based
azeotrope-like mixtures which offer alternatives for
refrigeration and heat pump applications and are efficient,
nontoxic, non ozone depleting and nonflammable. As pointed
out previously, although efficiency gains are observed
employing l,l-di1uoroethane, its high fla~nability is a
serious liability to its practical use.
Computer-based models have su~stantiated that
hydrofluorocarbons such as 1,1,1,2,3,3,3-heptafluoropropane
(HFC227ea) and l,l-difluoroethane (HFC1~2a) have no effect on
stratospheric ozone, i.e., their ozone depletion potential
(ODP) is zero.
Tlle use of clllorofluorocarbons (CFCs) as blowing agents
is well known in the art, but these materials are to be
~ WO94/21745 21 S 7 7 81 PCT~S94/02~
ul~imately banned due to their role in tlle destruc~ion of
stratospheric ozone. It is also taught in the art that
hydrochlorofluorocarbons (~ICFCs), for example
r 2,2-dichloro-1,1,1-trifluoroethane (CF3CEIC12), are useful
in foam blowing applications, see, e.g., I.R. Shanklarld,
Int. J. Refrig., 1~, 113 (199U). However, since the llCFCs
are characterized by nonzero ozone depletion potentials,
~heir use will also be restricted and likely banned in the
future.
It is also well known in the art to employ
chlorofluorocarbons (CFCs) as aerosol propellants, see, e.g.,
R.J. ~odson, in R.E. Banks, ec., "Organofluorine Cllemicals
and their Industrial Applications," Horwood, 1979, p. 79.
The ultimate ban of these materials due to their role in the
destruction of the stratospheric ozone creates, however, a
need for environmentally acceptable, nontoxic, nonflammable
alternatives.
It is accordingly an object of this invention to provide
novel azeotrope-like compositions based on
1,1,1,2,3,3,3-heptafluoropropane and l,l-difluoroetha}le which
are nonflammable, nontoxic, chemically stable, and present no
adverse threat to stratospheric ozone. Another object of the
invention is to provide novel environmentally acceptable
refrigerants which are useful in cooling and heating
applications. A further object of the invention is to
provide environmentally acceptable, non-toxic, nonflammable
aerosol propellants and foam blowing agents. Other objects
of the invention will become apparent from the following
description.
WO94/21745 PCT~S94/02~40
~5~
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~SCRIrTION OF T~IE rREFERRED ~BODIMENTS
In accordance Witll the invention, novel azeotrope-like
compositions have been discovered comprising
l,l,l,2,3,3,3-heptafluoropropane and l,l-difluoroethane. The
azeotrope-like compositions comprise from about 55 to about
95 weight percent l,l,l,2,3,3,3-heptafluoropropane and from
about 5 to about 45 weight percent l,l-difluoroethane. These
compositions have a boiling pOiIIt of about -l9.0C at l a~m.
These compositions are azeotrope-like because tlle composition
of said mixtures does not substantially change upon
evaporation or condensation.
In a preferred embodiment of the invention, SUCll
azeotrope-like compositions comprise from about 60 to about
90 weight percent l,l,l,2,3,3,3-heptafluoropropane and from
abou~ l0 to about 40 weight percent l,l-difluoroetllane. The
compound l,l,l,2,3,3,3-heptafluoropropane is known in the art
and has been shown to be an efficient fire suppression agent,
see, e.g., M. Robin, "Large Scale Testing of Halon
A1ternatives," l99l International CFC and ~alon Alternatives
Con~erence, Baltimore, MD, ~ecember 3-5, l99l. Hence,
non-flamma~le azeotrope-like mixtures are readily obtained by
combining l,l,l,2,3,3,3-heptafluoropropane with
l,l-difluoroethane.
l'he term "azeotropP-like" is used herein for mixtures of
the inven~ion because in tlle claimed proportions tlle
compositions of l,l,l,2,3,3,3-heptafluoropropane and
l,l-difluoroethane are constant boiliny or essentially
constant boiling. Furthermore, no or essentially no
fractionation occurs upon evaporating or condensing the
mixtures.
One me~hod ~or de~ermining whe~her a candidate mixture is
azeotrope-like is to determine whether the boiling point
versus composition curve passes through an extremum, see,
e.g., W. Swietoslawski, "Azeotropy and Polyazeotropy,"
~ WO94/2174S PCT~S94/02~
-- 2157781
E~ergamon, 1963, and J.M. Smith and H.C. Van Ness,
J "Introduction to Chemical Enyineering Thermodynamics,"
McGraw-Hill, 1987.
Alternatively, one can determine whether a candidate
5 mixture is azeotrope-like by determining whether the vapor
pressure versus composition curve passes througll an extremum,
see, e.g., M. McLinden and G. Morrison, NBS Technical Note
1226, National Bureau of Standards, p. 96, 1986, Smith and
Van Ness, Q cit., and U.S. Patent 4,978,467.
10 Azeotrope-like mixtures which possess a maximum in the vapor
pressure versus composition curve will exhibit a minimum in
tlle boiling point versus composition curve.
One of tile characteristics of an azeotrope-like mixture
is that there is a range of compositions containing th~ same
15 components in varying proportions which are azeotrope-like.
It is well known to those skilled in the art that an
azeotrope of two compounds represents a unique interaction
but with a variable composition depending on the temperature
and/or pressure. For example, to those skilled in the art it
20 is un~erstood that the boiling point and composition of an
azeotrope will vary with pressure.
Accordingly, another way to define an azeotrope-like
mixture within the meaning of this invention is to state that
such mixtures exhibit vapor pressures within about +/- 5 ps~a
(35 kPa) at 70F (21C) of the most preferred compositions
disclosed herein (about 65 psia at 70F (21C)).
As a further alternative, another way to define an
azeotrope-like mixture wit~lin tlle meaning of this invention
is that given by Bivens (Fluorocarbon Mixtures as CFC
Alternatives, 200th ACS National Meeting, Washington, DC,
August 18, 1990). As defined by Bivens, "near-azeotropes"
are those ~lixtures for which the dew point/bubble point delta
T is less than or equal to 5C. lt is to be understood that
the terms "near azeotropes" and "azeotrope-like mixtures" are
interchangeable in describing such systems. 'l'lle mixtures of
WO94/21745 PCT~S94/02~ ~
~S~7~ -6-
the present invention are azeotrope-like because for all
compositions, the bubble point/dew point delta T is less than
5C.
The inventive composi~ions are useful in a variety of
applications. ln one process embodiment of tlle inventioll,
tlle azeotrope-like compositions oE the invention may be used,
in the presence of a suitable lubricant if required, in a
method for producing refrigeration which comprises condensing
a refrigerant comprising the azeotropic-like compositions and
thereafter evaporating the refrigerant in the vicinity of the
body to be cooled. In another process embodiment of the
invention, the azeotrope-like compositions of the invention
may be used, in the presence of a suitable lubricant if
required, in a method for producing heating wllicll utilizes
condellsing a refrigerant comprising the azeotropic-like
compositions in the vicinity of the body to be heated, and
thereafter evaporating the refrigerant. As will also ~e
readily appreciated by those skilled in the art, the
azeotrope-like compositions of the invention are also useful
in foam blowing and aerosol propellant applications.
It should be understood that the present compositions may
include additional, non-interfering components so as to form
new azeotrope-like compositions. Any such compositions are
considered to be witllin the scope of tlle present invention.
The present invention is more fully illustrated by the
following examples, which are to be understood as exemplary
only, and non-limiting.
E~XAMPLE 1
This example demonstrates the inertion oE HFC-152a by
HE?C-227ea. Tlle concentration of E~FC-227ea required to inert
HFC-152a was measured in an 8.0 L explosion sphere,
consisting of two 304 stainless hemispheres welded on
stainless steel flanges, and equipped with instrurllentation
allowing the monitoring of pressure and ternperature as a
_ WO94/21745 PCT~S94/02~
-- 21S7781
~unction of time. A mixture of IIFC-152a and air and ~he
desired concentration of the inerting agent ~FC-227ea were
introduced into the sphere employing partial pressures to
7 determine tlle volumes of agent, fuel and air. The mixture
5 was then sub,jected to a DC spark of 70 J ignition energy,
located in the center of the sphere. Mixtures producing an
overpressure of greater than or equal to 1.0 psia following
activation of the spark are considered 1ammable, and
mix~ures producing an overpressure of less thall 1.0 psia are
10 considered nonflammable. By examining a series of mixtures
of varying ratios of air/fuel/HFC-227ea, the concentratioll of
HFC-227ea required to inert all combinations of the HFC-152a
and air can be determined. The flammability measurements
indicate that only 8.7% by volume of HFC-227ea is required to
15 render all combinations of HFC-152a and air nonflammab]e.
The flammability diagram determined from the experimental
data is shown in FIG. 1 for the HFC-227ea/HFC-152a~air
system. A straight line drawn from the origin and not
crossing into the flammable region gives the minimum ratio of
20 ~IFC-227ea to HFC-152a required ~o provide a nonElammable
mixture. It is found that mixtures of ~FC-227ea and HFC-152a
may contain up to approximately 25 weight percent of HFC-152a
and remain nonflammable.
EXAMPLE 2
This exampl2 demonstrates the azeotrope-like nature of
HFC-227ea/HFC-152a mixtures. Vapor pressure data for 80:20
and 30:70 by weight mixtures of HFC-227ea and HFC-152a are
shown in Tables 1 and 2.
WO94/21745 PCT~S94/029
21S~ 8-
TABLE 1: VAPOR PRESSURE OF A 80:20 BY WEIGIIT MIXTURE OF
HFC-227ea AND HFC-152a
Temperature (F) rressure (Dsia~
10.0 ]9.7
5 20.0 2~.7
30.0 30.7
40.0 37.6
5~.0 46.0
U.0 55.5
1070,0 66.0
~0.0 78.5
90.0 92.3
100.0 108.0
TABLE 2: VAPOR PRESSURE OF A 30:70 BY WEIGHT MIXTURE OF
15HFC-227ea and HFC-152a.
Temperature (F~ Pressure (Dsia)
40.0 43.3
50.0 52.4
60.0 62.7
2070.0 74.6
80.~ 88.1
90.0 103.5
100.0 121.1
Both sets of data were employed to determine the
Carnahan-Starling-DeSantis (CSD) binary interaction
coefficient for the mixtures. As described in NBS Technical
Note 1226, the CSD binary interaction coefficient allows the
calculation of accurate physical and thermodynamic properties
for mixtures of fluorinated compounds such as I~FC-152a and
HFC-227ea. The CSD equation of state accurately describes
the physical and thermodynamic properties of fluorocarbons,
and their mixtures, and also accurately represents the
zeotropic or azeotropic nature of such mixtures. From the
vapor pressure data, the binary interaction coefficient was
determined following the procedure described by Morrison and
McLinden ill NBS Techllical Note 1226. The binary interaction
coefficient was found to be -0.014, and to be independent of
the composition of tlle mixture. The phase (Pxy) diagram for
~ WO94/2174S PCT~S94/02~
2157781
g
the system l~FC-227ea/~FC-152a is shown in FIG. 2; ill this
figure the upper line is the bubble line (saturated liquid),
and ~he lower line is the dew line (saturated vapor). It is
seen from FIG. 2 that the dew point-but~ble point delta T is
less than 5C for all compositions. Hence, mixtures of
I~FC-227ea and HFC-152a are seen to be azeotrope-like over the
entire composition range. As an exarnple, an 80:20 by weight
mixture of HFC-227ea and HFC-152a is seen from FIG. 2 to be
charac~erized by a bubble point/dew point delta T of 0.7C.
EXAMPLE 3
This example demonstrates the nonflammability of the
mixtures. The 80:20 by weight mixture of HFC-227ea and
HFC-152a described in Example 2 was tested for flammability
in the following fashion. The sample cylinder was placed on
a concrete pad and the valve to the cylin~er opened slightly
to allow the escape of the sample. For a leakage percent
from 0 to 100%, the leaking vapor stream could not be ignited
with a flame source held approximately 0.5 to 3.0 inches from
the location of the leak. A similar test with pure HF~-152a
resulted in the ignition of the leaking HFC-152a gas stream
to produce a self-propagating 1ame; the gas stream continued
to burn on its own after removal of the flame source.
EXAMPLE 4
The foregoing formulations of Examples 1 and 2 aLe used
as propellants, heat transfer media, fire suppression agents,
gaseous dielectrics and as blowing agents in conventional
fas~ion, and suitable results are obtained.
Having described the inve~tion in detail and by reference
to preferred embodiments thereof, it will be apparent that
modifications and variations are possible without departing
from the scope of the invention defined in the appended
claims.
