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DESCRIPTION
FIELD OF THE INVENTION
This invention relates to azeotrope-like mixtures of
trichlorofluoromethane, dichlorotrifluoroethane and isopentane. These
mixtures are useful as blowing agents in the manufacture of rigid and
flexible polyurethane foams and polyisocyanurate foams.
BACKGROUND OF THE INVENTION
Polyurethane and polyisocyanurate foams are manufactured by reacting and
foaming a mixture of ingredients comprising in general an organic
isocyanate, such as pure or crude toluene diisocyanate or a polymeric
diisocyanate, with an appropriate amount of polyol or mixture of polyols,
in the presence of a volatile liquid blowing agent, which vaporizes during
the reaction, causing the polymerizing mixture of foam. The reactivity of
these ingredients is enhanced through the use of various additives such as
amine and/or tin catalysts and surfactant materials which serve to control
and adjust cell size as well as to stabilize the foam structure during its
formation.
Flexible polyurethane foams are generally manufactured using an excess of
diisocyanate which reacts with the water also included as a raw material,
producing gaseous carbon dioxide, causing foam expansion. Flexible foams
are widely used as cushioning materials in items such as furniture,
bedding and automobiles. Auxiliary physical blowing agents such as
methylene chloride and/or CFC-11 are required in addition to the
water/diisocyanate blowing mechanism in order to produce low density, soft
grades of flexible polyurethane foam.
Rigid polyurethane and polyisocyanurate foams are almost exclusively
expanded using CFC-11 as the blowing agent. Some rigid foam formulations
do incorporate small amounts of water in addition to the CFC-11, but the
CFC-11 is the major blowing agent component. Other formulations sometimes
use small amounts of the more volatile dichlorodifluoromethane (CFC-12) in
addition to CFC-11 for producing so-called froth-type foams. Rigid foams
are closed-cell foams in which the CFC-11 vapor is trapped in the matrix
of cells. These foams offer excellent thermal insulation characteristics,
due in part to the low vapor thermal conductivity of CFC-11, and are used
widely in thermal insulation applications such as roofing systems,
building panels, refrigerators and freezers and the like.
The fully halogenated chlorofluorocarbons such as CFC-11 are suspected of
causing environmental problems in connection with the earth's protective
ozone layer. Concern over the potential environmental impact of CFC
emissions has prompted a phased reduction in fully halogenated CFC
production and consumption. The azeotrope-like blowing agent blends
described in this invention offer the potential of a 34 percent reduction
in CFC-11 use. The other components of the blends, namely
dichlorotrifluoroethane and isopentane, have very low ozone depletion
potentials in comparison to CFC-11.
Although methylene chloride is used as an auxiliary blowing agent in
flexible polyurethane foam manufacture, it has found very little
application as a blowing agent in the rigid urethane-type foams. Methylene
chloride tends to remain dissolved in the polymeric back bone of the foam
due to its greater solvency characteristics. The residual methylene
chloride softens and plasticizes the polymer leading to foam collapse or
excessive shrinkage as well as a reduction in the strength properties of
the rigid foam. Some rigid foam formulations can tolerate small amounts of
methylene chloride as a component of the blowing agent, for example, Taub
and Ostrozynski in U.S. Pat. No. 4,055,521 demonstrate that a blend
consisting of 83 parts CFC-11, 12 parts isopentane and 5 parts methylene
chloride can be used to expand a rigid polyurethane foam with good
properties. However, use of even these small amounts of methylene chloride
in closed-cell foams may be objectionable due to the adverse toxicological
properties of methylene chloride.
Other volatile liquids such as hydrocarbons have not found acceptance as
blowing agents for polyurethane-type foams due to their extreme
flammability and poor thermal conductivity properties. These aspects
outweigh the economic advantages that hydrocarbons have over
fluorocarbons. Although the blends described in this invention do contain
a hydrocarbon, it is present as a minor component and overall the blends
are nonflammable as evidenced by flash point tests. Furthermore, as the
present blends are azeotrope-like in nature, their vapor and liquid
compositions are identical and the flammable hydrocarbon component will
not fractionate or segregate from the mixture during boiling or
evaporation.
U.S. Pat. Nos. 3,940,342 and 4,002,573 discloses binary constant boiling
compositions of 1,2-dichloro-1,1,2-trifluoroethane with
trichlorofluoromethane, with diethyl ether and with dichloromethane and
also ternary constant boiling compositions comprising
1,2-dichloro-1,1,2-trichloroethane, diethyl ether and
1,2-dibromo-1,1,2,2-tetrafluoroethane.
U.S. Pat. No. 4,624,970 discloses the use of mixtures of CFC-11 and
HCFC-123 or HCFC-123a to blow urethane type foams. Such blowing agent
mixtures were found to permit greater amounts of low cost aromatic
polyester polyols to be used in rigid foam formulations without serious
degredation in foam properties.
It is accordingly an object of this invention to provide novel
azeotrope-like compositions based on a fluorocarbon which is not fully
halogenated, which can be used as blowing agents to produce rigid and
flexible polyurethane foams and polyisocyanurate foams with good
properties.
Other objects and advantages of the invention will become apparent from the
following description of the invention.
In accordance with the invention, novel azeotrope-like compositions are
provided comprising trichlorofluoromethane, a dichlorotrifluoroethane
selected from the group consisting of 2,2-dichloro-1,1,1-trifluoroethane
ethane (HCFC-123) and 1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a) and
isopentane which are useful as blowing agents in the manufacture of rigid
and flexible polyurethane foams as well as polyisocyanurate foams. Such
azeotropic compositions are formed when either of the above recited
isomers of dichlorotrifluoroethane is employed in about the same
proportions.
In a preferred embodiment of the invention, azeotrope-like compositions
comprise from about 66 to about 80 weight percent trichlorofluoromethane
(CFC-11), from about 17 to 15 weight percent of the recited
dichlorotrifluoroethane isomers and from about 17 to 5 weight percent
isopentane. The dichlorotrifluoroethane isomers, not being perhalogenated,
are considered to be stratospherically safe. Both of the recited isomers
form azeotrope-like compositions with trichlorofluoromethane and
isopentane. Our best estimate of the minimum boiling azeotropic
composition is about 79 weight percent CFC-11, about 15 weight percent of
the recited dichlorofluoroethane isomers and about 6 weight percent
isopentane. These mixtures are nonflammable liquids, do not fractionate
upon evaporation or boiling and provide about 20 to 34 percent reduction
in the amount of fully halogenated CFC-11 required to expand the foam.
Their expansion efficiency (gas volume generated per unit weight) is
better than CFC-11 alone and they also produce foams with similar thermal
insulation characteristics to foams expanded with CFC-11.
DESCRIPTION OF THE INVENTION
The novel azeotrope-like compositions of the invention comprise CFC-11,
dichlorotrifluoroethane (HCFC-123 or HCFC-123a) and isopentane.
For ease of reference the HCFC-123 or HCFC-123a isomers will sometimes be
referred to collectively as "dichlorotrifluoroethane".
In a preferred embodiment of the invention, the azeotrope-like compositions
comprise from about 66 to about 80 weight percent CFC-11, from about 17 to
about 15 weight percent dichlorotrifluoroethane and from about 17 to about
5 weight percent isopentane.
Our best estimate of the true azeotrope containing HCFC-123 is about 79
weight percent CFC-11, about 15 weight percent HCFC-123 and about 6 weight
percent isopentane. The azeotropic composition of the isomeric system is
very similar, about 78 weight percent CFC-11, about 15 weight percent
HCFC-123a and about 7 weight percent isopentane.
The precise or true azeotrope compositions have not been determined but
have been ascertained to be within the indicated ranges. Regardless of
where the true azeotrope lies, all compositions within the indicated
ranges, as well as certain compositions outside the indicated ranges, are
azeotrope-like, as defined more particularly below.
The compositions of the invention are capable of expanding
polyurethane-type foams possessing very good characteristics in comparison
to foams expanded with CFC-11 alone. An advantage of using the
compositions of the invention to blow urethane-type foams is that foams
produced with such compositions consume less CFC-11 and will therefore
emit less CFC-11. The expansion efficiency of the blends, that is gas
volume generated per unit weight of blowing agent, is greater than that of
CFC-11.
Compositions within the azeotrope-like region do not exhibit flash points
and are classified as nonflammable liquids. At the low isopentane
composition the vapor phase does not possess flame limits while at the
high isopentane composition it does exhibit very narrow flame limits in
air. This narrow range of vapor flammability will not inhibit the use of
these blends as urethane foam blowing agents.
From fundamental principles, the thermodynamic state of a fluid is defined
by four variables: pressure, temperature, liquid composition and vapor
composition, or P-T-X-Y, respectively. An azeotrope is a unique
characteristic of a system of two or more components where X and Y are
equal at the stated P and T. In practice, this means that the components
of a mixture cannot be separated during evaporation or boiling and hence
simultaneous vaporization in a constant proportion of all the components
of the azeotrope-like mixture will occur during the foam forming process.
An additional consequence of the azeotrope-like behavior is that it is not
possible to separate the flammable isopentane component from the blend by
evaporation, which could happen if the blend were not azeotrope-like
leading to a potentially hazardous situation.
For the purpose of this discussion, by azeotrope-like composition is
intended to mean that the composition behaves like a true azeotrope in
terms of its constant boiling characteristics or tendency not to
fractionate upon boiling or evaporation. Such composition may or may not
be a true azeotrope. Thus, in such compositions, the composition of the
vapor formed during boiling or evaporation is identical or substantially
identical to the original liquid composition. Hence, during boiling or
evaporation, the liquid composition, if it changes at all, changes only to
a minimal or negligible extent. This is to be contrasted with
non-azeotrope-like compositions in which during boiling or evaporation,
the liquid composition changes to a substantial degree.
Thus, one way to determine whether a candidate mixture is "azeotrope-like"
within the meaning of this invention, is to distill a sample thereof under
conditions (i.e. resolution-number of plates) which would be expected to
separate the mixture into its separate components. If the mixture is
non-azeotropic or non-azeotrope-like, the mixture will fractionate, i.e.
separate into its various components with the lowest boiling component
distilling off first, and so on. If the mixture is azeotrope-like, some
finite amount of a first distillation cut will be obtained which contains
all of the mixture components and which is constant boiling or behaves as
a single substance. This phenomenon cannot occur if the mixture is not
azeotrope-like i.e., it is not part of an azeotropic system. If the degree
of fractionation of the candidate mixture is unduly great, then a
composition closer to the true azeotrope must be selected to minimize
fractionation.
It follows from the above that another characteristic of azeotropic-like
compositions is that there is a range of compositions containing the same
components in varying proportions which are azeotrope-like. All such
compositions are intended to be covered by the term azeotrope-like as used
herein. As an example, it is well known that at differing pressures, the
composition of a given azeotrope will vary at least slightly as does the
boiling point of the composition. Thus, an azeotrope of A and B represents
a unique type of relationship but with a variable composition depending on
temperature and/or pressure.
In the process embodiment of the invention, the azeotrope-like compositions
of the invention may be used as blowing agents for the preparation of
flexible and rigid polyurethane foams as well as rigid polyisocyanurate
foams by reacting and foaming a mixture of ingredients which will form the
polymeric foam in the presence of said blowing agent compositions.
EXAMPLE 1
This example confirms the existence of an azeotrope between CFC-11,
HCFC-123 and isopentane as well as confirming the existence of an
azeotrope between CFC-11, HCFC-123a and isopentane. The method of
distillation is employed in this example.
A 15-plate Oldershaw distillation column with a cold water cooled automated
liquid dividing head was used for this example. The distillation column
was first charged with approximately 580 grams of 79.5 weight percent
CFC-11, 14.5 weight percent HCFC-123 and 6.0 weight percent isopentane.
The mixture was heated under total reflux for a period of about one and
half hours to ensure equilibration. A 10:1 reflux ratio was used in this
distillation. About 60 percent of the original charge was collected in 7
overhead fractions. The composition of these fractions as well as the
composition of the residue in the distillation column were determined by
gas chromatography. Table I shows that the compositions of the starting
material, the compositions of the 7 distillate fractions, and the
composition of the column residue are identical within the uncertainty
associated with the analytical technique. The equivalent liquid and vapor
compositions indicate that the mixture is an azeotrope. The composition of
the azeotrope is in the region of about 79 weight percent CFC-11, about 15
weight percent HCFC-123 and about 6 weight percent isopentane.
TABLE I
______________________________________
CFC-11, HCFC-123 & Isopentane Distillation Data
Vapor Mixture Composition
Temperature
(parts by weight)
Mixture (.degree.C.)
HCFC-123 CFC-11 Isopentane
______________________________________
Original 14.4 79.8 5.8
Charge
Distillate
23.3 14.9 79.0 6.1
Fraction #1
Distillate
23.3 14.6 79.5 5.9
Fraction #2
Distillate
23.3 15.0 79.0 6.0
Fraction #3
Distillate
23.6 15.0 79.0 6.0
Fraction #4
Distillate
23.7 14.6 79.6 5.8
Fraction #5
Distillate
23.6 14.5 79.8 5.7
Fraction #6
Distillate
23.6 14.4 79.8 5.8
Fraction #7
Liquid 14.2 80.2 5.6
Residue
Barometric pressure = 754.6 mm Hg
______________________________________
A similar distillation, this time starting with a mixture in which the
isomer HCFC-123a is used in place of HCFC-123 also provides evidence of an
azeotrope. These distillation results are summarized in Table II. The
azeotropic composition for this mixture is about 78 weight percent CFC-11,
about 15 weight percent HCFC-123a and about 7 weight percent isopentane.
TABLE II
______________________________________
CFC-11, HCFC-123a & Isopentane Distillation Data
Vapor
Temper-
Mixture Composition
ature (parts by weight)
Mixture (.degree.C.)
HCFC-123a CFC-11 Isopentane
______________________________________
Original 16.3 76.7 7.0
Charge
Distillate
22.9 14.6 78.2 7.2
Fraction #1
Distillate
22.9 14.7 78.1 7.2
Fraction #2
Distillate
22.9 14.9 77.9 7.2
Fraction #3
Distillate
22.9 14.8 78.1 7.1
Fraction #4
Distillate
22.9 15.3 77.5 7.2
Fraction #5
Liquid 17.5 75.6 6.9
Residue
Barometric pressure = 735.5 mm Hg
______________________________________
Although in the present case the two isomers, HCFC-123 and HCFC-123a,
behave very similarly with respect to azeotrope formation with CFC-11 and
isopentane, this, as is well known, is not always the case with isomers.
For example, when the distillation of Table I is repeated using n-pentane
in place of the isopentane, the mixture is observed to fractionate,
indicating that the CFC-11/HCFC-123/n-pentane system is not an azeotrope
or azeotrope-like.
EXAMPLE 2
This example describes additional distillations of
CFC-11/HCFC-123/isopentane mixtures which are used to determine the
constant boiling or azeotrope-like composition range.
The distillations were performed using a 5-plate Oldershaw distillation
column at a 3:1 reflux ratio. The mixtures were heated at total reflux for
about an hour and a half to ensure equilibration before collecting 50
percent of the original charge in 4 distillate fractions.
The vapor and liquid compositions were analyzed using gas chromatography.
CFC-11/HCFC-123/isopentane blends with compositions (by weight) of
64.6/15.3/20.1 and 69.7/15.4/14.9 were distilled in order to map the
azeotrope-like region. The distillation date are shown in Table III.
TABLE III
______________________________________
Constant Boiling Characteristics
Vapor Mixture Composition
Temperature
(parts by weight)
Mixture (.degree.C.)
HCFC-123 CFC-11 Isopentane
______________________________________
Original 15.3 64.6 20.1
Charge
Distillate
23.0 17.4 65.6 17.0
Fraction #1
Distillate
23.0 17.2 65.2 17.6
Fraction #2
Distillate
24.0 17.1 64.8 18.1
Fraction #3
Distillate
24.0 15.8 65.9 18.3
Fraction #4
Liquid 12.8 63.4 23.9
Residue
Barometric pressure = 744.6 mm Hg
______________________________________
Original 15.4 69.7 14.9
Charge
Distillate
22.9 16.9 70.0 13.1
Fraction #1
Distillate
22.9 17.2 69.2 13.6
Fraction #2
Distillate
23.0 16.4 70.1 13.5
Fraction #3
Distillate
23.1 16.1 70.0 13.9
Fraction #4
Liquid 14.3 68.7 17.0
Residue
Barometric pressure = 744.6 mm Hg
______________________________________
These data, along with the data shown in Table I show that the region where
vapor and liquid compositions are essentially identical, that is, the
region where the mixture is azeotrope-like, includes the region of about
66 to 80 weight percent CFC-11, about 17 to 15 weight percent HCFC-123 and
about 17 to 5 weight percent isopentane.
EXAMPLE 3
Flammability characteristics of various CFC-11/HCFC-123/isopentane blends
are assessed in this example. The flammability of the liquids was
determined using both Tag open cup (ASTM D 1310-86) and Tag closed cup
(ASTM D 56-82) methods. Vapor flammability was measured using a eudiometer
apparatus similar to that described by Zabetakis et al. in Industrial and
Engineering Chemistry, Vol. 43, No. 9 p. 2120 (1951).
The flash point data (see Table IV) show that the
CFC-11/HCFC-123/isopentane blends begin to exhibit a flash point when the
isopentane composition is increased to about 20 weight percent. Mixtures
with compositions within the azeotrope-like region defined in the previous
example were shown not to exhibit a flash point, that is, they are
nonflammable liquids.
TABLE IV
______________________________________
Flash Point Data
CFC-11/HCFC-123/Isopentane
Flash Point (.degree.F.)
Composition Open Cup Closed Cup
______________________________________
78/15/7 None None
75/15/10 None None
70/15/15 None None
65/15/20 -27 None
______________________________________
Vapor flammability data are summarized in Table V. The isopentane rich end
of the azeotrope-like composition range does exhibit a narrow range of
vapor flammability. This behavior would not, however, preclude use of
these blends as a foam blowing agent.
TABLE V
______________________________________
Vapor Flammability Data
CFC-11/HCFC-123/Isopentane
Lower Limit Upper Limit
Composition Volume % Mixture
______________________________________
79/15/6 None None
75/15/10 14.6 15.6
70/15/15 8.0 15.8
______________________________________
EXAMPLE 4
This example describes an evaluation of the properties of rigid
polyurethane and polyisocyanurate foams prepared using a 79/15/6 blend of
CFC-11/HCFC-123/isopentane. Foams of similar density were prepared using
100 percent CFC-11 for comparison purposes.
Free-rise rigid polyurethane foams were prepared from the formulations
specified in Table VI using a Martin Sweets Co. Modern Module III urethane
foam machine at a delivery rate of 15 lbs./min. This polyurethane
formulation is one example of a pour-in-place rigid polyurethane
formulation which might be used as an appliance insulation.
The foams were characterized (Table VII) according to initial thermal
conductivity (K-factor), density, dimensional stability, porosity (%
closed-cells) and reactivity. Urethane foam produced using the
azeotrope-like blend possesses almost identical properties to the CFC-11
expanded foams.
An advantage of the azeotrope-like blends over CFC-11 is their expansion
efficiency. The above example shows that about 3% less blowing agent blend
is required to achieve the same density.
Polyisocyanurate foams were produced in a similar manner to the
polyurethane foams using the formulation described in Table VIII. Foam
properties are summarized in Table IX. Again the foam expanded with the
azeotrope-like blend possesses essentially identical properties to the
CFC-11 expanded foam while the blend exhibits greater expansion efficiency
over that of CFC-11.
TABLE VI
______________________________________
Rigid Polyurethane Formulation
Parts by Weight
Component (a) (b)
______________________________________
Pluracol 1114.sup.1 (420-OH#)
100. 100.
Silicone L-5340.sup.2 1.5 1.5
Thancat TD-33.sup.3 0.5 0.5
Thancat DME.sup.4 0.2 0.2
Catalyst T-12.sup.5 0.1 0.1
CFC-11 35. --
CFC-11/HFC-123/Isopentane
-- 34.1
(79/15/6)
Lupranate M20S.sup.6 (1.29 Index)
129. 129.
______________________________________
.sup.1 BASF Wyandotte Corp. polyether polyol
.sup.2 Union Carbide Corp. silicone surfactant
.sup.3 Texaco Inc. 33% triethylene diamine in propylene glycol
.sup.4 Texaco Inc. N,N--dimethylethanolamine
.sup.5 Metal & Thermit Co. dibutyl dilaurate
.sup.6 BASF Wyandotte Corp. polymethylene polyphenylisocyanate
TABLE VII
______________________________________
Rigid Urethane Foam Properties
Formulation
Formulation
Physical Properties
(a) (b)
______________________________________
Density (lb/cu.ft.)
2.0 2.0
K-factor* 0.130 0.136
(Btu in/hr ft.sup.2 .degree.F.)
Dimensional Stability*
% Vol. Change (-40.degree. C. 24 hr)
-0.4 0.0
% Vol. Change (70.degree. C. 16 hr)
0.4 0.0
Porosity (% Closed-Cells)
90.7 91.4
Reactivity
Cream Time (sec) 14. 9.
Gel Time (sec) 38. 30.
Tack Free Time (sec)
52. 41.
______________________________________
*5 day old foam
TABLE VIII
______________________________________
Polyisocyanurate Formulation
Parts by Weight
Component (c) (d)
______________________________________
Foamol 250.sup.1 (448-OH#)
60. 60.
Silicone L-5340.sup.2 2.0 2.0
DMP-30.sup.3 1.3 1.3
Foamcat 70.sup.4 4.0 4.0
PEG 200.sup.5 6.7 6.7
CFC-11 55.2 --
CFC-11/HCFC-123/Isopentane
-- 52.8
(79/15/6)
Mondur MR200.sup.6 (3.68 Index)
240. 240.
Percent Isocyanurate 18. 18.
______________________________________
.sup.1 Jim Walter Resources Inc.
.sup.2 Union Carbide Corp.
.sup.3 Rohm and Hass Co.
.sup.4 Jim Walter Resources Inc.
.sup.5 Union Carbide Corp.
.sup.6 Mobay Chemical Corp.
TABLE IX
______________________________________
Polyisocyanurate Foam Properties
Formulation
Formulation
Physical Properties
(c) (d)
______________________________________
Density (lb/cu.ft.)
1.83 1.83
K-factor* 0.141 0.141
(Btu in/hr ft.sup.2 .degree.F.)
Dimensional Stability*
% Vol. Change (-40.degree. C. 24 hr)
0.0 0.0
% Vol. Change (70.degree. C. 16 hr)
-0.1 0.0
Porosity (% Closed-Cells)
92.8 92.6
Reactivity
Cream Time (sec) 10 13.7
Gel Time (sec) 34. 23.2
Tack Free Time (sec)
46. 30.
______________________________________
*5 day old foam
* * * * *
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