Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITIONS AND METHODS FOR CLEANING
VAPOR COMPRESSION SYSTEMS
FIELD OF INVENTION
The present invention relates to non-azeotrope, azeotrope, and azeotrope-like
compositions. More specifically, this invention relates non-azeotrope,
azeotrope, and
azeotrope-like mixtures of hydrofluorocarbons and methods of using the same
for
removing contaminants from vapor compression systems.
BACKGROUND OF THE INVENTION
There exists a need to remove contaminants from vapor compression systems
and their ancillary components when these systems are manufactured and
serviced.
As used herein, the term "contaminants" refers to processing fluids,
lubricants,
particulates, sludge, and/or other materials that are used in the manufacture
of these
systems or generated during their use..In general, these contaminants comprise
compounds such as alkylbenzenes, mineral oils, esters, polyalkyleneglycols,
polyvinylethers and other compounds that are made primarily of carbon,
hydrogen
and oxygen.
Vapor compression systems are used in a wide variety of applications such as
heating and refrigeration. By compressing and expanding a heat transfer agent,
such
as a refrigerant, these systems are capable of absorbing and releasing heat
according
to the needs of a particular application. Common components of a vapor
compression
system include: vapor or gas compressors; liquid-cooled pumps; heat transfer
equipment such as gas coolers, intercoolers, aftercoolers, heat exchangers,
and
economizers; vapor condensers such as reciprocating piston compressors,
rotating
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screw compressors, centrifugal compressors, and scroll expanders; control
valves and
pressure-drop throttling devices such as capillaries; refrigerant-mixture
separating
chambers; steam-mixing chambers; connecting piping; and the like. These
compoiients are typically fabricated from copper, brass, steel, and the like,
and have
conventional gasket materials.
Many components of a vapor compression system require lubrication to
reduce friction caused by their relative physical contact and movements. These
lubricants, which are compounds primarily composed of carbon, hydrogen, and
oxygen, operate by coating the surfaces of component that are subjected to
friction.
Lubricants of a vapor compression system are typically mixed with the heat
transfer
agent which carries and disperses the lubricant throughout the system.
However,
during certain processes or procedures, it is desirable to remove these
lubricants from
the component surfaces, particularly during service operations. Such a need
arises,
for example, during the retrofitting of a chlorofluorocarbon (CFC) or
hydrochlorofluorocarbon (HCFC) refrigerant-based system to a hydrofluorocarbon
(HFC)-based system. There is also a need to remove processing lubricants
during the
manufacturing of a system. Failure to remove these types of contaminants from
the
system may lead to decreased efficiency or even to the failure of one or more
components.
In addition, a vapor compression system may require cleaning after a
catastrophic event, such as a compressor blowout. This type of event can
create
contaminants, such as acids, sludge, and particulates, within the sealed
system.
Failure to remove these types of contaminants from the system may also lead to
decreased efficiency or failure of one or more components.
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The aforementioned contaminants can typically be removed by flushing the
vapor compression system with a flushing agent in which the contaminants are
soluble or miscible. Generally, such flushing agents contain one or more
cleaning
agents (for example, solvents for various types of hydrocarbons) and a
propellant that
carries the cleaning agent through the vapor compression system. In some
cases, the
cleaning agent may also serve as the propellant. Until recently,
chlorofluorocarbons
(CFC's) such as tricholormethane (R-11) and dichlorofluoroethane (R-141) were
used
as flushing agents for such systems. Although effective, CFC's are now
considered
environmentally unacceptable because of their contribution to the depletion of
the
stratospheric ozone layer. As the use of CFC's is reduced and ultimately
phased out,
new flushing agents are needed that not only perform well, but also pose no
danger to
the ozone layer.
Many environmentally acceptable flushing compositions and methods have
been proposed, but their use has met with limited success. For example,
terpenes and
low viscosity esters are known solvents of several types of lubricants
commonly used
in vapor compression systems, such as polyalkylene glycols, polyol esters,
polyvinyl
ethers, and the like. However, many of these solvents have a boiling point
above 100
C and are difficult to remove from system coniponents once they have been
introduced during cleaning. Conventional techniques for removing these high
boiling
solvents prolongs the flushing operation which is economically
disadvantageous. In
addition, solvent remnants can have a deleterious effect on the performance of
the
vapor compression system.
One method that has been proposed to deliver a flushing composition through
a vapor compression system involves the use of compressed nitrogen as the
propellant. However, this method of delivery is difficult and uncertain
because the
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amount of pressure applied by the compressed nitrogen varies. The use of
pressurized
nitrogen as a propellant is also expensive. As an alternative to compressed
nitrogen,
compressed air may be used. However, the use of compressed air brings the
disadvantage that it often contains an unacceptably high amount of moisture.
Once
introduced, this moisture can be difficult to remove from the vapor
compression
system.
Therefore, Applicants have recognized a need for methods, systems, and
compositions that are environmentally-acceptable and which are capable of
effectively and efficiently removing contaminants from vapor compression
systems.
DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
Certain embodiments of the present invention meet the aforementioned needs,
among others, by providing novel non-azeotrope, azeotrope, and azeotrope-like
compositions comprising HFC-mixtures of 1,1,1,2-tetrafluoroethane (HFC- 1 34a)
and
one or more of 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,3,3-
pentafluorobutane (HFC-365), and 1,1,1,2,2,3,4,5,5,5-decafluoropentane (HFC-43-
10). Applicants have surprisingly discovered that when an effective amount of
HFC-
134a is combined with HFC-365, an azeotrope is formed, and when combined with
HFC-245fa, HFC 43-10, or some combination of HFC-245fa, HFC-365, and HFC 43-
10, an azeotrope-like composition is formed. Economical and efficient methods
for
using such compositions to remove contaminants from vapor compression systems
in
an environmentally acceptable manner are also provided.
The term "effective amount", as used herein, refers to the amount of HFC-
134a, that when combined with one or more of the other aforementioned
components,
results in the formation of an azeotrope or azeotrope-like composition.
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The term "azeotrope-like", as used herein, refers to a combination of two or
more compounds that behave substantially like a single compound in so far as
the
vapor in substantial equilibrium with the liquid has substantially the same
concentration of components present in the liquid. The term "azeotrope-like"
is
intended to refer to both true azeotrope compositions and to compositions
which are
not strictly azeotropic, but in which the concentration of components in the
vapor
phase of the composition are so close to the concentration of components in
the
equilibrium liquid phase of the composition as to make separation of the
components
by ordinary distillation not practically possible. In essence, the admixture
distills
without substantially changing its composition. This is to be contrasted with
non-
azeotrope (or "zeotrope") compositions wherein the liquid composition changes
to a
substantial degree during boiling or evaporation.
Azeotropes-like compositions according to the present invention include
absolute azeotropes (compositions in which azeotropic conditions are satisfied
over
all values of temperature (up to the critical stage)) or limited azeotropes
(compositions
in which azeotropic conditions are satisfied only in a certain temperature
range).
Azeotropes-like conipositions according to the present invention also include
homoazeotropes, wherein the composition exists in a single liquid phase, or
heteroazeotropes, wherein the composition exists as two or more liquid phases.
Moreover, azeotrope-like compositions according to the present invention can
be
binary, ternary, quaternary, or quinary azeotropes depending on whether the
composition is composed of 2, 3, 4, or 5 compounds, respectively.
The compounds HFC-245fa, HFC-365, and HFC-43-10 can be used as
flushing agents. However, when any of these compounds are used in a flushing
apparatus such as a flushing gun, or the like, a propellant may also be
required.
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Applicants have discovered that HFC-134a can serve as such a propellant.
Moreover,
as stated above, applicants have discovered that certain azeotrope-like
compositions
are formed by mixing
an effective amount of HFC-134a with HFC-245fa, HFC-365, HFC 43-10, or some
combination thereof. The azeotrope-like nature of these compositions is useful
when
the composition is utilized as a flushing agent, as a heat transfer agent, as
a blowing
agent for foams, or as an aerosols because it allows for uniform condensation
and
vaporization to occur at a single temperature. For example, in closed-loop
systems
such as flushing machines, an azeotrope-like flushing composition can be
recycled
because of its constant composition ratio in both liquid and vapor states.
However, it
is understood that azeotrope-like compositions according to the present
invention may
also be used in open-loop systems, such as flush guns, although non-azeotrope
compositions are preferred.
Applicants have discovered that the preferred azeotrope-like compositions of
the present invention have a number of attributes or properties that render
them
particularly effective as flushing agents for cleaning vapor compression
systems.
Many contaminants, including lubricants, that are commonly found in vapor
compression systems are adequately miscible or soluble in the preferred
azeotrope-
like compositions of the present invention. The term "adequately miscible", as
used
herein, refers to the azeotrope-like composition's ability to interact with a
contaminant to form a solution, emulsion, suspension, or mixture under normal
cleaning conditions in such a way that the contaminant can be effectively
removed
from the surface needing to be cleaned. Examples of such lubricants include,
but are
not limited to, mineral oils, alkylbenzenes, polyvinylethers, polyalkylene
glycols, and
polyol ester oils.
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One advantage of the preferred azeotrope-like compositions according to the
present invention is that it is possible to substantially remove these
compositions from
the treated surface, preferably with relatively little effort or complication.
For
example, the preferred azeotrope-like compositions evaporate readily using
conventional techniques known in the art such as flushing the system with an
inert
gas, pulling a vacuum on the system, and/or heating the system. Factors that
affect
evaporation include vapor pressure, the amount of heat that is applied, the
heat
conductivity of the liquid, the specific heat of the liquid, the latent heat
of
vaporization, surface tension, molecular weight, the rate at which the vapor
is
removed. The most appropriate method for removing the flushing agent for any
given
application is dependent upon the characteristics of the application involved
and one
skilled in the art could readily determine which method would be the most
appropriate
for each such application.
One advantage of the present compositions is that each of HFC-245fa, HFC-
134a, and HFC-43-10 are nonflammable as defined by ASTME681-94, and therefore
azeotrope-like compositions made from mixtures of these materials are also non-
flammable. Additionally, other azeotrope-like composition according to the
present
invention, such as certain azeotrope-like mixtures of HFC-365 and HFC 134a,
may
also be non-flammable. Generally, non-flammable mixtures of the present
invention
are preferred because they are less dangerous and therefore easier to handle.
How, it
is understood that mixtures according to the present invention may also be
flammable,
and that in certain application, the flammability of these mixtures may be
advantageous.
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The preferred azeotrope-like compositions of the present invention are
generally compatible with the materials of vapor compression systems,
including
metals and sealants.
The preferred azeotrope-like compositions of the present invention are
environmentally acceptable and do not to contribute to the depletion of the
earth's
stratospheric ozone layer.
Data is presented that demonstrates the existence of binary azeotrope-like
compositions. Non-flammable, substantially constant boiling compositions can
also
be formed using ternary compositions that comprise HFC-134a and two of the
other
components. However, it should be understood that the present invention also
provides compositions that may also include additional components so as to
form new
azeotrope-like compositions. Any such compositions are considered to be within
the
scope of the present invention provided that the compositions are essentially
azeotrope-like and contain all of the essential components described herein.
Preferred azeotrope-like compositions of the present invention include:
suitable mixtures of HFC-245fa and HFC-134a having from about 1 to about 99
weight percent HFC-134a and from about 99 to about 1 weight percent HFC-245fa;
suitable mixtures of HFC- 1 34a and HFC-3 65 having from about 60 to about 99
weight percent HFC-134a and from about 1 to about 40 weight percent HFC-365;
and
suitable mixtures of HFC-134a and HFC-43-10 having from about 45 to about 99
weight percent HFC-134a and from about 1.to about 55 weight percent HFC43-10.
The preferred ratio of components for these preferred azeotrope-like
compositions would depend on many factors, such as material availability and
cost,
the particular equipment to be cleaned, and the composition of the
contaminants. In
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view of the teaching contained herein, one skilled in the art could readily
select the
ratio of components for a specific application.
Coinpositions according to the present invention, including the preferred
azeotrope-like compositions, may include one or more components, such as
additives,
which may not form new azeotrope-like compositions. Known additives may be
used
in the present compositions in order to tailor the composition for a
particular use.
Inhibitors may also be added to the present compositions to inhibit
decomposition,
react with undesirable decomposition products, and/or prevent the corrosion of
metal
surfaces. Typically, up to about 2 percent of an inhibitor based on the total
weight of
the azeotrope-like composition may be used.
EXAMPLES
The following examples are illustrative of the practice of the present
invention:
EXAMPLE 1:
Eighteen grams of HFC-134a were added to an ebulliometer at atmospheric
pressure. It was determined that the compound boiled at about -25 C. HFC-
245fa
was added to the ebulliometer in increments until there was 7.04 weight
percent (wt.
%) of HFC-245fa. Surprisingly, the boiling point remained at about -25 C to
about -
26E C, indicating that an azeotrope-like composition had formed.
EXAMPLE 2:
A composition comprising 93 wt. % HFC-134a and 7 wt. % HFC-245fa was
produced and then transferred into a cylinder having a dip tube. To test the
cleaning
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efficacy of this azeotrope-like composition, a flushing apparatus was
assembled that
included a cylinder to hold an initial charge of the azeotrope-like
composition, a
vaporizing expansion device, an oil separator, and a compressor. An article
representing a typical vapor compression component, such as a condenser, was
weighed and then soiled by depositing approximately 15 grams of polyalkylene
glycol
(PAG) oil onto its interior surface. The article was then attached to the dip
leg of the
cylinder containing the azeotrope-like composition so that it could be
cleaned.
The azeotrope-like composition, while in liquid phase, was transferred from
the cylinder and through the article. As it passed through the article, it
contacted the
soiled surface. As a result of this contact, the PAG oil was dissolved by the
azeotrope-like composition, thereby removing it from the surface of the
article. As
the azeotrope-like composition and dissolved oil exited the article, they
passed
through the expansion device causing the liquid to evaporate. The resulting
vapor
was passed through an oil separator that removed the oil from the azeotrope-
like
composition. The azeotrope-like composition was then transferred to a
compressor
were it was transformed back to a liquid phase. The liquid azeotrope-like
composition was then recycled through the article to further clean the
article's
surface.
After the azeotrope-like composition had circulated through the article for 45
minutes, it was found that substantially all of the PAG oil was removed from
the
article. The apparatus was turned off and the article was weighed and found to
be
approximately at its original weight. It was found that none of the azeotrope-
like
composition remained in the article.
EXAMPLE 3:
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This example illustrates the formation of an azeotrope-like composition
according to the present invention and the cleaning efficacy of that
composition. For
this example, a mixture of 10 wt. % of HFC-134a and 90 wt. % of HFC-245fa was
formulated and utilized.
The procedure specified in Example 1 was followed to prepare the
composition, except that a mixture of 10 wt. % of HFC-134a and 90 wt. % of HFC-
245fa was formed. Surprisingly, this composition also exhibited azeotrope-like
characteristics.
The cleaning efficacy of this composition was tested using the same procedure
specified in Example 1. After this azeotrope-like composition had circulated
through
the article for 45 minutes, it was found that the substantially all of the PAG
oil was
removed from the article. The apparatus was turned off and the article was
weighted
and found to be approximately at its original weight. Thus, none of the
azeotrope-like
composition or PAG oil remained in the article.
EXAMPLE 4:
This example illustrates the cleaning efficacy of an azeotrope-like
composition according to this invention when a flush gun apparatus is
utilized. For
this example, two pounds of a mixture of 20 wt. % of HFC-134a and 80 wt. % of
HFC-245fa were formulated and then charged into a flush gun.
The interior of an air conditioning condenser was soiled with 15 grams of
PAG oil. The condenser is arranged so that the azeotrope-like composition can
flow
through it. The outlet of the condenser is connected to an evacuated recovery
cylinder
via a high pressure refrigeration hose. The recovery cylinder is cooled by dry
ice.
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The inlet of the condenser is attached to the nozzle of the flush gun by a
secure fitting
and valve.
The valve was opened to allow the azeotrope-like composition to flow from
the flush gun through the condenser and ultimately into the recovery cylinder.
As the
azeotrope-like composition passed through the condenser, it contacted the
condenser's
soiled surface. As a result of this contact, the PAG oil was dissolved by the
azeotrope-like composition, thereby removing it from the surface of the
condenser. If
required, any excess HFC-245fa that became trapped in the condenser was
removed
by dry nitrogen or by passing pure HFC-134a through the condenser.
After less than 45 minutes, the flushing procedure was stopped. It was found
that the substantially all of the PAG oil was removed from the condenser. It
was also
found that the condenser was substantially free of the azeotrope-like
composition.
EXAMPLE 5:
This example illustrates the cleaning efficacy of an azeotrope-like
composition according to this invention when a flush gun apparatus is
utilized. For
this example, a mixture of 20 wt. % of HFC-134a, 30 wt. % of HFC-365, and 50
wt.
% of HFC-245fa was formulated and utilized.
Two pounds of a mixture of 20 wt. % of HFC-134a, 30 wt. % of HFC-365,
and 50 wt. % of HFC-245fa was charged into a flush gun. The cleaning efficacy
of
this composition was tested using the same procedure specified in Example 3.
After less than 45 minutes, the flushing procedure was stopped. It was found
that the substantially all of the PAG oil was removed from the condenser. It
was also
found that the condenser was substantially free of the azeotrope-like
composition.
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EXAMPLE 6:
Approximately 18.97 grams of HFC- 1 34a was added to an ebulliometer
equipped with a vacuum jacket having a condenser on top and a quartz
thermometer.
HCF-365mfc is added in small increments. Temperature depression was observed
when the HFC-365mfc is added, indicating a minimum boiling azeotrope. As shown
in Table 1 below, the boiling point of this composition fluctuates only about
0.7E C as
the HFC134a: HFC-365mfc mixture changes from a weight ratio of 100:0 to a
weight
ratio of 65:35.
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Table 1
HFC134a : HFC365mfc Composition at 14.4 psia
Wt.% HFC 365 mfc Wt.% HFC 134a T (E C) ) from 100% HFC 134a
0.00 100.00 -25.6 --
0.66 99.34 -26.2 -0.5
3.85 96.15 -26.3 -0.7
6.83 93.17 -26.2 -0.6
12.28 87.72 -26.1 -0.5
17.13 82.87 -25.9 -0.3
23.47 76.53 -25.8 -0.2
28.92 71.08 -25.6 0.0
35.07 64.93 -25.1 0.5
EXAMPLE 7:
Approximately 19.86 grams of HFC-134a was added to the ebulliometer
described in Example 5. HCF-43-10 is added in small increments. Temperature
depression was observed when the HCF-43-10 is added, indicating a minimum
boiling azeotrope. As shown in Table 2 below, the boiling point of this
composition
fluctuates only about 0.7E C as the HFC134a : HCF-43-10 mixture changes from a
weight ratio of 100:0 to a weight ratio of 45:55.
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Table 2
HFC134a : HFC-43-10 Composition at 14.4 psia
Wt.% HFC-43-10 Wt.% HFC 134a T (E C) ) from 100% HFC 134a
0.00 100.00 -25.2 --
0.80 99.20 -25.8 -0.6
3.12 96.88 -25.9 -0.7
5.34 94.66 -25.9 -0.7
7.46 92.54 -25.9 -0.7
10.78 89.22 -25.8 -0.6
16.76 83.24 -25.6 -0.4
22.00 78.00 -25.5 -0.3
26.61 73.39 -25.4 -0.2
30.70 69.30 -25.4 -0.2
37.66 62.34 -25.2 0.0
43.35 56.65 -25.0 0.2
49.16 50.84 -25.0 0.2
53.88 46.12 -24.9 0.3
