WO1993023518A1

WO1993023518A1 - Azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; perfluorohexane; and perfluoroheptane and optionally nitromethane

Info

Publication number: WO1993023518A1
Application number: PCT/US1993/003959
Authority: WO
Inventors: Ellen Louise Swan; Rajat Subhra Basu
Original assignee: Allied-Signal Inc.
Priority date: 1992-05-21
Filing date: 1993-04-28
Publication date: 1993-11-25

Abstract

Azeotrope-like compositions comprising 1,1-dichloro-1-fluoroethane; perfluorohexane; and perfluoroheptane are stable and have utility as degreasing agents and as solvents in a variety of industrial cleaning applications including cold cleaning and defluxing of printed circuit boards and dry cleaning.

Description

AZEOTROPE-LIKE COMPOSITIONS OF

1.1-DICHLORO-1-FLUOROETHANE:

PERFLUOROHEXANE: AND PERFLUOROHEPTANE

AND OPTIONALLY NITROMETHANE

BACKGROUND OF THE INVENTION

Vapor degreasing and solvent cleaning with fluorocarbon based solvents have found widespread use in industry for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.

In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent.

For difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, the conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.

Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents and allowed to air dry.

Fluorocarbon solvents, such as trichlorotrifiuoroethane, have attained widespread use in recent years as effective, nontoxic, and nonflammable agents useful in degreasing applications and other solvent cleaning applications. Trichlorotrifiuoroethane has been found to have satisfactory solvent power for greases, oils, waxes and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts and the like.

Azeotropic or azβotropβ-like compositions are desired because they do not fractionate upon boiling. This behavior is desirable because in the previously described vapor degreasing equipment with which these solvents are employed, redistilled material is generated for final rinse-cleaning. Thus, tiie vapor degreasing system acts as a still. Unless the solvent composition exhibits a constant boiling point, i.e., is azeotrope-like, fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. Preferential evaporation of the more volatile components of the solvent mixtures, which would be the case if they were not azeotrope-like, would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency towards soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity. The art has looked towards azeotrope or azeotrope-like compositions including the desired fluorocarbon components such as trichlorotrifiuoroethane which include components which contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers.

The art is continually seeking new fluorocarbon, hydrofluorocarbon, and hydrochlorofluorocarbon based azeotrope-like mixtures which offer alternatives for new and special applications for vapor degreasing and other cleaning applications. Currently, of particular interest, are fluorocarbon, hydrofluorocarbon, and hydrochlorofluorocarbon based azeotrope-like mixtures with minimal or no chlorine which are considered to be stratospherically safe substitutes for presently used chiorofiuorocarbons (CFCs). The latter are suspected of causing environmental problems in connection with the earth's protective ozone layer.^' Mathematical models have substantiated that hydrochlorofluorocarbons, such as 1 ,1-dichloro-1-fluoroethane (known in the art as HCFC-141b), will not adversely affect atmospheric chemistry, being negligible contributors to ozone depletion and to green-house global warming in comparison to chiorofiuorocarbons such as 1 ,1 ,2-trichloro-1 ,2,2-trifluoroethane (CFC-113). HCFC-141b is known to be useful as a solvent.

U.S. Patent 4,994,202 teaches azeotropic mixtures of 1 ,1- dichloro-1-fluoroethane and perfluoro-dimethylcyclobutanβ. U.S. Patent 5,037,573 teaches azeotropic mixtures of 1 ,1-dichloro-1 fluoroethane and n-perfiuorobutylethylene.

DESCRIPTION OF THE INVENTION

Our solution to the need in the art for substitutes for chiorofluorocarbon solvents is mixtures comprising 1,1-dichloro-1 -fluoroethane; perfiuorohexane; and perfluoroheptane; and optionally nitromethane. Also, novel azeotrope-iike or constant-boiling compositions have been discovered comprising 1,1-dichloro-1 -fluoroethane; perfiuorohexane; and perfluoroheptane; and optionally nitromethane.

Preferably, the novel azeotrope-like compositions comprise effective amounts of 1,1-dichloro-1 -fluoroethane; perfiuorohexane; and perfluoroheptane; and optionally nitromethane. The term "effective amounts" as used herein means the amount of each component which upon combination with the other component, results in the formation of the present azeotrope-like composition.

Preferably, the azeotrope-like compositions comprise from about 30 to about 90 weight percent of 1,1-dichloro-1 -fluoroethane, from about 8 to about 50 weight percent of perfiuorohexane, and from about 2 to about 20 weight percent of perfluoroheptane, and from 0 to about 1 weight percent nitromethane wherein the compositions boil at about 28.5°C at 760 mm Hg (101 kPa).

The present azeotrope-like compositions are advantageous for the following reasons. The 1 ,1 -dichloro-1 -fluoroethane component is a negligible contributor to ozone depletion and has good solvent properties. The perfiuorohexane and perfluoroheptane components also have good solvent properties. Thus, when these components are combined in effective amounts, an efficient solvent results. The present ternary and quaternary solvents are azeotrope-like or have constant-boiling characteristics and as such, advantageously do not fractionate upon boiling or evaporation.

The preferred azeotrope-like compositions are in Table I below wherein the numerical ranges are understood to be prefaced by "about":

All compositions within the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below.

The precise azeotrope compositions have not been determined but have been ascertained to be within the above ranges. Regardless of where the true azeotropes lie, all compositions with the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below.

It has been found that these azeotrope-like compositions are on the whole nonflammable liquids, i.e. exhibit no flash point when tested by the Tag Open Cup test method - ASTM D 1310-86 and Tag Closed Cup Test Method - ASTM D 56-82.

The term "azeotrope-like composition" as used herein is intended to mean that the composition behaves like an azeotrope, i.e. has constant-boiling characteristics or a tendency not to fractionate upon boiling or evaporation. 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.

As is readily understood by persons skilled in the art, the boiling point of the azeotrope-like composition will vary with the pressure.

The azeotrope-like compositions of the invention are useful as solvents in a variety of vapor degreasing, cold cleaning and solvent cleaning applications including defluxing and dry cleaning.

In the process embodiment of the invention, the azeotrope-like compositions of the invention may be used to clean solid surfaces by treating said surfaces with said compositions in any manner well known to the art such as by dipping or spraying or use of conventional degreasing apparatus. Preferably, the azeotrope-like compositions of the invention are used to dissolve contaminants or remove contaminants from the surface of a substrate by treating the surface with the compositions in any manner well known to the art such as by dipping or spraying or use of conventional degreasing apparatus wherein the contaminants are substantially dissolved or removed.

The present azeotrope-iike compositions may be used to clean the surface of inorganic and organic substrates. Examples of inorganic substrates include metallic substrates, ceramic substrates, and glass substrates. Examples of organic substrates include polymeric substrates such as polycarbonate, poiyvinyl chloride, polystyrene, and acryionitrile-butadiene-styrene. The present azeotrope-like compositions also may be used to clean the surface of natural fabrics such as cotton, silk, fur, suede, leather, linen, and wool. The present azeotrope-like compositions also may be used to clean the surface of synthetic fabrics such as polyester, rayon, acrylics, nylon, and blends thereof, and blends of synthetic and natural fabrics.

The 1,1-dichloro-1 -fluoroethane; perfiuorohexane; perfluoroheptane; and nitromethane components of the novel solvent azeotrope-iike compositions of the invention are known materials and are commercially available. The term "perfiuorohexane" as used herein covers from "pure perfiuorohexane" which is 100 weight percent branched or straight chain perfiuorohexane to "commercial grade perfiuorohexane" which comprises at least 65 weight percent perfluoro-n-hexane, about 0.01 to about 5 weight percent perfluoroheptane, and the remainder is linear and branched perfluorocarbons having 5 to 18 carbon atoms. The term "perfluoroheptane" as used herein covers from "pure perfluoroheptane" which is 100 weight percent branched or straight chain perfluoroheptane to "commercial grade perfluoroheptane" which comprises at least 60 weight percent perfluoro-n-heptane, about 0.01 to about 5 weight percent perfiuorohexane, and the remainder is linear and branched perfluorocarbons having 5 to 18 carbon atoms.

Preferably, "commercial grade perfiuorohexane" and "commercial grade perfluoroheptane" are used in the present invention. "Commercial grade perfluorohexane" and "commercial grade perfluoroheptane" were used in the following Examples.

EXAMPLES 1-2

These examples confirm the existence of constant-boiling or azeotrope-like compositions of 1 ,1-dichloro-1 -fluoroethane; perfiuorohexane; and perfluoroheptane via the method of distillation. It also illustrates that these mixtures do not fractionate during distillation.

A 5-plate Oldershaw distillation column with a cold water condensed automatic liquid dividing head was used for these examples: The distillation column was charged with HCFC-141b, perfluorohexane, and perfluoroheptane in the amounts indicated for Example 1 in Table II below and for Example 2 in Table III below. Each composition was heated under total reflux for about an hour to ensure equilibration. A reflux ratio of 3:1 was employed for these particular distillations. Approximately 50 percent of the original charges were collected in four overhead fractions; the sizes of the fractions were not always the same. The compositions of these fractions, in addition to the composition of the liquid residue, were analyzed using gas chromatographγ. The averages of the distillate fractions and the overhead temperatures were quite constant within the uncertainty associated with determining the compositions, indicating that the mixtures are constant-boiling or azeotrope-like. For Example 1 , the overhead temperature at 751.9 mm Hg was 28.5°C (corrected to 760 mm Hg, 28.8°C). For Example 2, the overhead temperature at 751.9 mm Hg was 30.6°C (corrected to 760 mm Hg, 30.9°C).

TABLE II

No attempt was made to fully characterize and define the outer limits of the composition ranges which are constant-boiling. Anyone skilled in the art can readily ascertain other constant-boiling or essentially constant-boiling mixtures containing the same components.

EXAMPLE 3

To illustrate the azeotrope-like nature of the mixtures of this invention under conditions of actual use in vapor phase degreasing operation, a vapor phase degreasing machine was charged with a preferred azeotrope-like mixture in accordance with the invention comprising about 74.0 weight percent HCFC-141b, about 18.5 weight percent perfluorohexane, and about 7.5 weight percent perfluoroheptane. The mixture was evaluated for its constant boiling or non-segregating characteristics. The vapor phase degreasing machine utilized was a small water-cooled, three-sump vapor phase degreaser, which represents a type of system configuration comparable to machine types in the field today which would present the most rigorous test of solvent segregating behavior. Specifically, the degreaser employed to demonstrate the invention contained two overflowing rinse-sumps and a boil-sump. The boii-sump was electrically heated, and contained a low-level shut-off switch. Solvent vapors in the degreaser were condensed on water-cooled stainless-steel coils. The capacity of the unit was approximately 1.2 gallons. This degreaser was very similar to Baron Blakeslee 2 LLV 3-sump degreasers which are quite commonly used in commercial establishments. The solvents charge was brought to reflux and the compositions in the rinse sump and the boil sump where the overflow from the work sump was brought to the mixture boiling point, were determined with a Perkin Elmer 8500 gas chromatograph. The temperature of the liquid in the boil sump was monitored with a thermocouple temperature sensing device accurate to _±_ 0.2°C. Refluxing was continued for 48 hours and sump compositions were monitored throughout this time. A mixture was considered constant boiling or non-segregating if the maximum concentration difference between sumps for any mixture component was ±. 2 sigma around the mean value. Sigma is a standard deviation unit and it is our experience from many observations of vapor degreaser performance that commercial "azeotrope-like" vapor phase degreasing solvents exhibit at least a ± 2 sigma variation in composition with time and yet produce very satisfactory non-segregating cleaning behavior.

If the mixture were not azeotrope-like, the high boiling components would very quickly concentrate in the boil sump and be depleted in the rinse sump. This did not happen. Also, the concentration of each component in the sumps stayed well within _+_ 2 sigma. These results indicate that the compositions of this invention will not segregate in any types of large-scale commercial vapor degreasers, thereby avoiding potential safety, performance and handling problems. The preferred composition tested was also found to not have a flash point according to recommended procedure ASTM D 1310-86 (Tag Open Cup). The details of the segregation study are shown in Table IV.

EXAMPLES 4 THROUGH 6

Performance studies are conducted wherein metal coupons are cleaned using the present azeotrope-like compositions as solvents. The metal coupons are soiled with various types of oils and heated to 93°C so as to partially simulate the temperature attained while machining and grinding in the presence of these oils.

A stainless steel beaker with condensing coils near its lips is used. Each azeotrope-like composition is boiled in the beaker which condenses on the coils providing adequate vapor and the condensed solvent drips back to the beaker.

The metal coupons are held in the solvent vapor and then vapor rinsed for a period of 15 seconds to 2 minutes depending upon the oils selected. The azeotrope-like compositions of Examples 1 through 3 are used as the solvents. Cleanliness testing of coupons are done by measurement of the weight change of the coupons using an analytical balance to determine the total residual materials left after cleaning.

EXAMPLES 7 THROUGH 9

Each azeotrope-like composition of Examples 1 through 3 above is used as solvent and is added to mineral oil in a weight ratio of 50:50 at 27°C. Each solvent is miscible in the mineral oil.

EXAMPLES 10 THROUGH 12

Metal coupons are soiled with various types of oil. The soiled metal coupons are immersed in solvents of the azeotrope-like compositions of Examples 1 through 3 above for a period of 15 seconds to 2 minutes, removed, and allowed to air dry. Upon visual inspection, the soil appears to be substantially removed.

EXAMPLES 13 THROUGH 15

Metal coupons are soiled with various types of oil. The soiled metal coupons are sprayed with solvents of the azeotrope-like compositions of Examples 1 through 3 above and allowed to air dry. Upon visual inspection, the soil appears to be substantially removed. EXAMPLE 16 Acrylic and polycarbonate parts were refluxed in 1 ,1-dichloro-1- fluoroethane alone and a blend of 75 weight percent 1 ,1-dichloro-1- fluoroethane, 18 weight percent perfluorohexane, and 7 weight percent perfluoroheptane for 10 minutes which is a typical reflux time in commercial cleaning applications. 1 , 1 -dichloro-1 -fluoroethane alone had an adverse effect on numerous polymeric materials including polycarbonate, polystyrene, and acryonitrile-butadiene-styrene. Unexpectedly, the present blend showed no adverse effect on many polymeric materials.

Known additives may be used in the present-azeotrope-like compositions in order to tailor the composition for a particular use. Inhibitors may be added to the present azeotrope-like compositions to inhibit decomposition of the compositions; react with undesirable decomposition products of the compositions; and/or prevent corrosion of metal surfaces. Any or all of the following classes of inhibitors may be employed in the invention: alkanols having 4 to 7 carbon atoms, nitroalkanes having 2 to 3 carbon atoms, 1,2-epoxyalkanes having 2 to 7 carbon atoms, phosphite esters having 12 to 30 carbon atoms, ethers having 3 or 4 carbon atoms; unsaturated compounds having 4 to 6 carbon atoms, acetals having 4 to 7 carbon atoms, ketones having 3 to 5 carbon atoms, and amines having 6 to 8 carbon atoms. Other suitable inhibitors will readily occur to those skilled in the art. In spraying applications, the azeotrope-like compositions may be sprayed onto a surface by using a propellant.

The inhibitors may be used alone or in mixtures thereof in any proportions. Typically, up to about 2 percent based on the total weight of the azeotrope-like composition of inhibitor might be used.

Claims

What is claimed is:

1. Azeotrope-like compositions consisting essentially of from about 30 to about 90 weight percent of 1 ,1-dichioro-1 -fluoroethane, from about 8 to about 50 weight percent of perfiuorohexane, and from about 2 to about 20 weight percent of perfluoroheptane, and from 0 to about 1 weight percent nitromethane wherein said compositions boil at about 28.5°C at 760 mm Hg.

2. The azeotrope-like compositions of claim 1 consisting essentially of from about 42 to about 85 weight percent said 1 ,1-dichloro-1 -fluoroethane, from about 12 to about 42 weight percent said perfluorohexane, and from about 3 to about 16 weight percent said perfluoroheptane, and from 0 to about 0.5 weight percent said nitromethane.

3. The azeotrope-like compositions of claim 1 consisting essentially of from about 58 to about 81 weight percent said 1 ,1-dichloro-1 -fluoroethane, from about 15 to about 30 weight percent said perfluorohexane, and from about 4 to about 12 weight percent said perfluoroheptane, and from 0 to about 0.3 weight percent said nitromethane.

4. The azeotrope-like compositions of claim 1 wherein said perfluorohexane is at least 65 weight percent perfluoro-n-hexane and said perfluoroheptane is at least 60 weight percent perfluoro-n-heptane.

5. The azeotrope-like compositions of claim 2 wherein said perfluorohexane is at least 65 weight percent perfluoro-n-hexane and said perfluoroheptane is at least 60 weight percent perfluoro-n-heptane.

6. The azeotrope-iike compositions of claim 3 wherein said perfluorohexane is at least 65 weight percent perfluoro-n-hexane and said perfluoroheptane is at least 60 weight percent perfluoro-n-heptane.

7. The azeotrope-like compositions of claims 1 through 7 wherein said compositions additionally contain an inhibitor selected from the group consisting of alkanols having 4 to 7 carbon atoms, nitroalkanes having 2 to 3 carbon atoms, 1 ,2-epoxyalkanes having 2 to 7 carbon atoms, phosphite esters having 12 to 30 carbon atoms, ethers having 3 or 4 carbon atoms, unsaturated compounds having 4 to 6 carbon atoms, acetals having 4 to 7 carbon atoms, ketones having 3 to 5 carbon atoms, and amines having 6 to 8 carbon atoms.

8. A method of dissolving contaminants or removing contaminants from the surface of a substrate which comprises the step of: contacting said surface with said azeotrope-like composition of claim 3 as solvent.

9. The method of claim 8 wherein said method dissolves contaminants or removes contaminants from the surface of an organic substrate.