WO1993023519A1

WO1993023519A1 - Azeotrope-like compositions of 1,1-dichloro-1-fluoroethane, perfluorohexane, methanol or ethanol and optionally nitromethane

Info

Publication number: WO1993023519A1
Application number: PCT/US1993/003982
Authority: WO
Inventors: Rajat Subhra Basu; Richard Mervil Hollister
Original assignee: Allied-Signal Inc.
Priority date: 1992-05-13
Filing date: 1993-04-28
Publication date: 1993-11-25
Also published as: AU4034493A

Abstract

The invention relates to stable, environmentally acceptable azeotrope-like compositions of 1,1-dichloro-1-fluoroethane, perfluorohexane, methanol or ethanol and optionally nitromethane which are useful as degreasing agents and 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-DICHLOROl-FLUOROETHANE, PERFLUOROHEXANE, METHANOL OR ETHANOL

AND OPTIONALLY NTTROMETHANE

Background ofthe 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 no residue behind. This is not 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.

Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al. in U.S . Patent 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancillary equipment.

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 cloths or similar materials soaked in solvents and allowed to air dry.

Fluorocarbon solvents, such as trichlorotri- fluoroethane or CFC-113, have been used extensively in recent years in degreasing applications and other solvent cleaning applications. CFC-113 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 azeotrope-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, the 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. For example, in a non-azeotropic composition preferential evaporation of the more volatile components could result in mixtures having lower solvency towards soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity. The art continues to look toward fluorocarbon-based azeotrope or azeotrope-like compositions which include other components which contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers and which offer alternatives for new and special applications for vapor degreasing and other cleaning applications.

Currently, fluorocarbon, hydrofluorocarbon, and hydrochlorofluorocarbon based azeotrope-like mixtures with little or no chlorine are of particular interest since they are considered to be stratospherically safer substitutes for presently used chlorofluorocarbons

(CFCs) . CFC's are suspected of causing environmental problems related to the depletion of the earth's protective ozone layer. Mathematical models have substantiated that hydrochlorofluorocarbons, such as 1,1-dichloro-l-fluoroethane or HCFC-141b, will not adversely affect atmospheric chemistry, since they contribute negligibly to ozone depletion and green-house global warming in comparison to CFC's like CFC-113. DescriptionoftheInvention

Our solution to the need in the art for substitutes for chlorofluorocarbon based solvents is azeotrope-like compositions comprising effective amounts of 1,1-dichloro-l-fluoroethane (HCFC-141b) , perfluoro- hexane, methanol or ethanol, and optionally nitromethane.

Preferably, the azeotrope-like compositions comprise from about 32 to about 95 weight percent 1,1- dichloro-1-fluoroethane, from about 4 to about 64 weight percent of perfluorohexane and from about 1 to about 4 weight percent methanol and boil at about 25.4°C +.0.5°C at 760 mm Hg.

When ethanol is used, the azeotrope-like compositions of the invention comprise from about 34.8 to about 86.1 weight percent 1,1-dichloro-l-fluoroethane, from about 13.8 to about 60 weight percent perfluoro¬ hexane, and from about 0.1 to about 5.2 weight percent ethanol and boil at about 27.5°C ± 0.5°C at 760 mm Hg.

When nitromethane is included, the azeotrope-like compositions of the invention utilizing methanol comprise from about 31 to about 95 weight percent 1,1-dichloro-l- fluoroethane, from about 4 to about 64 weight percent perfluorohexane, from about 1 to about 4 weight percent methanol and from about 0.1 to about 1 weight percent nitromethane and boil at about 25.4°C + 0.5°C at 760 mm Hg.

When nitromethane is included, the azeotrope-like compositions of the invention utilizing ethanol comprise from about 33.8 to about 86 weight percent 1,1-dichloro- 1-fluoroethane, from about 13.8 to about 60 weight percent perfluorohexane, from about 0.1 to about 5.2 weight percent ethanol and from about 0.1 to about 1 weight percent nitromethane and boil at about 27.5°C ± 0.5°C at 760 mm Hg.

The 1,1-dichloro-l-fluoroethane component contributes negligibly to ozone depletion and has good solvent properties. The alkanol and fluorinated alkane components also have good solvent properties. The alkanol dissolves polar organic materials and amine hydrochlorides while the fluorinated alkane enhances the solubility of oils. Nitromethane is a stabilizer. Thus, when these components are combined in effective amounts, a stable, efficient, environmentally acceptable azeotrope-like solvent results.

The composition of the preferred azeotrope-like compositions of the invention are summarized in Table I below. Note that the composition ranges reported are in weight percent.

Table I

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. We expect that the compositions of the invention will be non-flammable since mixtures of HCFC-141b and. methanol or ethanol do not have flash points and perfluorocarbons do not have flash points. That is, since individual components or simple mixtures of components do not have flash points we would not expect mixtures of all of these components to have flash points.

The term "azeotrope-like composition" as used herein 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. 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 slightly. This is contrasted with non-azeotrope-like compositions in which the liquid composition changes substantially during boiling or evaporation.

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 one process embodiment of the invention, the azeotrope-like compositions of the invention may be 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 remov-st≥.

The l,l-dichloro-l-fluoroethane, perfluorohexane, methanol, ethanol, and nitromethane components of the novel solvent azeotrope-like compositions of the invention are known, commercially available materials.

The present invention is more fully illustrated by the following non-limiting Examples.

Iftgflm lft 1

This example confirms the existence of constant-boiling or azeotrope-like compositions of 1,1-dichloro-l-fluoroethane, perfluorohexaneandmethanol using a micro-ebulliometer. The perfluorohexane used in the Example -was FC-72 manufactured by Minnesota, Mining andManufacturing Company (3M) of Minneapolis, Minnesota. FC-72 is about 70% perfluorohexane in a mixture containing C₅ - C₁₈ perfluoroalkanes.

The temperature of boiling liquid mixtures was measured using an ebulliometric technique similar to that described by W. Swietoslawski in Ebulliometric Measurements, Reinhold Publishing Corp., (1945). A micro-ebulliometer which consisted of a spherical flask was charged with 2.8 cm³ of a 96.3/3.7 weight percent mixture of 1,1-dichloro-l-fluoroethane/methanol respectively. The flask was partially submerged in a constant temperature bath which served to heat the liquid contained in the flask. The liquid was stirred vigorously with a magnetic stirrer. The temperature of the boiling system was measured using a platinum resistance thermometer which was accurate to ± 0.2°C. The thermometer was placed just above the surface of the boiling liquid and was continually washed with condensed vapor. The system was operated under total reflux and boiling temperature and atmospheric pressure measurements were recorded after steady-state was attained. A weighed aliquot of perfluorohexane was then introduced into the ebulliometer and the temperature and pressure recorded again after steady-state was obtained. This process was repeated with additional aliquots of perfluorohexane. The prevailing barometric pressure was also recorded. By the above-described method we discovered that mixtures of about 32- 95/4 - 64/1 - 4/weight percent 1,1-dichloro-l- fluoroethane/perfluorohexane/methanol respectively are essentially constant boiling at about 25.4°C ± 0.5°C.

Iftqimplβ 2

The experiment outlined in Example 1 above was repeated for compositions of 1,1-dichloro-l-fluoro¬ ethane, perfluorohexane and ethanol except that initially 2.8 cm³ of a 64.7/35.3 weight percent mixture of 1,1- dichloro-1-fluoroethane/perfluorohexane respectivelywas charged to the micro-ebulliometer and measured amounts of ethanol were added. By the above-described method we discovered that mixtures of about 34.8 - 86.1/13.8 - 60/0.1 - 5.2 weight percent 1,1-dichloro-l-fluoro- ethane/perfluorohexane/ethanol respectively are constant boiling at about 27.5^βC ± 0.5°C.

Kampl^ -

The experiment outlined in Example 1 above is repeated for compositions of 1,1-dichloro-l-fluoro¬ ethane, perfluorohexane, methanol and nitromethane and compositions of 1,1-dichloro-l-fluoroethane, perfluoro¬ hexane, ethanol and nitromethane. By the above-described method we discover that mixtures of about 31 - 95/ 1 - 4/4 - 64/0.1 - 1 weight percent 1,1-dichloro-l- fluoroethane/methanol/perfluorohexane/nitromethane respectively are constant boiling at about 25.4°C±0.5°C and mixtures of about 33.8 - 86/0.1 - 5.2/13.8 - 60/0.1 - l weight percent 1,1-dichloro-l-fluoroethane/ethanol/ perfluorohexane/nitromethane respectively are constant boiling at about 27.5°C ± 0.5°C.

Fyam lPS 5 ■ S

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 rhile machining and grinding in the presence of these oli.s.

A stainless steel beaker with condensing coils near its lips is used. Each azeotrope-like composition is boiled in the beaker and condenses on the coils providing adequate vapor and the condensed solvent drips back into 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 - 4 are used as the solvents. The cleanliness of the coupons is determined by measuring the weight change of the coupons using an analytical balance to determine the total residual materials left after cleaning.

We discover that essentially no residual material is left after cleaning with the compositions of Examples 1 - 4 indicating that these compositions are effective cleaning solvents.

F.τampΪPi; - 12

Each of the compositions of Examples 1 - 4 above is added to mineral oil in a weight ratio of 50:50 at 27°C.

We discover through visual observation that each solvent is miscible in mineral oil.

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 1 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.

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

When the present azeotrope-like compositions are used to clean solid surfaces by spraying the surfaces with the compositions, preferably, the azeotrope-like compositions are sprayed onto the surfaces by using a propellant. Preferably, the propellant is selected from the group consisting of hydrocarbons, chlorofluoro¬ carbons, hydrochlorofluorocarbons, hydrofluorocarbons, dimethyl ether, carbon dioxide, nitrogen, nitrous oxide, methylene oxide, air, and mixtures thereof.

Having described the invention 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.

Claims

hat is claimed is:

1. Azeotrope-like compositions consisting essentially of from about 32 to about 95 weight percent 1,1-dichloro-l-fluoroethane, from about 4 to about 64 weight percent perfluorohexane, and from about 1 to about 4 weight percent methanol and boil at about 25.4°C at 760 mm Hg; or from about 34.8 to about 86.1 weight percent 1,1-dichloro-l-fluoroethane, from about 13.8 to about 60 weight percent perfluorohexane and from about 0.1 to about 5.2 weight percent ethanol and boil at about 27.5°C at 760 mm Hg; or from about 31 to about 95 weight percent 1,1-dichloro-l- fluoroethane, from about 4 to about 64 weight percent perfluorohexane, from about 1 to about 4 weight percent methanol and from about 0.1 to about 1 weight percent nitromethane and boil at 25.4°C at 760 mm Hg; or from about 33.8 to about 86 weight percent 1,1-dichloro-l-fluoroethane, from about 13.8 to about 60 weight percent perfluorohexane, from about 0.1 to about 5.2 weight percent ethanol and from about 0.1 to about 1 weight percent nitromethane and boil at about 27.5°C at 760 mm Hg.

2. The azeotrope-like compositions of claim 1 wherein said compositions of 1,1-dichloro-l-fluoroethane, perfluorohexane and methanol boil at about 25.4°C ± 0.5°C at 760 mm Hg.

3. The azeotrope-like compositions of claim 1 consisting essentially of from about 36 to.about 90.5 weight percent 1,1- dichloro-1-fluoroethane, from about 8 to about 60 weight percent perfluorohexane, from about 1.5 to about 4 weight percent methanol .

4. The azeotrope-like compositions of claim 1 consisting essentially of from about 38.8 to about 84.9 weight percent 1,1- dichloro-1-fluoroethane, from about 13.5 to about 57.4 weight percent perfluorohexane, from about 1.6 to about 3.8 weight percent methanol .

5. The azeotrope-like compositions of claim 1 consisting essentially of from about 42.8 to about 85.5 weight percent 1,1 dichloro-1-fluoroethane, from about 14.2 to about 54.7 weight percent perfluorohexane, and from about 0.3 to about 2.5 weight percent ethanol .

6. The azeotrope-like compositions of claim 1 consisting essentially of from about 36 to about 90.4 weight percent 1,1- dichloro-1-fluoroethane, from about 8 to about 60 weight percent perfluorohexane, from about 1.5 to about 4 weight percent methanol, and from about 0.1 to about 0.5 weight percent nitromethane.

7. The azeotrope-like compositions of claim 1 consisting essentially of from about 43.3 to about 85.5 weight percent 1,1- dichloro-I-fluoroethane, from about 14.1 to about 54.7 weight perfluorohexane, from about 0.3 to about 2.5 weight percent ethanol, and from about 0.1 to about 0.5 weight percent nitromethane.

8. The azeotrope-like compositions of claims 1 through 7 wherein said compositions additionally contain an inhibitor to accomplish at least one of the following: inhibit decomposition of the compositions; react with undesirable decomposition products of the compositions; and prevent corrosion of metal surfaces.

9. The azeotrope-like compositions of claims 1 through 7 wherein said inhibitor selected from the group consisting of alkanols having 4 to 7 carbon atoms, nitroalkanes having 1 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.

10. A method of cleaning a solid surface comprising contacting said surface with an azeotrope-like composition of claims 1 through 7.