COMPOSITION FOR THE DETECTION OF ELECTROPHILIC GASES AND METHODS OF USE THEREOF

Abstract: There is provided a composition for the detection of an electrophilic gas, such as chlorodifluoromethane or carbon dioxide, which comprises a Lewis base capable of removing a proton from the gas or reacting therewith in a similar electrophilic manner; a dye capable of visibly indicating a color change on protonation or deprotonation; a solvent for the dye, the base and the gas; and a rheology modifier capable of producing a non-newtonian gel of all of these components which is sufficiently translucent to permit visual detection of change of color of the dye and of sufficient pseudoplasticity/thixotropy to provide adhesion to vertical and horizontal surfaces.

Description: COMPOSITION FOR THE DETECTION OF ELECTROPHILIC GASES AND METHODS OF USE THEREOF Field of the invention Detection of electrophilic gases Discussion of the prior art The problem of leak detection of gases, particularly refrigerant gases has long been recognized. The principle approach to its solution has been the mix an indicator into the refrigerant itself and to look for external appearance of the indicator. Methods of detecting leakage of CIF 2 CH (chlorodifluoromethane) as a refrigerant based on a color change of an indicator as a result of an acid- base reaction are disclosed in U. S. patent 3,770,640 and Japan 61 - 97457). Organic bases such as amines have been used in the indicator compositions ( U. S. patents 3,770,640; 1 ,915,965; 3,370,010; and 5,560,855). US 1 ,915,965 to William describes a method of testing for leaks in a refrigerating system of the compression type. Examples are given of refrigerants which are the members of the halo-fluoro group. The property of certain basic dyes such as methylviolet base, crystal violet, auramine B, rhodamine B, etc. of permanently staining certain materials is employed. The disadvantage of internal indicators is that they may negatively affect the efficiency of the equipment containing them. Also a substantial amount of indicator must leak out to be detected. An external fluorescent leak detection composition comprising sodium fluorescein and a semisynthetic cellulose thickening agent is disclosed in US 4,249,412, to Townsend, III. This patent describes the use of methyl and ethyl cellulose derivatives in such compositions. The composition is applied to a cold surface, such as refrigeration tubes. Preferred thickening agents include the semisynthetic cellulose derivatives, such as carboxymethylcellulose, hydroxymethylcellulose, methylcellulose, ethylcellulose and mixtures thereof. This method is directed to bubble detection and not to chemical interaction with the refrigerant. Furthermore, it requires the use of a light source to excite the fluorescein. In view of the fact that certain refrigerants such as chlorodifluoromethane have been banned from future production since they have a highly deleterious environmental effect on the ozone layer, it is essential to develop an indicator system which is rapidly sensitive to the smallest leaks. Such leaks should be detectable with the naked eye. Summary of the invention There is provided a composition for the detection of a electrophilic gas, such as chlorodifluoromethane or carbon dioxide, which comprises a Lewis base capable of removing a proton from the gas or reacting therewith in a similar electrophilic manner; a dye capable of visibly indicating a color change on protonation or deprotonation, that is to say on pH change; a solvent for the dye, the base and the gas; and a rheology modifier capable of producing a non-newtonian gel of all of these components which is sufficiently translucent to permit visual detection of change of color of the dye and of sufficient pseudoplasticity/thixotropy to provide adhesion to vertical and horizontal surfaces. The Lewis base should be present in sufficient amount to bring the pH of the gel to between 6.9 and 14 and may be selected from the group consisting of alkali- and alkaline earth- metal hydroxides, alkoxides and carbonates; amines; quaternary ammonium hydroxides, alkoxyamines, hydroxylalkylamines and mixtures thereof. Any indicator giving a clear transition from base to acid, notably in the visible spectrum without enhancement (ie UV light) may be used. Suitably, the solvent is selected from the group consisting of alkanols, arylalkanols, alkyl halides, alkyl ketones, alkylamines, aralkylamines, alkyl esters of alkanoic acids, dimethylsulfoxide, water and mixtures thereof. It has been found desirable for the rheology modifier to be selected from the group consisting of hydroxyalkylcellulose, cellulosic semisynthetic polymers, polyvinyl alcohols, carbopols, alginates and natural gums. The composition is used by providing a coating of thereof on a conduit for said gas. It has also been found useful to preserve the coating by applying to it a solution, suitably a solution comprising a sprayable film forming topcoat composition settable at between about 0 - about 30°C and a solution therefor, wherein the film is sufficiently translucent to permit visual detection of change of color of the dye. Description of the preferred embodiments The detection method d isclosed (for example for chlorodifluoromethane) utilizes the following general reaction (wherein B " is a strong anion: B " + CIF 2 CH - > BH + CICF 2 - for example: NaOH + CIF 2 CH - > H 2 O + NaCICF 2 or, in the case of carbon dioxide: NaOH + CO 2 - > NaHCO 3 Detection of the reaction is made possible by using a pH sensitive organic (or inorganic) indicator, which exhibits a color change on with the decrease in [B " ]. A solution of an appropriate base and indicator, in an appropriate solvent, is gelled and applied to the system externally at the pipe joints. If the gas leaks, it must pass through the gel, where it reacts as above and creates the visible color change. To maintain the presence of sufficient solvent and prevent contamination of the gel, an appropriate top coat may be applied. The compositions of the present invention for the detection of an electrophilic gas, are especially useful for use with chlorodifluoromethane or carbon dioxide. The choice of the Lewis base is a wide one. Especially suitable as alkali- and alkaline earth- metal hydroxides, are sodium hydroxide and calcium or magnesium hydroxide, as alkoxides and carbonates, sodium ethoxide and sodium carbonate; as amines, quaternary ammonium hydroxides, alkoxyamines, and hydroxylalkylamines higher boiling members of this group or those having low vapor pressures at ambient temperatures are preferred. Especially preferred as Lewis bases are sodium hydroxide, sodium ethoxide or methoxide, ethyl hydroxylamine and triethylamine because of their low cost and ready availability. Among the suitable dyes used as indicators ( showing the appropriate color change) there may be mentioned: methylorange (yellow-red) thymol blue (blue to yellow); phenolphthalein (pink to clear);m-cresol purple (purple to yellow); phenol red (red to yellow); and thymolphthalein blue (blue to clear). A wide range of solvents may be used such as alkanols, glycols, glycolethers, arylalkanols, alkyl halides, alkyl ketones, alkylamines, aralkylamines, alkyl esters of alkanoic acids, dimethylsulfoxide and water. Suitably, the alkyl moieties may be straight chain-, branch chain- and cyclic- moieties and the alkanols and alkylamines may be primary, secondary and tertiary alkanols and alkylamines. Especially preferred are dimethylsulfoxide, water, tetrahydrofuran, acetone, ethyl acetate, ethyleneglycol monobutyl ether and methanol. Suitably, the solvent is utilized in a range relative to the sum of the Lewis base and the dye of between 1 and 99 parts by volume per part by weight of base plus dye. As a protective coating or topcoat composition there are preferably employed ethylcellulose, polyethylene, polytetrafluorethylene or mixtures thereof epoxy resins, polyurethane resins, siloxanes, as well as natural coatings such as modified and unmodified rosin, polyvinylpyrrolidone, alkyd resins and polyacrylates and mixtures thereof. Suitable solvents for the topcoat may include: aromatic hydrocarbons such as toluene, xylene, aromatic napthas, alkanes such as hexane, alkyl ketones such as methyl isobutyl ketone and acetone; straight or branched chain (C- to C 4 )alcohols such as methanol, ethanol, isoprbpanol and n- butanol; C-, to C 5 alkyl ethers; mono-, di-, and tri- glycols (Dowanols ® manufactured by Dow Chemical Corp.); mineral spirits; mineral, vegetable, animal or marine oils ; and\or mixtures thereof. EXAMPLES EXAMPLE 1 Preparation of indicator composition Thymolphthalein blue dye is added to dimethylsulfoxide (DMSO) to produce a 0.01 M solution. There is also added 0.1 ml of FD & C #5 (Yellow) per 50ml of total solution. Concentrated aqueous sodium hydroxide is added dropwise until the dye/DMSO solution has a pH of 1 1 . Sufficient hydroxyethylcellulose ( ~ 3g/100ml DMSO) is added to achieve a blue gel. EXAMPLE 2 Application of indicator composition All pipe contact joints and valves of a working air conditioning system containing chlorodiflouromethane are cleaned using methanol containing sufficient sodium hydroxide to provide a pH of ~ 10-1 1 . The blue gel is then applied to all of these pipe contact joints and valves. EXAMPLE 3 Application of top coat composition The gel applied as in Example 2 above, is then spray coated with an aerosol of ethylcellulose in methanol, previously similarly adjusted to pH of 1 1 using dropwise addition of concentrated aqueous sodium hydroxide in methanol and the top coat thus produced is allowed to dry. Upon release of chlorodiflouromethane, (in the ppm range of ~ 1 -10) the blue undercoat will completely change to yellow. It should be noted that while the actual color change is blue to clear, the presence of the FD&C yellow will show as yellow. The presence of this yellow dye is not enough to change the original blue to green. EXAMPLE 4 Preparation of another indicator composition M-Cresol purple added to dimethylsulfoxide (DMSO) to produce a 0.01 M solution. Concentrated aqueous sodium hydroxide is added dropwise until the dye/DMSO solution has a pH of 1 1 . Sufficient polyvinyl alcohol ( ~ 4g/100ml DMSO) is added to achieve a purple gel. EXAMPLE 5 Application of indicator composition All pipe contact joints and valves of a solvent extraction system containing liquid carbon dioxide are cleaned using methanol containing sufficient sodium hydroxide to provide a pH of - 10-1 1 . The purple gel of Example 4 is then applied to all of these pipe contact joints and valves. EXAMPLE 6 Application of top coat composition The gel applied as in Example 5 above, is then spray coated with an aerosol of polyethylene in toluene, similarly previously adjusted to pH of 1 1 using dropwise addition of concentrated aqueous sodium hydroxide in methanol and the top coat thus produced is allowed to dry. Upon release of carbon dioxide, (in the ppm range of - 1 -10) the purple undercoat will completely change to yellow. EXAMPLE 7 Preparation of yet another indicator composition Phenol red added to dimethylsulfoxide (DMSO) to produce a 0.01 M solution. Concentrated aqueous sodium hydroxide is added dropwise until the dye/DMSO solution has a pH of 1 1 . Sufficient sodium alginate ( ~ 5g/100ml DMSO) is added to achieve a red gel. EXAMPLE 8 Application of indicator composition All pipe contact joints and valves of a working air conditioning system containing chlorodifluoromethane are cleaned using methanol containing sufficient sodium hydroxide to provide a pH of ~ 10-1 1 . The red gel of Example 7 is then applied to all of these pipe contact joints and valves. EXAMPLE 9 Application of top coat composition The gel applied as in Example 8 above, is then spray coated with an aerosol of polytetrafluorethylene in toluene/methyl isobutyl ketone (solvent component ratio: 1 : 1 ), similarly adjusted to pH of 1 1 using dropwise addition of concentrated aqueous sodium hydroxide in methanol and the top coat thus produced is allowed to dry. Upon release of chlorodiflouromethane, (in the ppm range of - 1 -10) the red undercoat will change to yellow. EXAMPLE 10 In accordance with the procedures of Examples 1 -9 above, but where in place of the indicator, solvent, Lewis base, rheology modifier or topcoat utilized in those examples, there are utilized any of the other members of those groups listed hereinabove, a similar result is obtained, provided of course that different indicators will show different color transformations. EXAMPLE 1 1 Methyl orange is added to dimethylsulfoxide and ethylene glycolmonobutyl ether at a solvent ratio of 1 : 1 . The indicator concentration is adjusted to 0.5% hydroxyl-ethyl-ethylenediamine is added to raise the pH to 7.5% _+ . .1 . Hydroxypropyl-methyl-cellulose is added to achieve a concentration of 1 .0% of the rheology modifier. This result is a viscous yellow thixotropic solution of about 3000 - 5000 cps. at 21 °C. EXAMPLE 12 The joints of a conduit used for charging liquid carbon dioxide are pre- cleaned with an alkaline methanol/isopropanol solution with a pH of 1 1 -12. After allowing the conduit to dry, the mixture of Example 1 1 is applied to the joints using a brush. EXAMPLE 13 The gel in Example 12 above is coated via spraying with a topcoat consisting of a film former, i.e. maleic modified rosin, in an oil based solvent consisting of linseed oil and methylethyl ketone (70/30 mixture). The rosin film contains 0.5% octylphenol polyethoxy 2 ethanol as a plasticizer. The result is a transparent coating which allows visual detection of the gel color change upon exposure to gas (CO 2 ). Upon contacting the above with carbon dioxide, a color change from yellow to red was observed. EXAMPLE 14 A thixotropic viscous mixture was prepared according to Example 1 1 using the following components: Resulting composition is pink with viscosity 50,000 cps (at 21 °C). The mixture of Example 14 is applied to a gas conduit as outlined in the preceding Examples 12 and 13. EXAMPLE 15 The topcoat used to protect the thixotropic gel of Example 14 (hereafter referred to as the undercoat) has the following composition. 10 EXAMPLE 16 The application of the topcoat composite can be applied to the undercoat via spray (aerosol or spray-painting gun) brushed carefully, or dipped over the treated area. This coating is clear allowing visual detection of the pink gel while concurrently providing product integrity and reliability for extended periods of time. EXAMPLE 17 The composition of Example 14 (called the undercoat) and the composition of Example 15 (called the topcoat) was applied (after cleaning as outlined in previous examples) to a gas conduit having a known perforation (a leak) of about < 5 microns. In the same manner, the compositions were applied to a section on the conduit which had no known perforation. Upon passing an electrophilic gas through the conduit, the perforated portion turned clear while the control without perforation remained pink. EXAMPLE 18 A thixotropic undercoat of the following composition was prepared according to the previous examples. 1 1 Above produced a blue to aqua blue thixotropic gel useful for determination of mixed electrophilic gases. Initial pH 10-12. EXAMPLE 19 A topcoat of the following composites was prepared in accordance with the foregoing examples: The above topcoat was applied to the undercoat of Example 18 after treating a gas conduit with the latter. The former produced a durable clear coating .with excellent adhesion. 12 EXAMPLE 20 The topcoat of example 19 above was pressurized with solvent and propellant prior to application as follows: 13

Claims: Claims: 1 . A composition for the detection of an electrophilic gas comprising: a) a Lewis base capable of electrophilic reaction with said gas, b) a dye molecule capable of visibly indicating a color change on protonation or deprotonation, c) a solvent for said dye, said base and said gas, d) a rheology modifier capable of producing a non-newtonian gel of components (a) + (b) + (c) + (d) which is sufficiently translucent to permit visual detection of change of color of (b) and of sufficient pseudoplasticity/thixotropy to provide adhesion to vertical and horizontal surfaces. 2. The composition of Claim 1 wherein the Lewis base is present in sufficient amount to bring the pH of the gel to between 6.9 and 14. 3. The composition of Claim 1 wherein the Lewis base is selected from at least one member of the group consisting of alkali- and alkaline earth- metal hydroxides, alkoxides and carbonates; amines; quaternary ammonium hydroxides, alkoxyamines, and hydroxylalkylamines. 4. The composition of Claim 1 wherein the solvent is selected from at least one member of the group consisting of alkanols, arylalkanols, alkyl halides, alkyl ketones, alkylamines, aralkylamines, alkyl esters of alkanoic acids, dimethylsulfoxide, water and mixtures thereof. 5. The composition of Claim 5 wherein the alkyl moieties are selected from the group consisting of straight chain-, branch chain- and cyclic- moieties. 14 6. The composition of Claim 5 wherein the alkanols and alkylamines are selected from the group consisting of primary, secondary and tertiary alkanols and alkylamines. 7. The composition of Claim 1 wherein the solvent is selected from the group consisting of dimethylsulfoxide, water, tetrahydrofuran, acetone, ethyl acetate and methanol and mixtures thereof. 8. The composition of Claim 1 wherein the solvent is utilized in a range relative to the sum of (a) and (b) of between 1 and 99 parts by volume per part by weight of (a) + (b). 9. The composition of Claim 1 wherein the rheology modifier is selected from the group consisting of hydroxyalkylcellulose, cellulosic semisynthetic polymers, polyvinyl alcohols, carbopols, alginates, natural gums. 10. A coating of a composition of claim 1 when located on a conduit for said gas. 1 1 . The coating of claim 10 additionally comprising a sprayable, film forming topcoat composition settable at between about 0 - about 30°C wherein the film is sufficiently translucent to permit visual detection of change of color of (b). 12. A method for the detection of leaks of an electrophilic gas from a system containing the same, comprising the steps of applying to the exterior of said system, a coating of a composition comprising a) a Lewis base capable of removing a proton from said gas , 15 16 b) a dye molecule capable of visibly indicating a color change on protonation or deprotonation, c) a solvent for said dye, said base and said gas, d) a rheology modifier capable of producing a non-newtonian gel of components (a) + (b) + (c) -t- (d) which is sufficiently translucent to permit visual detection of change of color of (b) and of sufficient pseudoplasticity/thixotropy to provide adhesion to vertical and horizontal surfaces, and observing the change in color of said coating upon the occurrence of a leak of said gas. 13. The method of Claim 12 wherein the Lewis base is present in sufficient amount to bring the pH of the gel to between 6.9 and 14. 14. The method of Claim 12 wherein the Lewis base is selected from the group consisting of alkali- and alkaline earth- metal hydroxides, alkoxides and carbonates; amines; quaternary ammonium hydroxides, alkoxyamines, hydroxylalkylamines and mixtures thereof. 15. The method of Claim 12 wherein the solvent is selected from the group consisting of alkanols, arylalkanols, alkyl halides, alkyl ketones, alkylamines, aralkylamines, alkyl esters of alkanoic acids, dimethylsulfoxide, glycols, glycol ethers, water and mixtures thereof. 16. The method of Claim 15 wherein the alkyl moieties are selected from the group consisting of straight chain-, branch chain- and cyclic- moieties. /4 17 17. The method of Claim 15 wherein the alkanols and alkylamines are selected from the group consisting of primary, secondary and tertiary alkanols and alkylamines. 18. The method of Claim 15 wherein the solvent is selected from the group consisting of dimethylsulfoxide, water, tetrahydrofuran, acetone, ethyl acetate methanol and mixtures thereof. 19. The method of Claim 15 wherein the solvent is dimethylsulfoxide. 20. The method of Claim 15 wherein the solvent is dimethylsulfoxide and water. 21 . The method of Claim 15 wherein the Lewis base is sodium hydroxide. 22. The method of Claim 15 wherein the solvent is utilized in a range relative to the sum of (a) and (b) of between 1 and 99 parts by volume per part by weight of (a) + (b). 23. The method of Claim 15 wherein the rheology modifier is selected from the group consisting of hydroxyalkylcellulose, cellulosic semisynthetic polymers, polyvinyl alcohols, carbopols, alginates and natural gums. 24. The method of Claim 15 wherein the rheology modifier is selected from the group consisting of hydroxyalkylcellulose, polyvinyl alcohol and sodium alginate. 18 25. The method of Claim 15 comprising sodium hydroxide, dimethyl sulfoxide, a rheology modifier selected from the group consisting of hydroxyalkylcellulose, polyvinyl alcohol and sodium alginate and a dye molecule capable of visibly indicating a color change on protonation or deprotonation. 26. The method of claim 15 additionally comprising spraying a sprayable, film forming topcoat solution settable at between about 0 - about 30°C wherein the film is sufficiently translucent to permit visual detection of change of color of (b) onto said coating. 27. The method of claim 26 wherein the topcoat solution comprises a solvent and a member of the group consisting of epoxy resins, polyurethane resins, siloxanes, modified and unmodified rosin, polyvinylpyrrolidone, alkyd resins, polyacrylates, ethylcellulose, polyethylene, polytetrafluoroethylene and mixtures thereof. 28. The method of Claim 27 wherein the solvent is selected from the group consisting of aromatic hydrocarbons; alkanes; alkyl ketones; straight or branch chain alkanols; C r C 5 alkyl ethers; mono, di and tri glycols; mineral spirits; mineral, vegetable, animal and marine oils; and mixtures thereof. 29. The method of Claim 28 wherein the solvent is selected from the group consisting of xylene, toluene, hexane, methyl isobutyl ketone, acetone, methanol, ethanol, isopropanol, and n-butanol. c:\wp51\doc\gsen3o3.spc

Inventors: KAISER STEWART R, VERDICCHIO ROBERT J, WALSH SHAWN, KAISER, STEWART, R., VERDICCHIO, ROBERT, J., WALSH, SHAWN
Applicants: KAISER STEWART R, TECT INC R, VERDICCHIO ROBERT J, WALSH SHAWN, KAISER, STEWART, R., R-TECT, INC., VERDICCHIO, ROBERT, J., WALSH, SHAWN
Application year: 1998
Main classification: G01M3
IPC codes: B01J13, G01M3