US2983688A

US2983688A - Corrosion inhibition compositions

Info

Publication number: US2983688A
Application number: US626605A
Authority: US
Inventors: Glenn A Marsh; Schaschl Edward
Original assignee: Pure Oil Co
Current assignee: Pure Oil Co
Priority date: 1956-12-06
Filing date: 1956-12-06
Publication date: 1961-05-09
Anticipated expiration: 1978-05-09

Description

CORROSION INHIBITION COMPOSITIONS I Glenn A. Marsh and Edward Schaschl, 'Crystal Lake, 111., I assignors to The Pure Oil Company, Chicago, Ill., a I corporation of Ohio I No Drawing. Filed Dec. 6, 1956, Ser. No. 626,605,

15 Claims. (Cl. 252-389) This invention relates to a method of preventing the corrosion of ferrous metals by aqueous ammoma-ammonium nitrate environments. More particularly, the mvention relates to a stable, substantially thixotropic cor-' rosion-inhibiting composition containing Z-mercaptobenzothiazole as the principal active ingredient along with certain prescribed proportions of a metal nitrite and an oxidizing agent which are chemically inert to the mercaptobenzothiazole in an aqeuous gel composition. This application is a continuation-in-part of the application entitled, Corrosion Inhibition in Aqueous Ammonia-Ammonium Nitrate Systems, filed October 10, 1955, by Glenn A. Marsh and Edward Schaschl and bearing Serial Number 539,690, now abandoned.

In accordance with the aforesaid copending application, it is shown that environments containing ammonia-ammonium nitrate in an. aqueous medium are utilized as liquid fertilizers on a commercial scale. Such fertilizer solutions present a severe corrosion problem in the apparatus used in thepreparation, storing, handling, and dispensing of same. Ferrousmetal processing equipment as well as the tank cars, other types of metallic shipping containers, and dispensing apparatus for use in the field are subjected to very rapid corrosion by these fertilizer solutions, far exceeding that encountered when the ferrous metal is in contact with an ordinary aqueous environment. A particularly severe corrosion problem is evidenced where part of the ferrous metal is in contact with the corrosive fertilizer liquid and apart of the ferrous metal is exposed to an oxygen-containing environment, such as exists when a ferrous metal tank is only partially filled with the fertilizer solution and has an air space abovelthe liquid level. When dissolved oxygen is present in substantial amounts, that is more than about 0.1 p.p,m., the corrosion problem is accentuated.

Another instance in which the inhibition of corrosion of ferrous metal is particularly diflicultoccurs when .a metal surface has undergone exposure to certain agents, such as by contact or association with a more active metalffor example a steel container, zinc, or other active metal, or by contact with an abrasive, or by dipping the ferrous metal into .a strong acid such as hydrochloric acid of any suitable'concentration before exposure to the cor rosive environment. The present invention has three main purposes: First, that of providing a convenient means for bringing 'mercaptobenzothiazole into a corrosive environment of the general type aforementioned for the purpose of mitigating the corrosion. A second purpose of the invention is to provide a substantially thixotropic corrosion inhibitor composition containing the mercaptobenzothiazolea metal nitrite and an oxidizing agent in an aqueous medium, in which form the composition is easy toproduce, stable and, exhibits good corrosion-inhibiting properties... Thethird purpose of the invention is to provide a corrosion-inhbiting composition containing mercaptobenzothiazole which is in ,a form that is convenient for handling and packaging and also convenient for use in 2,983,683 Patented May 9, 1961 ,gicg

. properties of mercaptobenzothiazole in an ammonia-ammonium nitrate corrosive environment, or used to overcome corrosion under conditions of aeration or activation of the metal surface, which conditions having just been described. For the purpose of this invention, therefore, when the corrosive solution contains less than about 0.1 ppm. of oxygen, it is said to be deaerated and when it contains more than about 0.1 ppm. of oxygen it is said to be aerated.- Likewise, for purposes of this invention, the metal surfaceis said to be activated when a condition is imposed which renders the metal more easily corrodible in the presence of oxygen, as by a galvanic effect or acid etching. i i

'Heretofore many inhibitors have been proposed for retarding the corrosion of ferrous metals in aqueous en-' vironments. Inhibitors placed in ammonia-ammonium nitrate solutions retard corrosion only in the liquid and have no effect upon corrosion which occurs above the liquid level. The particular fertilizerJ solutions with which this invention is concerned, comprising as they do ammonia and ammonium nitrate in aqueous solution, afford a unique corrosive environment, particularly when substantial concentrations of these ingredients are present, such as fertilizer containing a concentration of approximately 10% or more of nitrogen by weight. The stability, physical form and effectiveness of the inhibitor" compositions of this invention for aqueous systems in an ammonia-aqueous ammonium nitrate environment cannot be predicted. 7 v V In accordance with this invention, it has been found that a stable, substantially thixotropic corrosion-inhibiting composition which is capable of being pumped can be made by thoroughly agitating between about 15 to 30 weight percent of finely divided mercaptobenzothiazole as the solid phase in a liquid phase comprising water.

The exact percentage of mercaptobenzothiazole that will form a stable suspension in an aqueous medium depends somewhat on the time, the rate of stirring, and the particle size of the mercaptobenzothiazole. However, by using the powdered form of mercaptobenzothiazole which is commercially available, a stable substantially thixO-- tropic suspension can be formed by thorough mixing of about 18 to 27% by weight of mercaptobenzothiazole with water.

In accordance with the aforesaid parent application, the disclosure of which is incorporated by reference, the

presence of certain limited amounts of a metal nitrite and an oxidizing agent enhance the corrosion inhibiting properties of the mercaptobenzothiazole. Now in accordance with this invention, as another aspect thereof, it has been found that the inclusion of these auxiliary nitrites and oxidizing agents, to be described, does not prevent the formation of a stable substantially thixotropic, fixed com-position suspension, of from 15 to 46 weight percent of mercaptobenzothiazole in water or aqueous suspensions containing up to 20 wt. percent of an anti-freeze agent.

Furthermore, it has been found that there is a certain essentially critical relationship between the ratio ofsolids to total liquids in the suspension and the weight of antifreeze agent present. These nitrites and oxidizing agents can be dissolved in the water phase either before or after the mercaptobenzothiazole is added and are carried in solution to the limit of their solubilities in the liquid" phase. The mercaptobenzothiazole forms the solid suspended phase. The preferredcorrosion-inhibitor compositions of this invention contain about 15 to 30 weight percent of mercaptobenzothiazole suspended in'suflicientwater to make and also include (1) such suspensions containing a metal nitrite-in an amount ofabout specific examples.

2 o 2, t mes he amount. t etq s cbsnzsthiazcle and an amount of an oxidizing agent, particularly sodium tion containing mercaptobenzothiazole, in, an aqueous,

suspension with or without a metal nitrite, an oxidizing agent and an antiefreeze agent.

freezing in a, temperate zone.

Thus, at, an anti-stream. concentration of A will be 0.2; and hence or is equal to 0.85. Also, S equals the weight of total solids per gram of mixture divided by 0.2 (the weight fraction of anti-freeze) plus the Weight of 'water. The

i shtc s l ds p u he weight. o er plus the w g of anti-freeze=l.0. By solvingthese equations the per- A'further object of this. invention is. to. provide. acorrosion-inhibiting compositioncontaining mercaptobenzo; I

thiazole, for use in. inhibiting thecorrosivityof ammoniaammonium nitrate environments, whichis of a substantially thixotropic chagacter and has asemi-solid con- I sistency, but which. is, upon the application of agitation I or shear, transformed into a mobile fluid for easy handling and dispensing.

Other objects of this invention will be apparent or set:

forth in thefollowing detailed description.

, The. invention m y be illustrated by the following EXAM LE 1 100 parts by, weight; of dry inhibitor consisting of a ,mixture of 77 parts ofpowdered mercaptobenzothiazole,

19.2 parts, ofi sodium nitrite, 3.8 parts ofi potassium 'chloratewere stirred with-372 parts of water at room temperature.

' about 78% water and; about 22%. th p p ope t es nd ad a m olid.

There resulted a suspension comprising solids which exhibited consistency similar to that of thickcream or a grease. Upon stand I I ing, the composition formed into a fairly firm gel. 1 Howe er. by tint nsthe ampl w a t r ns the gel structure was easily, hrolgenand; the composition became centage of solids=46%, the percentage. of water 3'4% and the percentage of anti-freeze=20% It is thus seen that by incorporating an anti-freeze agent in the composition to. the. extent of about 20% thetotal solids can be increased from about 22% to about 46%.

This is demonstrated: by the following experiments.

EXAMPLE 4 r ms o a ry h ito mixtur containin 7 Z-m QaP Qb Oth Qle, 12.2%. sodi m ni r te and 3.8% potassiumchlorate were'mixed with incremental amounts of, water and Formula 30, alcohol (81.12% by weight ethyl alcohol and18.88% by weight of methyl alcohol) and after each mixing the solids-liqnidmixture was allowed to stand. This procedure was repeated, each time adding more measured quantities of water and alcohol and observing. the results after thorough shaking of the mixture until a stable, thixotropic mixture was obtained. This occurred when 400 grams of water and I SO grams of alcohol had been added. On a weightpercent basis this composition contained about 32.4% mercaptobenz'othiazol'e', 8.1% sodium nitrite, 1.6% potassium chlorate, 42.1% water and 15.8% alcohol.

EXAMPLE 5' potassium chlorate were mixed with incremental amounts liquid; in form. Upon termination of agitationthe gel structure formed again. Several separate preparations w e r d u i t o eme ti ed man er i h e same results illustratingthe reproducibility ofthe stable Il Pt-I iQn.

E AMPLE 2 A portionof the gel composition from Example 1 was thoroughly agitated with about 10 parts by weight of water. It was'found that the gel dispersedin the water, but within a matter of hours it reverted to its original form as a separate layer under the additional added water. This illustrates the stability of the composition.

E AMP E 3 The. gradual addition of incremental amounts of pow dered mercaptobenzothiazolealone. to 400 grams .ofwater with constant agitation. produced aheavy, stable suspension having the consistency of cream when about 120 grams or 23% byweight-of mercaptobenzothiazole had been added. This materialwas transformed into a mobile liquid by the shearing action of a stirrer or pump.

It has been found that a substantial part of the water in the aforesaid compositions may be replaced with an anti-freeze material such as alcohol, glycerine. and the various glycols, including ethylene. glycol, without disturbing the thixotropic characteristics thereof. The antifreeze agent allows the percentage of solids to be increased in acertain relationship to the amount of the anti-freeze added. Methanol and ethanolor mixtures of same may be used as anti-freezeagents. This weight ratio is ex pressed as: follows:

where S .is theratio of solids to total liquids, and A is. theweight fraction of alcohol, or other antirfreeze agent, This relationship holds for antifreeze concentrations" up aahq t w. whi hisa ss; pper imit necessa y o; provide adequate protection of the' composition against of water aloneand after each mixing the solidsdiquid mixture was allowed to stand. When 370 gramsof water had been added a thixotropic mixture resulted I On a weight percent basis this. composition contained, 16.33%

mercaptobenzothiazole, 4.08% sodium. nitrite, 0.81% potassium chlorate and 78.73% water.

By substituting the data obtained in Examples 3, and 4, into the general equation for a straight 'line which is the values of a and b weredetermined to be- 2.851 and 0.28, respectively, where y isthe ratio of, solids to; total liquid and x is the weight. fraction of alcohol in the total mixture. Replacing y by S and x. by. A the equation referred to results.

The applicability of this equation was checked by calculating the theoretical composition. of a. thixotropic mixture containing 20% by weight of alcohol. It was calculated that a mixture of 46%, solids, 34% water and 20% alcohol should be thixotropic. This was sub: stantiated by mixing together 460 grams of. the solid inhibitor mixturewith 340 grams of, water and 200 grams of alcohol, which mixture exhibited thixotropic, properties. Furthermore, the addition of more water to the mixture did not destroy these properties.

The method of utilizing thethixotropicmixture of. this invention. does not depart from the method of usedescribed in the aforementioned co-pending continuation-inpart application, Serial Number 5 39 ,690. The thixotropic mixture is added directly tothe corrosive aqueous ammonium, nitrate-ammonia solution in any suitable manner, that is, all at once, or insmall, orlarge increments, or continuously, with or without agitation of. the resulting homogeneous solution, The. fact that the, corrosion-inhibiting composition is in a. mixed thixo mpic semi-liquid form ,does not change the minimum requiresion. The amount ofthe thixotropic mixture used is sufli aasaess cient to maintain or add aminimum of about 0.01% by. weight. of 'Z-meicaptobenzothiazole, and preferably about'0.l% by weight based on the weight of total solution. Accordingly, it is seen that very small amounts of the active ingredients of the thixotropic mixture may be used to obtain effective results. The addition of the inhibitor composition to the aqueous fertilizer solution in no way efiects its utility or ease of handling. The resulting blend is homogeneous and essentially colorless, although the thixotropic mixture of the inhibitor composition itself is a yellow color due to the mercaptobenzothiazole. If desired, the yellow color can be changed to a faint orange by the addition of small amounts, 0.1 to 2.0 percent by weight, of a red azo-dye, such as Congo red. The use of larger amounts of dye may destroy the suspension, so if it is desiredto color the composition, the effect of any contemplated dye must be determined by mixing experimentalbatches- I 1 The addition of the corrosion inhibiting composition to the aqueous ammonium nitrate-ammonia fertilizer solutons inhibits the corrosion of ferrous metals which are totally immersed therein andwhich are partially ex posed to an oxygen-free atmosphere where the oxygen is absent ffom the'solutionif the metal has been activated as before described. The composition of this invention is also effective in inhibiting the corrosion of totally immersed activated ferrous metals where dissolved oxygen is present, or of activated metals in contact with both an oxygen-containing ammonium nitrate-ammonia solution and with a non-oxygen-containing atmosphere, because To insure complete protection when-the ferrous metal or alloy is exposed not only to the liquid corrosive solution but also to an oxygen-containing gaseous phase adjacent the corrosive solution, additional protection must be afforded the metal or alloy to prevent corrosion of that portion exposed to the gaseous phase. This is accomplished by adding a blanket of a chemically inert liquid which is immiscible with the corrosive solution and lighter in gravity. This inert liquid may be any material which is liquid under existing conditions, is essentially immiscible and nonreactive with the corrosive solution and is lighter in gravity than the corrosive solution containing the in- -'hibitor mixture of this invention. Examples are liquified propane,'naphtha such as rubber solvent, textile spirits, V.M. and P.- naphtha, Stoddard solvent, kerosene, fuel oils of any viscosity and of a petroleum origin, prepared in any conventional manner, such as by fractionation, gas oils ofa petroleum-derived nature and prepared in any conventional manner, neutral lubricating oils, andhighly refined lubricating oil fractions, such as white oil. Aliphatic and/or alicyclic hydrocarbon-containing oils are 7 preferred and aromatic oils should not be used.

" The b lanketing immiscible liquid is added to the corrosive solution in a suflicient concentration to embody a surfactant and also completely extend over the surface of the corrosive solution in a layer of suflicient depth or thickness to act as an effective barrier against pene- I tration by the atmosphere above and form a thin film on of the inclusion of the nitrite and the inorganic oxidizing 7 agent. In addition to the sodium nitrite previously mentioned, other metal nitrites soluble in the corrosive solution may be used, such as potassium nitrite, lithium nitrite, cesium nitrite and barium nitrite. The solid inorganic oxidizing agent, chemically inert to the other components of the combination inhibitor and soluble in the corrosive solution, may include any alkali metal chromate such as sodium chromate, .or any alkali metal chlorate such as potassium chlorate. Ammonium chromatc, sodium chlorate or potassium chromate may be used. Where 15 parts of Z-mercaptobenzothiazole are used with 85 parts of water, with or without sufiicient antifreeze to prevent freezing of the mixture during winter months, the amount of nitrite present may be 3.75 parts and the amount of oxidizing agent present may be .75 part. Where parts of Z-mercaptobenzothiazole are used with 70 parts of water with or without suflicient. antifreeze to prevent freezing of the mixture during winter months, the amount of nitrite present may be 75 parts and the amount of oxidizing agent may be 6.0 parts. In this way between about 0.1 to 0.5 wt. percent of nitrite and 0.01 to 0.5% of oxidizing agent are incorporated in the corrosive ammonium nitrate-ammonia fertilizer solution. Preferably the concentration of the nitrite is between about 0.2 and- 0.5% and the oxidizing agent between about 0.01 and 0.5 wt. percent in the corrosive atmosphere. A minimum concentration of the combination inhibitor of about 0.12% by weight based on the corrosive solution should be used, as described and developed in the parent application, Serial Number 539,690, to effectively and substantially completely inhibit the corrosion of totally immersed ferrous metals contacted by the corrosive fertilizer solutions in the presence or absence of dissolved oxygen in the corrosive solution.

' The ferrous metal-containing apparatus to be protected from the, corrosive solution may be of any shape or size,

- such as storage tank, a tank carrier, flow pipe, conveying coil, measuring tank or any type of processing apparatus such as a mixing tank, settling tank, ammoniation tank, etc., and is constructed of metal or alloy, containing an appreciable amount of iron, such as cast iron, wrought iron or low carbon steel. As stated above, the metal to be protected may be in an unactivated or activated state.

the metal wall or surface as the level of the corrosive solution rises and falls in the metal container. 'A layer having a thickness of 4 inch issufiicient for most purposes. factant which renders the metallic surface hydrophobic may be used. The surfactant should be chemically inert to the otherchemical compounds present in the corrosive solution and essentially non-extractable by the corrosive solution. Any suitable surfactant having the above char acteristics, such as an amine salt (primary, secondary, or tertiary) or ammonium salt of a fatty acid containing more than about 12 carbon atoms, or any combination of two or more of such salts may be used. The surfactant is present in a total concentration of at least about 0.1%,

by Weight, of the blanketing agent. Concentrations of about 0.5 to 1.0% by weight are preferred, in general, but larger concentrations, such as 2% by Weight, may be employed and may even be desirable in those instances where there may be a tendency for the particular surfactant or combination of surfactants used to be extracted to some extent by the corrosive aqueous ammonia-ammoniurn nitrate solution.

Although any amine salt of a fatty acid, or any combination thereof, may be used without'reference to the chain length of the amine component ofthe salt, amines containing at least one long hydrocarbon chain above about 12 carbon atoms in length, particularly chains derived from fatty acids such as oleic, stearic, palmitic, linoleic, etc., are preferred. For example, a very satisfactory commercial product, Duomeen T dioleate, may be used in effective concentrations of about 0.1% by weight or more, preferably 0.2% by weight or more. Duomeen T dioleate is the dioleic acid salt of an organic base Duomeen T, which is a member of a group of'fatty diamines.-

Duomeen T dioleate is a product of the Armour Chemical Division of Armour & Company.

Other suitable surfactants are ammonium oleate, stearyl amine palmitate, oleylamine ricinoleate, and stearyl amine stearate. The function of the surfactant is to render the metal surface hydrophobic, reduce interfacial tensions and hinder or prevent creeping of the corrosion solution up on the metal surface above the liquid level. When the solution creeps upon the metal surface it evaporates and causes extensive corrosion, in conjunction with oxygen, and the formation of a thick crust on the metal on those wetted areas.

Handling of the gel-like suspension of this invention is Any oil-soluble, water-insoluble, semi-polar suraasaoss facilitated by the thixotropijc properties which meansthat agitationyshear, vibration, or coning may be used to trans: form. the suspension into. a mobile -liquid; The composition is readily handled by a slurry pump or the type of' pumps used to move drilling mud's. A Moyno pump has been found to be particularly adapted for this purpose.

The invention therefore comprises the discovery of a stable, substantially thixotropic =form of corrosion inhibiting composition. containing Z-mercaptobenzothiazole, with or without ametal nitrite, and with or without an oxidizing agent, as the solid phase suspended in an aqueous or aqu'eous-anti-freeze-containing solution which is particularly easy to handle, package and use in carrying out the'methodof corrosion inhibition described in the parent application heretofore. referred to. The following table showsjthe, composition of; eight difierent compositions prepared. in accordance with the invention, all of which exhibit the unusual property of resisting further dilution upon being mixed with water and exhibiting thixotropic nitrite and barium nitrite equivalent to about 0.25 to 2.5 times the amount of z nrercaptobenzothiazole; an amount of an oxidizing agent selected from the group of alkali metalchlorates and alkali metal chromates equivalent to about 0.05 to 01.2 the amount of 2-mercapt'obenzo= thiaz ol'e and an aliphatic alcohol antifreeze agenta's' parts or" the aqueous phase, the weight ratio of said solid phase t'o'the' total l-iqui'd phase-being equal to2.85A+0.28 where A is the weightfractioirof said aliphatic alcohol antifireeze" agent and A has an upper limit of about percent by weight based on the" total composition.

7. The thixotropic' composition in accordance to claim 6 in which the oxidizing agent isan alkali metal chromate.

81 The thixotropic composition in accordance with claim 6 in which the oxidizing agent is an alkali metal chlorate;

9. A thixotropiccompositionin accordance withclaim 6 in which the aliphatic alcohol antifreeze agent is ethyl alcohol.

THIXOTROPIO CORROSION INHIBITING. COMPOSITIONS.

Wt. Wt. Wt. Wt. Wt. 1 Wt. Wt. Wt. Parts Percent Parts Percent Parts Percent Parts Pereent Parts lercent Parts PercentParts Percent Parts Percent Water 70 64.2 70 38.7 70 39:6 1 70 61.7" 85 81.4 85 61.0 85 61.5 85 7935 Mercapto' bBHZOs. r V Mthiazole 27.5 30 16.6 30 17.0 I 30 26.4 15 1 23: 16 10:7 15' 10.9 15 14.1 9W 1 l Nitrite.-- 7.5- 6.8 75 41.4 75 42.5 7.5 6.6 3.16 3.6 37.5 p 26.2 37.5 26.9 3.75 3:5 oxidizing 1 Agent... 1.5 1.4 6 3.3 1.5 .85 6.0 5.3 .75 .7 3.0 p 2.1 .75 .6 3.0 2.9- 109.0 99.9 181.0 100.0. 176:5 99.9 113.5 100.0 104.50 100.0 140.5 100. 0 138.15 99.9 106175 100. 0

What isclaimed is: r

1. A stable, substantially thixotropiccomposition com: prising a. mixture of about 15.10 46 weight percentoflmercaptobenzothiazole. as the solid phase. suspended in. a sufiicient amount of an. aqueous phase containing an aliphatic alcohol antifreeze agent to make 100% total. composition. in which the weight ratio ofthe solid phase. to the total liquid phase is. equal to 2.85A+0.28 where. A. is aweight; fraction of said. aliphatic alcohol antifreeze. agent and. A has anupper limit of 20percent by weight.

2. A thixotropic.compositioniu accordance withclairn 1 in which the aliphatic alcohol autifreezeagent is ethyl alcohol.

3. A thixotrop ic composition in accordance with. claim 1;. in'which the .aliphaticalcohol antifreeze agent. is a mixture consisting of 81.12% by weight of ethyl alcoholand. 18.88% by weight of methyl alcohol.

' 4; Athixotropic composition. in accordance withclaim l in which the aliphatic alcohol antifreezeagent isa. glycol.

5. A thixotropic composition in accordance with .claim 4in which the glycolis ethylene glycol.

6. A stable substantially thixou'opic corrosion inhibiting composition capable of, inhibiting the corrosion. of ferrous metals by solutions. comprising ammonium nitrate, water and ammonia which. comprises about 15. to. 46 weight percent of Z-mercaptobenzothiazoleasthe solid phase suspended in. a suflicicnt amountofwaterto make 100 percentby weight total. composition, an. amount of' a metal nitritaselected from the. group consisting. of' sOdium nitrite, potassium nitrite,qlithiurn nitrite, cesium 10. A thix'otropic' composition in accordance with claim 6' in which'th'e'aliphatic alcoholantifreeze'agent is a mixture'consistiug of'81.18-% by Weight of ethyl alcohol and 18.88% by weight ofmethyl alcohol.

ILA thixotropic composition inaccordance with claim 6" in Whichthe aliphatic alcohol antifreeze agent is" a glycol.

12. The thixotropic composition in accordance with claim .7 in which the alkali metal chromate is sodium chromate- 13. The thixotropic" composition in accordance with claim. 8' in which"- the allali metal chlorate is= potassium chlorate:

14. A thixotropic composition in accordance with claim 1'1in which the glycol'is ethyleneglycol;

151 A" thixotropic? corrosion inhibiting composition consisting of a mixture of about 325470 by weightj-ot" mercaptobenzothiazole; about 821% by weight of sodiumnitrite; about 1.6% by; weight" of potassium chlorate;- about' 42.1% by wcigh't of" water" and about 15%- by weight of a mixture consisting"of 8ll12%' by weight-of ethyl alcohol and 18.88% by weigh't of 'nrethyl alcohol.

Refrences Citcd inthe filerof fthis patent UNITED STATES PATENTS

Claims

1. A STABLE SUBSTANTIALLY THIXOTROPIC COMPOSITION COMPRISING A MIXTURE OF ABOUT 15 TO 46 WEIGHT PERCENT OF 2MERCAPTOBENZOTHIAZOLE AS THE SOLID PHASE SUSPENDED IN A SUFFICIENT AMOUNT OF AN AQUEOUS PHASE CONTAINING AN ALIPHATIC ALCOHOL ANTIFREEZE AGENT TO MAKE 100% TOTAL COMPOSITION IN WHICH THE WEIGHT RATIO OF THE SOLID PHASE TO THE TOTAL LIQUID PHASE IS EQUAL TO 2.85A+0.28 WHERE A IS A WEIGHT FRACTION OF SAID ALIPHATIC ALCOHOL ANTIFREEZE AGENT AND A HAS AN UPPER LIMIT OF 20 PERCENT BY WEIGHT.