US 3764543 A
Alkylbenzyldialkysulfonium salts are discovered to be useful corrosion inhibitors in aqueous acid solutions. Said sulfonium salts have the formula WHEREIN N IS 1 OR 2; R1 is an alkyl radical with the aggregate carbon content of R1 being from 6 to about 24 carbon atoms; R2 and R3 are alkyl radicals and X<-> is an anion. The novel inhibitors are useful at very low concentrations even in the presence of ferric ions. E.g., an aqueous solution of ethylenediaminetetracetic acid as the ammonium salt at pH 5 and initially 3 x 10<->4M. in p-dodecylbenzyldimethylsulfonium chloride is illustrative of the inhibited solutions disclosed.
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Description (OCR text may contain errors)
United States Patent [191 Frenier et al.
[451 Oct. 9, 1973  Inventors: Wayne W. Frenier; William J.
Settineri, both of Midland, Mich.
 Assignee: The Dow Chemical Company,
[221 Filed: Feb. 23, 1971  Appl. No.: 118,175
 US. Cl 252/151, 252/87, 252/181, 252/395  Int. Cl Clld 7/34, C23g 1/06  Field of Search 252/151, 395, 87, 252/181; 260/607 B  References Cited UNITED STATES PATENTS 2,396,938 3/1946 Bersworth 252/142 X 3,060,156 10/1962 Rassweiler 260/79 3,216,979 11/1965 Sexsmith et a1... 260/79.3
3,419,501 12/1968 Levy 252/137 3,668,137 6/1972 Gardner 252/151 X 2,078,256 4/1937 Lieber et al. 252/77 X 3,409,660 11/1968 Lloyd 260/607 B X 2,941,949 6/1960 Saukatis. 252/151 2,121,823 6/1938 Piggutt 260/607 B X FOREIGN PATENTS OR APPLICATIONS 135 ,767 8/ l 969 Czechoslovakia 817,790 8/1959 Great Britain OTHER PUBLICATIONS Horner et al., Korrosion l6 Grundlagenforschung auf Verschiedenen Gebieten der Korrosion und der Werkstoffe, Verlag Chemie, pp. 57-71 (1963) (translation).
Horner et al., Werkstoffe und Korrosion, V01. 15, N0. 2, pp. 125-129 (1964) (translation).
Horner et al., lbid, Vol. 15, pp. 228-232 (1964) (translation).
Primary ExaminerLeon D. Rosdol Assistant Examiner-Harris A. Pitlick Attorney-Griswold & Burdick, Wayne L. White and C. E. Rehberg  ABSTRACT Alkylbenzyldialkysulfonium salts are discovered to be useful corrosion inhibitors in aqueous acid solutions. Said sulfonium salts have the formula 6 Q-cm-s mmx wherein n is l or 2; R is an alkyl radical with the aggregate carbon content of R being from 6 to about 24 carbon atoms; R and R are alkyl radicals and X is an anion. The novel inhibitors are useful at very low concentrations even in the presence of ferric ions. E.g., an aqueous solution of ethylenediaminetetracetic acid as the ammonium salt at pH 5 and initially 3 X 10 M. in p-dodecylbenzyldimethylsulfonium chloride is illustrative of the inhibited solutions disclosed.
16 Claims, No Drawings SULFONIUM COMPOUND AS A CORROSION INHIBITOR IN AQUEOUS ACID BACKGROUND OF THE INVENTION lron oxide encrustations, commonly known as rust or iron oxide scale, frequently form on ferrous metal surfaces. Such surface deposits are objectionable on ferrous articles which are scheduled to be refinished (e.g. sheet steel) and are particularly troublesome when located on the surfaces of tubing and other conduits (e.g., boiling tubing, heat exchangers, connecting piping, and the like) wherein the deposits can restrict flow and interfere with heat exchange.
Various methods of removing such surface deposits have been devised, a common one being to contact the ferrous surface with an aqueous acidic cleaning solution (e.g. aqueous l-ICl) and thereby dissolve and remove the iron oxide encrustations from the surface. An iron salt typically results from this operation, the specific salt depending upon the acidic cleaning medium used. E.g., FeCl and/or FeCl, are formed when BC] is used. v
Such iron salts are generally soluble to at least a limited extent in the cleaning media. Ferric ions thus result.
Corrosion of ferrous metal surfaces in contact with aqueous acids is known. It is also known that the presence of ferric ion causes severe corrosion problems of ferrous metal surfaces during the above mentioned acid cleaning process. Namely, the cleaning solution attacks (corrodes) the freshly cleaned metal surface with the attendant loss of metal. In the presence of oxygen, ferric ions are continually regenerated accentuating the problem.
Many compounds have been included as corrosion inhibitors in such cleaning solutions but their effectiveness in the presence of ferric ion is generally nonexistent or quite low.
Similarly, the corrosion of other common construction metals (and metal alloys) in contact with aqueous acid solution is a definite problem. E.g., in the abovementioned process of cleaning ferrous metal surfaces with acid solutions, other metals may be present as an integral part of the system being cleaned (e.g. copper, copper alloys, zinc, zinc alloys, stainless steels, etc), which may be similarly corroded.
It is therefore an object of this invention to inhibit the acid induced corrosion of metal surfaces, particularly ferrous and cuprous metal surfaces, in contact with aqueous acid solutions.
Another object of this invention is to inhibit acid induced corrosion of ferrous metal surfaces even in the presence of ferric ions.
SUMMARY OF THE INVENTION It has now been discovered that alkylbenzyldialkylsulfonium salts are unusually effective in inhibiting the corrosion of metals, particularly ferrous and cuprous metals, in contact with aqueous acid solutions. Said sulfonium saltsare represented by the formula as GHQ-S RgRaX wherein n is l or 2 (preferably 1); R, is an alkyl radical with the aggregate carbon content of the R radical(s) being from 6 to 24 carbon atoms; R, is preferably a C to C alkyl radical and is most preferably a linear or substantially linear C to C alkyl radical; R, and R are each independently alkyl radicals of from 1 to about 18 carbon atoms and are preferably alkyl radicals of from 1 to 4 carbon atoms; and X is an anion. The position(s) of R, on the aromatic ring is not critical and thus may be ortho, meta or para; the monosubstituted para moieties being currently preferred. The subject class of inhibitors are effective at low concentrations (e.g. 2 X 10 moles/liter) and are surprisingly effective even in the presence of ferric ions. Thus, the abovedescribed ferric ion corrosion problem experienced during the cleaning ferrous metal surfaces can be substantially reduced if not eliminated by incorporating into the acidic cleaning solution a small but sufficient amount of said sulfonium salts to produce the desired inhibition effect.
Examples of suitable sulfonium salts defined by I include those having the following values for Il -R and The above examples are meant to be merely illustrative of the well known class of compounds defined by I. The remaining compounds defined by I will be readily apparent to one skilled in the art. Mixtures of sulfonium salts can likewise be used. The choice of anion, X, is not critical and may be varied to convenience; e.g. the anion is generally chosen to be the same as the acid in solution. The anion may be selected by the method of preparing the sulfonium salt or by ion exchange means. Examples of suitable anions include chloride, bromide, iodide, nitrate, bisulfate, tosylate, acetate, benzoate, dihydrogen phosphate, and the like.
The acid solutions suitable for use herein are aqueous solutions of non-oxidizing inorganic acids, such as HF, I-ICl, H H PO etc., and mixtures thereof (oxidizing inorganic acids include HNO HClO CrO etc); or aqueous solutions of organic acids, such as formic acid acetic acid, sulfamic acid, hydroxy acetic, citric acid, etc., and mixtures thereof; or are aqueous solutions of known chelating agents, such as ethylenediaminetetracetic acid, hereafter EDTA (and the ammonium, amine, or alkali metal salts of EDTA), and other like polyaminepolycarboxylic acids and the like; and mixtures of such aqueous acid solutions. The most common cleaning solutions are' aqueous solutions of HG] and aqueous solutions of EDTA and amine or alkali metal salts of EDTA. The acid solutions may be buffered to maintain a desired pH level with conventional buffering agents, such as citric acid, acetic acid, and salts thereof. The pH values of acid cleaning solutions typically range from 1 to for aqueous solutions of organic acids, and from pH 2-5 for aqueous solutions of chelating agents, such as the EDTA type cleaning solutions. The normality of cleaning solutions using inorganic acids are typically greater than 1.
The concentration of sulfonium salt used in the acid solutions may vary depending upon the particular salt, the particular metal and the degree of corrosion inhibition desired. Typically, concentrations of from about 1 X to about 0.1 moles of sulfonium salt per liter of solution are sufficient and concentrations of from about 1 X 10 to 0.01 moles/liter are generally preferred.
SPECIFIC EMBODIMENTS The following examples further illustrate the inven tion.
GENERAL PROCEDURE Coupons of carbon steel (having 98.7% Fe; 0.3% Mn; and 0.05% C.) having approximately 40 square centimeters of surface area were (a) scrubbed thoroughly with a soap-filled pad of steel wool in warm water, (b) rinsed with water, (c) washed with acetone, (d) pickled for 5 minutes in 10% aqueous HCl, (e) dried in air, and (f) weighed. The coupons thus prepared were then suspended from glass hooks in a stirred acid cleaning solution at 25C. or 50C. for normally 16 hours; the coupons being completely immersed in the solution. The coupons were then removed from the acid solutions, washed with soap and warm water, rinsed, dried and weighed. The weight loss resulting from such treatment is a measure of corrosion. The weight loss rate (WLR), having the units lbs./ft /day is determined as follows:
WLR: (49.15) (weight loss in gm.)
(original weight in gm.) (SF) (time) wherein (a) 49.15 is a conversion factor for converting gm./cm. /hr. to lbs./ft. /day; (b) SF strip factor average ratio of surface area (cm?) to weight (gm.); and (c) the time is measured in hours.
The effectiveness of the sulfonium salts was determined by comparing the WLR of a cleaning solution containing the sulfonium salts (WLR (test)) against the WLR of an identical cleaning solution without the sulfonium salts (WLR (blank)). The comparative data is reported as the Percent Protection" which is calculated as follows:
WLR (blank)WLIt (test) Percent Protection: WLR (blank) X 100.
total weight basis, aqueous solution of H 50, and 0.1 percent by weight of FE (added as FeNl-I (S0,),- 12 R 0).
The results of several experiments using solution A" are tabulated in Table II below. The concentration of the sulfonium salt is reported in millimoles per liter. The neutralizing anion, X, in each case was chloride.
TABLE II Percent Temp. WL R protec- Ex. R R R Cone. C.) (test) tion 1 p-n C H1 CH CH3 0. 69 50 0. 0054 89 2 D-Il-C12Hz5 CH CH 0.20 25 0.0020 95 3 p-n-C12Hg CH3 CH 0.30 50 O. 0090 82 4. p-Il-Cl2Hz5 OH; n-C4H 0. 40 25 0. 0039 5 p-O 1H 5 CH3 CH3 0. 30 50 0. 020 61 TABLE III Percent Inhibitor Temp. WLR Protec- Ex. Solution Conc. ("C.) (test) tion 6 B 0.20 25 0.020 52 7 B 0.39 50 0.021 89 8 C 0.39 25 0.0065 Bl In other experiments, test solution A containing p-n-dodecylbenzyldimethylsulfonium chloride as the inhibitor was evaluated in a flow test wherein the solution was pumped through steel pipes for 6 to 7 hours and the degree of corrosion determined as above. The steel pipes used in this test were sections cut from the same length of pipe and measured approximately 1 foot in length and 0.75 inch in inside diameter. The pipes were cleaned free of rust by use of a commercial cleaning solution quite similar to solution A except that no Fe was added, and were scrubbed with soap and warm water, rinsed with water, rinsed with acetone, dried and weighed. After the flow test, the pipes were again scrubbed, rinsed with water, rinsed with acetone, dried and weighed. The WLR" and Percent Protection" were calculated as above. The results are summarized in Table IV below. The flow rate is measured in gallons/minute and the concentration of sulfonium salt (Conc.) is expressed as millimoles per liter.
TABLE IV Flow Temp. lnhlbltm WLR Percent Ex. Rate (C.) Cone. (teal) Protection 9 0.2 25 0.39 0.0] l 89 10 0.2 50 0.39 0.016 Bl ii 0.2 65 0.56 0.0l4 86 i2 5.0 25 0.39 0.0064 97 13 5.0 65 0.56 0.028 14 10.0 25 0.39 0.0064 99 In still other experiments, the subject sulfonium salts were evaluated as corrosion inhibitors in aqueous acid solutions which did not initially contain any significant amount of ferric ion. Examples 15 and 16 were conducted in 10 percent by weight, total weight basis, aqueous l-ICl solutions and Example 17 was conducted in a 10 percent by weight aqueous H SO solution. In
each of Examples -17 the I inhibitor was pdodecylbenzyldimethylsulfonium chloride and the metal coupons and the testing procedure used were substantially the same as those described in Example 1. The results are tabulated in Table V below. The concentration (Conc.) of sulfonium salt is expressed in millimoles per liter.
TABLE V lnhibitor Temp. WLR Percent Ex. Conc. C. (test) Protection 15 0.28 25 0.0027 9] l6 0.36 50 0.0047 98 17 0.30 25 0.0031 75 EXAMPLE l8 Using substantially the same procedure as Example 2, the corrosion of a copper alloy (78% Cu, 21% Zn, and 1% Sn) in contact with solution A at 25C. was found to be inhibited by p-dodecylbenzyldimethylsulfonium chloride (Cone. of 0.4 millimoles/liter). WLR (test) equals 0.0003. Percent Protection 96 percent EXAMPLE 19 wherein R had the designated meaning in the examples. E.g., coupons cleaned with the test solutions inhibited with p-dodecylbenzyldimethylsulfoniumchloride were observed to have a protective film of (predominantly) (p,p'-bisdodeeyl)bibenzyl and pdodecyltoluene on their surface; such coupons were suspended over water in a closed vessel for ll days and showed only small localized rust spots while coupons cleaned with the uninhibited solutions and concurrently aged over water were uniformly covered with red rust.
1. An aqueous acidic cleaning solution of at least one non-oxidizing inorganic acid or organic acid or mixtures thereof having incorporated therein at least one sulfonium salt of the formula wherein n is l or 2; each R, is independently an alkyl radical; the aggregate carbon content of said R radicals being from 6 to about 24 carbon atoms; R and R are each independently alkyl radicals of from 1 to about 18 carbon atoms; and X is an anion; said sulfonium salt being present in an amount at least sufficient to inhibit the corrosion of ferrous metal in contact with said solution and ferric ions.
2. The composition defined by claim 1 wherein n is l.
3. The composition defined by claim 2 wherein R is a para substituent on the aromatic ring.
4. The composition defined by claim 1 wherein each R is an alkyl radical of from 8 to l8 carbon atoms.
5. The composition defined by claim 1 wherein R and R are independently alkyl radicals of from 1 to 4 carbon atoms.
6. The composition defined by claim 1 wherein n is l, R, is an alkyl radical of from 8 to 18 carbon atoms and R and R are each independently alkyl radicals of from 1 to 4 carbon atoms.
7. The composition defined by claim 1 wherein said acid solution is an aqueous solution of a non-oxidizing inorganic acid or a mixture of such acids.
8. The composition defined by claim 1 wherein said acid solution is anaqueous solution of an organic carboxylic or polycarboxylic acid or a mixture thereof.
9. The composition defined by claim 1 wherein said acid solution is an aqueous solution of a polyaminepolycarboxylic acid or an ammonium-, amine, or alkali metal salt thereof, or mixtures thereof.
10. The composition defined by claim 1 wherein said acid solution is an aqueous solution of at least one of HCl, H SO ethylenediaminetetracetic acid (EDTA) or the ammonium-, amineor alkali metal salt of EDTA.
11. The composition defined by claim 1 wherein n is l; R, is p-dodecyl; and R and R are each indepen-' dently alkyl radicals of from 1 to 4 carbon atoms.
12. In the process of treating ferrous metal surfaces to remove iron oxide encrustations by treating said metal surface with an aqueous acid cleaning solution, 1 the improvement of using the composition defined by claim 1 as said cleaning solution.
13. The composition defined by claim 10 wherein said acid solution is an aqueous solution of at least one of EDTA and an ammonium'-, amineor alkali metal salt of EDTA;and wherein said solution is buffered to a pH of from 2 to 5.
14. The composition defined by claim 13 wherein n is 1; R is an alkyl radical of from 8 to 18 carbon atoms; and R and R are each independently alkyl radicals of from 1 to 4 carbon atoms.
15. A process of inhibiting acid-induced and ferric ion-induced corrosion ofmetal surfaces in contact with an aqueous acid solution of at least one non-oxidizing inorganic acid or organic acid or mixtures thereof, the process comprising incorporating in said acid solution a small but corrosion-inhibiting amount of at least one oqiums o the rmu wherein n is l or 2; each R is independently an alkyl radical; the aggregate carbon content of said R radicals being from 6 to about 24 carbon atoms; R; and R are each independently alkyl radicals of from 1 to about 18 carbon atoms; and X is an anion.
16. The process defined by claim 15 wherein n is 1; R is an alkyl radical of from 8 to 18 carbon atoms; and R and R are each independently alkyl radicals of from 1 to 4 carbon atoms.
i In in w n-