Corrosion inhibition

Abstract

The invention relates to a method of inhibiting corrosion by corrosive fluids, and more specifically to inhibiting corrosion of a metallic surface. The method comprising adding to the corrosive fluid a specifically selected ionic liquid which is added in an amount, based on the total weight of the corrosive fluid, effective to mitigate or alleviate corrosion.

Claims

1. A method of inhibiting corrosion of a metallic surface in contact with a corrosive fluid, the method comprising adding to the corrosive fluid an ionic liquid having the formula:
[Cat.sup.+][X.sup.Z-Bas] wherein: [Cat.sup.+] represents one or more cationic species; [X.sup.Z-Bas] represents one or more anionic species wherein: X.sup. represents an anionic moiety; Z is a covalent bond joining X.sup.and Bas, or a divalent linking group; and Bas is a basic moiety, in an amount of from 1 to 5,000 ppm by weight, based on the total weight of the corrosive fluid.

2. A method according to claim 1, wherein X.sup. represents a moiety selected from CO.sub.2.sup. and SO.sub.3.sup..

3. A method according to claim 1, wherein Bas represents a basic moiety which is the conjugate base of at least one member of a group consisting of: an acidic moiety having a pK.sub.a of 4.0 or greater and an acidic moiety having a pK.sub.a of less than 14.0.

4. A method according to claim 1, wherein Bas comprises at least one member of a group consisting of: basic nitrogen, phosphorus, sulfur, and oxygen atom.

5. A method according to claim 4, wherein Bas is selected from N(R.sup.1)(R.sup.2), P(R.sup.1)(R.sup.2), S(R.sup.1), and O(R.sup.3), wherein R.sup.1, R.sup.2, and R.sup.3 are independently selected from linear or branched (C.sub.1 to C.sub.8) alkyl, (C.sub.1 to C.sub.8) cycloalkyl, (C.sub.6 to C.sub.10) aryl, (C.sub.6 to C.sub.10) aralkyl and (C.sub.6 to C.sub.10) substituted aryl.

6. A method according to claim 1, wherein Z is a divalent organic radical having from 1 to 18 carbon atoms, or a covalent bond.

7. A method according to claim 6, wherein Z has the formula (CH.sub.2).sub.pCHR.sup.4(CH.sub.2).sub.q, wherein p+q is an integer of from 1 to 6, and R.sup.4 represents a C.sub.1 to C.sub.6 straight chain or branched alkyl group.

8. A method according to claim 6, wherein [X.sup.Z-Bas] is selected from: alaninate, argininate, asparaginate, monoanionic aspartate, dianionic aspartate, cysteinate, monoanionic glutamate, dianionic glutamate, glycinate, histidinate, isoleucinate, leucinate, lysinate, methioninate, phenylalaninate, prolinate, serinate, threoninate, tryptophanate, tyrosinate, valinate, taurinate, and cystine.

9. A method according to claim 1, wherein [Cat.sup.+] represents one or more cationic species selected from: ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4-diazabicyclo[2.2.2]octanium, diazabicyclo-undecenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, iso-oxazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, thiophenium, thiuronium, triazinium, triazolium, iso-triazolium, and uronium.

10. A method according to claim 9, wherein [Cat.sup.+] comprises a cationic species selected from: ##STR00014## wherein: R.sup.a, R.sup.b, R.sup.c,R.sup.d, R.sup.e, R.sup.f and R.sup.g are each independently selected from hydrogen, a C.sub.1 to C.sub.20, straight chain or branched alkyl group, a C.sub.3 to C.sub.8 cycloalkyl group, or a C.sub.6 to C.sub.10 aryl group, or any two of R.sup.b, R.sup.c, R.sup.d, R.sup.e and R.sup.f attached to adjacent carbon atoms form a methylene chain (CH.sub.2).sub.q wherein q is from 3 to 6; and wherein said alkyl, cycloalkyl or aryl groups or said methylene chain are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.12 alkoxyalkoxy, C.sub.3 to C.sub.8 cycloalkyl, C.sub.6 to C.sub.10 aryl, C.sub.7 to C.sub.10 alkaryl, C.sub.7 to C.sub.10 aralkyl, CN, OH, SH, NO.sub.2, CO.sub.2R.sup.x, OC(O)R.sup.x, C(O)R.sup.x, C(O)NR.sup.yR.sup.z, NR.sup.yR.sup.z, or a heterocyclic group, wherein R.sup.x, R.sup.y and R.sup.z are independently selected from hydrogen or C.sub.1 to C.sub.6 alkyl; preferably wherein [Cat.sup.+] comprises or consists of a cationic species selected from: ##STR00015##

11. A method according to claim 9, wherein [Cat.sup.+] comprises an acyclic cation selected from:
[N(R.sup.a) (R.sup.b)(R.sup.c) (R.sup.d)].sup.+, [P (R.sup.a) (R.sup.b)(R.sup.c) (R.sup.d)].sup.+, and [S(R.sup.a)(R.sup.b)(R.sup.c)].sup.+, wherein: R.sup.a, R.sup.b, R.sup.c, and R.sup.d are each independently selected from a C.sub.1 to C.sub.20, straight chain or branched alkyl group, a C.sub.3 to C.sub.8 cycloalkyl group, or a C.sub.6 to C.sub.10 aryl group; and wherein said alkyl, cycloalkyl or aryl groups are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.12 alkoxyalkoxy, C.sub.3 to C.sub.8 cycloalkyl, C.sub.6 to C.sub.10 aryl, C.sub.7 to C.sub.10 alkaryl, C.sub.7 to C.sub.10 aralkyl, CN, OH, SH, NO.sub.2, CO.sub.2R.sup.x, OC(O)R.sup.x, C(O)R.sup.x, C(O)NR.sup.yR.sup.z, NR.sup.yR.sup.z, or a heterocyclic group, wherein R.sup.x, R.sup.y and R.sup.z are independently selected from hydrogen or C.sub.1 to C.sub.6 alkyl; and wherein one of R.sup.a, R.sup.b, R.sup.c, and R.sup.d may be hydrogen; preferably wherein [Cat.sup.+] comprises or consists of an acyclic cation selected from:
[N(R.sup.a)(R.sub.b)(R.sub.c)(R.sub.d].sup.+, [P(R.sub.a)(R.sub.b) (R.sub.c)(R.sub.d)].sup.+.

12. A method according to claim 1, wherein [Cat.sup.+] comprises a basic cation having the formula:
[Cat.sup.+-Z-Bas] wherein: Cat.sup.+represents a positively charged moiety, and Z and Bas are as defined in claim 3.

13. A method according to claim 12, wherein [Cat.sup.+-Z-Bas] is selected from: ##STR00016## ##STR00017## wherein: Bas and Z are as defined in claim 3; and R.sup.b, R.sup.c, R.sup.d, R.sup.e, R.sup.f and R.sup.g are independently selected from hydrogen, a C.sub.1 to C.sub.20, straight chain or branched alkyl group, a C.sub.3 to C.sub.8 cycloalkyl group, or a C.sub.6 to C.sub.10 aryl group, or any two of R.sup.b, R.sup.c, R.sup.d, R.sup.e and R.sup.f attached to adjacent carbon atoms form a methylene chain (CH.sub.2).sub.q wherein q is from 3 to 6; and wherein said alkyl, cycloalkyl or aryl groups or said methylene chain are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.12 alkoxyalkoxy, C.sub.3 to C.sub.8 cycloalkyl, C.sub.6 to C.sub.10 aryl, C.sub.7 to C.sub.10 alkaryl, C.sub.7 to C.sub.10 aralkyl, CN, OH, SH, NO.sub.2, CO.sub.2R.sup.x, OC(O)R.sup.x, C(O)R.sup.x, C(O)NR.sup.yR.sup.z, NR.sup.yR.sup.z, or a heterocyclic group, wherein R.sup.x, R.sup.y and R.sup.z are independently selected from hydrogen or C.sub.1 to C.sub.6 alkyl; or wherein [Cat.sup.+-Z-Bas] is selected from:
[N(Z-Bas)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+ and [P(Z-Bas)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+ wherein: Bas and Z are as defined in claim 1, and R.sup.b, R.sup.c, and R.sup.d are independently selected from a C.sub.1 to C.sub.20, straight chain or branched alkyl group, a C.sub.3 to C.sub.8 cycloalkyl group, or a C.sub.6 to C.sub.10 aryl group, or any two of R.sup.b, R.sup.c, R.sup.d, R.sup.e and R.sup.f attached to adjacent carbon atoms form a methylene chain (CH.sub.2).sub.qwherein q is from 3 to 6; and wherein said alkyl, cycloalkyl or aryl groups or said methylene chain are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.12 alkoxyalkoxy, C.sub.3 to C.sub.8 cycloalkyl, C.sub.6 to C.sub.10 aryl, C.sub.7 to C.sub.10 alkaryl, C.sub.7 to C.sub.10 aralkyl, CN, OH, SH, NO.sub.2, CO.sub.2R.sup.x, OC(O)R.sup.x, C(O)R.sup.x, C(O)NR.sup.yR.sup.z, NR.sup.yR.sup.z, or a heterocyclic group, wherein R.sup.x, R.sup.y and R.sup.z are independently selected from hydrogen or C.sub.1 to C.sub.6 alkyl; and wherein one of R.sup.b, R.sup.c, and R.sup.d may be hydrogen.

14. A method according to claim 1, wherein the ionic liquid has a melting point of less than 150 C.

15. A method according to claim 1, wherein the basic ionic liquid is added to the corrosive fluid in an amount of from 10 to 2,000 ppm by weight, based on the total weight of the corrosive fluid.

16. A method of inhibiting corrosion of a metallic surface in contact with a corrosive fluid, the method comprising forming a dopant layer of an ionic liquid having the formula:
[Cat.sup.+][X.sup.Z-Bas] wherein: [Cat.sup.+] and [X.sup.Z-Bas] are as defined in claim 1; on the metallic surface prior to contacting the metallic surface with the corrosive fluid.

17. A method according to claim 1, wherein the corrosive fluid is an acid-containing hydrocarbon fluid.

18. A method according to claim 17, wherein the acid-containing hydrocarbon fluid comprises at least one member of a group consisting of: naphthenic acids and sulfur-containing acids.

19. A method according to claim 1, wherein the corrosive fluid is an acid-containing aqueous fluid having a pH of less than about 7.0.

20. A method according to claim 1, wherein the corrosive fluid is an aqueous solution of at least one salt.

21. A method according to claim 1, wherein the metallic surface is the surface of a reactor vessel or distillation vessel.

22. A method of distilling an acid-containing hydrocarbon fluid feed using a distillation apparatus having a metallic surface in contact with the acid-containing hydrocarbon fluid, the method comprising adding a basic ionic liquid having the formula:
[Cat.sup.+][X.sup.Z-Bas] to the acid-containing hydrocarbon fluid feed, wherein [Cat.sup.+] and [X.sup.Z-Bas] are as defined in claim 1.

23. A method according to claim 22, wherein the acid-containing hydrocarbon fluid is as defined in claim 18.

Description

EXAMPLES

Example 1

Corrosion Inhibition in Naphthenic Acids with a Range of Ionic Liquids

(1) Mild steel coupons (0.500 g) were degreased in absolute ethanol, dried in acetone, weighed, and stored under moisture-free conditions prior to use. To an autoclave containing a mixture of pure naphthenic acids (10.000 g) and 1.0 wt % (10,000 ppm wt.) of the ionic liquid was added a weighed mild steel coupon. The mixture was heated under a nitrogen atmosphere for 24 h at 250 C. After cooling, the coupon was carefully removed from the naphthenic acid/ionic liquid mixture, gently washed with toluene followed by acetone to remove any organics. After drying, the coupon was gently washed with 0.01 M HCl solution to remove any external corrosion. The coupon was then washed with distilled water followed by acetone and dried overnight at 80 C.

(2) Results for the ionic liquids triethylmethylammonium serinate ([N.sub.1,2,2,2][Ser]), tributylmethylammonium threoninate ([N.sub.1,4,4,4][Thr]), tetrabutylphosphonium serinate ([P.sub.4,4,4,4][Ser]), tetrabutylphosphonium taurinate ([P.sub.4,4,4,4][Tau]), and tributylmethylammonium lysinate ([N.sub.1,4,4,4][Lys]), as well as for a control using no ionic liquid are shown in Table 1. The quoted % weight loss figures represent an average over three runs.

(3) TABLE-US-00001 TABLE 1 Ionic Liquid % weight loss none 83 [N.sub.1,4,4,4][Lys] 25 [N.sub.1,2,2,2][Ser] 41 [N.sub.1,4,4,4][Thr] 45 [P.sub.4,4,4,4][Ser] 43 [P.sub.4,4,4,4][Tau] 54

Example 2

Corrosion Inhibition in Naphthenic Acids with Various Masses of Ionic Liquid

(4) The test described in Example 1 was repeated using varying amounts of the ionic liquid tributylmethylammonium lysinate ([N.sub.1,4,4,4][Lys]). The results in Table 2 show that the corrosion inhibition is maintained at substantially the same level, even when the concentration of the ionic liquid is reduced by a factor of 10 from those used in Example 1.

(5) TABLE-US-00002 TABLE 2 Ionic Liquid % weight loss [N.sub.1,4,4,4][Lys] (1000 ppm wt) 27 [N.sub.1,4,4,4][Lys] (2000 ppm wt) 28 [N.sub.1,4,4,4][Lys] (6000 ppm wt) 27

Example 3

Corrosion Inhibition in Naphthenic Acids by Surface Passivation

(6) A freshly cut mild steel coupon (0.500 g) was degreased in absolute ethanol, dried in acetone, weighed, and immersed in 1 mL of a 0.01M solution of [N.sub.1,4,4,4][Lys] in ethyl acetate for two hours. The coupon was then removed from the ionic liquid solution and dried in an oven at 140 C. for two hours. The ionic liquid doped coupon thus obtained was added to a glass-lined reactor containing pure naphthenic acids (10.000 g) and stirred at ambient temperature and atmospheric pressure for 24 hours. The coupon was carefully removed from the acid mixture and gently washed with deionised water followed by 0.01 M HCl solution to remove any external corrosion. The coupon was then washed with distilled water followed by acetone and dried overnight at 80 C. Results averaged over three runs are shown in Table 3.

(7) TABLE-US-00003 TABLE 3 Ionic Liquid % weight loss none 83 [N.sub.1,4,4,4][Lys] 9

Example 4

Corrosion Inhibition in Aqueous Sulphuric Acid

(8) A freshly cut mild steel coupon (0.500 g) was degreased in absolute ethanol, dried in acetone, weighed, and immersed in 1 mL of a 0.01M solution of [N.sub.1,4,4,4][Lys] in ethyl acetate for two hours.

(9) To an autoclave containing a mixture of 2M aqueous H.sub.2SO.sub.4 (10.000 g) and 0.02 wt % (200 ppm wt.) of methyltributylammonium cystinate ([N.sub.1,4,4,4].sub.2[Cys]) was added a weighed mild steel coupon. The mixture was heated under a nitrogen atmosphere for 24 h at 250 C. After cooling, the coupon was carefully removed from the sulphuric acid/ionic liquid mixture, and gently washed with deionised water followed by 0.01 M HCl solution to remove any external corrosion. The coupon was then washed with distilled water followed by acetone and dried overnight at 80 C. Results as an average over three runs are shown in Table 4.

(10) TABLE-US-00004 TABLE 4 Ionic Liquid % weight loss none 64 [N.sub.1,4,4,4].sub.2[Cys] 53

Example 5

Corrosion Inhibition in Aqueous Sulphuric Acid by Surface Passivation

(11) A freshly cut mild steel coupon (0.500 g) was degreased in absolute ethanol, dried in acetone, weighed, and immersed in 1 mL of a 0.01 M solution of [.sub.6,6,6,14].sub.2[Cys] in ethyl acetate for two hours. The coupon was then removed from the ionic liquid solution and dried in an oven at 140 C. for two hours. The ionic liquid doped coupon thus obtained was added to a glass-lined reactor containing a 2M aqueous solution of H.sub.2SO.sub.4 (10.000 g) and stirred at ambient temperature and atmospheric pressure for 24 hours. The coupon was carefully removed from the acid mixture and gently washed with deionised water followed by 0.01 M HCl solution to remove any external corrosion. The coupon was then washed with distilled water followed by acetone and dried overnight at 80 C.

(12) The same experiment was repeated using [N.sub.1,4,4,4].sub.2[Cys] instead of [P.sub.6,6,6,14].sub.2[Cys].

(13) Control experiments were also carried out in which degreased, dried and weighed mild steel coupons were (a) added directly to the H.sub.2SO.sub.4 solution; and (b) immersed in ethyl acetate containing no ionic liquid for two hours and dried as above, prior to being added to the H.sub.2SO.sub.4 solution.

(14) TABLE-US-00005 TABLE 5 Ionic Liquid % weight loss None 64 None* 62 [P.sub.6,6,6,14].sub.2[Cys] 17 [N.sub.1,4,4,4].sub.2[Cys] 22 *Mild steel coupon immersed in solvent containing no IL

Example 6

Corrosion Inhibition in Aqueous Acetic Acid

(15) A freshly cut mild steel coupon (0.500 g) was degreased in absolute ethanol, dried in acetone, weighed, and immersed in 1 mL of a 0.01M solution of [N.sub.1,4,4,4][Lys] in ethyl acetate for two hours.

(16) To an autoclave containing a mixture of 5M aqueous acetic acid (10.000 g) and 0.02 wt % (200 ppm wt.) of [N.sub.1,4,4,4].sub.2 was added a weighed mild steel coupon. The mixture was heated under a nitrogen atmosphere for 24 h at 250 C. After cooling, the coupon was carefully removed from the acetic acid/ionic liquid mixture, and gently washed with deionised water followed by 0.01 M HCl solution to remove any external corrosion. The coupon was then washed with distilled water followed by acetone and dried overnight at 80 C. Results as an average over three runs are shown in Table 6.

(17) TABLE-US-00006 TABLE 6 Ionic Liquid % weight loss none 11 [N.sub.1,4,4,4].sub.2[Cys] 8

Example 7

Corrosion Inhibition in Aqueous Acetic Acid by Surface Passivation

(18) An immersion test was used to evaluate inhibition of anodic-induced corrosion of mild steel in the presence of basic ionic liquids.

(19) A freshly cut mild steel coupon (0.500 g) was degreased in absolute ethanol, dried in acetone, weighed, and immersed in 1 mL of a 0.01 M solution of [P.sub.6,6,6,14].sub.2[Cys] in ethyl acetate for two hours. The coupon was then removed from the ionic liquid solution and dried in an oven at 140 C. for two hours. The ionic liquid doped coupon thus obtained was added to a glass-lined reactor containing a 5M aqueous solution of acetic acid (10.000 g) and stirred at ambient temperature and atmospheric pressure for 24 hours. The coupon was carefully removed from the acid mixture, and gently washed with deionised water followed by 0.01 M HCl solution to remove any external corrosion. The coupon was then washed with distilled water followed by acetone and dried overnight at 80 C.

(20) The same experiment was repeated using [N.sub.1,4,4,4].sub.2[Cys] instead of [P.sub.6,6,6,14].sub.2[Cys].

(21) Control experiments were also carried out in which degreased, dried and weighed mild steel coupons were (a) added directly to the acetic acid solution; and (b) immersed in ethyl acetate containing no ionic liquid for two hours and dried as above, prior to being added to the acetic acid solution.

(22) TABLE-US-00007 TABLE 7 Ionic Liquid % weight loss None 11 None* 12 [P.sub.6,6,6,14].sub.2[Cys] 3 [N.sub.1,4,4,4].sub.2[Cys] 2 *Mild steel coupon immersed in solvent containing no IL

Example 8

Corrosion Inhibition in Brine by Surface Passivation

(23) An immersion test was used to evaluate inhibition of anodic-induced corrosion of mild steel in the presence of basic ionic liquids.

(24) A freshly cut mild steel coupon (0.500 g) was degreased in absolute ethanol, dried in acetone, weighed, and immersed in 1 mL of a 0.01 M solution of [P.sub.66614].sub.2[Cys] in ethyl acetate for two hours. The coupon was then removed from the ionic liquid solution and dried in an oven at 140 C. for two hours. The ionic liquid doped coupon thus obtained was added to a glass-lined reactor containing a 10 wt % solution of NaCl in water (10.000 g) and stirred at ambient temperature and atmospheric pressure for 72 hours. The coupon was carefully removed from the acid mixture, and gently washed with deionised water followed by 0.01 M HCl solution to remove any external corrosion. The coupon was then washed with distilled water followed by acetone and dried overnight at 80 C.

(25) The same experiment was repeated using [N.sub.1,4,4,4].sub.2[Cys] instead of [P.sub.6,6,6,14].sub.2[Cys].

(26) Control experiments were also carried out in which degreased, dried and weighed mild steel coupons were (a) added directly to the NaCl solution; and (b) immersed in ethyl acetate containing no ionic liquid for two hours and dried as above, prior to being added to the NaCl solution.

(27) TABLE-US-00008 TABLE 8 Ionic Liquid % weight loss None 3.02 None* 4.26 [P.sub.6,6,6,14][Cys] 0.36 [N.sub.1,4,4,4].sub.2[Cys] 0.27 *Mild steel coupon immersed in solvent containing no IL