Corrosion inhibitors containing cationic surfactants

1 . The use of compositions containing metal salts of compounds of the formula (1)

in which R′ is C 1 - to C 29 -alkyl, C 2 - to C 29 -alkenyl, C 6 - to C 30 -aryl or C 7 - to C 30 -akylaryl, and cationic surfactants as corrosion inhibitors.

2 . The use as claimed in claim 1 , R′ being an alkyl or alkenyl group having 7 to 17 carbon atoms.

3 . The use as claimed in claim 1 and/or 2 , the metal salt being an alkali metal salt.

4 . The use as claimed in one or more of claims 1 to 3 , the cationic surfactant being a quaternary ammonium salt which contains at least one C 8 - to C 24 -alkyl or alkenyl group linked to the nitrogen atom of the ammonium group.

5 . The use as claimed in one or more of claims 1 to 4 , the cationic surfactant being an ester quat which is obtainable by esterification of an amino alcohol with a C 8 - to C 24 -fatty acid and subsequent quaternization of the amino groups with a methylating agent.

6 . The use as claimed in one or more of claims 1 to 5 , the cationic surfactant corresponding to the formula (2)

in which

R1 is C 5 - to C 22 -alkyl

R2 is methyl

R3 is methyl or -A-(OA) n -OH

R4 is -A-(OA) n -OH

A is —C 2 H 4 —

n is a number from 0 to 20

X is a suitable anion.

7 . The use as claimed in one or more of claims 1 to 6 , the cationic surfactant corresponding to the formulae (3) to (5)

in which

R is C 4 - to C 22 -alkyl, C 4 - to C 22 -alkenyl or C 4 - to C 22 -alkylaryl

R1 is H, C 1 - to C 3 -alkyl or C 2 - to C 3 -hydroxyalkyl

n is a number from 0 to 10

X is a suitable anion.

8 . The use as claimed in claim 6 or 7 , wherein X is an anion selected from chloride, bromide, iodide, fluoride, sulfate, hydrogen sulfate, carbonate, bicarbonate, acetate, citrate, phosphate, mono- and dihydrogen phosphate, pyrophosphate, polyphosphate, metaphosphate, nitrate, methylsulfate, phosphonate, methylphosphonate, methanedisulfonate, methylsulfonate, ethanesulfonate or an anion of the formulae R 6 SO 3 , R 7 SO 4 or R 6 COO, in which R 6 and R 7 are C 2 -C 20 -alkyl, preferably C 10 -C 18 -alkyl, and R 7 is additionally C 1 -C 18 -alkylphenyl.

9 . The use as claimed in one or more of claims 1 to 8 , wherein the total amount of metal salt to cationic surfactant is from 5 to 5000 ppm.

10 . The use as claimed in one or more of claims 1 to 9 , wherein the weight ratio of metal salt to cationic surfactant is from 1:9 to 9:1.

11 . The use as claimed in one or more of claims 1 to 10 as corrosion inhibitors in apparatuses for conveying and transporting hydrocarbons in oil production and processing.

12 . The use as claimed in one or more of claims 1 to 11 as corrosion inhibitors in metal processing compositions.

13 . A composition containing at least one metal salt of a compound of the formula (1)

in which R′ is C 1 - to C 29 -alkyl, C 2 - to C 29 -alkenyl, C 6 - to C 30 -aryl or C 7 - to C 30 -alkylaryl, and at least one cationic surfactant.

14 . The composition as claimed in claim 13 , wherein the weight ratio of metal salt to cationic surfactant is from 9:1 to 1:9.