Compositions – Preservative agents – Anti-corrosion
Reexamination Certificate
2000-04-03
2003-04-01
Anthony, Joseph D. (Department: 1714)
Compositions
Preservative agents
Anti-corrosion
C252S392000, C252S402000, C252S403000, C510S253000, C510S255000, C510S401000, C106S014160, C106S014420, C422S007000, C422S012000, C507S240000, C507S252000, C507S939000
Reexamination Certificate
active
06540943
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to corrosion inhibition and, more particularly, to a method of inhibiting corrosion of metal equipment which is cleaned with an inorganic acid.
BACKGROUND OF THE INVENTION
Acidic cleaning solutions are commonly employed to remove scale and rust from industrial equipment. However, acid is corrosive to the metal components of the equipment. Therefore, the cleaning solutions usually contain corrosion inhibitors to minimize the corrosive effect that the acid has on the equipment.
Cleaning solutions comprising an organic acid and a corrosion inhibitor are generally known (See, e.g., U.S. Pat. No. 4,637,899). However, because inorganic acids are more difficult to work with, protecting metal equipment which is cleaned with an inorganic acid from corrosion has been less successful.
There is a particular need for an effective inorganic acid corrosion inhibitor in mineral processing operations, such as the production or beneficiation of alumina trihydrate (also known as aluminum hydroxide, alumina and gibbsite), copper, gold and other metals. For example, in the production of alumina, bauxite is digested with a hot caustic soda solution. This results in the dissolution (digestion) of a considerable portion of the aluminum-bearing minerals, giving a supersaturated solution of sodium aluminate (pregnant liquor). After the physical separation of undigested mineral residues (red mud), the sodium aluminate solution is decomposed to afford alumina trihydrate, which is recovered by filtration. During the digestion of bauxite ore, the attack of caustic soda on certain silica-bearing components in the ore results in the release of soluble silica species into the liquor. These soluble silicates then react with alumina and soda to form insoluble sodium aluminosilicates which are also known as desilication products, or DSP. The desilication product is deposited as scale on the walls of pipes and vessels throughout the plant. Scaling by DSP is particularly severe on heated equipment surfaces, such as heat exchanger tubes. The exchanger tubes and other equipment are cleaned with an inorganic acid, usually sulfuric acid. Therefore, a corrosion inhibitor is necessary to protect the alumina refinery utility equipment from corrosion while the sulfuric acid is being recirculated during the cleaning process.
Accordingly, it would be desirable to provide an improved method for inhibiting the corrosion of metal equipment which is cleaned with an inorganic acid using an effective amount of a corrosion inhibitor composition. It would also be desirable for the composition to minimize the corrosive effect that the inorganic acid has on the metal equipment, while withstanding the harsh acidic environment, particularly in mineral processing operations where sulfuric acid is regularly used in the cleaning process.
SUMMARY OF THE INVENTION
The present invention calls for treating metal equipment which is cleaned with an inorganic acid with a corrosion inhibitor composition containing at least one quaternary ammonium compound, a sulfur-containing compound and a nonionic surfactant in a solvent. Treatment with the composition effectively inhibits the corrosion of the metal equipment.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a method of inhibiting corrosion of metal equipment which is cleaned with an inorganic acid. In accordance with this invention, a corrosion inhibitor composition comprising at least one quaternary ammonium compound, a sulfur-containing compound and a non-ionic surfactant in a solvent is used to treat the equipment to minimize the corrosive effect that the inorganic acid has on the equipment.
All types of industrial equipment which are commonly exposed to high concentrations of inorganic acids, such as mineral processing equipment, are contemplated within the scope of this invention, including pipes, vessels, heat exchanger tubes and holding tanks. The equipment, which is typically composed of metals such as iron, copper, copper alloys, zinc, zinc alloys, nickel, nickel alloys, stainless steel and the like, is most commonly cleaned with sulfuric acid. However, other suitable inorganic acids which may be used to clean the equipment include nitric, phosphoric, hydrochloric and phosphonic.
The quaternary ammonium compounds which may be used in the corrosion inhibitor composition in the practice of the invention are represented by the general formula:
(R)
4
N
+X
−
wherein each R is the same or a different group selected from long chain alkyl groups, cycloalkyl groups, aryl groups and heterocyclic groups, and X
−
is an anion such as a halide. The term “long chain” is used herein to mean hydrocarbon groups having in the range of from about 12 to about 20 carbon atoms.
Examples of suitable quaternary ammonium compounds which can be used in the corrosion inhibitor include N-alkyl, N-cycloalkyl and N-alkylaryl pyridinium halides such as N-cyclohexyl-pyridinium bromide, N-octylpyridinium bromide, N-nonylpyridinium bromide, N-decylpyridinium bromide, N-dodecyl-pyridinium bromide, N,N-didodecyldipyridinium dibromide, N-tetradecylpyridinium bromide, N-laurylpyridinium chloride, N-dodecylbenzylpyridinium chloride, N-dodecylquinolinium bromide, N-(1-methylnapthyl)quinolinium chloride, N-benzylquinolinium chloride and mixtures thereof. Other suitable quaternary ammonium compounds include monochloromethylated and bizchloromethylated pyridinium halides, ethoxylated and propoxylated quaternary ammonium compounds, sulfated ethoxylates of alkyphenols and primary and secondary fatty alcohols, didodecyldimethylammonium chloride, hexadecylethyldimethylammonium chloride, 2-hydroxy-3-(2-undecylamidoethylamino)-propane-1-triethylammonium hydroxide, 2-hydroxy-3-(2-heptadecylamidoethylamino)-propane-1-triethylammonium hydroxide and mixtures thereof. The preferred quaternary ammonium compound is alkylpyridine benzyl chloride quaternary.
The amount of the quaternary ammonium compound present in the corrosion inhibitor composition is in the range of about 30 to about 60 weight percent and, preferably, in the range of about 40 to about 50 weight percent.
The sulfur-containing compounds which may be used in the corrosion inhibitor composition include mercapto compounds, thiourea, thioacetamide, thionicotinamide ammonium thiocyanate and mixtures thereof. Preferably, mercapto compounds are used in the practice of this invention. Suitable mercapto compounds include 2-mercaptoethanol, thiol acetic acid, mercaptocarboxylic acid having from 2 to 6 carbon atoms (straight chain or branched), mercapto succinic acid, toluene thiol and ortho-mercapto benzoic acid. The most preferred mercapto compound is 2-mercaptoethanol.
The amount of sulfur-containing compound present in the corrosion inhibitor composition is in the range of about 1 to 20 weight percent and, preferably, in the range of about 2 to about 10 weight percent.
In order to facilitate the wetting of the metal surface, a wetting agent is employed. Such wetting agents are nonionic surfactants. Useful nonionic surfactants are alkoxylated alcohols, amines and glycols. These nonionic surfactants include ethylene oxide derivatives of long-chain alcohols such as octyl, decyl, lauryl or cetyl alcohol, ethylene oxide derivatives of long-chain monoamines such as octyl, decyl, lauryl, oleyl or tallow amine and long chain diamines. The diamines correspond to the following general formula:
(C
n
H
2n+1
)—NH—(CH
2
)
2
—NH—R
wherein n represents an integer from about 12 to 18 and R is an alkoxide group. Alkoxylated alcohols are the preferred nonionic surfactants, especially alkoxylated tridecyl alcohol.
The amount of the nonionic surfactant present in the corrosion inhibitor composition is in the range of about 5 to about 20 weight percent and, preferably, in the range of about 10 to about 15 weight percent.
The corrosion inhibitor composition may be in the form of a solution or in the form of dispersion in either water or an organic solvent. Suitable organic solvents include alcohols s
Treybig Duane S.
Williams Dennis A.
Anthony Joseph D.
Breininger Thomas M.
Cummings Kelly L.
Ondeo Nadco Company
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