Corrosion inhibitor composition

Corrosion inhibitor composition:

A corrosion inhibitor for ferrous metals comprising four different components of:

(a) an inorganic acid component (such as molybdate or tungstate),

(b) an aliphatic hydroxycarboxylic or aliphatic dicarboxylic acid or its salt (such as citric acid, gluconic acid or succinic acid),

(c) An inorganic heavy metal compound, like zinc chloride or stannous chloride, is employed. A water-soluble polymer component with a molecular weight of NUM0, such as acrylic homo or copolymer, is particularly beneficial for water recycling systems.)

1. A composition comprising:

(a) one or more inorganic acid components of molybdic acid or its alkali salt, tungstic acid or its alkali salt, or the alkali salt of nitrous acid;

(b) an aliphatic hydroxycarboxylic acid or aliphatic dicarboxylic acid having up to seven carbon atoms or salt thereof;

(c) an inorganic heavy metal compound selected from the group consisting of the sulfate, the chloride, the nitrate and the sulfanate of zinc, manganese, tin, and, nickel, and mixtures thereof, which can readily release a heavy metal ion in water; and

(d) a water-soluble polymer component having a molecular weight in the range of 500 to 100,000 of a homo- or co-polymer of acrylic acid, methacrylic acid or maleic acid; or a copolymer of any said three monomers with other copolymerizable compounds having an ethylenic double bond; or a mixture of said homocopolymer and copolymer; the weight ratio of components a:b:c:d: being about 1:0.2-30:0.1-5:0.1-5.

2. The composition is item

It contains the alkali salt of molybdic acid, tungstic acid, or nitrous acid. The lithium, sodium, potassium, or ammonium salt is present in the composition.

3. The composition as item 1

wherein the salt of the aliphatic hydroxycarboxylic acid or aliphatic dicarboxylic acid is the alkali metal salt or salt with an aliphatic amine having 6 or less carbon atoms.

4. The composition as item 3

wherein the aliphatic amine is mono, di or tri-alkylamine.

5. The composition as item 1

wherein the aliphatic hydroxycarboxylic acid or its salt is citric acid, malic acid or gluconic acid, or its sodium, ammonium, cyclohexylamine or morpholine salt.

6. The composition as item 1

wherein the aliphatic dicarboxylic acid or its salt is glutaric acid, succinic acid, or adipic acid, or its sodium, ammonium, cyclohexylamine, or morpholine salt.

7. The composition as item 1

wherein the homopolymer and the copolymer as a water-soluble polymer component have a molecular weight in the range of 500 to 20,000.

8. The composition as item 1

wherein the weight ratio of (a):(b):(c):(d) is 1:0.5-10:0.1-1.5:0.2-1.6.

9. A method for inhibiting

The corrosion of ferrous metals in a water system comprising adding to the water system a composition comprising

(a) one or more inorganic acid components of molybdic acid or its alkali salt, tungstic acid or its alkali salt, or alkali salt of nitrous acid;

(b) an aliphatic hydroxycarboxylic acid or aliphatic dicarboxylic acid having up to seven carbon atoms or salt thereof;

(d) a water-soluble polymer component having a molecular weight in the range of 500 to 100,000 of a homo- or copolymer of acrylic acid, methacrylic acid or maleic acid; or a copolymer of any of said three monomers with other copolymerizable compounds having an ethylenic double bond; or a mixture of said homopolymer and copolymer, in a total concentration of said four components of 1 to 200 ppm; the weight ratio of components a:b:c:d being about 1:0.2-30:0.1-5:0.1-5.

10. Item 9

specifies that components (a), (b), (c), and (d) are individually added to the water system.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composition and a method for using the same for the prevention of ferrous metals in machines and equipment for using water in the petroleum industry, chemical industry, paper making industry, iron industry, and other industries.

2. Description of the Prior Art

In view of the worsening supply condition of industrial water, efforts are being made to save water by recycling. For instance, efforts are being made to reduce water to be discharged from the water cooling system and to run the boiler without blowing water. Recycling of water, however, involves problems. The recycled water increases in concentration of salts, which leads to the formation of scale and to cause corrosion of metals in contact with it. Thus, the measure for these problems, or the treatment of recycled water, is a matter of great importance.

In order to solve the problems, we have proposed a corrosion inhibitor composed of gluconic acid or a salt thereof, a molybdate, and a specific acrylic acid polymer, for high concentrated recycling water (Japanese Patent Publication No. 43376/1978); a corrosion inhibiting composition of an aliphatic dicarboxylic acid, molybdate and nitrite (Japanese Unexamined Patent Publication No. 62181/1980) and a corrosion inhibitor of an aliphatic dicarboxylic acid and nitrite (Japanese Unexamined Patent Publication No. 62182/1980).A Japanese Unexamined Patent Publication proposes a new corrosion inhibiting composition: polymaleic acid, an aliphatic hydroxycarboxylic acid, zinc ion, and a triazole act as its components.

SUMMARY OF THE INVENTION

The present invention provides a corrosion inhibitor for ferrous metals such as iron, mild steel, and cast iron in water systems, which can exhibit an excellent effect when added to water, especially high concentrated recycling water in an apparatus such as heat exchanger, cooler, radiator, boiler and so forth.

More particularly, this invention provides a corrosion inhibitor which contains as the active ingredients:

(a) one or more inorganic acid components of molybdic acid or its alkali salt, tungstic acid or its alkali salt, or alkali salt of nitrous acid;

(b) an aliphatic hydroxycarboxylic acid or aliphatic dicarboxylic acid having up to seven carbon atoms or salt thereof;

(d) a water-soluble polymer component having a molecular weight in the range of 500 to 100,000, of a homo- or copolymer of acrylic acid, methacrylic acid or maleic acid; a copolymer of any of said three monomers with other copolymerizable compound having an ethylenic double bond; or a mixture of said homopolymer and copolymer.

The inhibitor of this invention is non-phosphorous composition and is highly effective for preventing ferrous metal corrosion in high concentrated water recycling systems or a boiler operating at a high temperature of 100°-200° C., coincidently preventing scale formation in such a system.

PREFERRED EMBODIMENTS OF THE INVENTION

In this invention, alkali salts of molybdic acid, tungstic acid, and nitrous acid are used. Examples of these salts include lithium salt, sodium salt, potassium salt, and ammonium salt.Economically preferable among them are sodium molybdate, ammonium molybdate, sodium tungstate, sodium nitrite, and ammonium nitrite. They may be used in combination.

Glycolic acid, citric acid, malic acid, tartaric acid, lactic acid, gluconic acid, and tartronic acid are the aliphatic hydroxycarboxylic acids with a carbon number of 7 or less used in this invention. The aliphatic dicarboxylic acid having the carbon number of 7 or less includes, for example, glutaric acid, adipic acid succinic acid.

The salts of the above-mentioned carboxylic acids include, for example, alkali metal salts such as lithium, sodium or potassium salt and ammonium salt; and salts with aliphatic amines having 6 or less carbon atoms such as mono, di or tri-alkylamine (e.g., methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, or dimethylamine, diethylamine or dipropylamine, or trimethylamine or triethylamine), cyclic alkylamine (e.g., cyclohexylamine or morpholine), or mono, di or tri-hydroxyalkylamine (e.g., ethanolamine, propanolamine, 3-hydroxy-2-methyl-propylamine, diethanolamine or dipropanolamine).

If the hydroxycarboxylic acids or dicarboxylic acids having a carbon number greater than 7 are used, the resulting corrosion inhibitor decreases in corrosion inhibiting effect and in solubility in water. In addition, if they are used in the form of salt, the resulting corrosion inhibitor causes foaming due to increased surface activity and combines with the compounds that make water hard to form insoluble salts which pass into sludge and scale.

An aliphatic amine having 7 or more carbon atoms reacts with a hydroxycarboxylic or dicarboxylic acid salt. The resulting corrosion inhibitor is more surface-active.

In situations involving the utilization of an aliphatic hydroxycarboxylic acid, it is advisable to consider citric acid, malic acid, and gluconic acid, as well as their sodium salt, ammonium salt, cyclohexylamine salt, and morpholine salt counterparts. In the case of using an aliphatic dicarboxylic acid, glutaric acid, succinic acid, and adipic acid, along with their sodium salt, ammonium salt, cyclohexylamine salt, and morpholine salt, are the preferable options.

Among the above-mentioned components, the preferable ones are: – Gluconic acid, succinic acid, citric acid, malic acid, glutaric acid, and adipic acid – Sodium salts, cyclohexylamine salts, and morpholine salts thereof.This suggests that the action on metals differs even among homologous compounds, depending on the functional group contained therein.

Sulfates, chlorides, nitrates, and sulfamates are some compounds capable of releasing heavy metal ions in water. These compounds include sulfates, chlorides, nitrates, and sulfamates of zinc, manganese, tin, cobalt, nickel, titanium, copper, and lead. Additionally, combinations of these compounds can also release heavy metal ions in water. Manganese and tin salts are most preferred and effectively used as corrosion inhibitors in boiler water, inhibiting corrosion in the boiler system with manganese and tin salts.

The water-soluble polymer utilized in this invention is either a polymer or copolymer of acrylic acid, methacrylic acid, or maleic acid. Its molecular weight ranges from 500 to 100,000, with a preference for 500 to 20,000. Examples of this polymer or copolymer include: Homopolymers of acrylic acid Homopolymers of methacrylic acid Homopolymers of maleic acid Mixtures thereof.Additionally, copolymers or terpolymers can be formed by combining these monomers with a copolymerizable compound containing an ethylenic double bond, such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylamide, methacrylamide, acrylamide-N propanesulfonic acid, fumaric acid, itaconic acid, and vinyl alcohol.

The copolymers should contain at least 20 mol% of any of the three monomers mentioned. A preference exists for 50 mol% or more of these monomers in the copolymers. Acrylic acid homopolymer Methacrylic acid homopolymer Maleic acid homopolymer Acylic acid-methacylic acid copolymer 5. Acrylic acid-maleic acid copolymer 6. Methacrylic acid-maleic acid copolymer 7. .Acrylic acid-acrylamide copolymer 8. Acrylic acid-acrylamide-N-propanesulfonic acid copolymer 9. /Acrylic acid-methacrylic acid-methyl acrylate terpolymer

2

The above-mentioned homopolymers or copolymers should be soluble in water and have a molecular weight of about 500 to 100,000. Flocculation is a tendency shown by polymers with a molecular weight greater than NUM0, which makes them less preferred due to this property, despite their solubility in water. In terms of synthesis convenience, it is preferable to use an acrylic acid polymer or methacrylic acid polymer.

The molecular weight of these polymers should range from approximately NUM0 to NUMA. Additionally, a maleic acid homopolymer with a molecular weight of about NUM2 to NUMA is also favored. When the molecular weight of the polymer falls within the specified range, it is not soluble in water. You can improve its solubility by converting its acid or ester groups into soluble salts, such as alkali metal salts, ammonium salts, or amine salts.

We formulate four components into a liquid formulation, or we mix them directly into a powdery formulation as their constituents. The aqueous solution should be neutral to alkaline.If it is acidic, molybdic acid or tungstic acid liberates and condenses. Or, nitrous acid decomposes. Alternatively, aliphatic hydroxycarboxylic acid oxidizes slowly. Thus, it is desirable to add an alkali such as sodium hydroxide and lower amine to adjust the pH.

The preferred weight ratio that permits the four components to exhibit their synergistic effect is 1:0.2-30:0.1-5:0.1-5, preferably 1:0.5-10:0.1-1.5:0.2-1.6, for (a):(b):(c):(d) by weight. In the case of liquid formulation, the total concentration of the four components is dependent on the solubility and pH of each component. A concentration of 5 to 60 wt% is suitable from the standpoint of stability of the formulation. In addition, the liquid formulation may contain a small quantity of stabilizer and other additives.

Add an amount of 1 to NUM0 ppm, preferably 15, of the formulation composed of the above-mentioned four components to the water. to 100 ppm, in terms of the total quantity of the four components, depending on the water quality and the area that requires corrosion inhibition.

Thus, the present invention provides a method for corrosion inhibition of metals.Each of the compounds (a, b, c, and d) can individually form a single formulation when added to water.

The corrosion inhibitor of this invention is effective for preventing heat exchangers, coolers, radiators, boilers, and the like from water corrosion. When incorporated into recycled water with elevated salt levels, it proves to be highly effective. It shields ferrous metals from corrosion and pitting, while also hindering scale buildup.

The mechanism by which the four components of this invention interact with the metal surface remains unclear. The combined passivating, dispersing, and film forming actions of the four components create a robust protective layer. Their superior performance supports this. This is backed up by their outperforming the other three.

The following non-limitative examples describe the invention in detail.

TEST 1

We conducted corrosion inhibition tests using corrosion inhibitors composed of the above-mentioned four components in varied quantities.

So, we used a stainless steel stirring rod to suspend a mild steel (SPCC). Test specimen with dimensions of 30×50×1 mm. We then submerged the liter of test solution with predetermined chemical concentrations in a flat-bottomed beaker. Placed it surrounded by a circular mantle heater that maintains a constant water temperature through a thermostat. A motor rotated the stirring rod at NUM0 rpm during the five-day experiments. While stirring continued, I maintained the water temperature at 50°C. Five times, I diluted city water from Osaka City to prepare the test solution. Table 1 details the characteristics of the test solution.

TABLE 1 Item Value pH

8.3Electric conductivity (μs/cm) 910.2P alkalinity (ppm) . 0M alkalinity (ppm) 71.0Total hardness (ppm) 238.8Chloride ion (ppm) 94.5Sulfate ion (ppm) 172.0Silica (SiO2) (ppm) 28.5Total iron (ppm). 0.50Calcium hardness (ppm) 190.0

After the prescribed testing period, we removed the test piece and dried it. We then measured its weight and recorded the result as M1 (mg). We treated the test piece according to JIS KNUM0 and measured its weight again. The result was recorded as M2 (mg). The m.d.d. (mg/day.dm2) was calculated according to the following formula:

m.d.d.=(A-M2)/(B×C)=D/0.3142×5

where:

A: Weight (mg) of test piece before testing,

B: Area (dm2) of test piece,

C: Number of days of test, and

D: Corrosion weight loss.

After completing the test, we filtered NUM0 ml of the test liquid using Toyo Filter Paper No. 6. We then dried the solids at NUM0°C for one day and measured their weight.To find the weight of the substance, we subtracted M1 from M2.) The formula defines the quantity of scale formed. Active voice

Scale (mg/liter)=P×2+(M1 -M2)

where P: dry weight of precipitates.