JPS6056080A - Anticorrosive for metal preventing formation of scale - Google Patents

Abstract

PURPOSE:To obtain an anticorrosive for metal preventing the formation of scale in a cooling water system or the like by blending polyphosphoric acid and/ or orthophosphoric acid with a copolymer consisting of prescribed monomers and styrenesulfonic acid. CONSTITUTION:The titled anticorrosive is composed of polyphosphoric acid and/ or orthophosphoric acid and a prescribed polymer. The polymer consists of 10-90wt% in total of maleic acid, maleic anhydride and a monomer having one or two carboxyl groups and 10-90wt% styrenesulfonic acid. The monomer having one or two carboxyl groups is represented by the formula (where each of R1- R4 is H, methyl or carboxyl, and one or two among R1-R4 are carboxyl).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a metal corrosion inhibitor that prevents scale formation in heat exchangers, piping, etc. in cooling water systems.

Prior Art Conventionally, there has been a method of adding polymerized phosphoric acids for the purpose of preventing corrosion of metals that come into contact with water in cooling water systems, etc.
It has been widely used. However, on the other hand, the addition of polymerized phosphoric acids as corrosion inhibitors has been viewed as a problem in that various secondary problems occur. For example, polymerized phosphoric acids are easily hydrolyzed in water by the action of heat and microorganisms to orthophosphoric acid, which has a poor anticorrosion effect.

In addition, orthophosphoric acid reacts with ions such as calcium, zinc, and iron in water to form scale deposits such as poorly soluble calcium phosphate, zinc phosphate, and iron phosphate, which inhibits heat transfer in heat exchangers. .

This causes problems such as blockage of waterways and crevice corrosion on metal surfaces.

Particularly in recent years, there has been a trend to minimize wastewater from cooling water systems in order to conserve water resources, eutrophication of lakes and marshes due to phosphorus-containing wastewater, and occurrence of red tide in inner bays. Residence time in the aqueous system increases and the potential for hydrolysis increases. At the same time, in the open circulation cooling water system, some of the cooling water evaporates, so reducing the amount of water discharged from the system increases the concentration rate of dissolved salts in the make-up water, which is added as a corrosion inhibitor. The orthophosphoric acid generated by the hydrolysis of the polymerized phosphoric acids promoted the formation of scale deposits.

Purpose of the Invention The inventors have conducted research for several years to overcome the various obstacles associated with the hydrolysis of polymerized phosphoric acids to orthophosphoric acid as described above, and as a result they have developed the present invention. I was able to complete it. That is, the purpose of the present invention is to solve problems in cooling water systems that use polymerized phosphoric acids as corrosion inhibitors, when the zero hydrolysis rate of polymerized phosphoric acid to orthophosphoric acid is high, or when orthophosphoric acids are added from the beginning. To provide a treatment agent for cooling water that exhibits a sufficient anticorrosion effect and can suppress the formation of poorly soluble phosphoric acid scale due to the reaction of orthophosphoric acid with cations in water. It is in. According to the present invention, pH control by adding acid to prevent phosphoric acid scale, such as conventional cooling water treatment using polymerized phosphoric acids, is not necessary in many cases. Furthermore, a sufficient anticorrosion effect can be expected even if orthophosphoric acids are added from the beginning instead of polymerized phosphoric acids.

Components of the Invention That is, the present invention relates to a metal corrosion inhibitor that prevents scale formation in a cooling water system, comprising (α) polymerized phosphoric acids and/or orthophosphoric acids, (h) maleic acid, maleic anhydride, and the following formula: and at least one monomer selected from the group consisting of monomers represented by; Here, R+, R2, Rs, and R4 are each independently hydrogen.

Methyl group or carboxyl group, R1゜&,
One or both of Rs and RJ are carboxyl groups, and a copolymer with styrene sulfonic acid.

Examples of polymerized phosphoric acids used in the present invention include chain phosphoric acids such as pyrophosphoric acid and tripolyphosphoric acid, monocyclic phosphoric acids such as trimetaphosphoric acid and tetrametaphosphoric acid, glassy polyphosphoric acids, ultrapolyphosphoric acids, and the like. Examples include water-soluble salts.

The orthophosphoric acids used in the present invention refer to phosphoric acids and water-soluble salts thereof. The water-soluble salt referred to here means that some or all of the protons of the phosphoric acid group are alkali metal,
Alkaline earth metal, zinc.

Substituted with ammonia and/or amines and soluble at the concentration used.

Examples of the above-mentioned copolymers in the present invention include copolymers of maleic acid or tua water, mashimaleic acid, tyrenesulfonic acid, acrylic acid and styrenesulfonic acid copolymers, methacrylic acid and styrenesulfonic acid copolymers, etc. can be given. The preferred polymerization ratio of the copolymer in the present invention is:
The total amount of (anhydrous) maleic acid and the monomer having a carboxyl group is 10 to 90 units (by weight), and the total amount of styrene sulfonic acid is 10 to 90 units (by weight). Further, the preferred molecular weight of the copolymer is 500 to 100 as a weight average molecular weight.
,0, O, more preferably 1,000 to 50,00
It is 0. In the copolymer of the present invention, some or all of the protons of carboxyl groups and sulfonic acid groups can be substituted with alkali metals, alkaline earth metals, zinc, ammonia and/or
Alternatively, it may be substituted with amines.

The orthophosphoric acids 9-polymerized phosphoric acids and copolymers may be added to the cooling water system alone, or may be added as a preparation with other compounds as necessary. These compounds and formulations are injected continuously or intermittently to maintain sufficient concentrations in the cooling water system to achieve corrosion protection and scale prevention. The amount of orthophosphoric acids and/or polymerized phosphoric acids added is 3 to 500 pPm (as PO4) as a total phosphoric acid concentration, but in most cases, after initial treatment with high concentration chemicals, 5 to 500 pPm is added. The Gero copolymer of the present invention, which can obtain a sufficient anticorrosion effect by maintaining 15 ppm (as PO4),
At a copolymer concentration lower than the stoichiometric ratio with respect to the concentration of cations in water, which is the source of poorly soluble scale,
It is possible to suppress phosphate scale. The preferred amount of the copolymer to be added depends on the pH2 temperature of the system, residence time, and orthophosphoric acid concentration.

It is determined by the cation concentration of scale species, etc.
Usually 1 to 200 pI)m is sufficient.

In the present invention, compounds that have conventionally been used in combination with polymerized phosphoric acids and orthophosphoric acids as cooling water treatment agents can also be used at the same time. Examples of these compounds include chromic acids, 9 dichromic acids, zinc salts, organic phosphonic acids, and organic phosphoric acid esters.

Lignosulfonic acids, tannins, azoles.

Examples include silicic acids and nitrites.

Next, the present invention will be explained in more detail with reference to Examples.

Copolymer example (I) Copolymer of maleic anhydride and styrene sulfonic acid (weight ratio 1:4) Molecular weight 5,000 ■ Copolymer of maleic anhydride and styrene sulfonic acid (
Weight ratio 1:1) Molecule t5,000 GID Copolymer of methacrylic acid and styrene sulfonic acid (weight ratio 2:1) Molecular weight 30,000 Example 1 and Comparative Example 1 The above copolymer and the copolymer The scale inhibition effect on phosphoric acid scale of the constituent homopolymer is shown.

Test water having the following water quality was prepared by dissolving calcium chloride, magnesium chloride, monobasic sodium phosphate, sodium bicarbonate, and zinc sulfate in deionized water. Ca
+250 pPm (as CaCQl).

Mg ++100 ppm (as CaC0,), H
CO3-1100pp (CaC0, closed), orthophosphoric acid 50 ppm (as PO4) *Z n”
10 ppl'n. The test compounds shown in Table 1 were added to the test water, and the l)H of the test water was diluted with ZO using NaOH.
Adjusted to. The test solution was placed in a sealed container and allowed to stand for 3 days in a constant temperature bath at 50°C.The test water was then filtered through a 0.45μ membrane filter and the phosphoric acid concentration was measured using the molybdenum blue method (JI).
SKOlol). The scale inhibition rate was calculated using the following formula. The test results are shown in Table 1.

In the formula, CA: Orthophosphoric acid concentration after the test of test water to which the test compound was added. CB: Test water to which the test compound was not added.

Orthophosphoric acid concentration Co: Initial concentration of orthophosphoric acid Table-1 Reference Example 2 and Comparative Example 2 This shows the anti-corrosion effect on steel when used in combination with phosphoric acid.

After pre-treating a steel test piece in accordance with JISKOloo (industrial water corrosion test method), it was immersed in test water and 1
It was rotated at 100 rpm. The water quality of the test water was M alkalinity 60 ppm, ICa hardness 1100pp.

Mg hardness was 50 ppm, chlorine ion was 6 sppm, sulfate ion was 52 ppm, and silica was 9.3 ppm. The pH of the solution after the test was 8.3 to 8.5. Add to test water
The test compounds and formulations shown in 2 were added and maintained at 50°C, and the test period was 18 hours. After the test was completed, the test pieces were immersed in hydrochloric acid (15%) containing a pickling corrosion inhibitor to remove rust, and then the corrosion loss was measured. The test results are shown in Table-2.

Table-1

Claims (1)

[Claims] 1. (α) polymerized phosphoric acids and/or orthophosphoric acids; (h) at least one monomer selected from the group consisting of maleic acid, maleic anhydride, and a monomer represented by the following formula; Here, R,1,R,, R8,R, are each independently hydrogen, a methyl group or a carboxyl group, but Rs,
A copolymer with styrene sulfonic acid, wherein one or both of R2-Rs and Ra are carboxyl groups; A metal corrosion inhibitor which prevents scale formation in a cooling water system. Claim 1, wherein the 2° copolymer comprises 10 to 90% by weight of the total amount of maleic acid, maleic anhydride, and a monomer having a carboxyl group, and 10 to 90% by weight of styrene sulfonic acid. corrosion inhibitor. 6. The molecular weight of the copolymer is 500 as a weight average molecular weight.
The corrosion inhibitor according to claim 1 or 2, comprising: -100,000. 4. The molecular weight of the copolymer is 1.0 as a weight average molecular weight.
00 to 50,000. 5. The corrosion inhibitor according to any one of claims 1 to 4, wherein the amount of the copolymer added is selected within the range of 1 to 200 ppm.