JPS60218487A - Anticorrosive for metal - Google Patents

Abstract

PURPOSE:To obtain an anticorrosive for metal in a water system with improved effectiveness by adding oxidized polysaccharides having specified carboxyl units as essential structural units and a water soluble zinc salt as principal components. CONSTITUTION:This anticorrosive for metal contains oxidized polysaccharides having carboxyl units represented by the general formula [where A is CH2OR or COOM, R is H or (CH2)nCOOM, and M is H, an alkali metallic ion or an ammonium group] as essential structural units and a water soluble zinc salt as effective components in about 20:1-1:2 weight ratio when the zinc salt is expressed in terms of Zn<2+>. The anticorrosive is added to a water system so that it is contained at about 1-100ppm concn. The anticorrosive shows a significant synergistic effect by combinedly using the compounds.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a corrosion inhibitor for metals in water, and more particularly to a corrosion inhibitor for metals, metal materials, etc. in fresh water.

"Prior Art and Problems" Conventionally, in freshwater, for example, in an open circulating cooling water system,
゛In order to prevent corrosion of metal materials such as heat exchangers, piping, pumps, etc., especially mild steel, anticorrosive agents consisting of phosphorus-containing substances such as polymerized phosphates and phosphonic acids, or a combination of these and water-soluble zinc salts. has been used.

However, when polymerized phosphate-based corrosion inhibitors are disposed of as wastewater,
It causes problems such as causing eutrophication of sea areas, rivers, lakes, etc., and is hydrolyzed in water to produce orthophosphoric acid, which causes calcium phosphate scale problems.

On the other hand, although phosphonic acids have improved their resistance to hydrolysis in water, they are still phosphorus-containing substances and inevitably cause eutrophication. It has the disadvantage that it is inferior to

In addition, as metal corrosion inhibitors that do not contain phosphorus, those whose main ingredients are oxycarboxylic acids such as citric acid, and synthetic polymer electrolytes such as polyacrylic acid and polymalenic acid are being considered; It is difficult to put it into practical use due to performance and price aspects.

``Means for solving problems'' It has been found that extremely significant anticorrosive effects can be obtained.

That is, the present invention relates to the general formula; [wherein A represents CH20R or C00M, and R
is a water-soluble The present invention relates to a metal corrosion inhibitor containing a zinc salt as an active ingredient.

The oxidized polysaccharide used in the present invention is obtained by oxidatively cleaving a polysaccharide having a six-membered monosaccharide ring, as described in the specification of the applicant's earlier application (Japanese Patent Application No. 187294/1982). It contains a carboxyl unit as an essential structural unit.

The oxidized polysaccharide contains at least one glucose unit in the molecule.
It is preferable to use one that has been modified to have 0%, preferably 40% or more carboxyl units. The molecular weight of these oxidized polysaccharides cannot be specified because they vary depending on the starting material and the oxidation method, but they are generally low molecular weight polymers with a significantly lower degree of polymerization than the starting material.

These are generally made by oxidizing polysaccharides such as starch or cellulose or their carboxymethyl etherified products as a starting material with sodium hypochlorite or halogens such as chlorine to cleave glucose groups and introduce carboxyl groups. Examples include those in which an aldehyde group is introduced by cleaving a glucose group with periodic acid or the like (commercially available as dialdehyde starch), and then the aldehyde group is converted into a carboxyl group with a halogen or the like. Among these, starch oxidized with halogen is preferred as a raw material, particularly from the viewpoint of reactivity and cost.

The water-soluble zinc salt used in the present invention is capable of dissociating zinc ions (Zn'') in water, and specific examples thereof include zinc sulfate and zinc chloride.

In the present invention, oxidized polysaccharide and water-soluble zinc salt (Zn2
It is preferable that the blending ratio of (calculated as +) is 20:1 to 1:2 (weight ratio), particularly 5:1 to 2:1.

The oxidized polysaccharide and water-soluble zinc salt may be blended in advance before use and then added to water, or may be added separately and blended in water. The amount added varies depending on the water quality of the target water system, operating conditions, etc., but is generally such that the concentration in water is 1 to 100 ppm.

In a normal open circulation cooling water system, the initial
-100 ppm, and then the retained concentration in water was adjusted to 5-2. A sufficient corrosion prevention effect can be obtained by setting the amount to Oppm.

"Effects of the Invention" The metal anticorrosive agent of the present invention has only a slight anticorrosion effect when each of the active ingredients, oxidized polysaccharide and water-soluble zinc salt, is used alone, but when used together, an extremely high synergistic effect is achieved. show.

In particular, the oxidized polysaccharide itself constituting the anticorrosive agent of the present invention is significantly inferior to the conventionally used or studied polymerized polysaccharides such as phosphonic acids, polymaleic acids, etc. The degree of improvement in the effect when used in combination with water-soluble zinc salts is extremely excellent, showing a much better synergistic effect than when conventional drugs are used together with water-soluble zinc salts.

The reason why the combination of the oxidized polysaccharide of the present invention and the water-soluble zinc salt has a particularly excellent synergistic effect is unknown, but the carboxyl unit of the oxidized polysaccharide used in the present invention is It is thought that the fact that they are combined has an important meaning.

According to the present invention, the combined use of an oxidized polysaccharide containing a carboxyl unit and a water-soluble zinc salt not only provides excellent performance, but also provides superior effects with a small amount of use. , which provides an inexpensive metal corrosion inhibitor.
It is extremely significant industrially.

"Effect" and "Examples" The present invention will be explained below with reference to production examples and examples.

Production Line Drawing 11 Production of Typical Oxidized Polysaccharides Used in Ashikusuru Imei Corn starch, cellulose, and carboxymethyl cellulose (CMC) were synthesized as polysaccharides using sodium hypochlorite as an oxidizing agent. The addition equivalent ratio of polysaccharides and available chlorine in sodium hypochlorite is 1=2, and 2096
30°C with pH maintained at 8.5 with sodium hydroxide solution.
The mixture was allowed to react for 4 hours. Methanol was added in an amount three times the amount of the liquid after the reaction to precipitate the target product. After repeating reprecipitation with methanol and confirming that chlorine ions were no longer detected, the precipitate was separated and dried at 50°C.

The yield and the content of carboxyl units in the product were determined by conductometric titration. The results are shown in Table-1.

Production Example 2 Production example of oxidized polysaccharide used in the present invention using commercially available dialdehyde starch as a starting material Commercially available dialdehyde starch [manufactured by Nippon Carlit, trade name: Caldas, containing 70% dialdehyde units] 20g 1 water 1oom, glacial acetic acid som
to > 80g of sodium chlorite (80%) in the mixture
was added and reacted for 4 hours.

After removing chlorine dioxide by passing nitrogen into the reaction solution, 409
The pH was adjusted to 8.5 with sodium hexahydroxide.

After that, the same method as in Production Example 1 was carried out by ζ straining, purification, measurement and analysis, and oxidized polysaccharide 21 containing 46.5% carboxyl units.
, '5 g was obtained.

Example 1 Using the compound (1) of Production Example 1 and zinc sulfate (calculated as Zn2+) as a water-soluble zinc salt, anticorrosive agents were prepared with varying blending ratios, and when 15 p, pm was added. The anticorrosion effect was investigated.

2! An anticorrosive agent was added to a beaker containing synthetic cooling water at 40°C.

A mild steel test piece (JIS G 3141 5PC) was placed in this water.
CB, disc type sq, 25d) was tested using the active ingredient of the present invention alone, and using sodium hexametaphosphate, phosphonic acid, sodium polyacrylate, and polymaleic acid.

Water-soluble inorganic salts other than water-soluble zinc salts were also tested.

The results are shown in Table-2, Table-5 and Table-4. Table-2, Table-
6 and Table 4, the oxidized polysaccharide of the present invention has only a slight effect by itself compared to other drugs, but when used in combination with a water-soluble zinc salt, the effect is dramatically increased. It is recognized that the amount increases.

The synthetic cooling water contains the reagent calcium chloride (CaC#
, 2H20), Magnesilla sulfate A (MgSO4
-7H20), calcium sulfate (C08O2-2H20
), sodium hydrogen carbonate (NaHCO3) was used to adjust the water quality to the following.

Synthetic cooling water quality table-2 Table-3 Example 2 Regarding the case where the compound of Production Examples 1 and 2 and the water-soluble zinc salt (using zinc chloride, calculated as Zn) were mixed at a ratio of 3+1 and the amount added was changed. The anticorrosion effect was evaluated using the same method as in Example 1.

The results are shown in Table-5. As can be seen from Table 5, it is recognized that a good anticorrosion effect is obtained even if the starting material of the oxidized polysaccharide is cellulose or CMC, or even if it is sodium chlorite oxide of dialdehyde starch.

Table 5 Example 3 Using the same method as Example 1, the compound 2+ (1) of Production Example 1 and zinc chloride (calculated as Zn) were mixed at a ratio of 3:
1, a 15-day test was conducted. The amount of the drug added is 50 or 100 ppm (initial addition amount),
One day later, the test solution was renewed and 5-20 ppm of the drug was added (maintenance addition it) and continued for an additional 12 days. The test solution was renewed once every 3 days, and the drug was adjusted to the maintenance addition lid each time.

The mdd value (W9/dm·day) was determined from the corrosion weight loss after 13 days.

The results are shown in Table-6. As shown in Table 6, in the initial stage 5
By adding ~100 ppm, then 5~2
(It is recognized that a sufficient anticorrosion effect can be obtained even with the addition of a small amount of lppm.

Table-6

Claims (1)

[Claims] [In the formula, A represents CH20R or C00M, R is H or (CH2) n -C00M, n is an integer from 1 to 6, and M represents H or an alkali metal ion or an ammonium group. . ] A metal anticorrosive agent characterized by containing an oxidized polysaccharide containing the carboxyl unit shown as an essential structural unit and a water-soluble zinc salt as active ingredients.