JPS60225697A - Scale inhibitor - Google Patents

Abstract

PURPOSE:To enhance the adhesion inhibiting effect of siliceous scale, by using a reaction product obtained by reacting starch and hydrogen peroxide under a specific condition as a chemical agent. CONSTITUTION:The quantity ratio of starch and hydrogen peroxide is set so that hydrogen peroxide is 1.5-4.0 equivalent to one equivalent of the glucose residue of starch. Reaction pH is adjusted to 4 or less at the beginning of reaction and the iron ion in a reaction liquid is allowed to be present in a concn. range of 0.5-10ppm. In reaction, a temp. is set to 80 deg.C or more and a heating reaction time is set until added hydrogen peroxide almost disappears. Thus obtained heating reaction product is added to an aqueous system as it is or after concn. or neutralization.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a scale inhibitor, and particularly to a scale inhibitor that exhibits an excellent prevention effect on the deposition of aqueous silica scale.

"Prior Art and Problems" With the recent development of industry, a huge amount of water is being used, and it is desired to conserve cooling water, which is in high demand.

Therefore, in buildings, factories, etc., magnesium ions, (bi)carbonate ions, sulfate ions, silicate ions, etc. accumulate when cooling water is recycled, resulting in the use of sparingly soluble salts and adhering to heat exchangers, reducing the heat exchange rate. This can cause scale problems such as a drop in water and blockage problems.

In particular, silica compounds, which are formed when accumulated silicate ions combine with calcium ions, magnesium ions, etc., have low thermal conductivity, so even a small amount of silica compounds attached to them can cause problems.

Another problem is that silica compounds are hard and, once attached, are difficult to remove by mechanical cleaning or chemical cleaning such as hydrochloric acid.

Problems caused by such silica-based scales are seen not only in cooling water systems, but also in water systems such as boiler water systems and geothermal power generation equipment.

Traditionally, commonly used scale inhibitors include:
There are phosphorus-containing compounds such as polymerized phosphates and phosphonic acids, and synthetic polymer electrolytes such as polysodium acrylate and polymaleic acid, but none of these are effective against scales such as calcium carbonate and magnesium hydroxide. However, it has almost no effect on silica scale. Therefore, although various drugs effective against silica scale have been studied, none of them have been put into practical use because their effects are insufficient or the amount used is too large.

British Patent No. 1,291,895 discloses that a starch derivative obtained by adding 1 to 25% by weight of hydrogen peroxide/starch to an aqueous dispersion of starch and heat treating the resulting starch derivative can be used as a scale inhibitor. As a result of the inventors' study of the starch derivative, calcium carbonate scale,
Although it is effective against magnesium-based scale, it is almost as effective against silica-based scale as conventional polyacrylic acid-based inhibitors, and a sufficient scale prevention effect was not observed.

In addition, the present applicant previously filed an invention for a scale inhibitor comprising an oxidized polysaccharide (Japanese Patent Application No. 187294/1982).

The scale preventive agent according to the invention of the earlier application shows a considerable effect on silica scale compared to conventional agents, but
It has been found that the effect is not necessarily sufficient in aqueous systems where significant adhesion of silica scale is observed.

``Means for Solving the Problem'' Therefore, the present inventors developed a drug that exhibits excellent performance even when a small amount of silicate ions are present in the aqueous system and a significant amount of silica scale is observed. As a result of extensive research, it was discovered that a product made by heating starch and hydrogen peroxide under acidic conditions and reacting at high temperatures in the presence of a trace amount of iron ions could achieve this goal.

That is, in the present invention, 1.5 to 4 equivalents of hydrogen peroxide are added to 1 equivalent of glucose residue in starch, the pH of the reaction solution is set to 4 or less, and the iron ion concentration in the reaction solution is set to 0.5.
It relates to a scale inhibitor consisting of a product obtained by heating at a reaction temperature of 80° C. or higher in the presence of ~10 ppm.

In producing the scale inhibitor of the present invention.

The conditions for the heating reaction between starch and hydrogen peroxide must be strictly observed.

That is, the ratio of starch to hydrogen peroxide is 1.5 to 1.5 to 1.5 to 1.5 to 1 equivalent of starch glucose residue.
It is necessary that the amount be in the range of 4.0 equivalents. In particular, 2 equivalents of hydrogen peroxide gives the best effect per 1 equivalent of the glucose residue. When the ratio of starch to hydrogen peroxide is outside the above range, the effectiveness is significantly reduced.

In addition, in the present invention, it is necessary that the reaction pH of the gluten residue is 4 or less, and if it is higher than that, an effective product cannot be obtained. Since the pH tends to decrease during the reaction, it is generally only necessary to adjust the pH to 4 or less at the start of the reaction. It is necessary to adjust the iron ion concentration in the reaction solution to a range of 0.5 to 10 ppm, but in general, the lower the pH at the start of the reaction, the better the iron ion concentration is to be in a trace amount. For example, if the pI at the start of the reaction is about 6.5, the iron ion concentration in the reaction solution is about 8 ppm, and if the pH is about 1.0, the iron ion concentration is about 2 ppm. It's good.

The reaction temperature must be 80°C or higher, and 80°C
At temperatures lower than that, the reaction will not proceed and only an almost ineffective product will be obtained. There is no specific upper limit for the reaction temperature, but in general it is sufficient to carry out the reaction at normal pressure in an aqueous system, so the upper limit is approximately 1.
The temperature is below 00℃.

Examples of the starch used in the present invention include corn, amashiyo, potato starch, wheat starch, etc.
Modified starches such as esters and etherified products of these can also be used.

However, from the viewpoint of price and availability, it is usually preferable to use corn starch.

6- Furthermore, the hydrogen peroxide used in the present invention is a hydrogen peroxide solution having various concentrations, but is usually a 60 to 60% by weight aqueous solution.

In the present invention, the reaction is carried out in the presence of a trace amount of iron ions in the reaction solution, but there are no particular restrictions on the substance that can donate trace amounts of iron ions as long as it is capable of causing iron ions to be present in the reaction solution. Na~・ga1 Usually ferrous sulfate, ferric sulfate.

Inorganic iron salts such as ferrous chloride and ferric chloride may be used.

Moreover, the heating reaction time for obtaining the scale inhibitor of the present invention may be carried out until the added hydrogen peroxide almost disappears, and is usually in the range of 5 to 10 hours. If starch can be used in the reaction, it can be a good scale inhibitor. However, since the heated reaction product can be used as it is as a scale inhibitor, if the starch or hydrogen peroxide concentration is too dilute, there will be disadvantages in transportation. Conveniently, the hydrogen oxide is reacted as a 30-60% by weight aqueous solution.

The scale inhibitor of the present invention can be used as a heated reaction product as it is,
Alternatively, it may be added to the aqueous system after concentration, neutralization, etc., and the addition method may be continuous or intermittently added to the aqueous system.

Further, the amount of the scale inhibitor of the present invention added to the aqueous system varies depending on the operating conditions and water quality of the target aqueous system, but is generally 1 to 100 ppm, preferably 5 to 50 ppm based on the concentration of raw starch. be. Even if 50 ppm or more is added, no significant improvement in the effect is observed.

In addition, the present applicant has an earlier application (Japanese Patent Application No. 187294/1983)
K in the specification disclosed that a starch derivative obtained by oxidizing starch with hydrogen peroxide in the presence of an iron salt is effective as a scale inhibitor. The scale inhibitor according to the prior invention and the scale inhibitor of the present invention have different products as active ingredients. That is, the active ingredient of the prior invention is a starch derivative in which carboxyl units are introduced by cleaving the glucose groups of starch through an oxidation reaction, but in the present invention, it is not essential to cleave the glucose groups and introduce carboxyl units. , the active ingredient is a product obtained by simply heating the reaction.

The fact that the heated reaction product as a scale inhibitor of the present invention is different from the product of the prior invention is recognized in the Examples described below, and is also clear from the differences in the manufacturing method and properties as described below.

b) In the present invention, a heating reaction is carried out at high temperature in the presence of a trace amount of iron ions, but in order to obtain the object of the prior invention, a relatively large amount of iron ions are present and the reaction is accomplished at around room temperature.

(1) The reaction product of the present invention is neutralized and does not form a precipitate even when a large excess of methanol is added, but the target product of the prior invention can be neutralized by adding an excess of methanol to the reaction product and causing precipitation. can get.

C) Viscosity of the reaction product of the present invention (25°C, B-type viscometer)
is 19-Cp8 or less at 20% by weight based on starch, but that of the prior invention is 2-3CpS.
within the range of

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

Production Example 1 The scale inhibitor of the present invention was produced using corn starch as the starch. In a 500 m/four-eye flask equipped with a stirrer, thermometer, and reflux condenser, add 45.2.1 iT of corn starch (gelcol residue:
0.28 equivalent as anhydride 162I) in pure water 10
It was suspended in 01R1 and added. 35% by weight hydrogen peroxide solution under stirring 54. 49 (o, 56 equivalent i!:) and ferrous sulfate (FeS04.7H20) in an amount such that the iron ion concentration in the reaction solution is 2 ppm (■/l), and the pH was adjusted with sulfuric acid.
was adjusted to 1.0. While stirring, the reaction solution was heated to 90°C in a hot bath.
The temperature was raised to 90℃, and the hydrogen peroxide concentration in the solution was 0.1 at 5℃.
% or less. The time required was 7 hours.

After cooling the resulting reaction solution, water was added to give a concentration of 2% based on starch.
The reaction product (1) of the present invention was obtained by adjusting the amount to 0% by weight.

Production Example 2 Production was carried out in the same manner as Production Example 1, except that the addition equivalent ratio of starch and hydrogen peroxide, the adjusted pH at the start of the reaction, the iron ion concentration in the reaction solution, or the type of iron salt used were changed. , 20% by weight based on starch, the reactant of the present invention (2) - (
6) was obtained. Table 1 shows the manufacturing conditions for obtaining the reactants (2) to (6) of the present invention. The reaction product (3) of the present invention was reduced to 20% by weight by concentrating the product.

Production example 3 Corn starch 45.2.9 in pure water 100dK
Make WA cloudy and add 35% by weight hydrogen peroxide 108.8
J7 and 0.1g of ferrous sulfate (Fe5O4JH20) (
Iron ion concentration in the reaction solution (100 ppm) was added, pI was adjusted to a range of 2 to 4 with sulfuric acid under stirring, and reaction was carried out at 25° C. for 2 hours with external cooling.

After the reaction, the resulting solution was adjusted to pH 6.5 with sodium hydroxide,
By repeating precipitation with a large excess of methanol, starch oxide containing 69.2% carboxyl units was obtained.
17.1.9 (anhydrous) was obtained.

Production Example 4 According to Example 7 of British Patent No. 1,291,895, 10 g of 35% hydrogen peroxide was added to 100 g of starch, and a starch derivative was prepared by heating at 60° C. for 3 hours.

Example 1 Reagents magnesium sulfate (MISOs-7HzO), sodium hydrogen carbonate (NaHCO3), metasilicic acid pH 8
, 5 test water was prepared. To achieve a predetermined concentration in advance,
The scale inhibitor of the present invention was added to cause magnesium silicate scale to adhere to the heater surface. The test water was circulated through the cooling pipe so that the temperature inside the beaker was 65°C.

Also, the test solution is 17! Supply and discharge at a rate of /hr, 1
The test time for each test was 5 hours. The attached scale was scraped off, and the sample was dried at 110° C., weighed, and calculated as the amount of attached material per 100 d.

Starch oxide obtained in Production Example 3 for comparison.

The starch derivative of Preparation Example 4 and a commercially available scale inhibitor were also tested.

The results are shown in Table-2. As can be seen from Table 2, it is recognized that the scale inhibitor of the present invention has an extremely excellent effect on silica scale.

@5- As is clear from the above examples, the scale inhibitor of the present invention has an excellent prevention effect even when used in a small amount, and exhibits an extremely excellent effect on silica scale in particular.

Although the inhibitor of the present invention has excellent performance on its own, it can also be used with conventionally used agents such as polymerized phosphates, phosphonic acids, sodium polyacrylate, polymaleic acid,
It is even more effective when used in combination with the oxidized polysaccharide into which carboxyl units of the prior invention have been introduced.

It is of extremely high industrial value, not only because it can be used for commercial purposes, but also because it uses inexpensive starch and hydrogen peroxide, and the reaction is easy to carry out, making it advantageous in terms of price and production equipment.

Patent applicant: Mitsubishi Gas Chemical Co., Ltd. Representative Kazuyoshi Nagano 118-

Claims (1)

[Claims] 1.5 to 4 equivalents of hydrogen peroxide is added to 1 equivalent of glucose residue in starch, the particle size of the reaction solution is set to 4 or less, iron ion concentration is present in the reaction solution of 0.5 to 10 ppm, and the reaction is carried out. A scale inhibitor consisting of a product obtained by heating at a temperature of 80°C or higher