JPH036226B2 - - Google Patents

Description

[Detailed description of the invention]

(A) Object of the Invention (Field of Industrial Application) The present invention relates to a method for suppressing the adhesion of sludge caused by anticorrosive agents in systems using seawater.
More specifically, the present invention relates to a method for preventing corrosion while preventing divalent iron ions, which are used to prevent corrosion of non-ferrous metals by seawater, from turning into iron oxide sludge that causes various problems within the system. (Prior Art) Currently, seawater is used as cooling water in many factories because of its low cost. however,
Seawater has the disadvantage of being more corrosive than ordinary fresh water. Therefore, non-ferrous metals (such as copper, zinc, aluminum, or various alloys thereof) that have excellent properties and good thermal conductivity generally have high corrosion resistance against fresh water, and have sufficient corrosion resistance against seawater. However, since last year, when seawater pollution was particularly severe, S ^2- ions were sometimes contained at mg/mg levels, and as they have high reactivity with metals, corrosion of these non-ferrous metals has become more serious. It has become a thing. As a countermeasure to these problems, a method of adding divalent iron ions was discovered overseas, and it gradually began to be adopted in Japan over ten years ago. This method is based on the fact that divalent iron ions form a strong iron oxide film as an anticorrosive agent on the surface of the nonferrous metal, which exhibits excellent anticorrosion performance. In this case, divalent iron ions first form an intermediate called hydroxy iron oxide in water, which then changes to trivalent iron oxide, and this hydroxy iron oxide acts on the surface of the metal to form a dense film. This substance is considered to be an important factor. On the other hand, trivalent iron ions do not have such a mechanism and are therefore considered to be less effective. Currently, divalent iron ions are usually added continuously or intermittently in a range of about 0.01 to 5 mg/distance, but considerable attention is paid to the position of addition. This is because divalent iron ions and hydroxy iron oxide have relatively short lifetimes. In addition, although there is a tendency to keep the amount added to the minimum necessary amount, the amount of added 2
It is virtually impossible for all of the valent iron ions to participate in film formation, and therefore a small amount of 2, which is not always used, is
Valent iron is still present, which converts to iron oxide (Fe ₂ O ₃ ) within a short time in water. The problem is that this not only adheres to the system piping and turns into scale and even sludge, contaminating the system, but especially if it adheres to heat transfer surfaces, it reduces the heat transfer effect and damages the entire system. It reduces functionality. In order to solve this problem, several proposals have been made to prevent sludge and scale by improving physical operations. Among these methods, a method using a sponge ball has been particularly used. This is a ball made of sponge with an abrasive such as carborundum attached to its outer surface.
This is a method of physically removing the sludge by forcing it to circulate inside the pipes where the sludge is attached. (Problems to be Solved by the Invention) However, physical adhesion suppression methods such as the above-mentioned sponge ball type pipe cleaning treatment have a very strong abrasive effect, so if used for a long period of time, the pipes may become damaged. There was a problem in that it caused significant wear. The present invention provides a method that solves these problems. (b) Structure of the invention Thus, according to this invention, two
When adding valent iron ions to prevent corrosion of non-ferrous metals in the system, the formation of iron oxide sludge is suppressed by adding an aliphatic oxycarboxylic acid having 10 or less carbon atoms or an alkali metal salt or ammonium salt thereof. Provided is a method for preventing corrosion of non-ferrous metals, which is characterized in that corrosion protection is performed at the same time. Specific examples of aliphatic oxycarboxylic acids having 10 or less carbon atoms or their alkali metal salts or ammonium salts as used in the present invention include glycolic acid, lactic acid,
Oxymalonic acid, malic acid, citric acid, isocitric acid, glyceric acid, tartaric acid, oxyglutaric acid, gluconic acid and its potassium, sodium,
Examples include, but are not limited to, ammonium salts. Among these, particularly preferred are citric acid, tartaric acid, malic acid, gluconic acid, and their sodium or ammonium salts. Of course, it is also possible to use two or more of such additive components in combination. The concentration of the aliphatic oxycarboxylic acid having 10 carbon atoms or less or its alkali metal salt or ammonium salt can be changed as appropriate depending on the amount of divalent iron ion used as an anticorrosive agent, but it is usually about 0.01.
When ~5 mg/divalent iron ions are present, approx.
0.0002 to 5 mg/, more preferably about 0.001 to
It is 1 mg/. However, if a larger amount of divalent iron ions is added for some reason, for example due to intermittent addition or prevention of sea life, approximately 20mg/
If a higher amount is used, a corresponding addition concentration of about 0.1 to 20 mg/g is appropriate. As described above, the ratio of the aliphatic oxycarboxylic acid having 10 or less carbon atoms or its alkali metal salt or ammonium salt to divalent iron ion is usually 1:0.01 to 1:1, more preferably 1:1. :
It may be added in a ratio of 0.02 to 1:0.2. The aliphatic oxycarboxylic acid having 10 or less carbon atoms or its alkali metal salt or ammonium salt, which is an additive component of the present invention, can be used as it is in the form of powder or tablet. It can also be added directly into the sea or in the form of a suitable solid that gradually dissolves in the sea. Usually, it is preferable to use a solution prepared by dissolving it in water or a water-soluble solvent such as alcohol. In some cases, it can also be added to the system as a mixed solution in an appropriate ratio with ferrous sulfate (FeSO ₄ ), which is mainly used as a source of divalent iron ions, just before use. Therefore, according to another aspect of the present invention, there is also provided a nonferrous metal corrosion inhibitor containing a ferrous ion supplying compound and an aliphatic oxycarboxylic acid having 10 or less carbon atoms, or an alkali metal salt or ammonium salt thereof. (Example) Next, the present invention will be described with reference to Examples. Example 1 A sludge invention suppression ability test was conducted using Seto Inland Sea seawater as the test liquid. First, a 1% ferrous sulfate aqueous solution was added in advance to a colorimetric tube so that the concentration of divalent iron ions in 100 c.c. of seawater was 20 mg/c. An iron ion dispersion was prepared by adding 100 c.c. The results are shown in Table 1. In addition, 1% sulfuric acid, which is a source of divalent iron ions,
FeSO ₄ .7H ₂ O was used as iron, and it was used within 30 minutes after preparing the solution.

[Table] As is clear from Table 1, the amount of the active ingredient of the present invention added is 2.0 mg/, and the amount of added amount of conventionally used drugs (test numbers 14 and 15) is 2.0 mg/.
When comparing mg/mg, it can be seen that there is a significant difference in effectiveness after 8 hours. Example 2 A test was conducted that was closer to the actual site than passing seawater.
The process is shown in FIG. 1, and the test procedure will be explained with reference to the drawings. First, store seawater in seawater pit F, and pump
Seawater flows through the system at P ₀ and is discharged from the system at point G. At this time, 50cm from pump P ₀
There is a pit 1 containing a 1% Na ₂ S aqueous solution near a distant point A, and from there, a pump P ₁ is used to continuously inject the 1% Na ₂ S aqueous solution into seawater at a concentration of 0.05 mg/S ion. ing. During this time, from point A
Near point B, 20 cm away, there is a pit 2 containing an aqueous solution of the active ingredient of the present invention, from which a predetermined amount is added to seawater using pump _P2 . Further, divalent iron ions are continuously added to a predetermined concentration from a pit 3 near point C, which is 10 cm away from point B, using pump _P3 . Furthermore, a test tube [commercial product name: Alblack (alloy containing zinc and copper as main components), size 16 x 90 x 1 mm] was installed at point D, which was 1 m away from point C, and then at point E, which was 10 m away from point D. Attach a test tube to the point. In addition, as shown in the figure, it is divided into six branch lines from pump P ₀ ,
A ₁ , A _{2 .} . . A ₆ are set at positions equidistant from point A, and 1% Na ₂ S aqueous solution is added in the same way.
Furthermore, the devices at points B, C, D, E, and G are similarly set. Piping other than the above test tube uses vinyl chloride pipes. When seawater flows through the test tube, the flow rate is 1.0m/sec for each system.
It is adjusted by pump P ₀ so that
The temperature of seawater is 20℃±2℃. Using such a device, divalent iron ions can be added at 0.01 to 0.04 mg/,
Examine the amount of film and sludge formed inside the test tube after continuous addition for 30 days. After the test, take out the test tube and read JISK-0100.
Its test tube corrosion rate in accordance with the method of
mdd (mg/day・dm ² ), i.e. /dm ² Measures the corrosion loss per day. The results obtained are shown in Table 2.

【table】

[Table] There it was.
As is clear from Table 2, when oxycarboxylic acid is added, the amount of deposits on the test tube (the amount dissolved in sulfuric acid) clearly decreases, and the deposition of iron oxide sludge is suppressed. (c) Effects of the Invention According to the method of the present invention, since the adhesion of iron oxide sludge is suppressed, the sponge ball treatment, which was required once every two months, can now be done about once every four months. This dramatically reduces damage caused by pipe wear and extends the life of the pipe.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the test process in Example 2 of the present invention. F... Seawater pit, D and E... Test tube.

Claims (1)

[Scope of Claims] 1. When divalent iron ions are added to a seawater system to prevent corrosion of non-ferrous metals in the system, aliphatic oxycarboxylic acids having 10 or more carbon atoms or their alkali metal salts or ammonium A method for preventing corrosion of non-ferrous metals, characterized in that corrosion protection is performed while suppressing the formation of iron oxide sludge by adding salt. 2 An aliphatic oxycarboxylic acid having 10 or less carbon atoms,
The method according to claim 1, wherein the acid is citric acid, tartaric acid, malic acid or gluconic acid. 3. The method according to claim 1 or 2, wherein the alkali metal salt of an aliphatic oxycarboxylic acid having 10 or less carbon atoms is a sodium salt or a potassium salt.