JP2852136B2 - Metal corrosion inhibitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a boiler
The present invention relates to a metal corrosion inhibitor for water-based general use such as a heat or cooling circulating water system , and more particularly to a metal corrosion inhibitor containing a copolymer of a phenolic compound and an aliphatic aldehyde.

[0002]

2. Description of the Related Art In order to suppress corrosion of metals, particularly carbon steel, in a boiler water system or a high-temperature water system of a heating or cooling circulation system, various anticorrosive agents such as oxygen scavengers have been conventionally used. Such anticorrosives suppress the corrosion of metals by removing dissolved oxygen in water, which is the main cause of corrosion, and forming an insoluble film on the surface of the metal, and isolating the metal from an environment containing a corrosive factor.

[0003] Commonly used anticorrosives include hydrazine, sodium sulfite, sodium bisulfite, glucose, tannin, lignin and the like.

[0004] In recent years, interest in safety as well as its effect on water treatment chemicals has been increasing, and water treatment chemicals such as anticorrosives in high-temperature water systems are no exception.

In a high-temperature water system, a deoxidizer for removing dissolved oxygen in water, which is a main cause of corrosion, is used to prevent corrosion on a heat transfer surface of a metal tube, a heat exchanger, a boiler, or the like. Water treatment used as a metal anticorrosive has been performed. The main oxygen scavengers used for such purposes include hydrazine and sodium sulfite.

[0006]

Problems to be Solved by the Invention When hydrazine is used, it cannot be used in hospitals or food factories where the generated steam or high-temperature water may come into direct contact with the human body or products due to its toxicity.

Although sodium sulfite has no problem with safety, it does not necessarily exhibit a sufficient anticorrosive effect because it reacts with oxygen to produce sulfate ions which cause corrosion. Significantly increases the concentration of dissolved solids and electrical conductivity (causes increased corrosion), resulting in an increase in the amount of blow, and the exchange of water-based media and heat loss resulting in increased energy costs. ing.

[0008] On the other hand, natural anticorrosives such as tannins have no problems of safety or excessive increase in the concentration of dissolved solids and electric conductivity of boiler water, but their quality (composition and chemicals). Characteristics) are not constant, and are susceptible to denaturation due to external environmental factors.

The present invention solves the problems of these conventional metal anticorrosives, and provides a metal anticorrosive which has no problems in safety, suppresses energy loss to a low level, and effectively suppresses corrosion. The purpose is to provide.

[0010]

According to the present invention, there is provided a boiler water system comprising a copolymer of a phenolic compound and an aliphatic aldehyde.
Alternatively, a metal corrosion inhibitor for water-based general use such as a heating or cooling circulating water system is provided.

The weight average molecular weight of the copolymer constituting the metal anticorrosive of the present invention is preferably from 200 to 5,000, more preferably from 200 to 2,000, from the viewpoint of exhibiting an excellent anticorrosion effect on metals in an aqueous system. It is.

The phenolic compound used in the synthesis of the copolymer of the present invention includes phenol, cresol, p
Examples include monovalent phenols such as chlorophenol and xylenol, divalent phenols such as resorcin, hydroquinone, catechol and bisphenol A, and trivalent phenols such as pyrogallol, hydroxyhydroquinone and gallic acid. From the viewpoint of exhibiting an excellent anticorrosive effect, cresol, catechol, pyrogallol and gallic acid are preferred. These phenolic compounds can be used alone or as a mixture.

The aliphatic aldehyde used in the synthesis of the copolymer of the present invention includes formaldehyde, acetaldehyde, propylaldehyde, n-butyraldehyde,
Examples thereof include isobutyraldehyde and n-caproaldehyde, and formaldehyde and acetaldehyde are preferred from the viewpoint of exhibiting an excellent anticorrosion effect on metals in an aqueous system . These aliphatic aldehydes can be used alone or as a mixture.

The amount of the aliphatic aldehyde used is preferably in the range of 0.01 to 1 mol, more preferably 0.05 to 0.5 mol, per 1 mol of the phenolic compound.

The above copolymer contained in the metal anticorrosive of the present invention may be in the form of a salt, if necessary. The type of salt is not particularly limited, and examples thereof include various metal salts (Na salt, K salt, etc.), ammonium salts and various amine salts (methylamine salt, ethylamine salt, ethanolamine salt, etc.).

The copolymer used in the metal anticorrosive of the present invention is prepared by reacting a phenolic compound with an aliphatic aldehyde at 50 to 250 ° C., preferably 100 ° C. under a nitrogen atmosphere using an acid catalyst.
It is produced by a copolymerization reaction at 200 to 200 ° C for 5 minutes to 10 hours, preferably 1 to 6 hours. Examples of the acid catalyst used herein include fluorides such as aluminum, boron, iron, zinc, tin and titanium, halides such as chlorides, or complex compounds thereof, inorganic acids such as hydrochloric acid and sulfuric acid, and paratoluenesulfonic acid. And the like.

[0017] The addition amount of the aqueous medium of the metal corrosion inhibitor of the present invention, the co to 1 as the polymer 5000 mg / 1, preferably of <br/> metal in effective aqueous With to not 10 500 mg / l Corrosion can be suppressed.

The aqueous medium using the metal anticorrosive agent of the present invention can be used for general aqueous purposes. However, in particular, the corrosion of metals in a boiler water system or a heating or cooling circulating water system having a remarkably high heat load can be used. Useful as an inhibitor.

If necessary, the metal anticorrosive of the present invention may contain a pH adjuster such as sodium hydroxide, a cleaning agent such as phosphate, a dispersant such as sodium polyacrylate or sodium polymaleate, And a steam-based corrosion inhibitor such as octadecylamine or cyclohexylamine, or a combination thereof at the time of addition, or can be used in combination by blending or the like.

The "weight average molecular weight" of the copolymer in the present specification is a value determined by gel permeation chromatography (GPC), and the measurement conditions are as follows.

GPC measurement condition apparatus Tosoh Corporation 8000 series detector Differential refractive index detector Column TSKgel G1000H + TSKgel G2000H (both from Tosoh Corporation) Temperature 40 ° C Eluent THF (tetrahydrofuran) Flow rate 1 ml / min Standard sample molecule Certain phenol condensates (2,
3, 4, 6-mer)

[0022]

The mechanism of the anticorrosive function of the metal anticorrosive agent of the present invention is determined by removing dissolved oxygen in water, which is a major cause of corrosion, and forming an insoluble adsorption film or oxide film with excellent stability on the metal surface. However, it is considered that the anticorrosion effect can be achieved by isolating from an environment containing a metal corrosion factor.

[0023]

EXAMPLES The present invention is described below by way of examples (production examples of copolymers).
In addition, a specific description will be given with reference to a deoxidation test and a corrosion test in comparison with the comparative example, but it goes without saying that the present invention is not limited to such examples.

Example 1 (Production of copolymer) Pyrogallol 200 g, cresol 20 g, formaldehyde
6.7 g was placed in a 1-liter reaction vessel, and 100
After the temperature was increased to 24 ° C., 24 g of p-toluenesulfonic acid (as a 60% by weight aqueous solution) was added as a catalyst. The temperature was further raised, and the system was dehydrated for 1 hour while refluxing at 110 ° C. under a nitrogen atmosphere, followed by reaction at 190 to 200 ° C. for 4 hours. After completion of the reaction, the reaction mixture was put into an ice bath and washed with water to obtain a reaction product. The weight average molecular weight of the obtained copolymer was 960.

Example 2 (Production of copolymer) Pyrogallol 200 g, cresol 10 g, formaldehyde
6.7 g was placed in a 1-liter reaction vessel, and 100
After the temperature was raised to 24 ° C., 24 g of p-toluenesulfonic acid (in the form of a 60% by weight aqueous solution) was added as a catalyst. The temperature was further raised, and the system was dehydrated for 1 hour while refluxing under a nitrogen atmosphere at 110 ° C., followed by a reaction at 190 to 200 ° C. for 2 hours. After completion of the reaction, the reaction mixture was put into an ice bath and washed with water to obtain a reaction product. The weight average molecular weight of the obtained copolymer was 340.

Example 3 (Production of copolymer) Pyrogallol 200 g, cresol 20 g, formaldehyde
6.7 g was placed in a 1-liter reaction vessel, and 100
After the temperature was raised to ° C., 45.6 g (as a 60% by weight aqueous solution) of p-toluenesulfonic acid was added as a catalyst. The temperature was further raised and refluxed at 110 ° C. under a nitrogen atmosphere for 1 hour.
After the system was dehydrated, it was reacted at 190 to 200 ° C. for 6 hours. After completion of the reaction, the reaction mixture was put into an ice bath and washed with water to obtain a reaction product. The weight average molecular weight of the obtained copolymer was 2,100.

[Deoxidation test] Each aqueous solution (pH: 11) obtained when a predetermined amount of each of the anticorrosive agent of the present invention and the existing anticorrosive agent was added to a certain amount of synthetic water as an aqueous medium shown in Table 1 OD meter that detects the amount of oxygen that can be reduced (oxygen consumption) (however, OD means oxygen demand)
(Temperature: 25 ° C., measurement period: 3 days). Table 2 shows the results.

[0028]

[Table 1] Synthetic water quality items Water quality pH 11.0 M- alkalinity (mgCaCO ₃ / l) 300 P- alkalinity (mgCaCO ₃ / l) 215 Chloride ion (mgCl ^- / l) 300

[0029]

[Table 2] Deoxygenation test results Molecular weight Addition amount (mg / l) Oxygen consumption (mgO / l) (weight average) Example 1 960 1000 385.0 Example 2 340 1000 489.0 Example 3 2,100 1000 276.5 Comparative example 1 126 1000 119.5 Comparative Example 2-1000 50.0 Comparative Example 3-1000 204.0 (Note) Corrosion inhibitor of Comparative Example 1: sodium sulfite Corrosion inhibitor of Comparative Example 2: sodium lignin sulfonate Corrosion inhibitor of Comparative Example 3: tannic acid

[Corrosion Test] A mild steel test tube (inner diameter 50 mm, length 500 mm) and a mild steel test piece (20 × 80 × 2 mm) were installed in a 10-liter test boiler, and a corrosion test was performed. Soft water shown in Table 3 was used as make-up water as an aqueous medium, and the anticorrosive of the present invention and an existing anti-corrosive were mixed in the make-up water in the amounts shown in Table 4 and supplied to the test boiler.

A small amount of caustic soda was added to the make-up water so that the pH of the boiler water became 10.5 or more. The test boiler was operated at a pressure of 1 MPa, a temperature of 183 ° C. and a 10-fold concentration for 150 hours continuously.

After the test, the test tube and the test piece were taken out, the state of occurrence of corrosion was observed, and the corrosion rate and the corrosion inhibition rate of the test piece were measured by the following equations.

[0033]

## EQU1 ## Corrosion degree = (weight before test−weight after test) / (surface area × test period)

[0034]

[Equation 2] Corrosion inhibition rate = [(empty test corrosion rate-chemical test corrosion rate) / empty test corrosion rate] x 100

Table 4 shows the results.

[0036]

[Table 3] Makeup water quality Item Soft water (Toda City water) pH 7.4 Electrical conductivity (μs / cm) 202 M- alkalinity (mgCaCO ₃ / l) 37 Total hardness (mgCaCO ₃ / l) 0 chloride ions (mgCl ^- / l) 38 sulfate ions (mgSO ₄ ^2- / l ) 27 Silica (mgSiO ₂ / l) 18 Total iron (mgFe / l) 0.07

[0037]

Table 4 Corrosion Test Results amount test tube appearance corrosion rate Corrosion inhibition rate (%) (mg / l) (mg / dm 2 · day) Comparative Example 1 200 pitting 18.8-Example 1 200 No pitting 0.1 99 Example 1 20 No pitting 0.4 98 Example 1 2 Slight pitting 2.7 86 Example 1 0.2 Pitting 10.6 44 Example 2 20 No pitting occurred 0.7 96 Example 3 20 Slight pitting occurred 1.2 94 Comparative Example 2 20 Pitting occurred 5.8 69 Comparative Example 2 2 Pitting occurred 21.9-Comparative Example 3 20 Slight pitting occurred 3.1 84 Comparative Example 3 2 Pitting occurred 15.3 19 Comparative example 4 20 Slight pitting occurred 1.7 91 Comparative example 4 2 Pitting occurred 9.9 47 (Note) Comparative Example 1: No anticorrosive added No anticorrosive of Comparative Example 2: same as anticorrosive of Comparative Example 1 in Table 2 (sodium sulfite) Anticorrosive of Comparative Example 3: Anticorrosive of Comparative Example 2 of Table 2 Same (sodium ligninsulfonate) Anticorrosive of Comparative Example 4: Same as anticorrosive of Comparative Example 3 in Table 2 (tannic acid)

[0038]

The copolymer constituting the metal anticorrosive of the present invention is an oligomer or a polymer, and therefore has no volatility and high safety. Even when it reacts with oxygen, the concentration of dissolved solids in boiler water and electric conductivity. Is not excessively increased, the blow amount can be reduced, and the energy cost can be reduced.

Since the above copolymer is a synthetic product,
Quality control is easy and lot-to-lot variation in composition and chemical properties can be minimized.

[0040] Moreover, metal corrosion inhibitor of the present invention, with the removal of dissolved oxygen in the aqueous medium, to form an adsorption film or oxide film stable insoluble metal surfaces, put in an aqueous
The anticorrosion effect is further improved, and a metal anticorrosion treatment of non-phosphorus and non-metal can be realized.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C23F 11/173 C09K 15 / 06,15 / 08 C08F 12 / 24,16 / 34

Claims (5)

(57) [Claims] 1. A boiler aqueous system comprising a copolymer of a phenolic compound and an aliphatic aldehyde.
Water-based general metal corrosion inhibitor such as heating or cooling circulating water system . 2. The metal anticorrosive according to claim 1, wherein the weight average molecular weight of the copolymer is from 200 to 5,000. 3. The phenolic compound is phenol,
Cresol, p chromatography chlorophenol, monohydric phenolic compounds such as xylenol and / or resorcinol, hydroquinone, catechol, dihydric phenolic compounds such as bisphenol A and / or pin Rogaroru, hydroxy hydroquinone, trivalent gallic acid The metal anticorrosive according to claim 1, wherein the metal anticorrosive is a phenolic compound. 4. The metal anticorrosive according to claim 1, wherein the aliphatic aldehyde is formaldehyde and / or acetaldehyde. 5. The metal anticorrosive according to claim 1, which is added to an aqueous medium in an amount of 1 to 5,000 mg / l as the copolymer, and is added to an aqueous boiler or heated or cooled.
A method for controlling corrosion of water-based general metals such as circulating water .