RU2339587C1 - Method of protection of water-circulation systems against corrosion and salt deposits - Google Patents

Abstract

FIELD: chemistry, technological processes.

SUBSTANCE: simultaneous processing of circulation water with ammonium salt of 1-oxyethylidendiphosphonic acid with 2-dimethylaminomethylphenol (salt "ОМЭД") and inorganic zinc salt. "ОМЭД" has formula

. Concentration of "ОМЭД" salt in circulation water constitutes 0.5-3 mg/l in terms of ion Zn²⁺. As inorganic zinc salt zinc sulfate can be used.

EFFECT: simultaneous efficient protection of water circulation systems against corrosion and salt deposits.

3 cl, 2 tbl, 9 ex

Description

The invention relates to the operation of water recycling systems and can be used to protect the equipment of these systems from corrosion and scaling (scale formation).

Known to the applicant analogues of the present invention in terms of protecting water circulating systems from corrosion are:

Methods of treating recycled water with individual salts of alkali, alkaline earth or transition metals (polyphosphates, chromates, nitrates, nitrites). (Corrosion under the influence of coolants, refrigerants, and working fluids: A reference guide. - L .: Chemistry, 1988, p. 82-98).

However, polyphosphates are prone to hydrolysis, nitrates and nitrites do not inhibit in water with high hardness (or high salinity), chromates are highly toxic compounds.

Methods for treating recycled water with salt mixtures. One of the most effective mixtures for water treatment is a mixture of potassium dichromate, sodium polyphosphate and zinc sulfate (Bergman J. Corrosion inhibitors. - M .: Chemistry, 1966).

However, this mixture has high toxicity (because the mixture contains potassium dichromate), is prone to hydrolysis (because the mixture contains sodium polyphosphate), is active only at certain pH values of the circulating water (because the mixture contains zinc sulfate is included).

Methods of treating recycled water with organic corrosion inhibitors containing sulfur, nitrogen and oxygen functional groups (Robinson, D.S., Corrosion inhibitors. - M .: Metallurgy, 1993, p. 272).

However, organic corrosion inhibitors in most cases are difficult to access, expensive, toxic, and require pre-treatment of the system.

There are also known methods of treating recycled water with organic complexones (Dyatlova N.M. et al. Metal complexones and complexonates. M: Chemistry, 1988, p. 466), for example, hydroxyethylidene diphosphonic acid (OEDP) (Kabachnik M.I. et al. Oxyethylidene diphosphonic acid and its use. - Chemical industry, 1975, No. 4, p.14-18).

However, organic complexones, possessing acidic properties, poorly protect metals (especially low-carbon steel) from corrosion. The solutions of these acids are unstable in environments with high rigidity, therefore, they are not effective enough to protect water circulation systems from carbonate deposits.

The closest to the claimed invention in terms of features (prototype) is a method of protecting water circulating systems from corrosion and carbonate deposits using a salt of hydroxyethylidene diphosphonic acid - zinc hydroxyethylidene diphosphonate (OEDPhC) (Yu.I. Kuznetsov et al. Protection of low-carbon steel with zinc phosphonates. - Protection of metals, 1987, No. 1, t. 23, p. 86).

However, the use of OEDFTS to protect water circulating systems from corrosion and carbonate deposits has the following disadvantages:

possessing a sufficient protective effect from scaling, OEDFTS protects against corrosion to a lesser extent; the anticorrosion effect is significantly manifested in a narrow pH value (5-6), with an increase in pH, the inhibition effect decreases; at high hardness, zinc ions are displaced from the complexonate and the effect of protection against corrosion and scaling is sharply reduced.

The objective of the invention is to increase the efficiency of protection against corrosion and scaling in water circulation systems.

This problem is achieved by the fact that in the method of protecting the water system from corrosion and scaling by introducing the hydroxyethylidene diphosphonic acid salt of the hydroxyethylidene diphosphonic acid according to the invention, the ammonium salt of 1-hydroxyethylidene diphosphonic acid with 2-dimethylaminomethylphenol (having the formula OME) is used

.

.

This task is also achieved by the fact that inorganic zinc is additionally introduced into the circulating water.

This problem is also achieved by the fact that the concentration of the ammonium salt of hydroxyethylidene diphosphonic acid with 2-dimethylaminomethylphenol in the circulating water is 0.5-10 mg / l, and the concentration of the inorganic zinc salt in the circulating water is 0.5-3 mg / l in terms of ion zinc (Zn ²⁺ ).

The method is as follows. A solution of the ammonium salt of hydroxyethylidene diphosphonic acid with 2-dimethylaminomethylphenol (OMED salt) is introduced into the circulating water of the water cycle from the solution tank by a dosing pump. The supply is carried out in the suction pipe of the circulating water pumps. A solution of an inorganic zinc salt, for example zinc sulfate, is also fed into the same pipeline from another solution tank using a metering pump. The components of the inhibitor are supplied to the circulating water until the concentration of OMED salt in it reaches 0.5-10 mg / L, zinc ions (Zn ²⁺ ) 0.5-3 mg / L. Then the supply of solutions of salt OMED and zinc sulfate in recycled water is stopped. Subsequently, solutions of OMED reagent and zinc sulfate are introduced into the feed pipe into the water cycle of makeup water. The reagent consumption is determined based on the concentration of OMED reagent in the make-up water of 0.5-10 mg / l, zinc ions (Zn ²⁺ ) 0.5-3 mg / l.

The following are specific examples of the implementation of the proposed method.

Example 1. The experiments are carried out in laboratory conditions by the method of "rotating disk". Recycled water from the water cycle is poured into the tank, having the following composition:

pH 7.8 Alkalinity, mg · equiv / l 2.0 Hardness, mg · equiv / l 3.3 Salt content, mg / l 600 Chlorides, mg / L 245 Sulfates, mg / L 26,4 COD, mgO ₂ / L 10.5

Control plates made of carbon steel with a size of 20 × 50 × 3 mm are fastened with a thread to the disk, which was above the container in a horizontal position. The disk is attached to a vertical axis, which is connected to the motor shaft. Control samples are immersed in water, turn on the electric motor to work and drive the disk with the plates attached to it in rotation. The rotation speed is set so that the linear velocity of the samples relative to the still water is 1 m / s. After 24 hours of contact with water, control samples were immersed in inhibited hydrochloric acid and the corrosion products dissolved therein. Then the control samples are washed with distilled water, dried and weighed. According to the mass loss during the experiment, the corrosion rate is calculated. Examining the samples under a microscope in reflected light determine the type of corrosion.

Test 1 (blank test) is carried out without treatment of the water with an inhibitor. The experimental results are shown in table 1, from which it follows that the corrosion rate of carbon steel (St3) in water in the absence of an inhibitor is 0.91 g / (m ² · h). Corrosion has an ulcerative appearance.

Table 1
Conditions and results of experiments to determine the speed and type of corrosion of control samples Experience Number Concentration, mg / l: The corrosion rate, g / (m ² · h) Type of corrosion OEDFTS OMED Zn ²⁺ one 0 0 0 0.91 Ulcerative 2 0.1 0 0 0.62 Peptic ulcer 3 5,0 0 0 0.43 Peptic ulcer four 10.0 0 0 0.09 Peptic ulcer 5 0 0.1 0 0.26 Spot 6 0 5,0 0 0.67 Peptic ulcer 7 0 10.0 0 0.81 Peptic ulcer 8 0 0.1 0.5 0.05 Ulcerative 9 0 5,0 0.5 0.06 Ulcerative 10 0 10.0 0.5 0,07 Ulcerative eleven 0 0.1 3.0 0,03 Ulcerative 12 0 5,0 3.0 0.05 Ulcerative 13 0 10.0 3.0 0.04 Ulcerative

Experiments 2-4 are carried out in accordance with a method pleasant for the prototype, in the presence in water of a zinc salt of hydroxyethylidene diphosphonic acid (OEDPTs). The results of the experiments are shown in table 1, from which it follows that the corrosion rate of carbon steel (St3) in water in the presence of HEDPF at a concentration of 0.5-10 mg / l is 0.09-0.62 g / (m ² · h ) Corrosion has a point-ulcerative appearance.

Experiments 5-7 are carried out in the presence of an ammonium salt of hydroxyethylidene diphosphonic acid with 2-dimethylaminomethylphenol (OMED salt), as provided by the proposed method, but without treating the water with an inorganic zinc salt. The results of the experiments are shown in table 1, from which it follows that the corrosion rate of carbon steel (St3) in water in the presence of one salt OMED at a concentration of 0.5-10 mg / l is 0.26-0.81 g / (m ² H). Corrosion has a point and ulcerative appearance.

Experiments 8-13 are carried out in accordance with the proposed method, in the presence in water of an OMED salt and an inorganic zinc salt, which is used as zinc sulfate. The results of the experiments are given in table 1, from which it follows that the corrosion rate of carbon steel (St3) in water in the presence of OMED at a concentration of 0.5-10 mg / l and zinc sulfate at a concentration of 0.5-3 mg / l (according to ion Zn ²⁺ ) is 0.04-0.07 g / (m ² · h). Corrosion has an ulcerative appearance.

Example 2. The experiments are carried out on a pilot installation simulating a water circulation system. The plant includes an organic glass cooling tower equipped with a nozzle from Raschig rings and a thermostat. Water heated in a thermostat to a temperature of 35 ° C is pumped to the upper part of the tower, where it is distributed evenly over the nozzle surface using a spray device. Flowing down the nozzle, the water cools and collects in the lower part of the tower, from where it flows by gravity to the thermostat. The duration of each experiment is 350 hours. During the experiment, water evaporates in the cooling tower, which is compensated by the addition of make-up water to the thermostat. The composition of the make-up water corresponds to the composition of water shown in Example 1. To determine the salt deposition rate, control plates made of stainless steel (X18H10T steel) with a size of 20 × 50 × 3 mm are placed in a thermostat. After the experiment, control images are removed from the thermostat, dried and weighed. The mass difference of the control samples before and after the experiment determines the mass of deposits on their surface.

The effectiveness of reducing scaling in the experience is determined by the formula

where Δm is the mass of deposits on the control sample in a blank without treatment of the circulating water with an inhibitor, g; Δm _i is the mass of deposits on the control sample in the i-th experiment; i is the number of experience.

Experiments 1-3 are carried out in accordance with the method adopted for the prototype, in the presence in the circulating water of the zinc salt of hydroxyethylidene diphosphonic acid (OEDFTS). The results of the experiments are shown in table 2, from which it follows that the efficiency of reducing scale formation, equal to 83.9-96.5%, is achieved when the concentration of HEDPC in circulating water is 3.0-10.0 mg / l.

table 2
The effectiveness of reducing scaling in the presence of inhibitors of OEDPZ and OMED-zinc sulfate Experience number Concentration in circulating water, mg / l The effectiveness of reducing scaling,% OEDFTS OMED Zn ²⁺ one 3 0 0 83.9 2 5 0 0 88.7 3 10 0 0 96.5 four 0 one one 90.2 5 0 5 one 95.1 6 0 10 one 99.5 7 0 one 3 90.8 8 0 5 3 96.6 9 0 10 3 99.6

Experiments 4-9 were carried out in accordance with the proposed method in the presence of OMED salt and inorganic zinc salt in circulating water, which was used zinc sulfate. The results of the experiments are given in table 2, from which it follows that when the concentration of OMED salt in the circulating water is 1 ÷ 10 mg / l, the concentration of the Zn ^{2+ ion is} 1 ÷ 3 mg / l, the efficiency of reducing scale formation is equal to 90.2 ÷ 99.6%.

An advantage of the proposed method is the simultaneous effective protection of water circulating systems against corrosion and salt deposits.

Claims (3)

1. A method of protecting water circulating systems from corrosion and carbonate deposits by introducing hydroxyethylidene diphosphonic acid salt into the circulating water, characterized in that the ammonium salt of 1-hydroxyethylidene diphosphonic acid with 2-dimethylaminomethylphenol having the formula

2. The method according to claim 1, characterized in that an inorganic zinc salt is additionally introduced into the circulating water. 3. The method according to claim 1 or 2, characterized in that the concentration of ammonium salt of 1-hydroxyethylidene diphosphonic acid with 2-dimethylaminomethylphenol in circulating water is 0.5-10 mg / l, and the concentration of inorganic zinc salt in circulating water is 0.5 -3 mg / l in terms of zinc ion (Zn ²⁺ ).