RU2283369C1 - Method for protection against corrosion and hydrogen absorption of steel in aqueous-saline medium - Google Patents

Abstract

FIELD: organic chemistry, anticorrosive substances.

SUBSTANCE: invention relates to a method for protection members, machines, constructions and buildings made of carbonic and low-alloyed steels against corrosion that in the exploitation process contact with aqueous solutions of salts, acids, industrial and domestic-sewage waters, sea water and wetted soils also. Method involves addition of inhibitor wherein aminoester salt is used as inhibitor of the general formula:

wherein R means -CH₂C₆H₅; -CH(C₆H₅)₂; -CH(C₆H₅)₃; -CH₂CH₃; -CH(CH₃)₂; -C(CH₃)₃; R' means -CH₃; -C₂H₅; -C₃H₇; -OC₂H₅; -OC₃H₇; R'' means 2HCl; 2HBr; HCl^.HBr; 2HF; HCl^.HF; HBr^.HF. Invention provides preparing inhibitor of corrosion combining properties of biocide and inhibitor of hydrogen absorption steel simultaneously, progressive reducing the steel corrosion rate with the increasing concentration of added organic substance.

EFFECT: improved method of steel protection, valuable properties of inhibitor.

8 tbl, 1 dwg

Description

The present invention relates to the protection of parts, machines, structures and structures from carbon and low alloy steels, which, under operating conditions, come into contact with aqueous solutions of salts, acids, industrial and domestic wastewater, sea water, and also moistened soils. In these cases, anaerobic conditions often develop on the surface of the steel, contributing to the development of sulfate-reducing bacteria (CRP). The specificity of the corrosive medium formed with the participation of CRP is that they release hydrogen sulfide and organic acids into it. These CRP metabolism products greatly accelerate the corrosion destruction of steels, and hydrogen sulfide is also a strong stimulator of hydrogen absorption by steel, which leads to a pronounced manifestation of hydrogen embrittlement, which manifests itself the stronger, the higher the carbon content in steel, i.e. on high-strength and spring steels .

A known inhibitor of hydrogenation of steel by A. with. No. 503942, M. cl. C 25 F 3/06, 1975, used in an acidic environment during the cathodic treatment, however, the disadvantage of this inhibitor is that it does not have biocidal properties with respect to CRP.

The closest analogue of the proposed invention is an inhibitor of microbiological corrosion and hydrogen picking of steel in aqueous-salt media containing sulfate-reducing bacteria according to the patent of the Russian Federation No. 2151819, M. cl. C 23 F 11/14, publ. 06/27/2000, Bull. No. 18, in which triazine derivatives are used as an inhibitor. However, some of their representatives (simazin, promethrin, zeazin) are well-known herbicides - artificially created substances used against weeds used in strictly defined permissible concentrations. Their use, storage, production, transportation and disposal must comply with the requirements of Federal Law No. 109-ФЗ dated 06/19/97 on Safe Handling of Pesticides and Agrochemicals, and the Rules for the Storage, Use and Transportation of Pesticides and Agrochemicals, approved by the Ministry Agriculture of the Russian Federation, Ministry of Health of the Russian Federation, April 29, 1999. Therefore, it is preferable to use more environmentally friendly, moderately or low toxic compounds, which, according to scientists, include amino ether salts at.

The aim of this invention is the use of a corrosion inhibitor that combines the properties of a biocide and a hydrogen inhibitor of steel at the same time.

This goal is achieved by the fact that as an inhibitor of corrosion and hydrogenation of steel in a medium containing sulfate-reducing bacteria, by introducing inhibitors, amino ester salts are used. Salts of amino esters are moderately or slightly toxic compounds, have pronounced antimicrobial properties.

Moreover, compounds of the general formula are used:

where: R: —CH ₂ C ₆ H ₅ ; -CH (C ₆ H ₅ ) ₂ ; -CH (C ₆ H ₅ ) ₃ ; -CH ₂ CH ₃ ; -CH (CH ₃ ) ₂ ; -C (CH ₃ ) ₃ ;

R ': -CH ₃ ; -C ₂ H ₅ , -C ₃ H ₇ , -OCH ₃ ; -OC ₂ H ₅ ; -OC ₃ H ₇ ;

R ": 2HCl; 2HBr; HCl · HBr; 2HF; HCl · HF; HBr · HF.

The technical result of the proposed invention is to obtain a corrosion inhibitor that combines the properties of a biocide and a hydrogen inhibitor of steel at the same time, providing a progressive decrease in the corrosion rate of steel with an increase in the concentration of introduced organic matter.

The inventive amino ester derivatives are hydrogen halide or mixed salts. Their molecules contain three main adsorption centers, which are two nitrogen atoms and an oxygen atom of the ether group. The decisive binding force during the adsorption of inhibitor molecules on the surface of the steel being protected is the electron density on these atoms. The nitrogen atoms of both imino groups have alkyl or alkoxy aromatic substituents that increase the electron density on the N atoms. According to theoretical ideas, compound 3 should be the best inhibitor (table 8), since its molecule has electron-donating alkyl substituents near the oxygen atom that displace electron density. However, the steric effect of the three methyl groups on the carbon atom bound to ether oxygen interferes with the manifestation of good shielding ability of this compound.

Two symmetric phenyl radicals at the terminal positions of compounds 1, 2, and 4 (Table 8) contribute to the screening of the metal surface, since the π-electrons of aromatic rings participate in adsorption, interacting with surface iron atoms, although the electron density on the oxygen atom is somewhat weakened two electrophilic phenyl groups. Compound 4 has the best corrosion inhibitory effect.

Thus, the formation of adsorption bonds between inhibitor molecules and surface Fe atoms is chemisorption in nature and the bond strength depends on the electron density on the heteroatoms of the molecule, as well as on the interaction of π-electrons of aromatic rings with a metal surface.

In addition, the claimed organic compounds in acidic environments behave as cationic. When they enter the water-salt medium, they partially (to a greater or lesser extent - depending on the pH of the medium and the pK of the compound) dissociate with the formation of organic cations. The surface of carbon steels in a corrosive medium formed as a result of the life of CRP, due to the formation of sulfide bridges, usually acquires a negative charge. This creates the prerequisites for electrostatic interaction (electrosorption) of the inhibitor particles in cationic form with the surface of the steel.

It is known that salts of amino esters are low toxic in various methods of administration, physiologically active compounds with pronounced antimicrobial properties. They are easily obtained from amino esters that exhibit long-term analgesic, antihypertensive and antiarrhythmic effects. The local anesthetic activity of some of them exceeds the activity of anesthetics known in world practice by 5-7 times. Amino esters have a high therapeutic index, a large breadth of pharmacological action and are promising for the creation of new drugs on their basis for the prevention and treatment of cardiovascular diseases.

To test the claimed compounds used their solutions in an aqueous-salt medium of the composition (table 1)

Table 1 Composition of Postgate B No. Name of the compound and its Amount, g / l one Sodium chloride 7.5 2 Magnesium sulfate 1.0 3 Sodium sulfate 2.0 four Sodium carbonate 1.0 5 Sodium dihydroorthophosphate 0.5 6 Calcium lactate 2.0

In corrosion studies, samples of St 3 mild steel were used. The samples were pre-sanded with sandpaper, degreased with Viennese lime and sterilized with a mercury-quartz lamp.

CRP is an anaerobic culture, that is, oxygen dissolved in the medium causes their transition to a latent state. To create anaerobic conditions, the medium was sterilized by boiling, then it was inoculated with an accumulation culture of CRP obtained by reseeding samples from a natural source. At the time of loading the samples, 1 ml of this medium contained 4.0 × 10 ⁷ cells of sulfate-reducing bacteria of the genus Desulfovibrio.

Hermetically sealed sample tubes were placed in a thermostat (37 ° C). 48 hours after introducing the accumulative culture into the sterile medium, the St 3 mild steel samples were replaced with new ones.

Corrosion processes on steel were studied by gravimetric, potentiometric and potentiostatic methods.

Observations of the life of CRP were carried out by daily counting under a microscope of the number of microorganisms using a Goryaev’s camera in phase contrast. The concentration of sulfate residue was determined by iodometric titration according to a calibration graph. The pH and redox potential of the media were determined potentiometrically. The hydrogen content was determined by the method of layer-by-layer anodic dissolution of steel samples.

The essence of the method is to determine the decrease in the concentration of oxygen dissolved in the electrolyte, which interacts in the presence of a platinum catalyst with hydrogen released during the anodic dissolution of steel. The concentration of oxygen dissolved in the electrolyte before and after anodic dissolution was determined photometrically by the method of Kovaltsev and Aleskovsky using safranin T as an oxygen reagent.

After preparing the surface, the sample was isolated so that the working surface was 1.8 cm ² . Then the sample was anodically dissolved at a strictly maintained current density D _a = ± 0.02 A / cm ² (I = 36 mA). Anolyte samples were taken every 20 minutes and the photometer cuvette was filled. 0.4 ml of leucosafranin was added and the solution in the cuvette was stirred with a magnetic stirrer. The optical density was measured and the hydrogen content in the dissolved metal layer was determined from the measurement results according to the graph obtained on the basis of the formula:

where V _el - electrolyte volume, ml;

1.429 - mass 1 ml 0 ₂ , mg;

Δm is the mass of the dissolved metal layer, mg;

ΔC is the change in the concentration of oxygen in the anolyte after dissolution of the surface layer in comparison with the concentration of oxygen in the anolyte before dissolution.

The thickness of the adsorbed hydrogen layer was determined by the formula:

where Δm is the mass of the dissolved metal layer, g;

S _arr - the area of the steel sample, cm ² ;

d = 7.8 g / cm ³ is the density of steel.

Fat-free and UV-irradiated samples and the inventive substances were introduced into the corrosive medium after 48 h, necessary for the development of CRP in a corrosive environment, and the first readings of the physicochemical parameters (electrode potential of the steel surface, oxidation-reduction potential, and hydrogen indicator of corrosion environment, concentration of biogenic hydrogen sulfide, the number of bacterial cells).

The values of the electrode potential (ε) of the steel sample in the presence of all the claimed organic compounds on the third day of the experiment are shifted towards more positive values. The highest enrichment ε is observed in the presence of additive No. 4 (table 2). The smallest shift in ε was caused by additive No. 1.

table 2 The change in the electrode potential of steel with an increase in the concentration of the claimed substances at the 72nd hour of exposure Compound The electrode potential of steel, mV, at various concentrations of substances, mmol / l 0.5 1.0 2.0 4.0 5.0 10.0 one -630 -627 -621 -615 -610 -616 2 -626 -620 -611 -605 -598 -591 3 -620 -617 -602 -587 -557 -542 four -610 -603 -584 -562 -548 -523

On the 3-4th day of the experiment, a shift in the redox potential (ε _h ) was also observed towards more positive values compared to the control series. Moreover, the shift ε _h the stronger, the greater the concentration of the claimed substances. The greatest shift ε _h was observed in the presence of compounds. No. 4, and the smallest with the introduction of the compound. No. 1 (table 3).

In the presence of all the claimed organic substances after the completion of the life cycle of microorganisms (day 7 of the experiment), the values of ε _{h are} slightly shifted towards more negative values.

Table 3 The redox potential of a corrosive medium with the described substances at an exposure of 72 hours Compound Redox potential of the medium, mV, at concentrations of substances, mmol / l 0.5 1.0 2.0 4.0 5.0 10.0 one 300 297 290 283 271 259 2 319 305 296 274 259 232 3 325 301 292 263 250 227 four 340 330 305 277 230 219

In the presence of all the claimed compounds on the 4th day of exposure, a shift in the pH of the medium (pH) was observed towards slightly acidic values compared with the control. As a rule, this shift was the stronger, the greater the concentration of the claimed substances. So conn. No. 4 at C = 1 mmol / L causes the greatest pH shift from 8.9 to 8.1, and at high concentrations (C = 5.0 mmol / L) to values of 6.1. Subsequently, starting from the sixth day of exposure, in all cases, in the presence of salts of amino esters, the pH monotonically shifted toward alkaline values. Of all the studied salts of amino esters, the strongest shift of the pH of the medium to the alkaline region was observed in media with the addition of No. 4 (table 4).

Table 4 Change in the hydrogen index of a corrosive medium with an increase in the concentration of introduced substances at the 72nd hour of exposure Compound Hydrogen indicator of Postgate 'B' medium at concentrations of the studied substances, mmol / l 0.5 1.0 2.0 4.0 5.0 10.0 one 7.2 7.5 7.7 7.7 7.8 7.3 2 7.3 7.4 7.4 7.5 7.5 7.1 3 7.7 7.6 7.4 7.3 7.2 6.7 four 7.6 7.5 7.5 7.4 7.3 6.9

On the 3-4th day of the experiment, a “surge” in the number of CRP was observed in a sterile medium. In samples with the claimed compounds, on the contrary, a day after the introduction of substances, the number of cells decreased sharply. After 48 hours, a slight increase in the number of CRP cells was observed, which is associated with the ability of bacteria to adapt to changes in environmental conditions. Then, as the nutrient properties of the medium were depleted, the number of CRP decreased monotonously. Compounds No. 4 and No. 3 cause a greater decrease in the number of microorganisms (table 5).

Table 5 The change in the number of microbial cells with an increase in the concentration of the claimed substances at the 72nd hour of exposure Compound The number of microbial cells, units · 10 ^-7 ml ^-1 at the concentrations of the described substances, mmol / l 0.5 1.0 2.0 4.0 5,0 10.0 one 353 349 324 213 300 291 2 307 300 284 253 220 261 3 284 279 271 264 260 254 four 285 283 276 270 275 250

A day after the introduction of salts of amino esters into the corrosive medium, a decrease in the content of the main metabolite of bacteria, hydrogen sulfide, was observed. As the SRV life cycle ends, the concentration of hydrogen sulfide assumes a constant value. Compound No. 4 caused the greatest decrease in the concentration of hydrogen sulfide in a corrosive environment (table 6).

Table 6 The change in the content of hydrogen sulfide with an increase in the concentration of the claimed substances at the 96th hour of exposure Compound The content of hydrogen sulfide, mg / l, at various concentrations of substances, mmol / l 0.5 1.0 2.0 4.0 5.0 10.0 one 85 83 82 81 80 74 2 81 79 80 82 83 72 3 84 82 83 85 87 63 four 82 80 72 63 67 57

From table 7 it is seen that the corrosion rate of steel in the presence of the inventive substances decreases uniformly with increasing concentrations of input organic substances, reaching very small values. In the presence of compound No. 4, the corrosion rate is minimal.

According to the degree of protection of the corrosive metal, the described salts of amino esters can be arranged in a row: No. 4> No. 3> No. 2> No. 1. Inhibitors No. 4 and No. 3 possess the best of the described claimed substances inhibitory and biocidal properties.

The effect of the claimed compounds on corrosion is in good agreement with their effect on the hydrogen content of the surface layers of steel, which correlated in an inhibited medium with CRP.

The drawing shows the dependence of the hydrogen content on the depth of the dissolved layer of steel samples in the presence of salts of amino esters. Even at a concentration of the organic substances under discussion of 1 mmol / L, the maximum hydrogen content of the sample corroded in the presence of compounds. No. 4, decreases almost twice as compared with the maximum hydrogen content of the sample, which corroded in a medium without organic inhibitors.

The accumulation of absorbed hydrogen in a relatively thin surface layer of steel - 10 ... 15 μm in all cases of application of the studied organic substances is due to the fact that a large number of collectors filled with molecular hydrogen are formed in the surface layers of steel with a special stress-strain state, part of which, located in close proximity to the surface, it opens out and hydrogen from this layer is partially desorbed. But in part it penetrates over time into deeper layers.

The resulting collectors reduce the likelihood of penetration of protons diffusing in the steel into the deep layers, because when protons reach the inner surface of the collector, they are combined with electrons and the formed hydrogen atoms are molded, which leads to an increase in the pressure of molecular hydrogen in the collector. The diffusion of hydrogen into the deeper layers is obviously carried out already through the deformed metal surrounding the collectors. The probability of reverse dissociation of hydrogen molecules into atoms inside the collectors at room temperature is negligible, therefore, the hydrogen contained in the collectors is non-diffusive.

Collectors filled with gaseous hydrogen and located in a relatively thin surface layer of steel play the role of a kind of barrier that regulates the flow of hydrogen penetrating into the deep layers of steel. The number of atoms - protons penetrating this barrier is obviously small, because the concentration of hydrogen in the deep layers is low.

When studying the effect of salts of amino esters on the hydrogen content of steel, the same sequence of their location in terms of the effect on hydrogenation as on corrosion of steel was established, and compound No. 4 showed the greatest efficiency.

It should be noted that the studies of salts of amino esters were carried out at C = 0.5 ... 10 mmol / L, but the most advantageous and appropriate use of these substances as inhibitors of corrosion and hydrogenation of steel at medium concentrations.

Table 7 VALUE OF CORROSION SPEEDS AND PROTECTIVE EFFECT OF ORGANIC ADDITIVES DEPENDING ON CONCENTRATION p / p CONNECTION NAME Concentration, mmol / L Corrosion rate, g / m day Protective effect,% one 2 3 four 5 No inhibitor 0,0 0,047 0 1. Hydrobromide hydrochloride of 2-benzhydryloxy-1,3-bis- (N-p-methoxyphenyl-amino) propane 0.5 0,073 8 1,0 0,068 eighteen 2.0 0,065 fourteen 5,0 0,029 63 2. 2-Benzhydryloxy-1,3-bis- (N-p-tollylamino) propane hydrobromide hydrochloride 0.5 0,074 6 1,0 0,061 23 2.0 0,054 32 5,0 0.019 76 3. 2-tert.-butyloxy-1,3-bis- (N-m-tollylamino) propane dihydrochloride 0.5 0,069 13 1,0 0,067 28 2.0 0,050 37 5,0 0.009 89 4. 2-Benzyl-hydroxy-1,3-bis- (N-p-tollylamino) propane dihydrochloride 0.5 0,067 fifteen 1,0 0,068 eighteen 2.0 0,041 48 5,0 0.004 95

Claims (1)

A method of protecting against corrosion and hydrogenation of steel in aqueous salt media containing sulfate-reducing bacteria by introducing an inhibitor, characterized in that an amino ester salt of the general formula is used as an inhibitor

where R: —CH ₂ C ₆ H ₅ ; -CH (C ₆ H ₅ ) ₂ ; -CH (C ₆ H ₅ ) ₃ ; -CH ₂ CH ₃ ; -CH (CH ₃ ) ₂ ; -C (CH ₃ ) ₃ ; R ': -CH ₃ ; -C ₂ H ₅ , -C ₃ H ₇ , -OCH ₃ ; -OC ₂ H ₅ ; -OC ₃ H ₇ ; R ": 2HCl; 2HBr; HCl · HBr; 2HF; HCl · HF; HBr · HF.