RU2804360C1 - Corrosion inhibitor - Google Patents

Abstract

FIELD: corrosion inhibitors.

SUBSTANCE: carbon steel corrosion inhibitors, and specifically to corrosion inhibitors that slow down the corrosion of pipelines, valves, internal parts of pumps used in the manufacture of urea-ammonia mixtures (UAM) in the form of aqueous solutions, and also slow down the corrosion of special containers and equipment used to transport and store such UAM. The corrosion inhibitor contains, wt.%: sodium nitrite – 10.0-45.0; potassium hydroxide – 0.5-5.0; phosphonobutanetricarboxylic acid – 0.1-3.0; sodium tetraborate – 0.5-5.0; 1,2,3-benzotriazole – 0.1-2.0; demineralized water – balance.

EFFECT: improved efficiency of inhibition of equipment corrosion processes, providing a carbon steel corrosion rate of not more than 0.004 mm/year, while ensuring compatibility with other additives in the treated media.

1 cl, 2 tbl, 4 ex

Description

The invention relates to corrosion inhibitors of carbon steel, and specifically to corrosion inhibitors that slow down the corrosion processes of pipelines, shut-off valves, internal parts of pumps used in the manufacture of urea-ammonium mixtures (UAM) in the form of aqueous solutions, and also slow down the corrosion processes of special containers and equipment used for transportation and storage of such UAN.

An effective method of combating corrosion is exposure to an aggressive environment by introducing corrosion inhibitors into it. However, using a large number of inhibitors creates its own problems, including increased cost, increased waste, and an increased likelihood that the inhibitor will interfere with the desired properties of the treated medium. In addition, even when using higher amounts of inhibitor, it is not always possible to effectively control the environmental impact of the inhibitor.

Both individual inorganic compounds and their compositions are used as corrosion inhibitors. Of the inorganic inhibitors, chromates, tungsten, molybdates, and vanadates of alkali metals are widely used. However, these inhibitors are expensive and contain highly toxic components in the form of heavy metals.

An accessible and widespread method of protecting steel from corrosion is a method based on the use of sodium nitrite as an inhibitor. However, sodium nitrite is usually used in high concentrations, since at low concentrations it, as an anodic passivator, causes increased pitting corrosion. Therefore, sodium nitrite is often used as a component of inhibitor compositions.

It is known to use 0.2% ammonium thiocyanate (Yakovlev L.M., Pakhomova N.M. et al. Corrosion resistance of carbon steel in liquid nitrogen fertilizers. Chemistry in Agriculture, 1985, No. 9, pp. 78-80). However, the corrosion rate decreases slightly, and the performance properties of the solution do not improve significantly.

“Corrosion inhibitors for liquid fertilizers” are known (see US patent 5704961 A, publication 2016-10-17), which proposes non-aggressive nitrogen-containing solutions of substances that contain a large number of reaction inhibitors that consume monocarboxylic acids or polycarboxylic acids, or their salts , or mixtures thereof. However, a known inhibitor is used to prevent corrosion of metal surfaces of transport, storage and application devices by concentrated aqueous solutions of fertilizers containing nitrogen compounds, including ammonia; ammonium salts such as ammonium nitrate, ammonium sulfate, ammonium phosphate, etc.; nitrates such as potassium nitrate, sodium nitrate, etc.; nitrogen-based organic compounds such as urea, ammonium carbamate, etc., and mixtures thereof. The known inhibitor is characterized by low solubility in aqueous solutions of UAN.

A known inhibitor of metal corrosion in acidic environments containing hexamethylenetetramine and oxyethylidene diphosphonic acid (see RU patent No. 2094531, published 10.27.1997). However, the known corrosion inhibitor is intended to protect steel and titanium equipment in environments containing sulfuric or phosphoric acid.

An inhibitor containing sodium nitrite and sodium tetraborate is known (see RU, patent No. 2124579, publ. 10. 01.1999). The invention relates to means of protection against corrosion and can be used to protect equipment made of steel when exposed to aggressive environments close to neutral. The objects of application of the known technical solution are heat and power water circulation systems in stop modes and in other cases. This corrosion inhibitor was chosen as the closest analogue.

The problem to be solved by the claimed invention is to create a corrosion inhibitor composition that will effectively inhibit corrosion processes of equipment used both for the production of UAN and for the transportation and storage of UAN. The claimed corrosion inhibitor should provide increased efficiency and improved performance properties of liquid fertilizer based on urea and ammonium nitrate, and the corrosion rate of carbon steel should be no more than 0.004 mm/year in a urea-ammonium mixture. The corrosion inhibitor must be compatible with other additives in the treated environment and have less impact on the environment.

The technical result of the claimed invention is to increase the efficiency of inhibition of equipment corrosion processes, ensuring a corrosion rate of carbon steel of no more than 0.004 mm/year, and to ensure compatibility with other additives in the treated environment. An additional technical result is to increase the service life of equipment for pumping, transporting and storing UAN.

The specified technical result is achieved by introducing an inhibitor composition into the aggressive working environment with the following ratio of components, wt. %:

Sodium nitrite 10.0-45.0 Potassium hydroxide 0.5-5.0 Phosphonobutanetricarboxylic acid 0.1-3.0 Sodium tetroborate 0.5-5.0 1,2,3-Benzotriazole 0.1-2.0 Demineralized water rest

Sodium nitrite, which is an inhibitor of the anodic process, promotes the transition of the metal to a passive state, increasing the inhibition of the anodic corrosion process.

Potassium hydroxide and the introduction of sodium tetroborate make it possible to increase the buffering capacity of the resulting mixture, increase the hydrate alkalinity and pH level of the inhibitor.

The introduction of phosphonobutanetricarboxylic acid helps reduce crevice and pitting corrosion, ensuring the occurrence of controlled uniform (linear) corrosion over the entire contact surface between the medium and the metal.

The introduction of 1,2,3-benzotriazole is used to inhibit galvanic (contact) corrosion. The use of 1,2,3-benzotriazole allows you to bind free ions of non-ferrous metals, preventing them from settling in places with high electrochemical potential (ferrous metal alloys).

Demineralized water is used as an effective solvent with a minimum content of salts, free ions and impurities that affect the quality characteristics of the solution and the production of active ingredients.

A distinctive feature of the proposed corrosion inhibitor is the strict regulation of the quantitative and qualitative composition of the components it contains. In the process of obtaining the claimed corrosion inhibitor, the chemical substances included in its composition react with each other, ensuring the production of a corrosion inhibitor that allows solving the problem. This result is achieved as a result of a synergistic effect, in which the effect of one component is enhanced in the presence of the other. It is due to the synergistic effect of the combination of components of the corrosion inhibitor, with their stated quantitative ratio, that the task was solved and the specified technical result was achieved. This was confirmed experimentally. At the same time, the effectiveness of the proposed corrosion inhibitor is significantly influenced by the quantitative ratio of all its constituent components, which was selected experimentally. The optimal parameters were selected in each specific case depending on the type and technological characteristics of the equipment used. As experiments have shown, overestimating or underestimating the content of each of the components negatively affected the effectiveness of the proposed product.

A comparative analysis of the claimed corrosion inhibitor with the composition of the prototype allows us to conclude that the claimed composition of the corrosion inhibitor differs from the known one by the introduction of new components, wt. %:

Potassium hydroxide 0.5-5.0 Phosphonobutanetricarboxylic acid 0.1-3.0 1,2,3-Benzotriazole 0.1-2.0

and the use of demineralized water.

In combination with known features, these distinctive features make it possible to increase the effectiveness of inhibiting equipment corrosion in a urea-ammonium mixture, ensuring a carbon steel corrosion rate of no more than 0.004 mm/year, and to ensure compatibility with other additives in the treated environment. The most important factor determining the choice of these components was their availability, relatively low cost, efficiency of their use and environmental safety.

In the prior art there is no information about the possibility of obtaining the above technical result due to the above distinctive features. In this case, the mentioned features can be called a new means for obtaining the above technical result, since this result has not yet been obtained using such features.

The essence of the claimed invention is illustrated by the following general description of an example of the preparation of the claimed corrosion inhibitor.

To prepare the proposed corrosion inhibitor, the following are used: sodium nitrite (GOST 19906-74), potassium hydroxide (GOST 9285-78), phosphonobutanetricarboxylic acid (international CAS number 37971-36-1), sodium tetroborate (GOST 8429-77), 1.2 ,3-benzotriazole (international CAS number 95-14-7), demineralized water. The starting components are weighed on scales. A calculated amount of demineralized water is poured into an enameled reactor with a capacity of 50 liters, equipped with a cooling jacket and a stirrer, and a calculated amount of sodium nitrite, potassium hydroxide, phosphonbutanetricarboxylic acid, sodium tetraborate and 1,2,3-benzotriazole are added. Stirring is carried out until the salts are completely dissolved and the solution density reaches 1.20-1.40 g/cm ³ . The technology for preparing the proposed inhibitor is environmentally friendly and can be implemented on standard equipment used in industrial conditions for the production of corrosion inhibitors.

Examples of the specific composition of components for the manufacture of a corrosion inhibitor are given in Table 1.

The inventive corrosion inhibitor was produced in laboratory conditions as described above. A mixed aqueous solution of urea (35 wt. %) and ammonium nitrate (45 wt. %), which corresponds to liquid nitrogen fertilizer containing 32% nitrogen (grade KAS32), was used as the treated (background) medium. The solution was filled into a glass beaker, into which a rectangular carbon steel plate (steel 20) was placed under a layer of liquid. The flask was sealed with a stopper and placed for long-term storage at room temperature. After 1 month, the experiment was stopped, and the necessary observations and measurements were made. Based on the weight loss of the sample over the entire test period, the average corrosion rate was determined. The corrosion rate was assessed using the gravimetric method in accordance with GOST 9.506-87. The data obtained during the tests (Table 2) show that the proposed corrosion inhibitor allows effective corrosion protection of carbon steel structures in a urea-ammonium mixture. The corrosion rate of carbon steel was no more than 0.004 mm/year. The effective dosage of the claimed corrosion inhibitor is 200-400 mg/l of the total volume of the urea-ammonium mixture.

Experiments have shown that the claimed corrosion inhibitor makes it possible to effectively inhibit corrosion processes of pipelines, shut-off valves, internal parts of pumps, and containers consisting of carbon steel used for transporting and storing urea-ammonium mixtures. The corrosion inhibitor made it possible to increase the efficiency of equipment corrosion inhibition, ensuring a corrosion rate of carbon steel of no more than 0.004 mm/year in a urea-ammonium mixture. Compatibility with other additives in the treated environment is ensured. There has been an improvement in the performance properties of liquid fertilizer based on urea and ammonium nitrate.

The service life of equipment for pumping, transporting and storing UAN is increasing. Accordingly, capital and operating costs for carbon steel equipment for UAN transportation and storage are reduced. The need to purchase expensive imported corrosion-resistant equipment for UAN transportation and storage is eliminated. A result has been achieved that could not be achieved for a long time.

Claims (2)

A corrosion inhibitor containing sodium nitrate and sodium tetraborate, characterized in that it additionally contains potassium hydroxide, phosphonobutanetricarboxylic acid, 1,2,3-benzotriazole and demineralized water in the following ratio of components, wt. %: Sodium nitrite 10.0-45.0 Potassium hydroxide 0.5-5.0 Phosphonobutanetricarboxylic acid 0.1-3.0 Sodium tetroborate 0.5-5.0 1,2,3-Benzotriazole 0.1-2.0 Demineralized water rest