The nitric acid production industry: technology, stages, characteristics

Nitric acid — among the most popular types of industrial raw materials. Its production can be carried out by different methods — depending on, which varieties of acid must be supplied to the customer. What is the essence of appropriate technology? How do they compare with the type produced in a factory of nitric acid?

The Industrial production of nitric acid: a history of technology development

First of all, it will be useful to study the historical facts about the evolution of the production of nitric acid in Russia. In the domestic industry the production of the substance, if you follow the available information, was initiated by Peter I. Later the M. V. Lomonosov was the proposed method of production of nitric acid from saltpetre — the substance is in fact to the early 20th century was considered the main raw material for production of the substances in question.

Along with nitrate, manufacture of nitric acid in industry was carried out using sulfuric acid. Consider two substances, interacting with each other, forming nitric acid and sulfuric sodium oxide. The advantage of this method was the possibility to obtain nitric acid in a concentration of the order of 96-98 % (assuming the use of raw materials of the required quality).

The Corresponding technology is actively improved — in favor of increasing the speed of processing of raw materials and the output of a larger volume of product. But gradually she gave way to the concept, according to which the nitric acid production was carried out by means of the contact oxidation of ammonia.

Was Also invented a method by which as the main raw material for the production of acid used nitric oxide produced by oxidation of the corresponding arc of gas from the atmosphere. Common point of view, according to which the first method — more cost-effective.

With the improvement of technological approaches to production of nitric acid formed approach in which the most optimal variant of production of the relevant substance — use of its industrial infrastructure, functioning under high pressure. The alternative — the production of acid at atmospheric pressure, which is considered less profitable from an economic point of view.

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Release substances under normal or elevated pressure require the production of nitric acid from ammonia. There is a combined method that combines the advantages of the other two. Features of the production of nitric acid by the combined method are, firstly, the oxidation of ammonia at atmospheric pressure, and the implementation of its absorption — at increased.

Ammonia is now considered the main raw material for production of the substance in question, along with water and atmospheric air. Learn the specifics of their application in the production of more acid.

Raw materials for production of nitric acid

So, the main raw material used in the production of the substances in question — that ammonia, air, and water.

This requires the use of ammonia in purified form. For this, he in the various production cycles is cleared on a special evaporative and distillation equipment. Similarly, when the release of nitric acid should be applied and clean air. He also filtered using special equipment. In turn, the water that is used in the production of nitric acid, cleaned of impurities and salts. In many cases, obtaining the substances concerned is necessary to use clean condensate.

Examine the varieties of the considered substance can be represented, and how is each type of nitric acid.

Varieties of nitric acid and main stages of its release

There are 2 kinds of nitric acid produced in modern enterprises — diluted and concentrated. The production of dilute nitric acid is carried out in the framework of 3 basic steps:

• Conversion of ammonia (end product — nitric oxide);
• Obtaining of nitrogen dioxide;
• Implementation of the absorption of nitrogen oxides by using water.

In modern enterprises widespread production of dilute nitric acid in the so-called schema-AK-72. But there are certainly other technologies in the production of this substance.

In turn, the production of concentrated nitric acid can be carried out by raising the levels of the relevant substance in diluted form or by direct synthesis. The first method usually allows to obtain the acid solution in a concentration of about 68 %, which may not be sufficient for application of the substances present in a number of areas. Therefore, it is also a common method of direct synthesis, allowing to obtain the substance in a concentration of the order of 97-98 %.

Let us Consider in more detail how the production of nitric acid in a particular species.Above, we noted that the release of the diluted substance can be carried out scheme of AK-72. Learn to start its specificity.

Production of the dilute acid technology AK-72

The scheme, through which the manufacture of nitric acid involves the use of a closed cycle involving:

• Conversion of ammonia;
• Cooling seam gas at a pressure of about 0,42-0,47 MPa:
• The implementation of the absorption of the oxides under a pressure of 1,1-1,26 MPa.

The End product of schematic AK-72 — nitric acid in a concentration of about 60%. The production of nitric acid in the present technology is carried out in the framework of such stages as:

• The supply of air from the atmosphere in the industrial unit and the implementation of its cleanup;
• Compression of the air, its division into process streams;
• Implementation of the evaporation of ammonia, purification of the corresponding gas from the oil and other impurities, and then heating it;
• Mixing purified of ammonia and air, subsequent purification of this mixture and transfer it to the catalyst;
• Obtaining nitrous gases and to cool them;
• Condensate with nitric acid;
• Concentration and absorption of nitric acid;
• Cooling and purification of the resulting product.

The Finished acid is sent to storage or to the customer.

Along with the considered technology, which is used for production of nitric acid — the AK-72 applies a different popular concept of issue of the relevant substance, which involves ensuring the functioning of industrial infrastructure under a pressure of 0.7 MPa. Consider its features.

Technology for manufacture of product under a pressure of 0.7 MPa: nuances

Through technology, in question, is the production of diluted nitric acid — as an alternative concept AC-72. It involves the implementation of further stages of production of the substances in question.

First of all, as in the previous technology, purifies the air. For this purpose, as a rule, used a two-stage filter. Further, the air prosesi cleaning, compressed through air compressor — approximately 0.35 MPa. The air heats up — to a temperature of about 175 degrees, and it is necessary to cool. After this problem is solved, he goes into the area of compression in which its pressure is increased to about 0,716 MPa. The emerging stream of air in turn is heated to a high temperature — about 270 degrees by the impact nitrotek gases. After it is mixed with ammonia in the special field of industrial Assembly. The substance involved in the release of acid initially in the gaseous state that is formed due to evaporation of the liquid. In addition, the ammonia needs to be cleaned. After preparation the gas is heated and fed into the mixer simultaneously with the air. This mixture is also filtered and after purification is supplied to the conversion of ammonia. The procedure is carried out using the grid alloy of platinum and rhodium at very high temperatures — about 900 degrees. The conversion rate is about 96%.

Production of weak nitric acid on the considered technology involves the formation of nitrous gases. They are displayed in a special area of the industrial unit in which they are cooled. Due to this, the evaporation of purified water and the appearance of steam with high pressure. Conducted through the appropriate area of the industrial unit nitrous gases are moved to the oxidizer. It is worth noting that their oxidation is partially already in the previous stage of acid production. But in the oxidizer, it becomes even more intense. While nitrous gases are heated to a temperature of 335 degrees. Subsequently, they are cooled in a special heat exchanger, and then — are sent to the condenser.

After this, the formed nitric acid at low concentration. From it is necessary to separate the remaining nitrous gases — this is a separator. Of it the nitric acid is served in the absorption region of the industrial unit. Acid subsequently flows into the region of the device below. However, she interacts with nitrogen oxides, owing to which its concentration increases. At the exit it is about 55-58 %. It usually contains dissolved oxides, you want to extract: this substance is directed to the purge area of the unit. Using heated air, the oxides are removed from the acid. The finished product is placed in stock or shipped to the customer.

Production of concentrated acid: direct synthesis

Having Considered how the production of dilute nitric acid, to study the specific issue of concentrated substances. Among the most cost-effective technology employed in the enterprises of the corresponding profile — obtaining acid by direct synthesis from raw materials in the form of oxides of nitrogen.

The Essence of this method — to stimulate a chemical reaction between said substance, water and oxygen under a pressure of 5 MPa. The technology on which the manufacture of nitric acid, the concentrated kind, based on diluted, hascaveat: transitions of nitrogen dioxide in liquid form is possible with pressure and temperature close to atmospheric. However, in some reactions the concentration of the relevant substance is not enough to transfer into a liquid state at normal pressure, and it has to be raised.

Production of concentrated acid based on diluted

In this case, it is assumed the concentration of the acid by means of absorbent substances — such as sulphuric, phosphoric acid, various solutions of nitrates. The main stages of production of concentrated nitric acid type on the basis of diluted with the use of sulfuric acid the following.

First, the raw material is divided into 2 streams: the first is fed into the evaporator, the second — falls into the cold region of the industrial unit. Sulfuric acid is supplied in the region of the device located above the second stream of dilute nitric acid. In the lower part of the unit, in turn, is steam, which heats the mixture used, as a result of it evaporates nitric acid. Its vapors rise up the machine and then displays it in the fridge. There's a pair of acid congenerous — until, until its concentration reaches 98-99 %.

Some part of the audience within this stage of the production of nitrogen oxides is absorbed by the acid. They must be extracted from the product: most often are used for this purpose pairs of nitric acid, which are sent to the condenser. The extracted nitrogen oxides, and acid pairs that are not formed condensate is sent to another area of the device — on absorption, where the treatment water. The result is a diluted acid, which is re-fed to the condensation and cooling. The finished product is sent to the warehouse or to the customer.

Features of the concentrate with sulphuric acid

The Main task, which characterizes the production of nitric acid in industry — implementation of profitable and effective concentration. There are several approaches to development of the optimal scheme of its solution. It will be useful to consider those that are the most common.

Above we noted that for the concentration of the substance in question, may be used sulfuric acid. There is a fairly common method of increasing the efficiency of its application — a pre-increase in the concentration of nitric acid by evaporation. Optimally, prior to treatment with sulfuric acid the substance will have a concentration of around 59-60 %. It is worth noting that, in practice, this technology of production of nitric acid is characterized by a low level of sustainability. Therefore, as an alternative to the use of sulfuric acid common use of nitrates. Examine their specifics in more detail.

Concentration using nitrate

Most Often for the solution of the considered problem, characterizing the production of nitric acid from ammonia, apply the nitrate of magnesium or zinc. First of all, it is significantly more environmentally friendly than the method involving the use of sulfuric acid. In addition, this technology allows to ensure the highest quality nitric acid as the final product.

However it has some shortcomings, which determine the emergence of widespread difficulties in its application. First of all — this is quite a high cost production process. In addition, this technology in many cases assumes the appearance of solid wastes, processing of which can be complicated.

The Use of catalysts with the release of nitric acid

It is Useful to consider what other substances are applied along with the main raw material for production of the product in question in the industrial (most often as such are considered catalysts) production of nitric acid. Use of the substances in question, due to the necessity of increasing the profitability of production of acid, increased the dynamics of its release at an industrial unit.

The Main requirement of the catalyst in the production of the product in question — selectivity. That is, it needs to act on the main chemical reaction without affecting the secondary processes. Most often in the production of acids are utilized, the catalyst includes platinum.

Above we noted that when releasing low-concentrated substances at high pressure are utilized catalysts based on platinum and rhodium. In some cases, there are alloys with the addition of palladium. But the metal in them — platinum, its content is usually not less than 81%. The nature of the catalyst in this case — to encourage quick passage of the main chemical reaction. As a rule, it passes through vneshnetorgovogo of the site.

The process depends on the limits of oxygen diffusion relative to the surface of the catalyst. This feature leads to a higher concentration of ammonia — the main raw material for production of nitric acid on the surface of one or sometimes of a catalyst, if we compare the corresponding figure with the concentration in the air. It is possible to increase the weights of the different side reactions in which there isincomplete oxidation and the formation of nitrogen or its oxide. In this regard, the oxygen at the surface should be sufficient to displace ammonia. In this case, you will be able to reach sufficiently deep oxidation.

It Can be noted that, along with platinum catalysts, in the manufacture of nitric acid are also employed combined substance. In particular, chromium. They significantly reduce the economic costs that characterizes the production of the substances in question.

So, we have considered methods of production of nitric acid, have identified its main types. How many stages of production of nitric acid you need to implement depends on its variety, as well as specific technologies of issue of the relevant substance. It will be useful now to consider what are the difficulties that characterize the industrial production of this demand in many spheres of the economy of the product.

The Main problems in the manufacture of nitric acid

So, as we already know, the production of nitric acid by contact method — one of the most common in modern industry, requires the incorporation of a catalyst to accelerate oxidation of ammonia and increasing the yield of the product. The main problem of the release of the product in question — the relatively high price of the corresponding catalyst. However, his selectivity does not always reach the optimal value. In addition, a significant portion of platinum that is used as a basic element for the catalyst, can be lost during production. As a result, again, decreases the economic efficiency of product release.

Another problem that characterizes the production of nitric acid — environmental. Above we noted that when the concentration of raw materials there can be used sulfuric acid, and upon passage of the production cycle are formed harmful substances. The alternative in this case can be the use of nitrates — but this, again, implies an increase in economic costs. However, the environmental factor for modern producers today are as significant as the level of profitability.