Ammonia in the laboratory can be collected by the method. Ammonia, structure, production and properties

DEFINITION

Ammonia- hydrogen nitride.

Formula - NH 3. Molar mass - 17 g / mol.

Physical properties of ammonia

Ammonia (NH 3) is a colorless gas with a pungent odor (the smell of "ammonia"), lighter than air, highly soluble in water (one volume of water will dissolve up to 700 volumes of ammonia). The concentrated ammonia solution contains 25% (mass) ammonia and has a density of 0.91 g/cm 3 .

The bonds between atoms in the ammonia molecule are covalent. General view of the AB 3 molecule. All valence orbitals of the nitrogen atom enter into hybridization, therefore, the type of hybridization of the ammonia molecule is sp 3. Ammonia has a geometric structure of the AB 3 E type - a trigonal pyramid (Fig. 1).

Rice. 1. The structure of the ammonia molecule.

Chemical properties of ammonia

Chemically, ammonia is quite active: it reacts with many substances. The degree of oxidation of nitrogen in ammonia "-3" is minimal, so ammonia exhibits only reducing properties.

When ammonia is heated with halogens, heavy metal oxides and oxygen, nitrogen is formed:

2NH 3 + 3Br 2 = N 2 + 6HBr

2NH 3 + 3CuO \u003d 3Cu + N 2 + 3H 2 O

4NH 3 + 3O 2 \u003d 2N 2 + 6H 2 O

In the presence of a catalyst, ammonia is able to oxidize to nitric oxide (II):

4NH 3 + 5O 2 \u003d 4NO + 6H 2 O (catalyst - platinum)

Unlike hydrogen compounds of non-metals of groups VI and VII, ammonia does not exhibit acidic properties. However, hydrogen atoms in its molecule are still capable of being replaced by metal atoms. With the complete replacement of hydrogen by a metal, the formation of compounds called nitrides occurs, which can also be obtained by direct interaction of nitrogen with a metal at high temperature.

The main properties of ammonia are due to the presence of a lone pair of electrons at the nitrogen atom. Ammonia solution in water is alkaline:

NH 3 + H 2 O ↔ NH 4 OH ↔ NH 4 + + OH -

When ammonia reacts with acids, ammonium salts are formed, which decompose when heated:

NH 3 + HCl = NH 4 Cl

NH 4 Cl \u003d NH 3 + HCl (when heated)

Getting ammonia

Allocate industrial and laboratory methods for producing ammonia. In the laboratory, ammonia is obtained by the action of alkalis on solutions of ammonium salts when heated:

NH 4 Cl + KOH \u003d NH 3 + KCl + H 2 O

NH 4 + + OH - = NH 3 + H 2 O

This reaction is qualitative for ammonium ions.

Application of ammonia

Ammonia production is one of the most important technological processes worldwide. About 100 million tons of ammonia are produced annually in the world. The release of ammonia is carried out in liquid form or in the form of a 25% aqueous solution - ammonia water. The main areas of use of ammonia are the production of nitric acid (production of nitrogen-containing mineral fertilizers later), ammonium salts, urea, urotropine, synthetic fibers (nylon and capron). Ammonia is used as a refrigerant in industrial refrigeration, as a bleach in the cleaning and dyeing of cotton, wool and silk.

Examples of problem solving

EXAMPLE 1

Exercise	What is the mass and volume of ammonia required to produce 5 tons of ammonium nitrate?
Solution	Let's write the reaction equation for obtaining ammonium nitrate from ammonia and nitric acid: NH 3 + HNO 3 \u003d NH 4 NO 3 According to the reaction equation, the amount of ammonium nitrate substance is 1 mol - v (NH 4 NO 3) \u003d 1 mol. Then, the mass of ammonium nitrate, calculated according to the reaction equation: m(NH 4 NO 3) = v(NH 4 NO 3)×M(NH 4 NO 3); m(NH 4 NO 3) \u003d 1 × 80 \u003d 80 t According to the reaction equation, the amount of ammonia substance is also 1 mol - v (NH 3) \u003d 1 mol. Then, the mass of ammonia, calculated by the equation: m (NH 3) \u003d v (NH 3) × M (NH 3); m (NH 3) \u003d 1 × 17 \u003d 17 t Let's make a proportion and find the mass of ammonia (practical): x g NH 3 - 5 t NH 4 NO 3 17 t NH 3 – 80 t NH 4 NO 3 x \u003d 17 × 5 / 80 \u003d 1.06 m (NH 3) \u003d 1.06 t We will compose a similar proportion to find the volume of ammonia: 1.06 g NH 3 - xl NH 3 17 t NH 3 - 22.4 × 10 3 m 3 NH 3 x \u003d 22.4 × 10 3 × 1.06 / 17 \u003d 1.4 × 10 3 V (NH 3) \u003d 1.4 × 10 3 m 3
Answer	Ammonia mass - 1.06 tons, ammonia volume - 1.4 × 10 m

Ammonia (NH 3) is a compound of nitrogen and hydrogen. It is a light gas with a pungent odor. The production of ammonia in industry and laboratories is necessary for the production of fertilizers, polymers, nitric acid and other substances.

In industry

Ammonia is produced industrially from nitrogen by combining it with hydrogen. Nitrogen is taken from the air, hydrogen - from water. The method was first developed by the German chemist Fritz Haber. The industrial method for producing ammonia began to be called the Haber process.

The reaction proceeds with a decrease in volume and the release of energy in the form of heat:

3H 2 + N 2 → 2NH 3 + Q.

The reaction is reversible, so several conditions must be met. At high pressure and low temperatures, the amount of ammonia produced increases. However, low temperatures slow down the rate of the reaction, and an increase in temperature increases the rate of the reverse reaction.

Empirically, the necessary conditions for the reaction were found:

• temperature- 500°C;
• pressure- 350 atm;
• catalyst- iron oxide Fe 3 O 4 (magnetite) with impurities of oxides of silver, potassium, calcium and other substances.

Under these conditions, the resulting gas contains 30% ammonia. To avoid a reverse reaction, the substance is rapidly cooled. At low temperatures, the resulting gas turns into a liquid. Unspent gases - nitrogen and hydrogen - are returned back to the synthesis column. This method helps to quickly obtain large volumes of ammonia, maximizing the use of raw materials.

Rice. 1. Obtaining ammonia industrially.

To find the right catalyst, 20,000 different substances were tried.

In the laboratory

To obtain ammonia in the laboratory, the reaction of alkalis to ammonium salts is used:

NH 4 Cl + NaOH → NH 3 + NaCl + H 2 O

Also, ammonia can be obtained in the laboratory from ammonium chloride heated together with slaked lime, or by decomposition of ammonium hydroxide:

• 2NH 4 Cl + Ca(OH) 2 → CaCl 2 + 2NH 3 + 2H 2 O;
• NH 4 OH ↔ NH 3 + H 2 O.

Rice. 2. Obtaining ammonia in the laboratory.

Ammonia can be completely dried using a mixture of lime and caustic soda, through which the resulting gas is passed. For the same purpose, liquid ammonia is mixed with sodium metal and subjected to distillation.

Ammonia is lighter than air, so the test tube is held upside down to collect it.

Application

Ammonia is used in various industries:

• in agriculture - for the production of nitrogen-containing fertilizers;
• in industry - for the production of polymers, explosives, artificial ice;
• in chemistry - for the manufacture of nitric acid, soda;
• in medicine - as ammonia.

Rice. 3. Manufacture of fertilizers.

What have we learned?

Ammonia is produced by industrial and laboratory methods. For production on an industrial scale, nitrogen and hydrogen are used. Mixing under high temperature, pressure and under the action of a catalyst, simple substances form ammonia. To prevent the reaction at high temperature from going in the opposite direction, the gas is cooled. In the laboratory, ammonia is obtained by reacting ammonium salts with alkalis, slaked lime, or by decomposing ammonium hydroxide. Ammonia is used in the chemical industry, agriculture, medicine, and chemistry.

Topic quiz

Report Evaluation

Average rating: 4.2. Total ratings received: 263.

Ammonia (hydrogen nitride, formula NH 3) under normal conditions is a colorless gas with a pungent characteristic odor. It is one of the most important products of the chemical industry. Its annual world production reaches 150 million tons. It is mainly used for the manufacture of nitrogen fertilizers (ammonium nitrate and sulfate, urea), explosives and polymers, nitric acid, soda (ammonia method) and other chemical products. Liquid ammonia is used as a solvent.

In refrigeration, it is used as a refrigerant (R717).

In medicine, a 10% solution of ammonia, often called ammonia, is used for fainting (to stimulate breathing), to stimulate vomiting, and also externally for neuralgia, myositis, insect bites, and to treat the surgeon's hands. If used improperly, it can cause burns of the esophagus and stomach (in case of taking an undiluted solution), reflex respiratory arrest (when inhaled in high concentrations).

Ammonia production technology + video how to get

As part of this direction, today many companies have begun to develop and design the following technologies:

• Conversion of excess ammonia to methanol production.
• Development of production based on modern technologies for the replacement of active units.
• Creation of integrated production and modernization.

For the production of one ton of ammonia in Russia, an average of 1200 nm³ of natural gas is consumed, in Europe - 900 nm³. The Belarusian "Grodno Azot" consumes 1200 Nm³, after the modernization the consumption is expected to decrease to 876 Nm³. Ukrainian producers consume from 750 nm³ to 1170 nm³. According to the UHDE technology, the consumption of 6.7 - 7.4 Gcal of energy resources per ton is declared.

The industrial method for producing ammonia is based on the direct interaction of hydrogen and nitrogen:

N 2 + 3H 2 ⇄ 2NH 3 + + 91.84 kJ

This is the so-called Haber process (German physicist, developed the physico-chemical foundations of the method). The reaction occurs with the release of heat and a decrease in volume. Therefore, based on the Le Chatelier principle, the reaction should be carried out at the lowest possible temperatures and at high pressures - then the equilibrium will be shifted to the right. However, the reaction rate at low temperatures is negligible, and at high temperatures, the rate of the reverse reaction increases. Carrying out the reaction at very high pressures requires the creation of special equipment that can withstand high pressure, and hence a large investment. In addition, the equilibrium of the reaction, even at 700°C, is established too slowly for its practical use. The yield of ammonia (in volume percent) in the Haber process at various temperatures and pressures has the following values:

The use of a catalyst (porous iron with Al2O3 and K2O impurities) made it possible to accelerate the achievement of an equilibrium state. Interestingly, in the search for a catalyst for this role, more than 20 thousand different substances were tried.

Considering all the above factors, the production process is carried out under the following conditions:

• temperature 500 °C;
• pressure 350 atmospheres;
• catalyst.

The yield of ammonia under such conditions is about 30%. Under industrial conditions, the principle of circulation is used - ammonia is removed by cooling, and unreacted nitrogen and hydrogen are returned to the synthesis column. This turns out to be more economical than achieving a higher reaction yield by increasing the pressure. To obtain it in the laboratory, the action of strong alkalis on ammonium salts is used:

NH 4 Cl + NaOH → NH 3 + NaCl + H 2 O

Ammonia is usually obtained in the laboratory by weak heating of a mixture of ammonium chloride and slaked lime.

2NH 4 Cl + Ca(OH) 2 → CaCl 2 + 2NH 3 + 2H 2 O

To dry ammonia, it is passed through a mixture of lime and caustic soda. Very dry can be obtained by dissolving metallic sodium in it and subsequently distilling. This is best done in a system made of metal under vacuum. The system must withstand high pressure (at room temperature, the saturated vapor pressure is about 10 atmospheres). In industrial production, absorption columns are usually used for drying.

Video how to do it:

Ammonia production should not bypass technical progress. This is mainly about energy saving. During the development of modern technologies, great importance is given to the software necessary for modeling chemical and technological processes.

Nitrogen compounds are of exceptional importance for various industries and agriculture. They are consumed by the production of nitric acid, various mineral fertilizers, polymeric materials, explosives and rocket fuels, dyes, and pharmaceuticals.

Nitrogen is one of the fairly common chemical elements. Its clarke (% wt.) for the planet as a whole is 0.01, for the earth's crust it is 0.04, for the atmosphere - 75.5. Forms of existence of nitrogen in the earth's crust are very diverse. It is found in minerals, coal, oil and other fossil fuels. Nitrogen is of paramount importance for life on Earth, being one of the elements that make up protein structures. On fig. 8.1 shows the forms of existence of nitrogen on earth and the content of the element in them.

Figure 8.1 - Forms of the existence of nitrogen in the lithosphere

The main natural source of nitrogen is the atmosphere. The mass of nitrogen in it is 4 × 10 15 tons. However, gaseous molecular nitrogen is one of the most stable chemicals. The binding energy in a nitrogen molecule is 940.5 kJ/mol. Under natural conditions, only a small amount of atmospheric nitrogen passes into a biologically assimilable form as a result of lightning discharges according to the reaction

or directly fixed by limited plant species in the form of amino acids during photosynthesis catalyzed by enzymes

Most organisms (higher plants and animals) assimilate nitrogen in the form of its compounds with an oxidation state of -3 and cannot use atmospheric nitrogen. The same applies to the use of nitrogen compounds in industry.

The rate of conversion of atmospheric nitrogen into a state in which it can be assimilated or realized is very low in natural processes. On average, half of the nitrogen necessary for life returns through the atmosphere in 10 8 years. At the same time, the organization of modern cultural farming is associated with the continuous removal of assimilable nitrogen from sown areas, reaching 88 million tons per year, which is 90% of the nitrogen needed for plant nutrition. Therefore, the primary task is the continuous replenishment of nitrogen reserves in the soil in a form assimilated by plants. Until the end of the 19th century, the source of "bound" nitrogen was natural fertilizers and only to a small extent natural salts - sodium and potassium nitrates, the reserves of which in nature are very limited. The increase in the scale of cultivated farming and the needs of industry for a variety of nitrogen compounds required the development of industrial methods for obtaining these compounds, that is, methods for "binding" atmospheric nitrogen.

8.1.2. Atmospheric nitrogen fixation methods

At the beginning of the 20th century, three technical methods for the synthesis of compounds from molecular nitrogen were developed almost simultaneously: arc, cyanamide and ammonia.

The comparative energy consumption of these methods of nitrogen fixation is given in Table. 8.1

Table 8.1 - Energy intensity of nitrogen fixation methods

Method	Energy costs for the production of 1 ton of ammonia, kJ
Arc
cyanamide
Ammonia

The ammonia method of fixation is the most energetically favorable, which led to its widespread industrial implementation.

8.2. Getting ammonia. General information

Ammonia is the most important and practically the only nitrogen compound produced on an industrial scale from atmospheric nitrogen. Thus, it should be considered as an intermediate for obtaining all other nitrogen compounds.

8.2.1. Technological properties of ammonia

Ammonia NH 3 is a colorless gas with a pungent odor with a boiling point of -33.35 0 C and a melting point of -77.75 0 C. Abnormally high boiling and melting points of ammonia are explained by the association of its molecules due to their high polarity and the formation of hydrogen bonds. Ammonia is highly soluble in water (750 liters per liter of water), sparingly soluble in organic solvents.

Aqueous solutions of ammonia contain its composition hydrates, which form eutectics, as well as a small amount of ionized molecules as a result of the reaction

The equilibrium constant of this reaction is , which corresponds to the degree of dissociation of 0.004. At temperatures above 1300 0 C, ammonia dissociates into nitrogen and hydrogen:

Dry ammonia forms explosive mixtures with air, the explosive limits of which depend on temperature and at 18 0 C are limited by the range of ammonia content in the gas mixture from 0.155 to 0.270 vol. shares. This feature of the "ammonia-air" system is taken into account in the production of nitric acid by the oxidation of ammonia, in which the raw material is an ammonia-air mixture.

8.2.2. Areas of use of ammonia

Ammonia is a key product for the production of numerous nitrogen-containing substances used in industry, agriculture and everyday life. Almost all nitrogen compounds used as target products and semi-products of inorganic and organic technology are currently produced on the basis of ammonia. On fig. 8.2 shows the main areas of ammonia use in industry and agriculture.

Figure 8.2 - Use of ammonia

8.2.3. Raw materials for ammonia production

Nitrogen mixture (ABC)- raw materials in the production of ammonia of stoichiometric composition N 2: H 2 = 1: 3. Since the resources of atmospheric nitrogen are practically inexhaustible, the raw material base of ammonia production is determined by the second component of the mixture - hydrogen, which can be obtained by separation of reverse coke gas, gasification of solid fuel, conversion natural gas (Fig. 8.3).

Figure 8.3 - Raw materials for ammonia production

The structure of the raw material base for ammonia production has changed, and now more than 90% of ammonia is produced on the basis of natural gas. In table. 8.2 shows the dynamics of changes in the structure of the main types of raw materials for ammonia production.

Table 8.2 - Changes in the raw material base of ammonia production

Types of raw materials	Share of raw materials by years, %					Energy intensity, tons cond. fuel
	1960	1965	1970	1975	1980
solid fuel
coke oven gas
Natural gas

The nitric-hydrogen mixture, regardless of the method of its preparation, contains impurities of substances, some of which are catalytic poisons, causing both reversible (oxygen, carbon oxides, water vapor) and irreversible (various compounds of sulfur and phosphorus) poisoning of the catalyst. In order to remove these substances, the ABC is subjected to preliminary purification, the methods and depth of which depend on their nature and content, that is, on the method of production of the ABC. Usually ABC obtained by conversion of natural gas contains carbon monoxide (IV), methane, argon, traces of oxygen and up to 0.4% vol. carbon monoxide (II).

To purify ABC in industry, absorption methods with liquid absorbers (wet method) and adsorption with solid absorbers (dry method) are used. In this case, the cleaning process can be carried out at various stages of production:

• source gas before submitting it for conversion;
• converted gas to remove carbon monoxide (IV) from it;
• nitric mixture immediately before the synthesis of ammonia (fine purification ABC).

Fine purification of ABCs is achieved by chemisorption of impurities with liquid reagents and finally their catalytic hydrogenation or washing of ABCs with liquid nitrogen.

To remove carbon monoxide (IV) and hydrogen sulfide, ABC is washed in towers with a packing with alkaline reagents that form unstable thermal salts with them: an aqueous solution of ethanolamine or a hot solution of potassium carbonate activated by the addition of diethanolamine. In this case, the reactions proceed accordingly:

Carbon monoxide (II) is removed from the ABC by washing it with a copper-ammonia solution of copper acetate

The absorbers used for chemisorption form unstable compounds with those absorbed from ABC. Therefore, when their solutions are heated and the pressure is reduced, the dissolved impurities are desorbed, which makes it easy to regenerate the absorbent, return it to the process, and ensure the cyclic absorption operation according to the scheme

where P is the admixture absorbed from ABC; A - absorbent; PA is a combination of an admixture and an absorbent.

A more effective method of ABC purification from carbon monoxide (II) is the washing of ABC with liquid nitrogen at –190 0 С, which is used in modern installations, during which, in addition to carbon monoxide (II), methane and argon are removed from it.

Methane, or precatalysis- a method for the final purification of ABC by catalytic hydrogenation of impurities. This process is carried out in special methanation units (Fig. 8.4) at a temperature of 250–300 0 С and a pressure of about 30 MPa on a nickel-aluminum catalyst (Ni + Al 2 O 3). In this case, exothermic reactions of reduction of oxygen-containing impurities to methane, which is not a poison for an iron catalyst, proceed, and water condenses when the purified gas is cooled and is removed from it:

If an iron catalyst is used in the pre-catalysis, then some ammonia is also formed during the hydrogenation process, in this case the pre-catalysis is called producing.

The purified ABC supplied for synthesis contains up to 0.0025 volume fractions of argon, 0.0075 volume fractions of methane, and not more than 0.00004 volume fractions of carbon monoxide (II), which is the most powerful catalyst poison.

Figure 8.4 - Scheme of the ABC methanation plant:

1. compressor;
2. heater;
3. methanation reactor;
4. methanation reactor;
5. water heater;
6. capacitor;
7. dehumidifier

8.3. Chemical and circuit diagrams of production

The main stage of the ammonia synthesis process from a nitric-hydrogen mixture is described by the equation

Since the predominant method for obtaining ABC is the conversion of methane with air and steam, the chemical scheme for the production of ammonia includes, in addition to this reaction, several reactions of air and steam reforming:

and subsequent conversion of carbon monoxide (II) to carbon monoxide (IV):

After removing carbon monoxide (IV) from the gas mixture and correcting its composition, ABC is obtained with a nitrogen and hydrogen content in a ratio of 1: 3.

Thus, the modern production of ammonia consists of two stages: ABC preparation and its conversion into ammonia, representing a single energy-technological scheme that combines the operations of obtaining ABC, its purification and ammonia synthesis and effectively uses the thermal effects of all stages of the process, which allows several times reduce electricity costs. On fig. 8.5 shows a schematic diagram of the production of ammonia, corresponding to the chemical scheme discussed above.

Figure 8.5 - Schematic diagram of ammonia production:

1. purification of natural gas from sulfur compounds;
2. steam reforming of methane;
3. air conversion of methane;
4. conversion of carbon monoxide (II);
5. chemisorption purification ABC;
6. methanation;
7. ammonia synthesis;
8. absorption of ammonia;
9. ammonia compression.

8.4. Physical and chemical bases of ammonia synthesis

8.4.1. Equilibrium and speed of the process in the system

Balance in the system. Ammonia synthesis reaction from ABC- heterogeneously catalytic reversible, exothermic reaction proceeds with a decrease in volume without the formation of any by-products and is described by the equation

The thermal effect of the reaction depends on temperature and pressure and is 111.6 kJ at a temperature of 500 0 C and a pressure of 30 MPa.

The reaction equilibrium constant has the form

In table. 8.3 shows the content of ammonia in the equilibrium gas mixture for various temperatures at medium (30 MPa) and high (100 MPa) pressures.

Table 8.3 - Ammonia content (vol. shares) in the gas mixture

Pressure, MPa	Temperature, 0 C

The dependence of the ammonia content in the equilibrium gas mixture on temperature and pressure is shown in fig. 8.6.

Figure 8.6 - Dependence of the ammonia content in the mixture on temperature (a) and pressure (b)

From Table. 8.3 and fig. 8.6 it follows that an increase in pressure and a decrease in temperature shift the equilibrium of the synthesis reaction and increase the equilibrium yield of ammonia. However, the equilibrium content of ammonia in the gas, sufficiently high for practical purposes, can only be achieved at a temperature not exceeding 400 0 C, that is, under conditions where the process rate and, consequently, the time to reach the equilibrium state are very low. Therefore, under real conditions, the content of ammonia in the gas mixture will be negligible, which makes the synthesis process inefficient and economically inexpedient.

Process speed. Even at relatively high temperatures, the activation energy of nitrogen molecules is high, and the process of ammonia synthesis in a homogeneous gas phase is practically unfeasible. To reduce the activation energy, catalysts are used to significantly reduce the process temperature.

The ammonia synthesis reaction is catalyzed by metals that have incompletely built-up d- and f-electronic levels. These include iron, rhodium, tungsten, rhenium, osmium, platinum, uranium and some other metals. In industry, contact masses based on iron are used, for example, GIAP catalyst composition

It is cheap, quite active at a temperature of 450–500 0 C, less sensitive to catalytic poisons than other catalysts. promoters as part of the contact mass, they contribute to the creation of a highly developed surface, prevent the recrystallization of the catalyst and increase its activity.

The contact mass is prepared by fusing in a nitrogen atmosphere a mixture of iron oxides Fe 3 O 4 , aluminum Al 2 O 3 , potassium K 2 O, calcium CaO and silicon SiO 2 or metal powders - iron and aluminum - with oxides of calcium and silicon and potassium carbonate, followed by grinding the mass to the size of catalyst grains (5 mm) and reducing them with hydrogen in the ammonia synthesis column. At the same time reactions take place

Since iron catalysts have maximum activity at a temperature not lower than 400–500 0 C, at which a high degree of ABC conversion into ammonia cannot be ensured, ammonia synthesis is carried out under conditions far from equilibrium, and the direct reaction rate has a decisive influence on the overall rate of the process.

The rate constant depends on the temperature, activity and condition of the catalysts. The dependence of the constant on temperature is expressed by the Arrhenius equation

in which the activation energy for reactions on an industrial iron catalyst is 165 kJ/mol.

8.4.2. Optimal mode of the synthesis process

In 8.4.1 it was shown that temperature and pressure affect the state of the system and the rate of ammonia synthesis in the opposite way, that is, there is a contradiction between the thermodynamics and the kinetics of the process. Therefore, the yield of ammonia and the specific productivity of the catalyst depend primarily on these parameters, as well as on the composition and space velocity of the gas mixture, the activity of the catalyst, and the design of the reactor.

Application of high pressures increases the speed of the synthesis process by increasing the driving force of the process and reducing the rate of the reverse reaction of the dissociation of ammonia and promotes the separation of the formed ammonia from the gas mixture by its condensation.

Optimal temperature process is determined by the general laws of the influence of temperature on the product yield of an exothermic reversible catalytic process, which is the production of ammonia (Fig. 8.7).

Figure 8.7 - Dependence of the ammonia content in the gas after synthesis on the temperature and gas volumetric velocity (W3 > W2 > W1).

For each value of the space velocity of the gas mixture W, the ammonia content in it increases with increasing temperature up to a certain limit corresponding to the maximum process rate and ammonia content in the gas. Obviously, this temperature corresponds to the highest intensity of the catalyst.

Increasing the space velocity reduces the output of ammonia. Line A, connecting the maxima of the curves w NH3 = f(T) for different values ​​of the volumetric velocity w, corresponds to the optimal temperature curve, line BB represents the equilibrium curve.

However, with an increase in the volumetric velocity of the gas, the intensity of the catalyst increases (Fig. 8.8). Therefore, an increase in the volumetric velocity of the gas up to a certain limit has a positive effect on the output of ammonia.

Figure 8.8 - Dependence of the intensity of the catalyst on the space velocity at Р1 > P2

A further increase in it leads to an increase in the cost of gas transportation, a violation of autothermality, and a decrease in the completeness of ammonia release from the gas mixture. The upper limit of the space velocity is usually determined precisely by the autothermal nature of the synthesis process. In practice, in medium-pressure installations, the gas volumetric velocity is chosen within h.

Since the degree of conversion does not exceed 0.14 - 0.20 dollars. unit, then the ammonia synthesis process is built according to the circulation scheme with the separation of the resulting ammonia from the unreacted ABC and the return of its remaining part to the reactor, as shown in Fig. 8.9 Since the synthesis of ammonia occurs with a reduction in volume, inert impurities (argon, methane) accumulate in the circulating ABC, which leads to a decrease in the yield of ammonia due to a decrease in the concentration of nitrogen and hydrogen in it. To eliminate this, part of the circulating ABC is periodically withdrawn from the ammonia cycle as a purge gas (stripping).

Figure 8.9 - Circulation scheme of synthesis

Figure 8.10 - dependence of ammonia yield on contact time at various temperatures.

To isolate the resulting ammonia from ABC, it is cooled to the ammonia liquefaction temperature. In this case, part of the ammonia remains in the ABC. Its concentration depends on temperature and varies from 0.015 vol. shares at -20 0 С up to 0.073 vol. USD at +20 0 C at a pressure of about 30 MPa. When using water and ammonia cooling, this provides a residual ammonia content in the circulating ABC of 0.03 - 0.05 vol. USD

An increase in the contact time cannot be used to ensure an equilibrium state in the system, since in practice the synthesis of ammonia is carried out under conditions that are far from equilibrium (see above). However, at higher temperatures, the equilibrium state is approached more quickly. On fig. 8.10 shows the dependence of the yield of ammonia on the time of contact at various temperatures. It follows from this that at a higher temperature T 2 the equilibrium state can be reached faster than at a lower temperature T 1 , although the yield of ammonia is lower.

8.5. Technological scheme of ammonia production

8.5.1. Choice of production scheme

The determining parameter in the production of ammonia from a nitric mixture is the synthesis pressure. Depending on the applied pressure, all systems for the production of synthetic ammonia are divided into:

• low pressure systems (10–15 MPa);
• medium pressure systems (25–60 MPa);
• high pressure systems (60–100 MPa).

By the method of mathematical modeling, it was found that the most economically advantageous is to carry out the process at medium pressure. At the stages of gas compression, ammonia synthesis and its condensation from ABC, capital and energy costs decrease with increasing pressure to a certain limit. The optimum pressure is 32 MPa. A further increase in pressure does not lead to a significant reduction in costs, but complicates the technological scheme of production.

In the medium pressure system, a sufficiently high speed of the process is ensured, the ease of separation of ammonia from the gas mixture, the possibility of simultaneously obtaining liquid and gaseous products. As a result, medium-pressure installations are common in world and domestic practice.

5.2. Technological scheme of production

On fig. 8.11 shows the technological scheme of modern ammonia production, at an average pressure, the productivity is 1360 tons / day. Its mode of operation is characterized by the following parameters:

Figure 8.11 - Technological scheme of ammonia production:

1. synthesis column;
2. water condenser;
3. mixer (injector) of fresh ABC and circulating gas;
4. condensation column;
5. gas separator;
6. liquid ammonia evaporator;
7. remote heat exchanger (waste heat boiler);
8. pipe compressor.

contact temperature

• 450–550 0 С;
• pressure 32 MPa;
• volumetric velocity of the gas mixture 4 × 10 4 nm 3 /m 3 h;
• the composition of the nitric-hydrogen mixture is stoichiometric.

A mixture of fresh ABC and circulating gas under pressure is supplied from the mixer 3 to the condensation column 4, where part of the ammonia is condensed from the circulating gas, from where it enters the synthesis column 1. The gas leaving the column contains up to 0.2 vol. ) is sent to the water cooler-condenser 2 and then to the gas separator 5, where liquid ammonia is separated from it. The remaining gas after compressor 8 is mixed with fresh ABC and sent first to the condensation column 4, and then to the liquid ammonia evaporator 6, where, when cooled to -20 0 С, most of the ammonia also condenses. Then the circulation gas containing about 0.03 vol.% of ammonia enters the synthesis column 1. In the evaporator 6, simultaneously with the cooling of the circulation gas and the condensation of the ammonia contained in it, the evaporation of liquid ammonia occurs with the formation of a commercial gaseous product.

The main apparatus of the technological scheme is the synthesis column, which is a RIV-N reactor. The column consists of a body and a nozzle of various devices, including a catalyst box with a contact mass placed in it, and a system of heat exchange pipes. For the ammonia synthesis process, the optimal temperature regime is essential. To ensure the maximum synthesis rate, the process should be started at a high temperature and, as the degree of conversion increases, it should be lowered in accordance with the line of optimal temperatures (OTT), as shown in Fig. 8.12a. Temperature control and process autothermality are ensured by means of heat exchangers located in the contact mass layer and additionally by supplying part of the cold ABC to the contact mass, bypassing the heat exchanger (Fig. 8.12).

Taking into account the sequential change in temperature during the passage of the reaction mixture and reaction products through heat exchange devices, a catalyst box and a waste heat boiler, the temperature regime of the synthesis column can be represented by a graph (Fig. 8.13).

To protect the column body from high temperatures, which contribute to the diffusion of hydrogen into steel and its destruction, cold ABC entering the column, before passing into the catalyst box, first passes through the annular space between the body and the packing, continuously washing the column walls and cooling them.

Figure 8.12 - Temperature change in the catalyst box (a). Scheme of ABC entry into the catalyst box (b).

Figure 8.13 - Graph of temperature changes in the synthesis column

In industry, two grades (first and second) of liquid ammonia and its aqueous solution (ammonia water) are produced. According to GOST 6221–75, first grade ammonia must contain at least 99.9% and second grade at least 99.6% NH 3 . Ammonia of the 1st grade is used as a refrigerant in refrigeration machines and mineral fertilizer, the 2nd grade is used in the production of nitric acid.

8.6. Improving ammonia production

Improving the industrial production of ammonia is in the following main areas:

• cooperation of ammonia production with the production of basic organic synthesis based on the use of natural gas and oil refining gases;
• creation of aggregates of large (up to 3000 tons/day) unit capacity;
• the use of synthesis columns with a fluidized bed of a catalyst;
• development of new catalysts resistant to poisons with a low (300 0 C) ignition temperature, allowing the synthesis process to be carried out without reducing the ammonia yield at low (10 MPa) pressures.

Ammonia is a substance that is probably familiar to every adult. It's all about the physiological role played by ammonia.

The rapid growth of ammonia output is traditionally facilitated by the relative availability of the raw materials necessary for its production.

The chemical formula of ammonia is well known to everyone since school - NH 3. It is obvious from it: nitrogen and hydrogen are required to obtain it.

Normal atmospheric air is a perfect source of nitrogen here. This resource is almost limitless. Thus, the raw material base for the production of ammonia (and, accordingly, for the entire nitrogen industry) is limited by hydrogen. Or rather, the fuel necessary to obtain it.

As a rule, natural gas is used for these purposes. This circumstance, by the way, greatly contributed to the development of the domestic nitrogen industry: Russia is rich in gas.

However, if anyone from the above is under the impression that large-scale ammonia production is an easy and affordable process, then this is certainly a mistake. The creation of truly efficient industries required serious scientific efforts and technological solutions.

Suffice it to say that the process of obtaining ammonia in practice is carried out in the presence of a catalyst at a temperature of about 500°C and a pressure of 350 atmospheres. From this it is clear how energy-intensive the corresponding production is. But the creation of such conditions makes it possible to achieve a yield of the desired substance at a level of approximately 30 percent.

In general, according to experts, the history of the development of large-tonnage ammonia production should be viewed as a constant struggle to increase the useful use of energy: electrical, thermal, and mechanical. But this process gave excellent results in the end. If at the first industrial plants the efficiency was only about 10 percent, then at modern high-performance plants capable of "producing" half a million tons of products per year, this figure is five times higher.

The work of a modern ammonia plant is very complex. This statement seems surprising if you "focus" only on a fairly simple reaction equation, which is the basis for the synthesis of ammonia. However, the statement about the complexity of the industrial synthesis of ammonia will not seem excessive after the first acquaintance with the scheme of operation of an ammonia plant operating on natural gas.

First stage in the process of ammonia synthesis, it includes a desulfurizer - a technical device for removing sulfur from natural gas. This is an absolutely necessary step, since sulfur is a catalytic poison and "poisons" the nickel catalyst in the subsequent stage of hydrogen production.

Second stage industrial synthesis involves the conversion of methane (industrial production of hydrogen). Methane conversion is a reversible reaction that takes place at 700 - 800 ° C and a pressure of 30 - 40 atm using a nickel catalyst when methane is mixed with water vapor: CH 4 + H 2 O ↔ CO + 3H 2

The hydrogen formed by this reaction, it would seem, can already be used for the synthesis of ammonia - for this it is necessary to put air containing nitrogen into the reactor. This is done, but at this stage other processes take place. Partial combustion of hydrogen in atmospheric oxygen occurs:

2H 2 + O 2 \u003d H 2 O (steam)

As a result, at this stage, a mixture of water vapor, carbon monoxide (II) and nitrogen is obtained. Water vapor, in turn, is reduced again to form hydrogen, as in the second stage. Thus, after the first three stages, there is a mixture of hydrogen, nitrogen and "undesirable" carbon monoxide (II).

The oxidation of CO formed in the two previous stages to CO2 is carried out precisely according to this reaction:

CO + H 2 O (steam) ↔ CO 2 + H 2 (3)

The "shear" process is carried out sequentially in two "shear reactors". In the first of them, the Fe 3 O 4 catalyst is used and the process takes place at a sufficiently high temperature of about 400 °C. The second process uses a more efficient copper catalyst and can be run at a lower temperature.

At the fifth degree, carbon monoxide (IV) is removed from the gas mixture by absorption with a solution of aMDEA (activated methyl diethanol amine).

At the beginning, carbon dioxide is absorbed, then it is desorbed and removed from the process.

However, the quality of aMDEA purification is not enough for the nitrogen-hydrogen mixture to be used for ammonia synthesis. The remaining amount of CO is quite enough to ruin the iron catalyst at the main stage of ammonia synthesis (1). At the 6th stage, carbon monoxide (II) is removed by the conversion reaction with hydrogen to methane on a special nickel catalyst at temperatures of 300 - 400 ºС:

CO + 3H 2 ↔ CH 4 + H 2 O

The gas mixture, which now contains ≈ 75% hydrogen and 25% nitrogen, is compressed; its pressure at the same time increases from 25 - 30 to 200 - 250 atm. In accordance with the Klaiperon-Mendeleev equation, such compression leads to a very sharp increase in the temperature of the mixture. Immediately after compression, it is necessary to cool to 350 - 450 ºС.

Previous567891011121314151617181920Next

VIEW MORE:

AMMONIA PRODUCTION

For the normal life of plants and animals, nitrogen is needed only in an assimilable form. However, due to the high chemical inertness of nitrogen, its inexhaustible resources* are practically inaccessible to living nature. To solve the food problem, mankind converts nitrogen into an assimilable form, "binding" it to the simplest compound - ammonia, from which nitric acid and mineral fertilizers are then obtained.

The growth rate of ammonia production is constantly increasing. At the same time, the quantitative growth of production is accompanied by qualitative changes in the structure of the production base. The capacities of single units for the synthesis of ammonia are being enlarged, ** new efficient catalysts and sorbents are being introduced, progressive equipment and technological schemes are being developed that ensure a more complete use of raw materials and fuel.

In recent years, due to better heat recovery, ammonia production can be organized according to the energy technology principle, in which the process is completely self-sufficient in steam and mechanical energy.

The production of ammonia consists of three stages: obtaining a nitrogen-hydrogen mixture, its purification, and the actual synthesis of ammonia.

First stage - obtaining a nitric mixture. The raw materials for the production of ammonia are nitrogen and hydrogen. Nitrogen is isolated from air - a gas mixture containing by volume 78.05% nitrogen, 20.95% oxygen, 0.94% argon and small amounts of carbon dioxide, neon, helium, krypton and xenon. To do this, the air is transferred into a liquid state by deep cooling, and then by rectification based on the difference in the boiling points of individual gases, it is divided into its constituent parts.

Hydrogen is produced in one of the following ways: electrolysis of water or aqueous solutions of table salt; from coke oven gas by successive liquefaction of all its components except hydrogen; conversion of carbon monoxide of generator gas; conversion of methane or its homologues.

Hydrogen production is the most expensive stage of production. At present, most of the hydrogen for the synthesis of ammonia is obtained from the cheapest types of raw materials - gases containing methane and its homologues. These include associated gases of oil production, natural gas, and refinery gases. In the presence of water vapor and oxygen, methane is converted to hydrogen:

CH 4 + H 2 O CO + H 2 - Q

CH 4 + 0.5O 2 CO + 2H 2 + Q

and the resulting carbon monoxide is converted to CO 2 and H 2:

CO + H 2 0 C0 2 + H 2 + Q

The conversion of natural gas is carried out at atmospheric or elevated pressure with the use of catalysts (catalytic conversion) or without them (high temperature conversion). Often the process on a nickel catalyst is carried out so that the residual concentration of methane is 8 - 10%. At such a concentration of methane, its further conversion with air (i.e., with a mixture of nitrogen and oxygen in a ratio of 4:1) makes it possible to immediately obtain a nitric-hydrogen mixture with a ratio of N 2: H 2 = 1:3. This eliminates the need to build expensive and energy-intensive air separation plants and significantly improves the technical and economic performance of the process.

However, the resulting nitrogen, hydrogen and nitric mixture are contaminated with sulfur compounds that have come from natural gas, as well as carbon oxides and dioxides formed during conversion.

Due to the high sensitivity of the ammonia synthesis catalyst to these impurities, which greatly reduce its activity and cause irreversible poisoning (especially compounds containing sulfur), the gas is subjected to thorough purification.

Second stage - gas purification. For removal of impurities of sulfur compounds such as carbon disulfide CS 2 , carbon sulphide COS and mercaptans R-SH they are hydrogenated on a cobalt-molybdenum catalyst at a temperature of 350-450 ° C to easily captured hydrogen sulfide

9H 2 + impurities (CS 2 + COS + R - SH) 4H 2 S + 2CH 4 4+ H 2 O

The resulting hydrogen sulfide is removed from the gas using various absorbers, such as zinc oxide: ZnO + H 2 S à ZnS + H 2 O

After such purification, the gas contains hydrogen sulfide not more than 1 mg/m 3 .

Gas purification from CO 2 is carried out with the help of liquid absorbers. Water purification, which consumed a large amount of water and energy for its pumping, was replaced by more efficient purification using aqueous solutions of ethanolamines or hot solutions of potash activated with arsenic. When washing the gas with the indicated aqueous solutions, CO 2 impurities form carbonates and bicarbonates. Regeneration of absorbers with removal of CO 2 in the desorber is carried out: for ethanolamines - by heating to 120 °C, for potash solutions - by pressure reduction.

CO impurities are removed from the gas by absorption of a copper-ammonia solution of weak acetic or formic acid. The cleaning efficiency increases with increasing pressure up to 30 MPa and lowering the temperature to 25 - 0 °C. After purification, no more than 0.003% CO remains in the gas. When cleaning the nitric-hydrogen mixture obtained from coke oven gas, the residual CO is removed by washing with liquid nitrogen. When this part of the nitrogen evaporates and passes into the nitric mixture, providing a ratio of N 2: H 2 close to 1:3. By diluting the mixture with an additional amount of nitrogen, it is brought to the exact ratio of N 2: H 2 = 1:3 necessary for the synthesis of ammonia. In cases where the residual amounts of CO and CO 2 in the gas are small (up to 1%), the removal of impurities is carried out by their hydrogenation (methanation) according to the reactions

CO + ZN 2 CH 4 + H 2 O; CO 2 + 4H 2 CH 4 + 2H 2 O

The process temperature is 200 - 400 °C, the catalyst is nickel deposited on aluminum oxide.

Third stage - ammonia synthesis. The formation of ammonia by the reaction

N 2 + 3H 2 2NH 3 + Q proceeds quickly enough only in the presence of catalysts containing oxides of aluminium, potassium and calcium as activators. The thermal effect of the reaction increases with increasing temperature, and the equilibrium yield depends not only on temperature, but also on pressure.

The synthesis of ammonia is a reversible exothermic process.

According to Le Chatelier's principle, the removal of heat should shift the reaction to the right. For this purpose, intermediate cooling of the gas mixture by a less heated counter flow is carried out after each contact with the catalyst. This ensures the autothermal process. However, despite the removal of heat, the temperature during the process still increases somewhat. Therefore, in the ammonia synthesis column, catalysts are used that operate effectively in various temperature ranges.

Modern ammonia synthesis columns of large unit capacity have four shelves with catalysts. On the first (along the gas flow) there is a low-temperature catalyst (350-500 °C), on the second - medium-temperature (400-550 °C); on the third and fourth - high-temperature (550 - 700 ° C).

In addition to the above factors, the actual output of ammonia is influenced by the activity of the catalyst, the composition of the gas mixture, the design features of the apparatus (the lower the hydraulic resistance in them, the higher the throughput and the lower the energy costs) and the duration of contact of the gas with the catalyst (or the reciprocal value, called the space velocity gas). With an increase in the space velocity, the removal of ammonia from 1 m 3 of the contact mass increases sharply. But at the same time, the volume of the unreacted nitric-hydrogen mixture increases. To avoid losses, this mixture must be repeatedly pumped through the catalyst in a closed cycle. This increases the energy consumption for pumping. From an economic point of view, such costs can be minimized at certain optimal values ​​of the gas space velocity (from 15,000 to 30,000 m 3 of the gas mixture through 1 m 3 of the catalyst per hour).

The technical and economic indicators of this production can be improved by the transition to energy-, resource- and labor-saving technology. This is achieved by using units of large unit capacity, low-water circuits and process control systems. Particular attention is paid to the utilization of the heat of flue gases leaving the methane heating furnace, as well as gas streams leaving the organic sulfur hydrogenation reactor, methane and carbon monoxide converters, ammonia synthesis columns, methanator, etc.

The recovered high-potential heat is used to produce high-pressure steam. The energy of this steam in the turbines is converted into mechanical energy for compressing and moving gases with the help of compressors. Low-potential heat is utilized to obtain low-pressure process steam, water heating, cold production, etc. Such an energy saving principle provides the process with steam and mechanical energy. For areas lacking in fuel, this allows organizing production with minimal energy consumption. Replacing water cooling with air significantly reduces water consumption. These principles are used in modern schemes for the production of ammonia on units of large (1500 t/day) unit capacity. One such unit provides annual savings in operating costs in the amount of 15 million rubles. and capital investments up to 25 million rubles. The specified scheme includes blocks for obtaining a nitric-hydrogen mixture, gas purification and ammonia synthesis.

In the ammonia synthesis unit, for compressing the nitric-hydrogen mixture to 30 MPa and circulating it, the utilized heat is converted into mechanical energy of compression and displacement (Fig. 7.6). To do this, high pressure and temperature steam obtained in the waste heat boiler is sent to the steam turbine 7, on the shaft of which a turbocharger is installed. 2.

The turbocompressor compresses the fresh nitrogen-hydrogen mixture, and in the last stage it is also mixed with the N 2 + 3H 2 return mixture that has not reacted on the catalyst, containing up to 2-3% NH 3 . To capture ammonia, the gas after the turbocharger is passed through an ammonia cooler. 3, where it condenses and as a liquid is easily separated in the separator 4. After the separator, the mixture of nitrogen and hydrogen passes through two heat exchangers 5 and 6, heats up to 425 °С

and is sent to the shelf synthesis column 7. Compared with the traditional contact apparatus with a double heat exchange tube in the shelf radial columns, the hydraulic resistance, and hence the energy loss, is significantly reduced. In such a column with an internal diameter of up to 2.1 m, a height of up to 25 m and a wall thickness of chromium-molybdenum steel of 10 - 30 cm, there are four shelves. The shelves are loaded with catalyst in increasing amounts and with an increasing range of operating temperatures from the first to the last.

To maintain the specified temperature regime along the height of the column, after each shelf, the heat of the exothermic reaction is removed to the waste heat boiler. Fine temperature control is achieved by introducing a certain amount of cold mixture into the hot gas mixture.

Approximately 15-20% of the nitric mixture on the catalyst is converted into ammonia. Leaving the synthesis column with a temperature of 320 - 380 ° C, the mixture successively gives off heat to the feed water of the waste heat boiler in the water heater 8, and then heats the oncoming cold gas flow in the "hot" heat exchanger 6. Then it is cooled in the air cooler 9 and the "cold" heat exchanger 5. At a pressure of about 30 MPa in such a gas mixture, ammonia condenses already at a temperature of 25 - 40 ° C and after separation in the separator 10 sent to storage.

Gas mixture containing up to 2 - 3% of uncondensed ammonia, and unreacted nitrogen and hydrogen by a turbocharger 2 back into production.

The degree of conversion of the nitric mixture into ammonia in the synthesis column ranges from 15 to 20%. But due to its repeated circulation in a closed circuit, the actual ammonia yield in medium pressure systems is 91 - 95%. Compared to systems operating at low (10 MPa) and high (100 MPa) pressure, medium-pressure systems, which are most widely used in the world, successfully solve the issues of ammonia release at a sufficient process speed in the contact apparatus. In addition to liquid ammonia, gaseous ammonia is also obtained, which is usually immediately processed into urea, ammonium nitrate, and nitric acid.

Flowchart - Production - Ammonia

Page 1

Technological schemes for the production of ammonia include from 5 to 9 main technological blocks, such as purification of feedstock, production of a nitric mixture, ammonia synthesis, and others.

If the technological scheme of ammonia production includes gas flushing with liquid nitrogen, it is advisable to carry out high-temperature conversion of natural gas under pressure up to 30 am at a temperature of about 1350 C. In this case, the dry converted gas contains approximately 96% (CO H2) with a residual concentration of methane of about 1% and low consumption coefficients for natural gas and oxygen.

If the technological scheme of ammonia production includes gas flushing with liquid nitrogen, it is advisable to carry out high-temperature conversion of natural gas under pressure up to 30 MPa at a temperature of about -1350 C. In this case, dry converted gas contains approximately 95 5% (СО Н2) at a residual concentration of methane of about 1% and low flow rates for natural gas and oxygen.

If the technological scheme of ammonia production does not provide for flushing with liquid nitrogen, but there is copper-ammonia purification, it is advisable to use oxygen-enriched air for high-temperature conversion of natural gas. In this case, the residual concentration of methane in the converted gas should not exceed approximately 0 5%; this is achieved by raising the reaction temperature to 1400 C.

If the technological scheme of ammonia production does not provide for gas flushing with liquid nitrogen, but there are departments for low-temperature conversion of carbon monoxide and methanation, it is advisable to use air enriched with oxygen for high-temperature conversion of natural gas. In this case, the residual concentration of methane in the converted gas should not exceed approximately 0 5%, which is associated with an increase in the reaction temperature to 1400 C.

Depending on the technological scheme of ammonia production, the oil dissolved and dispersed in the compressed gas affects the following stages of ammonia production in different ways. If the plant has copper-ammonia treatment under the same pressure as synthesis, the gas stream containing oil enters, first of all, copper-ammonia scrubbers, where it pollutes the solution, worsens the conditions for gas purification and regeneration of copper-ammonia solution, increases consumption coefficients. There is evidence that the purification of gas from oil only at the stage of copper-ammonia purification gives.

Depending on the technological scheme of ammonia production, high-temperature conversion of natural gas is carried out in a mixture with technical oxygen or oxygen-enriched air.

On fig. 3 shows a process flow diagram for the production of ammonia from natural gas.

The unit is the head unit in the technological scheme of ammonia production, and the correct maintenance of the regime in it ultimately determines the required composition of the nitric mixture for ammonia synthesis. Compliance with the thermal regime contributes to the normal and stable operation of the vaporization system.

The technological schemes currently being created for the production of ammonia with a capacity of over 1000 t MN3 on land from one unit do not provide for the separation of the converted gas from carbon monoxide with copper-ammonia solutions or washing with liquid nitrogen.

15 is a simplified flow diagram for the production of ammonia from natural gas. As you can see, the scheme is complex.

Thus, technological schemes for the production of ammonia with a capacity of one unit of 400 tons per unit are currently being introduced. And in the prospective period, equipment for the production of ammonia up to 800 tf will be mastered.

The transition of the industry of bound nitrogen to cheap natural gas significantly reduces the cost of raw materials. In addition, in this way, working conditions are improved at plants producing synthetic ammonia. This also leads to a simplification of the technological scheme for the production of ammonia.

Pages:      1

Municipal educational institution

Novosafonovskaya secondary school

Ammonia production: a brief description

Prokopevsky district 2006

Introduction

1. Methods for obtaining ammonia

2. Modern ammonia production process

List of used literature

Introduction

The overall economic objective of every chemical enterprise is to produce chemicals of high quality and in sufficient quantity to make a profit. Related to this is the requirement that all resources be used as efficiently as possible. However, this can only be achieved if the chemical process itself is as efficient as possible. In the chemical industry, instead of the concept of "reagents", the terms "source materials", "raw materials" or simply raw materials, sometimes "ore" are used much more often. For any process to be economically justified, it is necessary to achieve the optimal yield of the target product from the raw materials. The optimal yield is not necessarily the same as the theoretical yield, or even the maximum achievable yield. Obtaining the maximum achievable yield may, for example, require too much consumption of some expensive starting material, or too long a process, or extreme conditions are created (very high temperatures or pressures), fraught with dangerous emergency situations, etc., - all of which can make the maximum achievable yield uneconomical.

The actual yield of each particular chemical process may depend on a number of factors, the main ones being temperature, pressure, the presence of a catalyst, the purity of the starting materials, and the efficiency of the extraction of the final product. Industrial production of substances implies an excellent knowledge of the theoretical patterns of chemical reactions (energetics of chemical reactions, chemical kinetics and catalysis, chemical equilibrium).

All of the factors listed below are important, especially when it comes to such large-scale production, such as, for example, the production of ammonia.

Designers of chemical plants create heavy-duty plants for the production of ammonia. For example, installations have been created that produce 1000-1200 tons of ammonia per day. Currently, about 5 million tons of ammonia are produced annually throughout the world.

1. Methods for obtaining ammonia

ammonia cyanamide process desulfurizer

The first industrial process that was used to produce ammonia was the cyanamide process. When lime CaO and carbon were heated, calcium carbide CaC2 was obtained. The carbide was then heated under nitrogen to give calcium cyanamide CaCN2; further ammonia was obtained by hydrolysis of cyanamide:

CaCN2 (tv) + 3H2O \u003d 2NH3‍‍ + CaCO3 (tv)

This process required a lot of energy and was economically unprofitable.

In 1908, the German chemist F. Gaber discovered that ammonia can be obtained from hydrogen and atmospheric nitrogen on an iron catalyst. The first plant to produce ammonia using this method used hydrogen, which was obtained by electrolysis of water. Subsequently, hydrogen began to be obtained from water by reduction with coke. This method of producing hydrogen is much more economical. After the discovery of Haber, the production of ammonia began to grow rapidly, this is not surprising, since huge amounts of ammonia are needed to produce nitrogen-containing fertilizers. Approximately 80% of all ammonia produced in the world is used for their manufacture. Together with nitrogen-containing fertilizers, nitrogen is introduced into the soil in a soluble form, which most plants need. The remaining ≈20% of the ammonia produced is used to make polymers, explosives, dyes, and other products.

The modern process of obtaining ammonia is based on its synthesis from nitrogen and hydrogen using a special catalyst:

N2 + 3H2 ↔ 2NH3 + 45.9 kJ (1)

Since this reaction is reversible, the question arises: at what temperatures and pressures is it most advantageous to achieve the maximum yield

product? Since the reaction is exothermic, it is clear from Le Chatelier's principle that the lower the temperature of the process, the more the equilibrium will shift towards the formation of ammonia, and it can be assumed that the temperature should be lowered as much as possible. But in reality, everything is more complicated: at low temperatures, the reaction practically does not occur, so a compromise solution has to be made. Since a low temperature is required to establish the optimal equilibrium state of the reaction, and a high temperature is required to achieve a satisfactory rate, in practice the process is carried out at a temperature of ≈ 400–500 °C.

But even at such a high temperature, the presence of a special catalyst is required to achieve a sufficient reaction rate. Sponge iron activated with potassium and aluminum oxides is used as a catalyst.

It can be seen from the reaction equation that the total number of moles decreases from 4 to 2. According to Le Chatelier's principle, in this case it is advantageous to carry out the process by increasing the pressure. But this conclusion is only qualitative, in practice it is necessary to know exactly how much the output of NH3 will increase (by 10% or only 0.1%) with increasing pressure. Table 1 quantifies the effect of temperature and pressure on the ammonia yield (percentage of ammonia in the equilibrium mixture) from the reaction.

This table shows that an increase in temperature at any pressure significantly reduces the ammonia content in the gas mixture, however, at temperatures below 500 ° C, the reaction rate is very low, therefore, in practice, the process is usually carried out at a temperature of 450 ° C.

Table 1

As for pressure, pressures of the order of 300 - 100 atm are used here, but most often the "average" pressure is ≈ 250 atm. Although under these conditions only about 20% of the starting substances are converted to ammonia, however, as a result of the use of a circulating technological scheme (reintroducing unreacted H2 and N2 into the reaction), the total degree of conversion of the starting substances to ammonia is very high.

2. Modern ammonia production process

The work of a modern ammonia plant is very complex. This statement seems surprising if we “focus” only on the fairly simple-looking reaction equation (1), which is the basis for the synthesis of ammonia. However, the statement about the complexity of the industrial synthesis of ammonia will not seem excessive after the first acquaintance with the scheme of operation of an ammonia plant operating on natural gas (Fig. 1). The first step in the ammonia synthesis process includes a desulfurizer. A desulfurizer is a technical device for removing sulfur from natural gas. This is an absolutely necessary step, since sulfur is a catalytic poison and "poisons" the nickel catalyst in the subsequent stage of hydrogen production.

The second stage of the industrial synthesis of ammonia involves the conversion of methane (industrial production of hydrogen). Methane conversion is a reversible reaction that occurs at 700–800 °C and a pressure of 30–40 atm using a nickel catalyst when methane is mixed with water vapor:

CH4 + H2O ↔ CO + 3H2 (2)

The hydrogen formed by this reaction, it would seem, can already be used for the synthesis of ammonia according to reaction (1) - for this it is necessary to put air containing nitrogen into the reactor. This is done at stage (3), but at this stage other processes take place.

Partial combustion of hydrogen in atmospheric oxygen occurs:

2H2 + O2 \u003d H2O (steam)

As a result, at this stage, a mixture of water vapor, carbon monoxide (II) and nitrogen is obtained. Water vapor, in turn, is reduced again with the formation of hydrogen, as in the second stage of the second stage, according to them, after the first three stages there is a mixture of hydrogen, nitrogen and "undesirable" carbon monoxide (II).

In Fig. 1, stage (4) is designated as a "shift" reaction, but it can take place at two temperature regimes and different catalysts. Oxidation

CO, formed in the two previous stages, to CO2 is carried out precisely according to this reaction:

CO + H2O (steam) ↔ CO2 + H2 (3)

The "shear" process is carried out sequentially in two "shear reactors". In the first of them, the Fe3O4 catalyst is used and the process takes place at a sufficiently high temperature of about 400 °C. The second process uses a more efficient copper catalyst and can be run at a lower temperature.

At the fifth degree, carbon monoxide (IV) is "washed out" from the gas mixture by absorption with an alkaline solution:

KOH + CO2 = K2CO3.

The “shift” reaction (3) is reversible, and after the 4th stage, in fact, ≈ 0.5% CO still remains in the gas mixture. This amount of CO is quite sufficient to ruin the iron catalyst at the main stage of ammonia(1) synthesis. At the 6th stage, carbon monoxide (II) is removed by the conversion reaction with hydrogen to methane on a special nickel catalyst at temperatures of 300–400 °C:

CO + 3H2 ↔ CH4 + H2O

The gas mixture, which now contains ≈ 75% hydrogen and 25% nitrogen, is compressed; its pressure at the same time increases from 25 - 30 to 200 - 250 atm.

In accordance with the Klaiperon-Mendeleev equation, such compression leads to a very sharp increase in the temperature of the mixture.

Immediately after compression, it is necessary to cool to 350 - 450 °C. It is this process that is described with accuracy by reaction (1).

List of used literature

1.N.E. Kuzmenko, V.V. Eremin, V.A. Popkov. Chemistry. Theory and tasks. - M .: ONIX 21st century, "World and Education", 2003.

What is ammonia

Ammonia, or hydrogen nitride, is one of the compounds of nitrogen. It is a colorless gas with a pungent characteristic odor and has the chemical formula NH3. When frozen or under pressure, ammonia turns into a liquid form.

Ammonia is widely used in industry, and is also a key component in the production of nitrogen fertilizers.

Nitrogen is essential for plants to develop and grow properly. The use of fertilizers increases the nitrogen content of the soil, increasing crop yields.

The use of ammonia in agriculture

Ammonia is mainly used to produce many types of nitrogen fertilizers, such as urea and nitrate (ammonium nitrate) and ammonium sulfate. Most of the ammonia produced in the world is sold to agricultural or industrial consumers.

Wide use in industry

Ammonia is one of the most important substances for the chemical industry. It is used to produce polymers, textiles, explosives, ethanol. Ammonia is used both as a solvent and a coolant. Ammonia is used in the manufacture of medicines and cosmetics.

Ammonia production

Ammonia is produced by combining nitrogen and hydrogen at temperatures of 380 - 500 degrees Celsius and a pressure of 250 atm in the presence of a catalyst.

Coal, coke and coke oven gas can be used as raw materials for the production of ammonia, but ammonia is mainly produced from natural gas. Ammonia production is characterized by high energy intensity, natural gas consumption is one of the most important factors determining profitability.

Use of ammonia

As a fertilizer

Independently, anhydrous ammonia is used as a fertilizer, which is obtained by liquefying gaseous ammonia under high pressure. It is a liquid with a nitrogen content of 82.3%, making it the most concentrated and cost effective nitrogen fertilizer available.

Many types of nitrogen fertilizers are produced from ammonia.

The most important of these are urea, ammonium nitrate and ammonium sulfate.

Carbamide (urea) is made from ammonia and carbon dioxide.

It comes in granular and micro granular form and contains 46% nitrogen making it the most concentrated nitrogen fertilizer available.

Ammonium nitrate (NH 4 NO3) - the most common universal nitrogen fertilizer containing 35% nitrogen, is used as the main fertilizer and for top dressing.

Ammonium sulfate contains 21% nitrogen and up to 24% sulfur, therefore it is also a source of sulfur nutrition. Well absorbed, not washed out of the soil, used for all crops.

Industrial use

Ammonia is one of the most important products of the chemical industry. Substances produced from ammonia serve as the basis for the production of propylene, textile fibers, wires, pipes, containers, tires, car parts and telephones. Explosives are also produced from ammonia.

Liquid ammonia is used as a solvent and refrigerant. Ammonia is also used as an antifreeze additive to dry mortars.

Ammonia derivatives amines are used in the field of medicine. These are ammonia, components of cosmetics and medicines.

Aqueous ammonia is used as a source of nitrogen in the yeast production process. There is a growing demand for ethanol around the world, and yeast is the only type of microorganism used to turn sugar into ethanol.

Storage and transportation

When frozen or under pressure, ammonia becomes liquid and requires special equipment and machinery for transportation and storage.

Liquid ammonia is stored in interconnected tanks equipped with safety valves. To increase safety, tanks are dug in, additional pallets and walls are installed.

When storing large volumes of hydrocarbon gases, underground gas storage facilities are the most efficient. The storage of ammonia in isothermal gasholders has become widespread.

Transportation of ammonia is carried out in special transport containers by rail, water and vehicles or through main pipelines.

Main consumers

The main demand for the product comes from China, whose enterprises consume about 30% of the ammonia produced in the world. Several other countries and regions demonstrate approximately the same level of ammonia consumption: these are the USA (10%), the countries of the CIS and Western Europe (8-9% each), and India (8%).

Demand for ammonia

According to experts' forecasts, in 2020 ammonia production will be about 190 million tons per year. About three quarters of the ammonia produced in the world is used for the production of fertilizers, about 50% goes to the production of carbamide alone.

Currently, the demand for carbamide is growing in the world market, therefore it is predicted that the demand for ammonia, from which it is produced, will grow at a rate of at least 2% per year until 2020.

The projected increase in demand for the product creates opportunities for newly built urea plants.