Sulfuric acid production scheme. Technological scheme for the production of sulfuric acid by the contact method according to the method "DK - DA. Justification of the production method

1. Commodity and technology-determining properties of sulfuric acid.

Sulfuric acid- one of the main large-tonnage products of the chemical industry. It is used in various industries National economy, since it has a set of special properties that facilitate its technological use. Sulfuric acid does not smoke, has no color and odor, is in a liquid state at ordinary temperatures, and in concentrated form does not corrode ferrous metals. At the same time, sulfuric acid is one of the strong mineral acids, forms numerous stable salts and is cheap.

In technology, sulfuric acid is understood as systems consisting of sulfur oxide (VI) and water of various compositions: p SO 3 t H 2 O.

At n = t = 1, this is sulfuric acid monohydrate (100% sulfuric acid), at t > n - aqueous solutions monohydrate, at t< п – растворы оксида серы (VI) в моногидрате (олеум).

Sulfuric acid monohydrate is a colorless oily liquid with a crystallization temperature of 10.37 ° C, a boiling point of 296.2 ° C and a density of 1.85 t / m 3. It mixes with water and sulfur oxide (VI) in all respects, forming hydrates of the composition H 2 SO 4 H 2 O, H 2 SO 4 2H 2 O, H 2 SO 4 4H 2 O and compounds with sulfur oxide H 2 SO 4 SO 3 and H 2 SO 4 2SO 3.

These hydrates and sulfur oxide compounds have different crystallization temperatures and form a range of eutectics. Some of these eutectics have crystallization temperatures below or close to zero. These features of sulfuric acid solutions are taken into account when choosing its commercial grades, which, according to the conditions of production and storage, should have a low crystallization temperature.

The boiling point of sulfuric acid also depends on its concentration, that is, the composition of the "sulfur oxide (VI) - water" system. With an increase in the concentration of aqueous sulfuric acid, its boiling point increases and reaches a maximum of 336.5 ° C at a concentration of 98.3%, which corresponds to the azeotropic composition, and then decreases. The boiling point of oleum with an increase in the content of free sulfur oxide (VI) decreases from 296.2 o C (boiling point of monohydrate) to 44.7 o C, corresponding to the boiling point of 100% sulfur oxide (VI).

When sulfuric acid vapor is heated above 400 ° C, it undergoes thermal dissociation according to the scheme:

400 o C 700 o C

2 H 2 SO 4<=>2H 2 O + 2SO 3<=>2H 2 O + 2SO 2 + O 2.

Among mineral acids, sulfuric acid ranks first in terms of production and consumption. Its world production has more than tripled over the past 25 years and currently stands at more than 160 million tons per year.

The fields of application of sulfuric acid and oleum are very diverse. A significant part of it is used in the production of mineral fertilizers (from 30 to 60%), as well as in the production of dyes (from 2 to 16%), chemical fibers (from 5 to 15%) and metallurgy (from 2 to 3%). It is used for various technological purposes in the textile, food and other industries. On fig. 1 shows the use of sulfuric acid and oleum in the national economy.

Rice. 1. The use of sulfuric acid.

2. Raw sources for obtaining sulfuric acid.

The raw material in the production of sulfuric acid can be elemental sulfur and various sulfur-containing compounds, from which sulfur or directly sulfur oxide (IV) can be obtained.

Natural deposits native sulfur are small, although its clarke is 0.1%. Most often, sulfur is found in nature in the form of metal sulfides and metal sulfates, and is also part of oil, coal, natural and associated gases. Significant amounts of sulfur are contained in the form of sulfur oxide in flue gases and non-ferrous metallurgy gases and in the form of hydrogen sulfide released during the purification of combustible gases.

Thus, the raw materials for the production of sulfuric acid are quite diverse, although until now, elemental sulfur and iron pyrites are mainly used as raw materials. The limited use of such raw materials as flue gases from thermal power plants and gases from copper smelting is explained by the low concentration of sulfur oxide (IV) in them.

At the same time, the share of pyrites in the balance of raw materials decreases, and the share of sulfur increases.

In the general scheme of sulfuric acid production, the first two stages are essential - the preparation of raw materials and their combustion or roasting. Their content and instrumentation significantly depend on the nature of the raw material, which to a large extent determines the complexity of the technological production of sulfuric acid.

3. Short description contemporary industrial ways obtaining sulfuric acid. Ways of improvement and prospects for the development of production.

The production of sulfuric acid from sulfur-containing raw materials involves several chemical processes in which the oxidation state of raw materials and intermediate products changes. This can be represented as the following diagram:

where I is the stage of production of furnace gas (sulfur oxide (IV)),

II - the stage of catalytic oxidation of sulfur oxide (IV) to sulfur oxide (VI) and its absorption (processing into sulfuric acid).

In real production, these chemical processes are supplemented by the processes of preparing raw materials, cleaning furnace gas, and other mechanical and physicochemical operations. AT general case production of sulfuric acid can be expressed as:

Raw materials Preparation of raw materials Burning (roasting) of raw materials

flue gas cleaning contact absorption

contacted gas SULFURIC ACID

The specific technological scheme of production depends on the type of raw material, the characteristics of the catalytic oxidation of sulfur oxide (IV), the presence or absence of the stage of absorption of sulfur oxide (VI).

Depending on how the process of oxidation of SO 2 to SO 3 is carried out, there are two main methods for producing sulfuric acid.

In the contact method for obtaining sulfuric acid, the process of oxidation of SO 2 to SO 3 is carried out on solid catalysts.

Sulfur trioxide is converted into sulfuric acid at the last stage of the process - the absorption of sulfur trioxide, which can be simplified by the reaction equation:

SO 3 + H 2 O H 2 SO 4

When carrying out the process according to the nitrous (tower) method, nitrogen oxides are used as an oxygen carrier.

The oxidation of sulfur dioxide is carried out in the liquid phase and the end product is sulfuric acid:

SO 3 + N 2 O 3 + H 2 O H 2 SO 4 + 2NO

At present, the industry mainly uses the contact method for obtaining sulfuric acid, which makes it possible to use apparatuses with greater intensity.

Consider the process of obtaining sulfuric acid by the contact method from two types of raw materials: sulfuric (iron) pyrites and sulfur.

1) The chemical scheme for obtaining sulfuric acid from pyrites includes three successive stages:

Oxidation of iron disulfide of pyrite concentrate with atmospheric oxygen:

Catalytic oxidation of sulfur oxide (IV) with an excess of furnace gas oxygen:

2SO 2 + O 2 2SO 3

Absorption of sulfur oxide (VI) with the formation of sulfuric acid:

SO 3 + H 2 O H 2 SO 4

In terms of technological design, the production of sulfuric acid from iron pyrites is the most complex and consists of several successive stages.

The principal (structural) diagram of this production is shown in fig. 2:

Rice. 2 Block diagram of the production of sulfuric acid from flotation pyrite by the single contact method.

I - obtaining roasting gas: 1 - pyrites roasting; 2 – gas cooling in the waste heat boiler; 3 - general gas cleaning, 4 - special gas cleaning; II - contacting: 5 - gas heating in the heat exchanger; 6 - contacting; III - absorption: 7 - absorption of sulfur oxide (IV) and the formation of sulfuric acid.

Pyrite roasting in an air stream is an irreversible non-catalytic heterogeneous process that proceeds with heat release through the stages of thermal dissociation of iron disulfide:

FeS 2 \u003d 2FeS + S 2

and oxidation of dissociation products:

S 2 + 2O 2 \u003d 2SO 2

4FeS + 7О 2 = 2Fe 2 S 3 + 4SO 2

what is described general equation

4FeS 2 + 11O 2 \u003d 2Fe 2 S 3 + 8SO 2,

where ΔН = 3400 kJ.

An increase in the driving force of the firing process is achieved by pyrite flotation, which increases the content of iron disulfide in the raw material, by enriching the air with oxygen and by using excess air during firing up to 30% over the stoichiometric amount. In practice, firing is carried out at a temperature not exceeding 1000 ° C, since beyond this limit the sintering of the particles of the fired raw material begins, which leads to a decrease in their surface and makes it difficult to wash the particles with an air stream.

Furnaces of various designs can be used as reactors for roasting pyrites: mechanical, dust-like roasting, fluidized bed (CF). Fluidized bed furnaces are characterized by high intensity (up to 10,000 kg / m 2 day), provide more complete burnout of iron disulfide (sulfur content in the cinder does not exceed 0.005 wt. parts) and temperature control, facilitate the process of utilizing the heat of the firing reaction. The disadvantages of KS furnaces include an increased dust content in the firing gas, which makes it difficult to clean. Currently, KS furnaces have completely replaced other types of furnaces in the production of sulfuric acid from pyrites.

2) The technological process for the production of sulfuric acid from elemental sulfur by the contact method differs from the production process from pyrites in a number of features. These include:

- a special design of furnaces for the production of furnace gas;

– increased content of sulfur oxide (IV) in furnace gas;

– no stage of pre-treatment of furnace gas.

The subsequent operations of contacting sulfur oxide (IV) in terms of physical and chemical principles and instrumentation do not differ from those for the process based on pyrites and are usually executed according to the DKDA scheme. Temperature control of the gas in the contact apparatus in this method is usually carried out by introducing cold air between the catalyst layers.

A schematic diagram of the production of sulfuric acid from sulfur is shown in fig. 3:

Rice. 3. Block diagram of the production of sulfuric acid from sulfur.

1 - air drying; 2 – sulfur burning; 3 – gas cooling, 4 – contacting; 5 - absorption of sulfur oxide (IV) and the formation of sulfuric acid.

There is also a method for the production of sulfuric acid from hydrogen sulfide, called "wet" catalysis, which consists in the fact that a mixture of sulfur oxide (IV) and water vapor, obtained by burning hydrogen sulfide in an air stream, is fed without separation to contacting, where sulfur oxide (IV) oxidized on a solid vanadium catalyst to sulfur oxide (VI). The gas mixture is then cooled in a condenser, where the vapors of the resulting sulfuric acid are converted into a liquid product.

Thus, in contrast to the methods of production of sulfuric acid from pyrites and sulfur, in the process of wet catalysis there is no special stage of absorption of sulfur oxide (VI) and the whole process includes only three successive stages:

1. Combustion of hydrogen sulfide:

H 2 S + 1.5O 2 \u003d SO 2 + H 2 O - ΔH 1, where ΔH 1 \u003d 519 kJ

with the formation of a mixture of sulfur oxide (IV) and water vapor of equimolecular composition (1: 1).

2. Oxidation of sulfur oxide (IV) to sulfur oxide (VI):

SO 2 + 0.5O 2<=>SO 3 - ΔН 2, where ΔН 2 = 96 kJ,

while maintaining the equimolecular composition of the mixture of sulfur oxide (IV) and water vapor (1: 1).

3. Vapor condensation and formation of sulfuric acid:

SO 3 + H 2 O<=>H 2 SO 4 - ΔH 3, where ΔH 3 \u003d 92 kJ

thus, the process of wet catalysis is described by the overall equation:

H 2 S + 2O 2 \u003d H 2 SO 4 - ΔH, where ΔH \u003d 707 kJ.

The large scale of production of sulfuric acid poses a particularly acute problem of its improvement. The following main areas can be distinguished here:

1. Expansion of the raw material base through the use of waste gases from boiler houses of combined heat and power plants and various industries.

2. Increasing the unit capacity of installations. An increase in power by two or three times reduces the cost of production by 25 - 30%.

3. Intensification of the burning process of raw materials by using oxygen or air enriched with oxygen. This reduces the volume of gas passing through the apparatus and improves its performance.

4. Increasing the pressure in the process, which contributes to an increase in the intensity of the main equipment.

5. Application of new catalysts with increased activity and low ignition temperature.

6. Increasing the concentration of sulfur oxide (IV) in the furnace gas supplied to the contact.

7. The introduction of fluidized bed reactors at the stages of burning raw materials and contacting.

8. Use of thermal effects chemical reactions at all stages of production, including for the generation of power steam.

The most important task in the production of sulfuric acid is to increase the degree of conversion of SO 2 to SO 3. In addition to increasing the productivity of sulfuric acid, the implementation of this task makes it possible to solve ecological problems– reduce emissions of the harmful component SO 2 into the environment.

Increasing the degree of conversion of SO 2 can be achieved in different ways. The most common of these is the creation of double contact and double absorption (DKDA) schemes.

4. Physicochemical characteristics system underlying the chemical-technological process of sulfur dioxide oxidation.

The oxidation reaction of sulfur oxide (IV) to sulfur oxide (IV), which underlies the process of contacting the roasting gas, is a heterogeneous catalytic, reversible, exothermic reaction and is described by the equation:

SO 2 + 0.5O 2<=>SO 3 - ΔH.

The thermal effect of the reaction depends on the temperature and is equal to 96.05 kJ at 25°C and about 93 kJ at the contact temperature. The "SO 2 - O 2 - SO 3" system is characterized by the state of equilibrium in it and the rate of oxidation of sulfur oxide (IV), on which the overall result of the process depends.

The equilibrium constant of the oxidation reaction of sulfur oxide (IV) is equal to:

(1)

where are the equilibrium partial pressures of sulfur (VI) oxide, sulfur (IV) oxide, and oxygen, respectively.

The degree of conversion of sulfur oxide (IV) to sulfur oxide (VI) or the degree of contact achieved on the catalyst depends on the activity of the catalyst, temperature, pressure, composition of the contacted gas and contact time and is described by the equation:

(2)

where are the same values as in formula (1)

From equations (1) and (2) it follows that the equilibrium degree of conversion of sulfur oxide (IV) is associated with the equilibrium constant of the oxidation reaction:

(3)

The dependence of Хр on temperature, pressure and the content of sulfur oxide (IV) in the combustion gas is presented in Table. 1 and in fig. 4.

Table 1. Dependence of Хр on temperature, pressure and content of sulfur oxide (IV) in the roasting gas

Rice. Fig. 4. Dependence of the equilibrium degree of conversion of sulfur oxide (IV) into sulfur oxide (VI) on temperature (a), pressure (b) and content of sulfur oxide (IV) in gas (c).

From equation (3) and tab. 4 it follows that with decreasing temperature and increasing pressure of the contacted gas, the equilibrium degree of conversion Хр increases, which is consistent with the Le Chatelier principle. At the same time, at constant temperature and pressure, the equilibrium degree of conversion is the greater, the lower the content of sulfur oxide (IV) in the gas, that is, the lower the SO 2: O 2 ratio. This ratio depends on the type of raw materials to be fired and the excess air. This dependence is based on the operation of adjusting the composition of furnace gas, that is, diluting it with air to reduce the content of sulfur oxide (IV).

The degree of oxidation of sulfur oxide (IV) increases with increasing contact time, approaching equilibrium along a decaying curve (Fig. 5).

Rice. 5. Dependence of Хр on contact time.

Therefore, the contact time must be such as to ensure that equilibrium is reached in the system. From fig. 5 it follows that the higher the temperature, the sooner equilibrium is reached (t 1< t 2), но тем меньше степень превращения (Х 1 < Х 2 при Т 1 >T 2). Thus, the yield of sulfur oxide (IV) depends on both temperature and contact time. In this case, for each contact time, the dependence of the output on temperature is expressed by the corresponding curve, which has a maximum. It is obvious that the AA line that envelops these maxima (Fig. 6) represents the curve of optimal temperatures for different contact times, which is close to the equilibrium curve.

Rice. Fig. 6. Dependence of the yield of sulfur oxide (IV) on temperature at different contact times.

The amount of sulfur oxide (IV) oxidized per unit time depends on the oxidation rate, and, consequently, the volume of the contact mass, the dimensions of the reactor, and other characteristics of the process. The organization of this stage of production should provide the highest possible oxidation rate at maximum degree contact, achievable under given conditions.

The activation energy for the oxidation of sulfur oxide (IV) with oxygen to sulfur oxide (VI) is very high. Therefore, in the absence of a catalyst, the oxidation reaction practically does not proceed even at a high temperature. The use of a catalyst makes it possible to reduce the activation energy and increase the rate of oxidation.

In the production of sulfuric acid, contact masses based on vanadium (V) oxide of the BAV and SVD grades are used as a catalyst, named after the initial letters of the elements that make up them.

BAS (barium, aluminum, vanadium) composition:

V 2 O 5 (7%) + K 2 SO 4 + ВаSO 4 + Al 2 (SO 4) 3 + SiO 2 (silica)

SVD (sulfo-vanadate-diatom) composition

V 2 O 5 (7%) + K 2 S 2 O 7 + diatomite + gypsum

catalyst activator carrier

To describe the rate of oxidation of sulfur oxide (IV) to sulfur oxide (VI) on a vanadium catalyst with a fixed catalyst bed, various methods have been proposed. kinetic equations. These include, for example, equation (4), which relates the reaction rate to the degree of conversion of sulfur oxide (IV), the reaction rate constant, the equilibrium constant, and the gas pressure:

(4)

where X is the equilibrium degree of conversion of sulfur oxide (IV),

k is the oxidation rate constant,

a is the initial concentration of sulfur oxide (IV) in the gas,

b is the initial concentration of oxygen in the gas,

P is the total pressure in the gas,

K p is the equilibrium constant of the reaction.

It follows from equations (4) and (5) that the rate of oxidation depends on the rate constant of the reaction, which strongly increases with increasing temperature. However, in this case, the equilibrium constant K p decreases and the value of the term in equation (4). Thus, the rate of the oxidation of sulfur oxide (IV) depends on two quantities that change with increasing temperatures in the opposite direction. As a result, the temperature dependence of the oxidation rate should pass through a maximum. It also follows from equation (4) that the rate of oxidation of sulfur oxide (IV) is the greater, the lower the degree of conversion of sulfur oxide (IV) into sulfur oxide (VI) achieved in this process. As a result, for each degree of conversion, the dependence of the reaction rate on temperature will be expressed by an individual curve with a maximum. On fig. 7 shows a series of similar curves corresponding to different degrees of conversion for a gas of constant composition. It follows from this that the rate of the oxidation reaction reaches a maximum at certain temperatures, which is the higher, the lower this degree of conversion, and obviously represent optimal temperatures.

Rice. Fig. 7. Dependence of the rate of oxidation of sulfur oxide (IV) on temperature at various degrees of conversion X 1< Х 2 < Х 3 < Х 4

The line AA connecting the points of optimum temperatures is called the line of optimum temperature sequence (OTS) and indicates that in order to achieve the best results, the contacting process should be started at a high temperature, which ensures a high process speed (in practice, about 600 ° C), and then to achieve high degree transformations to reduce the temperature, maintaining the temperature regime according to LOT. Lines BB and CC in fig. 7 outline the area of acceptable temperatures in the actual technological process of contacting.

Table 2 shows the operating temperature of a 4-layer contact apparatus with intermediate heat exchange, set in accordance with the above principle:

Table 2. Temperature conditions of the contact assembly

Thus, the contradiction between the kinetics and thermodynamics of the sulfur oxide (IV) oxidation process is quite successfully removed by the design and temperature regime of the contact apparatus. This is achieved by dividing the process into stages, each of which corresponds to the optimal conditions for the contacting process. Thus, the initial parameters of the contact mode are also determined: temperature 400 - 440 ° C, pressure 0.1 MPa, content of sulfur oxide (IV) in the gas 0.07 vol. shares, the oxygen content in the gas is 0.11 vol. shares.

5. Hardware-technological scheme of fine purification of sulfur dioxide and oxidation of sulfur dioxide in a four-layer contact apparatus with filtering catalyst layers.

According to their design, reactors or contact apparatuses for the catalytic oxidation of sulfur oxide (IV) are divided into apparatuses with a fixed catalyst bed (shelf or filter), in which the contact mass is located in 4-5 layers, and fluidized bed apparatuses. Heat removal after the gas passes through each layer of the catalyst is carried out by introducing cold air or gas into the apparatus, or with the help of heat exchangers built into the apparatus or separately removed.

At present, in the production of sulfuric acid and oleum by the contact method, the most common is the technological scheme using the principle of double contact "DKDA" (double contact - double absorption). A part of such a scheme, with the exception of the furnace section and the general gas purification section, which are technologically the same for all schemes, is shown in Fig. nine.

Plant capacity up to 1500 t/day for monohydrate. Consumption ratios (per 1 ton of monohydrate): pyrite 0.82 t, water 50 m 3 , electricity 82 kWh.

Rice. 9. Technological scheme for the production of sulfuric acid from pyrites by double contacting with DKDA.

1 - hollow washing tower, 2 - washing tower with a packing, 3 - humidifying tower, 4 - electrostatic precipitators, 5 - drying tower, 6 - turbo blower, 7 - 75% acid collectors, 8 - production acid collector, 9 - heat exchangers, 10 - contact apparatus, 11 - oleum absorber, 12 and 13 - monohydrate absorbers. Product streams: I - furnace gas at 300 ° C, II - 75% sulfuric acid, III - chilled 98% acid, IV - production acid for cooling, V - chilled oleum or monohydrate, VI - production oleum for cooling , VII – exhaust gases.

6. Material balance of the 1st stage of the contact apparatus for the oxidation of sulfur dioxide.

Data for calculation:

1. Total productivity for sulfuric acid in terms of monohydrate - 127 t/h;

2. complete absorption of sulfuric anhydride - 99.8%;

3. composition of the source gas:

SO 2 - 6.82% (vol.), O 2 - 10.4% (vol.), CO 2 - 0.4% (vol.), N 2 - 82.38% (vol.);

temperature 520 about C;

the degree of achievement of equilibrium - α = 0.650

1. Calculate the equilibrium degree of conversion of SO 2 to SO 3. Let us consider the calculation of equilibrium using the known values of K p for the reaction of sulfur dioxide oxidation:

SO 2 + 0.5O 2 + CO 2 + N 2<=>SO 3 + CO 2 + N 2

where a, b, t, p are the number (mol) of the components of the initial mixture SO 2, O 2, CO 2 and N 2 (a + b + t + p \u003d 1).

The amount of each component (mol) upon reaching the equilibrium degree of transformation x A, e will be

SO 2 O 2 CO 2 N 2 SO 3

a – a x A,e b – 0.5a x A,e t p a x A,e

Total number equilibrium mixture:

a - a x A, e + b - 0.5a x A, e + t + p + a x A, e \u003d 1 - 0.5a x A, e

Equilibrium constant

can be calculated according to the equation (p. 433, ):

At a temperature of 520 ° C (793 K), the equilibrium constant is:

The equilibrium state of a reaction can be characterized by the values of the equilibrium degree of conversion

Denoting the total pressure as p, we express the equilibrium pressures of the components:

(6)

Substituting the initial data into equation (6), we obtain (p = 0.1 MPa):

Whence by iteration we find and, therefore, the equilibrium mixture contains:

SO 3 - 6.38% (vol.), SO 2 - 0.688% (vol.), O 2 - 7.54% (vol.), CO 2 - 0.412% (vol.), N 2 - 84.98 % (about.);

2. The practical degree of transformation is equal to:

3. The overall equation for the oxidation of sulfur oxide (IV) to sulfur oxide (VI) and the absorption of sulfur oxide (VI) with the formation of sulfuric acid:

SO 2 + 0.5O 2 + H 2 O H 2 SO 4

64 g/mol 98 g/mol

Based on the reaction equation, to obtain 127 kg / h of sulfuric acid, sulfur oxide (IV) is necessary:

Taking into account the calculated degree of conversion and the given completeness of absorption, sulfur oxide (IV) is practically necessary:

mole

4. Let's recalculate the volumetric composition of the gas into mass.

mole

The number of components of the initial mixture is:

mole

The number of components of the resulting gas:

mole

The total number of moles of the gas mixture is

mole

The calculation results are summarized in Table 3

Table 3. Material balance of the contact apparatus for the oxidation of sulfur dioxide.

Literature.

1. Kutepov A. M., Bondareva T. I., Berengarten M. G. General chemical technology. M. Higher. school. 1990.

2. Sokolov R. S. Chemical technology. - M: Humanite. ed. BLADOS Center, 2000.

3. Calculations of chemical-technological processes // Under the general. ed. I. P. Mukhlenova. - L .: Chemistry, 1976

4. Beskov V. S., Safronov V. S. General chemical technology and basics of industrial ecology. - M.: Chemistry, 1999.

5. General chemical technology and fundamentals of industrial ecology.// ed. V. I. Ksenzenko. - M.: "Koloss", 2003.

“There is hardly any other, artificially produced substance, so often used in technology, as sulfuric acid.

Where there are no factories for its extraction, the profitable production of many other substances of great technical importance is unthinkable”

DI. Mendeleev

Sulfuric acid is used in a variety of chemical industries:

mineral fertilizers, plastics, dyes, artificial fibers, mineral acids, detergents;
in the oil and petrochemical industry:

for oil refining, obtaining paraffins;

in non-ferrous metallurgy:

for the production of non-ferrous metals - zinc, copper, nickel, etc.

in ferrous metallurgy:

for pickling metals;

in the pulp and paper, food and light industries (for the production of starch, molasses, fabric bleaching), etc.

Sulfuric acid production

Sulfuric acid is produced in industry in two ways: contact and nitrous.

Contact method for the production of sulfuric acid

Sulfuric acid is produced by the contact method in large quantities at sulfuric acid plants.

Currently, the main method for the production of sulfuric acid is contact, because. this method has advantages over others:

Obtaining a product in the form of a pure concentrated acid acceptable to all consumers;

- reduction of emissions of harmful substances into the atmosphere with exhaust gases

I. Raw materials used for the production of sulfuric acid.

Main raw material

sulfur - S

sulfur pyrite (pyrite) - FeS 2

non-ferrous metal sulfides - Cu2S, ZnS, PbS

hydrogen sulfide - H 2 S

Auxiliary material

Catalyst - vanadium oxide - V 2 O 5

II. Preparation of raw materials.

Let's analyze the production of sulfuric acid from pyrite FeS 2.

1) Grinding of pyrite. Before use, large pieces of pyrite are crushed in crushers. You know that when a substance is crushed, the reaction rate increases, because. the surface area of contact of the reactants increases.

2) Purification of pyrite. After crushing pyrite, it is purified from impurities (waste rock and earth) by flotation. To do this, crushed pyrite is lowered into huge vats of water, mixed, the waste rock floats up, then the waste rock is removed.

III. Basic chemical processes:

4 FeS 2 + 11 O 2 t = 800°C→ 2 Fe 2 O 3 + 8 SO 2 + Q or burning sulfur S+O2 t ° C→ SO2

2SO2 + O2 400-500° With,V2O5 , p↔ 2SO 3 + Q

SO 3 + H 2 O → H 2 SO 4 + Q

IV . Technological principles:

The principle of continuity;

The principle of integrated use of raw materials,use of waste from other production;

The principle of non-waste production;

The principle of heat transfer;

Counterflow principle (“fluidized bed”);

The principle of automation and mechanization of production processes.

V . Technological processes:

Continuity principle: roasting pyrite in a kiln → supply of sulfur oxide ( IV ) and oxygen into the purification system → into the contact apparatus → supply of sulfur oxide ( VI ) into the absorption tower.

VI . Environmental protection:

1) tightness of pipelines and equipment

2) gas cleaning filters

VII. Chemistry of production :

FIRST STAGE - roasting pyrite in a furnace for roasting in a "fluidized bed".

Sulfuric acid is mainly used flotation pyrites- production waste during the enrichment of copper ores containing mixtures of sulfur compounds of copper and iron. The process of enrichment of these ores takes place at the Norilsk and Talnakh enrichment plants, which are the main suppliers of raw materials. This raw material is more profitable, because. sulfur pyrite is mined mainly in the Urals, and, naturally, its delivery can be very expensive. Possible use sulfur, which is also formed during the enrichment of non-ferrous metal ores mined in mines. Sulfur is also supplied by the Pacific Fleet and the NOF. (concentrating factories).

First stage reaction equation

4FeS2 + 11O2 t = 800°C → 2Fe 2 O 3 + 8SO 2 + Q

Crushed, cleaned, wet (after flotation) pyrite is poured from above into a furnace for firing in a "fluidized bed". From below (counterflow principle) air enriched with oxygen is passed through for a more complete firing of pyrite. The temperature in the kiln reaches 800°C. Pyrite is heated to red and is in a "suspended state" due to the air blown from below. It all looks like a boiling red hot liquid. Even the smallest particles of pyrite do not cake in the “fluidized bed”. Therefore, the firing process is very fast. If earlier it took 5-6 hours to burn pyrite, now it takes only a few seconds. Moreover, in the "fluidized bed" it is possible to maintain a temperature of 800°C.

Due to the heat released as a result of the reaction, the temperature in the furnace is maintained. Excess heat is removed: pipes with water run along the perimeter of the furnace, which is heated. hot water further used for central heating of adjacent premises.

The resulting iron oxide Fe 2 O 3 (cinder) is not used in the production of sulfuric acid. But it is collected and sent to a metallurgical plant, where iron metal and its alloys with carbon are obtained from iron oxide - steel (2% carbon C in the alloy) and cast iron (4% carbon C in the alloy).

Thus, principle of chemical production- non-waste production.

Coming out of the oven furnace gas , the composition of which: SO 2, O 2, water vapor (pyrite was wet!) And the smallest particles of cinder (iron oxide). Such furnace gas must be cleaned from impurities of solid particles of cinder and water vapor.

Purification of furnace gas from solid particles of cinder is carried out in two stages - in a cyclone (centrifugal force is used, solid particles of cinder hit the walls of the cyclone and fall down). To remove small particles, the mixture is sent to electrostatic precipitators, where it is cleaned under the action of a high voltage current of ~ 60,000 V (electrostatic attraction is used, cinder particles stick to the electrified plates of the electrostatic precipitator, with sufficient accumulation under their own weight, they fall down), to remove water vapor in the furnace gas (drying furnace gas) use concentrated sulfuric acid, which is a very good desiccant because it absorbs water.

Drying of furnace gas is carried out in a drying tower - furnace gas rises from bottom to top, and concentrated sulfuric acid flows from top to bottom. To increase the contact surface of gas and liquid, the tower is filled with ceramic rings.

At the outlet of the drying tower, the kiln gas no longer contains any cinder particles or water vapor. Furnace gas is now a mixture of sulfur oxide SO 2 and oxygen O 2 .

SECOND STAGE - catalytic oxidation of SO 2 to SO 3 with oxygen in a contact device.

The reaction equation for this stage is:

2SO2 + O2 400-500°С, V 2 O 5 ,p ↔ 2 SO 3 + Q

The complexity of the second stage lies in the fact that the process of oxidation of one oxide into another is reversible. Therefore, it is necessary to choose the optimal conditions for the flow of the direct reaction (obtaining SO 3).

It follows from the equation that the reaction is reversible, which means that at this stage it is necessary to maintain such conditions that the equilibrium shifts towards the exit SO 3 otherwise the whole process will be broken. Because the reaction proceeds with a decrease in volume (3 V↔2V ), an increased pressure is required. Increase the pressure to 7-12 atmospheres. The reaction is exothermic, therefore, taking into account the Le Chatelier principle, this process cannot be carried out at a high temperature, because. the balance will shift to the left. The reaction starts at a temperature = 420 degrees, but due to the multi-layer catalyst (5 layers), we can increase it to 550 degrees, which greatly speeds up the process. The catalyst used is vanadium (V 2 O 5). It is cheap and lasts a long time (5-6 years). the most resistant to the action of toxic impurities. In addition, it contributes to the shift of balance to the right.

The mixture (SO 2 and O 2) is heated in a heat exchanger and moves through pipes, between which a cold mixture passes in the opposite direction, which must be heated. As a result, there heat exchange: the starting materials are heated, and the reaction products are cooled to the desired temperatures.

THIRD STAGE - absorption of SO 3 by sulfuric acid in the absorption tower.

Why sulfur oxide SO 3 do not absorb water? After all, it would be possible to dissolve sulfur oxide in water: SO 3 + H 2 O → H 2 SO 4 . But the fact is that if water is used to absorb sulfur oxide, sulfuric acid is formed in the form of a mist consisting of tiny droplets of sulfuric acid (sulfur oxide dissolves in water with the release of a large number heat, sulfuric acid is so heated that it boils and turns into steam). In order to avoid the formation of sulfuric acid mist, use 98% concentrated sulfuric acid. Two percent water is so small that heating the liquid will be weak and harmless. Sulfur oxide dissolves very well in such an acid, forming oleum: H 2 SO 4 nSO 3 .

The reaction equation for this process is:

NSO 3 + H 2 SO 4 → H 2 SO 4 nSO 3

The resulting oleum is poured into metal tanks and sent to the warehouse. Then tanks are filled with oleum, trains are formed and sent to the consumer.

The initial reagents for the production of sulfuric acid can be elemental sulfur and sulfur-containing compounds, from which either sulfur or sulfur dioxide can be obtained.

Traditionally, the main sources of raw materials are sulfur and iron (sulfur) pyrites. About half of sulfuric acid is obtained from sulfur, a third - from pyrites. A significant place in the raw material balance is occupied by off-gases from non-ferrous metallurgy, containing sulfur dioxide.

At the same time, exhaust gases are the cheapest raw material, wholesale prices for pyrite are also low, while sulfur is the most expensive raw material. Therefore, in order for the production of sulfuric acid from sulfur to be economically viable, a scheme must be developed in which the cost of its processing will be significantly lower than the cost of processing pyrite or off-gases.

Obtaining sulfuric acid from hydrogen sulfide

Sulfuric acid is produced from hydrogen sulfide by wet catalysis. Depending on the composition of combustible gases and the method of their purification, hydrogen sulfide gas can be concentrated (up to 90%) and weak (6-10%). This determines the scheme for processing it into sulfuric acid.

Figure 1.1 shows a scheme for the production of sulfuric acid from concentrated hydrogen sulfide gas. Hydrogen sulfide mixed with air purified in the filter 1 enters the furnace 3 for combustion. In the waste heat boiler 4, the temperature of the gas leaving the furnace decreases from 1000 to 450 °C, after which the gas enters the contact apparatus 5. The temperature of the gas leaving the layers of the contact mass is reduced by blowing in dry cold air. From the contact apparatus, the gas containing SO 3 enters the condenser tower 7, which is a scrubber with a nozzle irrigated with acid. The temperature of the irrigating acid at the entrance to the tower is 50-60°С, at the exit 80-90°С. In this mode, in the lower part of the tower, the gas containing H 2 O and SO 3 vapors is rapidly cooled, high supersaturation occurs and a fog of sulfuric acid is formed (up to 30-35% of all output goes into fog), which is then captured in the electrostatic precipitator 8. For For the best deposition of fog droplets in electrostatic precipitators (or filters of another type), it is desirable that these droplets be large. This is achieved by increasing the temperature of the spray acid, which leads to an increase in the temperature of the acid flowing out of the tower (an increase in the temperature of the condensation surface) and contributes to the coarsening of the fog droplets. The scheme for the production of sulfuric acid from weak hydrogen sulfide gas differs from the scheme shown in Figure 1.1 in that the air supplied to the furnace is preheated in heat exchangers by the gas leaving the catalyst layers, and the condensation process is carried out in a bubbling condenser of the Chemiko concentrator type.

The gas passes through the acid layer in succession in three chambers of the bubbling apparatus, the temperature of the acid in them is controlled by supplying water, the evaporation of which absorbs heat. Due to the high temperature of the acid in the first chamber (230-240°C), H 2 SO 4 vapors condense in it without fog formation.

1-filter, 2-fan, 3-furnace, 4-steam waste-heat boiler, 5-pin apparatus, 6-refrigerator, 7-tower-condenser, 8-electric filter, 9-circulation collector, 10-pump.

Figure 1.1 Scheme for the production of sulfuric acid from high concentration hydrogen sulfide gas:

In the two subsequent chambers (the temperature of the acid in them, respectively, is about 160 and 100 °C), fog is formed. However, due to the rather high temperature of the acid and the large amount of water vapor in the gas, corresponding to the pressure saturated steam water over the acid in the chambers, the mist is formed in the form of large droplets, which are easily deposited in the electrostatic precipitator.

Productive acid flows out of the first (along the gas) chamber, is cooled in the refrigerator and fed to the warehouse. The surface of refrigerators in such an absorption compartment is 15 times smaller than in an absorption compartment with a condenser tower, due to the fact that the main amount of heat is removed by water evaporation. The concentration of acid in the first chamber (production acid) is about 93.5%, in the second and third chambers, respectively, 85 and 30%. .

1. Commodity and technology-determining properties of sulfuric acid.

Sulfuric acid is one of the main large-tonnage products of the chemical industry. It is used in various sectors of the national economy, since it has a set of special properties that facilitate its technological use. Sulfuric acid does not smoke, has no color and odor, is in a liquid state at ordinary temperatures, and in concentrated form does not corrode ferrous metals. At the same time, sulfuric acid is one of the strong mineral acids, forms numerous stable salts and is cheap.

In technology, sulfuric acid is understood as systems consisting of sulfur oxide (VI) and water of various compositions: p SO 3 t H 2 O.

At n = t = 1, this is sulfuric acid monohydrate (100% sulfuric acid), at t > n - aqueous solutions of the monohydrate, at t< п – растворы оксида серы (VI) в моногидрате (олеум).

When sulfuric acid vapor is heated above 400 ° C, it undergoes thermal dissociation according to the scheme:

400 o C 700 o C

2 H 2 SO 4<=>2H 2 O + 2SO 3<=>2H 2 O + 2SO 2 + O 2.

Rice. 1. The use of sulfuric acid.

2. Raw sources for obtaining sulfuric acid.

The raw material in the production of sulfuric acid can be elemental sulfur and various sulfur-containing compounds, from which sulfur or directly sulfur oxide (IV) can be obtained.

Natural deposits of native sulfur are small, although its clarke is 0.1%. Most often, sulfur is found in nature in the form of metal sulfides and metal sulfates, and is also part of oil, coal, natural and associated gases. Significant amounts of sulfur are contained in the form of sulfur oxide in flue gases and non-ferrous metallurgy gases and in the form of hydrogen sulfide released during the purification of combustible gases.

At the same time, the share of pyrites in the balance of raw materials decreases, and the share of sulfur increases.

3. A brief description of modern industrial methods for producing sulfuric acid. Ways of improvement and prospects for the development of production.

where I is the stage of production of furnace gas (sulfur oxide (IV)),

II - the stage of catalytic oxidation of sulfur oxide (IV) to sulfur oxide (VI) and its absorption (processing into sulfuric acid).

In real production, these chemical processes are supplemented by the processes of preparing raw materials, cleaning furnace gas, and other mechanical and physicochemical operations. In general, the production of sulfuric acid can be expressed as:

preparation of raw materials combustion (roasting) of raw materials cleaning of furnace gas contacting absorption

contacted gas

SULFURIC ACID

Depending on how the process of oxidation of SO 2 to SO 3 is carried out, there are two main methods for producing sulfuric acid.

In the contact method for obtaining sulfuric acid, the process of oxidation of SO 2 to SO 3 is carried out on solid catalysts.

Sulfur trioxide is converted into sulfuric acid at the last stage of the process - the absorption of sulfur trioxide, which can be simplified by the reaction equation:

SO 3 + H 2 O

H 2 SO 4

When carrying out the process according to the nitrous (tower) method, nitrogen oxides are used as an oxygen carrier.

The oxidation of sulfur dioxide is carried out in the liquid phase and the end product is sulfuric acid:

SO 3 + N 2 O 3 + H 2 O

H 2 SO 4 + 2NO

At present, the industry mainly uses the contact method for obtaining sulfuric acid, which makes it possible to use apparatuses with greater intensity.

Consider the process of obtaining sulfuric acid by the contact method from two types of raw materials: sulfuric (iron) pyrites and sulfur.

1) The chemical scheme for obtaining sulfuric acid from pyrites includes three successive stages:

Oxidation of iron disulfide of pyrite concentrate with atmospheric oxygen:

4FeS 2 + 11O 2 \u003d 2Fe 2 S 3 + 8SO 2,

Catalytic oxidation of sulfur oxide (IV) with an excess of furnace gas oxygen:

2SO 3

Absorption of sulfur oxide (VI) with the formation of sulfuric acid:

SO 3 + H 2 O

H 2 SO 4

In terms of technological design, the production of sulfuric acid from iron pyrites is the most complex and consists of several successive stages.

The principal (structural) diagram of this production is shown in fig. 2:

Rice. 2 Block diagram of the production of sulfuric acid from flotation pyrite by the single contact method.

Sulfuric acid is produced in large quantities in sulfuric acid plants.

I. Raw materials used for the production of sulfuric acid:

II. Preparation of raw materials.

Let's analyze the production of sulfuric acid from pyrite FeS2.

1) Grinding of pyrite.

Before use, large pieces of pyrite are crushed in crushers. You know that when a substance is crushed, the reaction rate increases, because. the surface area of contact of the reactants increases.

2) Purification of pyrite.

After crushing pyrite, it is purified from impurities (waste rock and earth) by flotation. To do this, crushed pyrite is lowered into huge vats of water, mixed, the waste rock floats up, then the waste rock is removed.

III. Production chemistry.

The production of sulfuric acid from pyrite consists of three stages.

FIRST STAGE - pyrite roasting in a "fluidized bed" kiln.

First stage reaction equation

4FeS2 + 11O2 2Fe2O3 + 8SO2 + Q

Due to the heat released as a result of the reaction, the temperature in the furnace is maintained. Excess heat is removed: pipes with water run along the perimeter of the furnace, which is heated. Hot water is used further for central heating of adjacent premises.

The formed iron oxide Fe2O3 (calcine) is not used in the production of sulfuric acid. But it is collected and sent to a metallurgical plant, where iron metal and its alloys with carbon are obtained from iron oxide - steel (2% carbon C in the alloy) and cast iron (4% carbon C in the alloy).

Thus, the principle of chemical production is fulfilled - waste-free production.

Furnace gas comes out of the furnace, the composition of which is: SO2, O2, water vapor (pyrite was wet!) And the smallest particles of cinder (iron oxide). Such furnace gas must be cleaned from impurities of solid particles of cinder and water vapor.

Purification of furnace gas from solid particles of cinder is carried out in two stages - in a cyclone (centrifugal force is used, solid particles of cinder hit the walls of the cyclone and fall down) and in electrostatic precipitators (electrostatic attraction is used, particles of cinder stick to the electrified plates of the electrostatic precipitator, with sufficient accumulation of under they fall down with their own weight), to remove water vapor in the furnace gas (drying the furnace gas), concentrated sulfuric acid is used, which is a very good desiccant, since it absorbs water.

Drying of furnace gas is carried out in a drying tower - furnace gas rises from bottom to top, and concentrated sulfuric acid flows from top to bottom. At the outlet of the drying tower, the kiln gas no longer contains any cinder particles or water vapor. Furnace gas is now a mixture of sulfur oxide SO2 and oxygen O2.

SECOND STAGE - oxidation of SO2 to SO3 by oxygen.

It flows in the contact device.

The reaction equation for this stage is: 2SO2 + O2 2SO3 + Q

a) temperature:

The direct reaction is exothermic +Q, according to the rules for shifting chemical equilibrium, in order to shift the reaction equilibrium towards an exothermic reaction, the temperature in the system must be lowered. But, on the other hand, at low temperatures, the reaction rate drops significantly. Experimentally, chemists-technologists have established that the optimal temperature for the direct reaction to proceed with the maximum formation of SO3 is a temperature of 400-500 ° C. This is enough low temperature in chemical industries. In order to increase the reaction rate at such a low temperature, a catalyst is introduced into the reaction. It has been experimentally established that the best catalyst for this process is vanadium oxide V2O5.

b) pressure:

The direct reaction proceeds with a decrease in the volumes of gases: on the left, 3V gases (2V SO2 and 1V O2), and on the right, 2V SO3. Since the direct reaction proceeds with a decrease in the volume of gases, then, according to the rules for shifting chemical equilibrium, the pressure in the system must be increased. Therefore, this process is carried out at elevated pressure.

Before the mixture of SO2 and O2 enters the contact apparatus, it must be heated to a temperature of 400-500°C. Heating of the mixture begins in the heat exchanger, which is installed in front of the contact apparatus. The mixture passes between the tubes of the heat exchanger and is heated from these tubes. Inside the tubes, hot SO3 passes from the contact apparatus. Getting into the contact apparatus, the mixture of SO2 and O2 continues to heat up to the desired temperature, passing between the tubes in the contact apparatus.

The temperature of 400-500°C in the contact apparatus is maintained due to the release of heat in the reaction of the conversion of SO2 to SO3. As soon as the mixture of sulfur oxide and oxygen reaches the catalyst beds, the process of oxidation of SO2 to SO3 begins.

The formed sulfur oxide SO3 leaves the contact apparatus and enters the absorption tower through the heat exchanger.

THIRD STAGE - absorption of SO3 by sulfuric acid.

It flows in the absorption tower.

Why is sulfur oxide SO3 not absorbed by water? After all, sulfur oxide could be dissolved in water: SO3 + H2O H2SO4. But the fact is that if water is used to absorb sulfur oxide, sulfuric acid is formed in the form of a mist consisting of tiny droplets of sulfuric acid (sulfur oxide dissolves in water with the release of a large amount of heat, sulfuric acid is so hot that it boils and turns into steam ). In order to avoid the formation of sulfuric acid mist, use 98% concentrated sulfuric acid. Two percent water is so small that heating the liquid will be weak and harmless. Sulfur oxide dissolves very well in such an acid, forming oleum: H2SO4 nSO3.

The reaction equation for this process is nSO3 + H2SO4 H2SO4 nSO3

The resulting oleum is poured into metal tanks and sent to the warehouse. Then tanks are filled with oleum, trains are formed and sent to the consumer.

environmental protection,

associated with the production of sulfuric acid.

The main raw material for the production of sulfuric acid is sulfur. It is one of the most common chemical elements on our planet.

Sulfuric acid is produced in three stages: SO2 is produced in the first stage, FeS2 is calcined, then SO3, after which sulfuric acid is obtained in the third stage.

The scientific and technological revolution and the intensive growth of chemical production associated with it causes significant negative changes in environment. For example poisoning fresh water, pollution of the earth's atmosphere, extermination of animals and birds. As a result, the world is in the grip of an ecological crisis. Harmful emissions from sulfuric acid plants should be assessed not only by the effect of the sulfur oxide they contain on the areas located near the enterprise, but also other factors should be taken into account - an increase in the number of cases of respiratory diseases in humans and animals, the death of vegetation and the suppression of its growth, the destruction of structures made of limestone and marble, increase in corrosion wear of metals. Due to the fault of "sour" rains, architectural monuments (Taj Makal) were damaged.

In the zone up to 300 km from the source of pollution (SO2) sulfuric acid is dangerous, in the zone up to 600 km. - sulfates. Sulfuric acid and sulfates slow down the growth of agricultural crops. Acidification of water bodies (in spring, when snow melts, causes the death of eggs and juvenile fish. In addition to environmental damage, there is economic damage - huge amounts are lost every year due to soil deoxidation.

Let's take a look at chemical cleaning methods for the most common gaseous air pollutants. More than 60 methods are known. The most promising methods are based on the absorption of sulfur oxide by limestone, a solution of sulfite - ammonium hydrosulfite and an alkaline solution of sodium aluminate. Also of interest are catalytic methods for the oxidation of sulfur oxide in the presence of vanadium oxide.

Of particular importance is the purification of gases from fluorine-containing impurities, which, even in small concentrations, adversely affect vegetation. If the gases contain hydrogen fluoride and fluorine, then they are passed through columns with countercurrent packing in relation to a 5-10% sodium hydroxide solution. The following reactions take place within one minute:

F2+2NaOH->O2+H2O+2NaF

HF+NaOH->NaF+H2O;

The resulting sodium fluoride is treated to regenerate sodium hydroxide.