Sulphuric acid H 2 SO 4, molar mass 98.082; colorless, oily, odorless. Very strong dibasic acid, at 18 ° С p K a 1 - 2.8, K 2 1.2 10 -2, pK a 2 1.92; bond lengths in S \u003d O 0.143 nm, S-OH 0.154 nm, HOSOH angle 104 °, OSO 119 °; boils with decomposition, forming (98.3% H 2 SO 4 and 1.7% H 2 O with a boiling point of 338.8 ° C; see also Table 1). Sulphuric acidcorresponding to 100% content of H 2 SO 4, has the composition (%): H 2 SO 4 99.5%, HSO 4 - 0.18%, H 3 SO 4 + 0.14%, H 3 O + 0 , 09%, H 2 S 2 O 7 0.04%, HS 2 O 7 0.05%. Mixes up with and SO 3 in all proportions. In aqueous solutions sulphuric acid almost completely dissociates into H +, HSO 4 - and SO 4 2-. Forms H 2 SO 4 · nH 2 O, where n\u003d 1, 2, 3, 4 and 6.5.

sO 3 solutions in sulfuric acid are called oleum, they form two compounds H 2 SO 4 · SO 3 and H 2 SO 4 · 2SO 3. Oleum also contains pyrosulfuric acid, obtained by the reaction: H 2 SO 4 + SO 3 \u003d H 2 S 2 O 7.

Sulfuric acid production

Raw materials for obtaining sulfuric acid serve: S, metal sulfides, H 2 S, waste heat power plants, sulfates of Fe, Ca, etc. The main stages of obtaining sulfuric acid: 1) raw materials with obtaining SO 2; 2) SO 2 to SO 3 (conversion); 3) SO 3. The industry uses two methods of obtaining sulfuric acid, differing in the way of oxidation of SO 2, - contact using solid catalysts (contacts) and nitrous - with nitrogen oxides. For getting sulfuric acid vanadium catalysts are used by the contact method at modern factories, replacing Pt and Fe oxides. Pure V 2 O 5 has a weak catalytic activity, which sharply increases in the presence of alkali metals, and the greatest influence is exerted by the salts K. The promoting role of alkali metals is due to the formation of low-melting pyrosulfovanadates (3K 2 S 2 O 7 V 2 O 5, 2K 2 S 2 O 7 V 2 O 5 and K 2 S 2 O 7 V 2 O 5, decomposing, respectively, at 315-330, 365-380 and 400-405 ° C). The active component is in a molten state under catalysis conditions.

The oxidation scheme of SO 2 to SO 3 can be represented as follows:

At the first stage, equilibrium is achieved, the second stage is slow and determines the speed of the process.

Production sulfuric acid from sulfur by the method of double contact and double absorption (Fig. 1) consists of the following stages. The air after cleaning from dust is supplied by a gas blower to the drying tower, where it is dehumidified with 93-98% sulfuric acid to a moisture content of 0.01% by volume. The dried air enters the sulfuric furnace after preheating in one of the heat exchangers of the contact unit. Sulfur supplied by nozzles is burned in the furnace: S + О 2 \u003d SO 2 + 297.028 kJ. Gas containing 10-14% by volume SO 2 is cooled in a boiler and after dilution with air to an SO 2 content of 9-10% by volume at 420 ° C enters the contact apparatus for the first stage of conversion, which takes place on three catalyst beds (SO 2 + V 2 O 2 \u003d SO 3 + 96.296 kJ), after which the gas is cooled in heat exchangers. Then the gas containing 8.5-9.5% SO 3 at 200 ° C enters the first stage of absorption into the absorber, irrigated and 98% sulfuric acid: SO 3 + H 2 O \u003d H 2 SO 4 + 130.56 kJ. Then the gas is cleaned from splashes sulfuric acid, heats up to 420 ° C and enters the second conversion stage, which takes place on two catalyst beds. Before the second stage of absorption, the gas is cooled in the economizer and fed to the absorber of the second stage, irrigated with 98% sulfuric acid, and then, after cleaning from splashes, is released into the atmosphere.

1 - sulfuric furnace; 2 - waste heat boiler; 3 - economizer; 4 - starting furnace; 5, 6 - starting furnace heat exchangers; 7 - contact device; 8 - heat exchangers; 9 - oleum absorber; 10 - drying tower; 11 and 12, respectively, the first and second monohydrate absorbers; 13 - acid collectors.

1 - disc feeder; 2 - oven; 3 - waste heat boiler; 4 - cyclones; 5 - electrostatic precipitators; 6 - washing towers; 7 - wet electrostatic precipitators; 8 - blowing tower; 9 - drying tower; 10 - spray trap; 11 - the first monohydrate absorber; 12 - heat exchangers; 13 - contact device; 14 - oleum absorber; 15 - the second monohydrate absorber; 16 - refrigerators; 17 - collections.

1 - denitration tower; 2, 3 - first and second production towers; 4 - oxidizing tower; 5, 6, 7 - absorption towers; 8 - electrostatic precipitators.

Production sulfuric acid from metal sulfides (Fig. 2) is much more complicated and consists of the following operations. FeS 2 roasting is carried out in a fluidized bed furnace on air blast: 4FeS 2 + 11O 2 \u003d 2Fe 2 O 3 + 8SO 2 + 13476 kJ. Firing gas with SO 2 content of 13-14%, having a temperature of 900 ° C, enters the boiler, where it is cooled to 450 ° C. Dust removal is carried out in a cyclone and an electrostatic precipitator. Then the gas passes through two washing towers, irrigated with 40% and 10% sulfuric acid... In this case, the gas is finally cleaned of dust, fluorine and arsenic. For cleaning gas from aerosol sulfuric acidformed in the washing towers, two stages of wet electrostatic precipitators are provided. After drying in a drying tower, in front of which the gas is diluted to a content of 9% SO 2, it is blown into the first conversion stage (3 catalyst beds). In heat exchangers, the gas is heated to 420 ° C due to the heat of the gas coming from the first stage of conversion. SO 2, oxidized by 92-95% in SO 3, goes to the first stage of absorption in oleum and monohydrate absorbers, where it is freed from SO 3. Further, gas with SO 2 content ~ 0.5% enters the second conversion stage, which takes place on one or two catalyst beds. The gas is preliminarily heated in another group of heat exchangers to 420 ° C due to the heat of the gases coming from the second stage of catalysis. After separation of SO 3 in a second absorption stage, the gas is vented to the atmosphere.

The degree of conversion of SO 2 to SO 3 in the contact method is 99.7%, the degree of absorption of SO 3 is 99.97%. Production sulfuric acid carried out in one stage of catalysis, while the degree of conversion of SO 2 to SO 3 does not exceed 98.5%. Before being released into the atmosphere, the gas is purified from the remaining SO 2 (see). The productivity of modern plants is 1500-3100 tons / day.

The essence of the nitrous method (Fig. 3) is that the firing gas, after cooling and cleaning from dust, is treated with the so-called nitrose - sulfuric acidin which nitrogen oxides are dissolved. SO 2 is absorbed by nitrose and then oxidized: SO 2 + N 2 O 3 + H 2 O \u003d H 2 SO 4 + NO. The resulting NO is poorly soluble in nitrose and is released from it, and then partially oxidized by oxygen in the gas phase to NO 2. The mixture of NO and NO 2 is reabsorbed sulfuric acid etc. Nitrogen oxides are not consumed in the nitrous process and are returned to the production cycle due to their incomplete absorption sulfuric acid they are partially carried away by the waste gases. Advantages of the nitrous method: simplicity of hardware design, lower prime cost (10-15% lower than the contact one), possibility of 100% processing of SO 2.

The equipment of the tower nitrous process is not difficult: SO 2 is processed in 7-8 lined towers with ceramic packing, one of the towers (hollow) is a regulated oxidizing volume. The towers have acid collectors, refrigerators, pumps supplying acid to the pressure tanks above the towers. A tail fan is installed in front of the last two towers. For cleaning gas from aerosol sulfuric acid serves as an electrostatic precipitator. The nitrogen oxides required for the process are obtained from HNO 3. To reduce the emission of nitrogen oxides into the atmosphere and 100% recycling of SO 2, a nitrous-free SO 2 recycling cycle is established between the production and absorption zones in combination with the water-acid method of deep capture of nitrogen oxides. The disadvantage of the nitrous method is poor product quality: concentration sulfuric acid 75%, presence of nitrogen oxides, Fe and other impurities.

To reduce the possibility of crystallization sulfuric acid during transportation and storage, standards for commercial varieties are established sulfuric acid, the concentration of which corresponds to the lowest crystallization temperatures. Content sulfuric acid in technical grades (%): tower (nitrous) 75, contact 92.5-98.0, oleum 104.5, high-percentage oleum 114.6, battery 92-94. Sulfuric acid stored in steel tanks with a volume of up to 5000 m 3, their total capacity in the warehouse is designed for ten-day production. Oleum and sulfuric acid transported in steel rail tank cars. Concentrated and rechargeable sulfuric acid transported in acid-resistant steel tanks. Tanks for transporting oleum are covered with thermal insulation and heated before pouring the oleum.

Define sulfuric acid colorimetrically and photometrically, in the form of a suspension of BaSO 4 - phototurbidimetric, as well as coulometric method.

Application of sulfuric acid

Sulfuric acid is used in the production of mineral fertilizers, as an electrolyte in lead batteries, for the production of various mineral acids and salts, chemical fibers, dyes, smoke-forming substances and explosives, in the oil, metalworking, textile, leather and other industries. It is used in industrial organic synthesis in dehydration reactions (obtaining diethyl ether, esters), hydration (ethanol from ethylene), sulfonation (and intermediate products in the production of dyes), alkylation (obtaining isooctane, polyethylene glycol, caprolactam), etc. The largest consumer sulfuric acid - production of mineral fertilizers. For 1 ton of P 2 O 5 phosphorus fertilizers 2.2-3.4 tons are consumed sulfuric acid, and for 1 t (NH 4) 2 SO 4 - 0.75 t sulfuric acid... Therefore, they strive to build sulfuric acid plants in conjunction with factories for the production of mineral fertilizers. World production sulfuric acid in 1987 reached 152 million tons.

Sulphuric acid and oleum - extremely aggressive substances that affect the respiratory tract, skin, mucous membranes, cause difficulty breathing, cough, often - laryngitis, tracheitis, bronchitis, etc. MPC of sulfuric acid aerosol in the air of the working area is 1.0 mg / m 3, in the atmospheric air 0.3 mg / m 3 (maximum one-time) and 0.1 mg / m 3 (daily average). Amazing vapor concentration sulfuric acid 0.008 mg / l (exposure 60 min), lethal 0.18 mg / l (60 min). Hazard class 2. Aerosol sulfuric acid can be formed in the atmosphere as a result of emissions from chemical and metallurgical industries containing S oxides, and fall out in the form of acid rain.

SULPHURIC ACID H 2 SO 4, molecular weight 98.082; colorless odorless oily liquid. Very strong dibasic acid, at 18 ° C pK a 1 - 2.8, K 2 1.2 10 -2, pK a 2 l, 92; bond lengths in the molecule S \u003d O 0.143 nm, S-OH 0.154 nm, HOSOH angle 104 °, OSO 119 °; boils with various, forming an azeotropic mixture (98.3% H 2 SO 4 and 1.7% H 2 O with a boiling point of 338.8 ° C; see also Table 1). SULFURIC ACID, which corresponds to 100% content of H 2 SO 4, has a composition (%): H 2 SO 4 99.5, 0.18, 0.14, H 3 O + 0.09, H 2 S 2 O 7 0.04, HS 2 O 7 0.05. Miscible with water and SO 3 in all proportions. In aqueous solutions, SULFURIC ACID k. Almost completely dissociates into H +, and. Forms hydrates H 2 SO 4 nH 2 O, where n \u003d 1, 2, 3, 4 and 6.5.

SO 3 solutions in SULFURIC ACID are called oleum, they form two compounds H 2 SO 4 SO 3 and H 2 SO 4 2SO 3. Oleum also contains pyrosulfuric acid, obtained by the reaction: H 2 SO 4 + + SO 3: H 2 S 2 O 7.

The boiling point of aqueous solutions of SULFURIC ACID increases with an increase in its concentration and reaches a maximum at a content of 98.3% H 2 SO 4 (Table 2). The boiling point of oleum decreases with increasing SO 3 content. With an increase in the concentration of aqueous solutions, SULFURIC ACID K. the total vapor pressure over the solutions decreases and at a content of 98.3% H 2 SO 4 reaches a minimum. With an increase in the concentration of SO 3 in oleum, the total vapor pressure above it increases. The vapor pressure over aqueous solutions of SULFURIC ACID to. And oleum can be calculated by the equation: lgp (Pa) \u003d A - B / T + 2.126, the values \u200b\u200bof the coefficient A and B depend on the concentration of SULFURIC ACID to. Steam over aqueous solutions of SULFURIC ACID to. Consists from a mixture of water vapor, H 2 SO 4 and SO 3, while the composition of the vapor differs from the composition of the liquid at all concentrations of SULFURIC ACID, except for the corresponding azeotropic mixture.

As the temperature rises, the dissociation of H 2 SO 4 H 2 O + SO 3 - Q increases, the equation temperature dependence equilibrium constants lnК p \u003d 14.74965 - 6.71464ln (298 / T) - 8, 10161 10 4 T 2 -9643.04 / T-9.4577 10 -3 T + 2.19062 x 10 -6 T 2. At normal pressure, the degree of dissociation: 10 -5 (373 K), 2.5 (473 K), 27.1 (573 K), 69.1 (673 K). The density of 100% SULFURIC ACID to. Can be determined by the equation: d \u003d 1.8517 - - 1.1 10 -3 t + 2 10 -6 t 2 g / cm 3. With an increase in the concentration of SULFURIC ACID solutions, their heat capacity decreases and reaches a minimum for 100% SULFURIC ACID to., The heat capacity of oleum increases with increasing SO 3 content.

With an increase in concentration and a decrease in temperature, the thermal conductivity l decreases: l \u003d 0.518 + 0.0016t - (0.25 + + t / 1293) С / 100, where С is the concentration of SULFURIC ACID, in%. Max. the viscosity has oleum H 2 SO 4 SO 3, with increasing temperature h decreases. Electric. resistance to SULFURIC ACID to. minimum at a concentration of 30 and 92% H 2 SO 4 and maximum at a concentration of 84 and 99.8% H 2 SO 4. For oleum, min. r at a concentration of 10% SO 3. With increasing temperature r SULFURIC ACID K increases. Dielectric permeability of 100% SULFURIC ACID 101 (298.15 K), 122 (281.15 K); cryoscopic constant 6.12, ebulioscopic. constant 5.33; vapor diffusion coefficient SULFURIC ACID K. in air changes with temperature; D \u003d 1.67 10 -5 T 3/2 cm 2 / s.

SULFURIC ACID K. is a rather strong oxidizing agent, especially when heated; oxidizes HI and partially HBr to free halogens, carbon to CO 2, S to SO 2, oxidizes many metals (Cu, Hg, etc.). In this case, SULFURIC ACID is reduced to SO 2, and the most powerful reducing agents to S and H 2 S. Conc. H 2 SO 4 is partially reduced by H 2, which is why it cannot be used for drying it. Debt. H 2 SO 4 interaction with all metals in the electrochemical series of voltages to the left of hydrogen, with the release of H 2. Oxidite. properties for dilute H 2 SO 4 are uncommon. SULFURIC ACID to. Gives two series of salts: medium-sulfates and acidic-hydrosulfates (see. Inorganic sulfates), as well as ethers (see. Organic sulfates). Known peroxomonosulfuric acid (Caro acid) H 2 SO 5 and peroxodisulfuric H 2 S 2 O 8 acids (see Sulfur).

Receiving.Raw materials for obtaining SULFURIC ACID are: S, metal sulfides, H 2 S, waste gases from thermal power plants, sulfates of Fe, Ca, etc. Main. stages of obtaining SULFURIC ACID K.: 1) roasting of raw materials with obtaining SO 2; 2) oxidation of SO 2 to SO 3 (conversion); 3) absorption of SO 3. In industry, two methods are used to obtain SULFURIC ACID, differing in the way of oxidation of SO 2, - contact with the use of solid catalysts (contacts) and nitrous - with nitrogen oxides. To obtain SULFURIC ACID by the contact method, vanadium catalysts are used in modern factories, displacing Pt and Fe oxides. Pure V 2 O 5 has a weak catalytic activity, which sharply increases in the presence of alkali metal salts, and the most influencing are the K salts. The promoting role of alkali metals is due to the formation of low-melting pyrosulfovanadates (3K 2 S 2 O 7 V 2 O 5, 2K 2 S 2 O 7 V 2 O 5 and K 2 S 2 O 7 V 2 O 5, decomposing at 315-330, 365-380 and 400-405 ° C, respectively). The active component is in a molten state under catalysis conditions.

The oxidation scheme of SO 2 to SO 3 can be represented as follows:

At the first stage equilibrium is achieved, the second stage is slow and determines the speed of the process.

The production of SULFURIC ACID from sulfur by the method of double contacting and double absorption (Fig. 1) consists of the following stages. The air after cleaning from dust is supplied by a gas blower to the drying tower, where it is dried with 93-98% SULFURIC ACID to a moisture content of 0.01% by volume. The dehumidified air enters the sulfuric furnace after the preheating. heating in one of the heat exchangers of the contact unit. Sulfur supplied by nozzles is burned in the furnace: S + О 2: SO 2 + + 297.028 kJ. Gas containing 10-14% by volume of SO 2 is cooled in a boiler and, after dilution with air to an SO 2 content of 9-10% by volume at 420 ° C, enters the contact apparatus for the first stage of conversion, which takes place on three catalyst beds (SO 2 + V 2 O 2:: SO 3 + 96.296 kJ), after which the gas is cooled in heat exchangers. Then the gas containing 8.5-9.5% SO 3 at 200 ° C enters the first stage of absorption into the absorber irrigated with oleum and 98% SULFURIC ACID to: SO 3 + H 2 O: H 2 SO 4 + + 130.56 kJ. Then the gas is cleaned from splashes of SULFURIC ACID, is heated to 420 ° C and enters the second stage of conversion, which takes place on two catalyst beds. Before the second stage of absorption, the gas is cooled in an economizer and fed to the absorber of the second stage, irrigated with 98% SULFURIC ACID, and then, after being cleaned from splashes, is released into the atmosphere.

Figure: 1. Scheme of production of sulfuric acid from sulfur: 1-sulfur furnace; 2-waste heat boiler; 3 - economizer; 4-start furnace; 5, 6-heat exchangers of the starting furnace; 7-pin device; 8-heat exchangers; 9-oleum absorber; 10-drying tower; 11 and 12, respectively, the first and second monohydrate absorbers; 13-collectors of acid.

Fig. 2. Scheme of sulfuric acid production from pyrite: 1-disc feeder; 2-oven; 3-waste heat boiler; 4-cyclones; 5-electrostatic precipitators; 6 washing towers; 7-wet electrostatic precipitators; 8-blowing tower; 9-drying tower; 10-splash trap; 11-first monohydrate absorber; 12-heat exchange wiki; 13 - contact device; 14-oleum absorber; 15-second monohydrate absorber; 16 refrigerators; 17 collections.

Figure: 3. Scheme of production of sulfuric acid by nitrous method: 1 - denitrac. tower; 2, 3 are the first and second products. towers; 4-oxidizes. tower; 5, 6, 7-absorb. towers; 8 - electrostatic precipitators.

The production of SULFURIC ACID from metal sulfides (Fig. 2) is much more complicated and consists of the following operations. FeS 2 roasting is carried out in a fluidized bed furnace on air blast: 4FeS 2 + 11O 2: 2Fe 2 O 3 + 8SO 2 + 13476 kJ. Firing gas with a SO 2 content of 13-14%, having a temperature of 900 ° C, enters the boiler, where it is cooled to 450 ° C. Dust removal is carried out in a cyclone and an electrostatic precipitator. Then the gas passes through two washing towers, irrigated with 40% and 10% SULFURIC ACID. In this case, the gas is finally cleaned of dust, fluorine and arsenic. To clean the gas from the SULFURIC ACID aerosol generated in the washing towers, two stages of wet electrostatic precipitators are provided. After drying in a drying tower, in front of which the gas is diluted to a content of 9% SO 2, it is blown into the first conversion stage (3 catalyst beds). In heat exchangers, the gas is heated to 420 ° C due to the heat of the gas coming from the first stage of conversion. SO 2, oxidized by 92-95% in SO 3, goes to the first stage of absorption in oleum and monohydrate absorbers, where it is freed from SO 3. Further, gas with SO 2 content ~ 0.5% enters the second conversion stage, which takes place on one or two catalyst beds. The gas is preliminarily heated in another group of heat exchangers to 420 ° C due to the heat of the gases coming from the second stage of catalysis. After separation of SO 3 in a second absorption stage, the gas is vented to the atmosphere.

The degree of conversion of SO 2 to SO 3 in the contact method is 99.7%, the degree of absorption of SO 3 is 99.97%. The production of SULFURIC ACID to. Is carried out in one stage of catalysis, while the degree of conversion of SO 2 to SO 3 does not exceed 98.5%. Before being released into the atmosphere, the gas is purified from the remaining SO 2 (see Gas purification). The productivity of modern installations is 1500-3100 tons / day.

The essence of the nitrous method (Fig. 3) is that the firing gas, after cooling and cleaning from dust, is treated with so-called nitrose-C. K., in which sol. nitrogen oxides. SO 2 is absorbed by nitrose and then oxidized: SO 2 + N 2 O 3 + H 2 O: H 2 SO 4 + NO. The resulting NO is poorly soluble in nitrose and is released from it, and then partially oxidized by oxygen in the gas phase to NO 2. The mixture of NO and NO 2 is again absorbed by SULFURIC ACID. etc. Nitrogen oxides are not consumed in the nitrous process and are returned to production. cycle, due to incomplete absorption of their SULFURIC ACID because they are partially carried away by the exhaust gases. Advantages of the nitrous method: simplicity of hardware design, lower cost (10-15% lower than the contact one), the possibility of 100% processing of SO 2.

The equipment of the tower nitrous process is not complicated: SO 2 is processed in 7-8 lined towers with ceramic. nozzle, one of the towers (hollow) is adjustable to oxidize. volume. The towers have acid collectors, refrigerators, pumps supplying acid to the pressure tanks above the towers. A tail fan is installed in front of the last two towers. An electrostatic precipitator is used to clean the gas from aerosol SULFURIC ACID. The nitrogen oxides required for the process are obtained from HNO 3. To reduce the emission of nitrogen oxides into the atmosphere and 100% recycling of SO 2, a nitrous-free SO 2 recycling cycle is established between the production and absorption zones in combination with the water-acid method of deep capture of nitrogen oxides. The disadvantage of the nitrous method is low product quality: the concentration of SULFURIC ACID is up to 75%, the presence of nitrogen oxides, Fe and other impurities.

To reduce the possibility of crystallization SULFURIC ACID, during transportation and storage, standards have been established for commercial grades of SULFURIC ACID, the concentration of which corresponds to the lowest crystallization temperatures. Contents SULFURIC ACID to. In tech. grades (%): tower (nitrous) 75, contact 92.5-98.0, oleum 104.5, high-percentage oleum 114.6, battery 92-94. SULFURIC ACID is stored in steel tanks with a volume of up to 5000 m 3, their total storage capacity is designed for ten-day production. Oleum and SULFURIC ACID are transported in steel railway tanks. Conc. and battery SULFURIC ACID K. are transported in acid-resistant steel tanks. Tanks for transportation of oleum are covered with thermal insulation and heated before pouring oleum.

Determine SULFURIC ACID K. colorimetrically and photometrically, in the form of a suspension of BaSO 4 - phototurbidimetric, and also coulometric method.

Application. SULFURIC ACID is used in the production of mineral fertilizers, as an electrolyte in lead batteries, for the production of various mineral acids and salts, chemical fibers, dyes, smoke-forming substances and explosives, in the oil, metalworking, textile, leather and other industries. It is used in the industry. organic synthesis in dehydration reactions (obtaining diethyl ether, esters), hydration (ethanol from ethylene), sulfonation (synthetic detergents and intermediate products in the production of dyes), alkylation (obtaining isooctane, polyethylene glycol, caprolactam), etc. The largest consumer of SULFURIC ACID is the production of mineral fertilizers. For 1 ton of P 2 O 5 phosphoric fertilizers 2.2-3.4 tons of SULFURIC ACID are consumed, and for 1 ton of (NH 4) 2 SO 4 -0.75 tons of SULFURIC ACID. Therefore, sulfuric acid plants tend to be built in a complex with factories for the production of mineral fertilizers. The world production of SULFURIC ACID in 1987 reached 152 million tons.

SULFURIC ACID K. and oleum are extremely aggressive substances that affect the respiratory tract, skin, mucous membranes, cause difficulty breathing, cough, often laryngitis, tracheitis, bronchitis, etc. MPC aerosol SULFURIC ACID K. in the air of the working zone 1, 0 mg / m 3, in atm. air 0.3 mg / m 3 (max. one-time) and 0.1 mg / m 3 (average daily). Striking concentration of vapors of SULFURIC ACID k. 0.008 mg / l (exposure 60 min), lethal 0.18 mg / l (60 min). Hazard class 2. SULFURIC ACID aerosol k. Can be formed in the atmosphere as a result of chemical and metallurgical emissions. industries containing S oxides and fall out in the form of acid rain.

Literature: Handbook of sulfuric acid, ed. K.M. Malina, 2nd ed., M., 1971; Amelin A.G., Technology of sulfuric acid, 2nd ed., M., 1983; Vasiliev B.T., Otvagina M.I., Technology of sulfuric acid, M., 1985. Yu.V. Filatov.

Chemical encyclopedia. Volume 4 \u003e\u003e

DEFINITION

Anhydrous sulphuric acid is a heavy, viscous liquid that easily mixes with water in any proportion: the interaction is characterized by an extremely high exothermic effect (~ 880 kJ / mol with infinite dilution) and can lead to explosive boiling and splashing of the mixture if water is added to an acid; therefore it is so important to always use the reverse order in preparing solutions and add acid to water, slowly and with stirring.

Some of the physical properties of sulfuric acid are shown in the table.

Anhydrous H 2 SO 4 is a remarkable compound with an unusually high dielectric constant and very high electrical conductivity, which is due to ionic autodissociation (autoprotolysis) of the compound, as well as the relay-race conduction mechanism with proton transfer, which ensures the flow of electric current through a viscous liquid with a large number hydrogen bonds.

Table 1. Physical properties sulfuric acid.

Sulfuric acid production

Sulfuric acid is the most important industrial chemical and the cheapest high-volume acid in any country in the world.

Concentrated sulfuric acid ("vitriol oil") was first obtained by heating "green vitriol" FeSO 4 × nH 2 O and consumed in large quantities to obtain Na 2 SO 4 and NaCl.

In the modern process for the production of sulfuric acid, a catalyst consisting of vanadium (V) oxide with the addition of potassium sulfate on a support of silica or diatomaceous earth is used. Sulfur dioxide SO 2 is obtained by burning pure sulfur or by roasting sulfide ore (primarily pyrite or ores of Cu, Ni and Zn) in the process of extracting these metals. Then SO 2 is oxidized to trioxide, and then sulfuric acid is obtained by dissolving in water:

S + O 2 → SO 2 (ΔH 0 - 297 kJ / mol);

SO 2 + ½ O 2 → SO 3 (ΔH 0 - 9.8 kJ / mol);

SO 3 + H 2 O → H 2 SO 4 (ΔH 0 - 130 kJ / mol).

Chemical properties of sulfuric acid

Sulfuric acid is a strong dibasic acid. At the first stage in solutions of low concentration, it dissociates almost completely:

H 2 SO 4 ↔H + + HSO 4 -.

Dissociation in the second stage

HSO 4 - ↔H + + SO 4 2-

proceeds to a lesser extent. The dissociation constant of sulfuric acid in the second stage, expressed through the activity of ions, K 2 \u003d 10 -2.

As a dibasic acid, sulfuric acid forms two series of salts: medium and acidic. Medium salts of sulfuric acid are called sulfates, and acidic salts are called hydrosulfates.

Sulfuric acid greedily absorbs water vapor and is therefore often used to dry gases. The ability to absorb water also explains the charring of many organic matter, especially those related to the class of carbohydrates (fiber, sugar, etc.), when exposed to concentrated sulfuric acid. Sulfuric acid removes hydrogen and oxygen from carbohydrates, which form water, and carbon is released in the form of coal.

Concentrated sulfuric acid, especially when hot, is an energetic oxidizing agent. It oxidizes HI and HBr (but not HCl) to free halogens, coal to CO 2, sulfur to SO 2. These reactions are expressed by the equations:

8HI + H 2 SO 4 \u003d 4I 2 + H 2 S + 4H 2 O;

2HBr + H 2 SO 4 \u003d Br 2 + SO 2 + 2H 2 O;

C + 2H 2 SO 4 \u003d CO 2 + 2SO 2 + 2H 2 O;

S + 2H 2 SO 4 \u003d 3SO 2 + 2H 2 O.

The interaction of sulfuric acid with metals proceeds differently depending on its concentration. Diluted sulfuric acid oxidizes with its hydrogen ion. Therefore, it interacts only with those metals that stand in the series of stresses only up to hydrogen, for example:

Zn + H 2 SO 4 \u003d ZnSO 4 + H 2.

However, lead is not soluble in dilute acid because the resulting PbSO 4 salt is insoluble.

Concentrated sulfuric acid is an oxidizing agent due to sulfur (VI). It oxidizes metals up to and including silver. The products of its reduction can be different depending on the activity of the metal and on the conditions (acid concentration, temperature). When interacting with low-activity metals, for example, with copper, the acid is reduced to SO 2:

Cu + 2H 2 SO 4 \u003d CuSO 4 + SO 2 + 2H 2 O.

When interacting with more active metals, the reduction products can be both dioxide and free sulfur and hydrogen sulfide. For example, when interacting with zinc, reactions can occur:

Zn + 2H 2 SO 4 \u003d ZnSO 4 + SO 2 + 2H 2 O;

3Zn + 4H 2 SO 4 \u003d 3ZnSO 4 + S ↓ + 4H 2 O;

4Zn + 5H 2 SO 4 \u003d 4ZnSO 4 + H 2 S + 4H 2 O.

Application of sulfuric acid

The use of sulfuric acid varies from country to country and from decade to decade. So, for example, in the United States at present main area consumption of H 2 SO 4 - production of fertilizers (70%), followed by chemical production, metallurgy, oil refining (~ 5% in each region). In the UK, the distribution of consumption by industry is different: only 30% of the H 2 SO 4 produced is used in the production of fertilizers, but 18% goes to paints, pigments and intermediate products for the production of dyes, 16% to the chemical industry, 12% to the production of soap and detergents, 10 % for the production of natural and artificial fibers and 2.5% is used in metallurgy.

Examples of problem solving

EXAMPLE 1

Sulfuric acid properties

Anhydrous sulfuric acid (monohydrate) is a heavy oily liquid that is miscible with water in all proportions to release a large number heat. The density at 0 ° C is 1.85 g / cm 3. It boils at 296 ° C and freezes at -10 ° C. Not only monohydrate is called sulfuric acid, but also aqueous solutions it (), as well as solutions of sulfur trioxide in monohydrate (), called oleum. Oleum "smokes" in air due to desorption from it. Pure sulfuric acid is colorless, technical is colored by impurities in a dark color.

The physical properties of sulfuric acid, such as density, crystallization temperature, boiling point, depend on its composition. In fig. 1 shows a diagram of the crystallization of the system. The maxima in it correspond to the composition of the compounds or, the presence of minima is explained by the fact that the crystallization temperature of mixtures of two substances is lower than the crystallization temperature of each of them.

Figure: 1

Anhydrous 100% sulfuric acid has a relatively high crystallization temperature of 10.7 ° C. To reduce the possibility of freezing of a commercial product during transportation and storage, the concentration of technical sulfuric acid is chosen such that it has a sufficiently low crystallization temperature. The industry produces three types of commercial sulfuric acid.

Sulfuric acid is very active. It dissolves metal oxides and most pure metals; displaces all other acids from salts at elevated temperatures. Sulfuric acid is especially eagerly combined with water due to its ability to give hydrates. It takes water away from other acids, from crystalline salts of salts and even oxygen derivatives of hydrocarbons, which do not contain water, but hydrogen and oxygen in a combination of H: O \u003d 2.tree and other plant and animal tissues containing cellulose, starch and sugar are destroyed in concentrated sulfuric acid; water binds to acid and only finely dispersed carbon remains from the fabric. In dilute acid, cellulose and starch break down to form sugars. Concentrated sulfuric acid causes burns if it comes into contact with human skin.

The high activity of sulfuric acid in combination with the relatively low cost of production predetermined the enormous scale and extraordinary variety of its application (Fig. 2). It is difficult to find an industry that has not consumed sulfuric acid or products made from it in certain quantities.

Figure: 2

The largest consumer of sulfuric acid is the production of mineral fertilizers: superphosphate, ammonium sulfate, etc. Many acids (for example, phosphoric, acetic, hydrochloric) and salts are produced in large part with the help of sulfuric acid. Sulfuric acid is widely used in the production of non-ferrous and rare metals. In the metalworking industry, sulfuric acid or its salts are used for pickling steel products before painting, tinning, nickel plating, chrome plating, etc. significant amounts of sulfuric acid are spent on refining petroleum products. The production of a number of dyes (for fabrics), varnishes and paints (for buildings and machines), medicinal substances and some plastics is also associated with the use of sulfuric acid. With the help of sulfuric acid, ethyl and other alcohols, some esters, synthetic detergents, and a number of pesticides are produced to combat agricultural pests and weeds. Diluted solutions of sulfuric acid and its salts are used in the production of artificial silk, in the textile industry for processing fibers or fabrics before dyeing them, as well as in other branches of light industry. IN food Industry sulfuric acid is used in the production of starch, molasses and a number of other products. Transport uses lead sulfuric acid batteries. Sulfuric acid is used for drying gases and for concentrating acids. Finally, sulfuric acid is used in nitration processes and in the manufacture of most explosives.