Application of catalysis in industry. Types of industrial catalysts Examples of industrial processes using catalysts

The rapid industrial growth that we are now experiencing would not have been possible without the development of new chemical technologies. To a large extent, this progress is determined by the widespread use of catalysts, with the help of which low-grade raw materials are converted into high-value products. Figuratively speaking, catalyst- this is the philosopher's stone of the modern alchemist, only he does not turn lead into gold, but raw materials into medicines, plastics, chemical reagents, fuel, fertilizers and other useful products. Perhaps, the very first catalytic process that man has learned to use is fermentation. Recipes for the preparation of alcoholic beverages were known to the Sumerians as early as 3500 BC. See WINE; BEER.

A significant milestone in practical application catalysis became margarine production catalytic hydrogenation of vegetable oil. This reaction was first carried out on an industrial scale around 1900. And since the 1920s, catalytic methods for obtaining new organic materials especially plastics. The key point was the catalytic production of olefins, nitriles, esters, acids, etc. - "bricks" for the chemical "building" of plastics. The third wave of industrial use of catalytic processes belongs to the 1930s and associated with oil refining. In terms of volume, this production soon left all others far behind. Oil refining consists of several catalytic processes:

cracking,

reforming,

Hydrosulfonation,

Hydrocracking,

isomerization,

Polymerization

Alkylation.

And finally fourth wave in the use of catalysis related to security environment . The most famous achievement in this area is creation of a catalytic converter for vehicle exhaust gases. Catalytic converters, which have been installed in cars since 1975, have played a big role in improving air quality and have saved many lives in this way.

For work in the field of catalysis and related areas About a dozen Nobel Prizes have been awarded. The practical significance of catalytic processes is evidenced by the fact that the share nitrogen, which is part of the nitrogen-containing compounds obtained industrially, accounts for about half of the total nitrogen that is part of food products. The amount of nitrogen compounds produced naturally is limited, so that the production of dietary protein depends on the amount of nitrogen applied to the soil with fertilizers. It would be impossible to feed even half of humanity without synthetic ammonia, which is produced almost exclusively by catalytic Haber-Bosch process. The scope of catalysts is constantly expanding. It is also important that catalysis can significantly increase the efficiency of previously developed technologies. An example is the improvement of catalytic cracking through the use of zeolites.

Hydrogenation. A large number of catalytic reactions are associated with the activation of a hydrogen atom and some other molecule, leading to their chemical interaction. This process is called hydrogenation and underlies many stages of oil refining and the production of liquid fuels from coal ( Bergius process). The production of aviation gasoline and motor fuel from coal was developed in Germany during the Second World War, since this country does not have oil fields. The Bergius process is the direct addition of hydrogen to carbon. Coal is heated under pressure in the presence of hydrogen and a liquid product is obtained, which is then processed into aviation gasoline and motor fuel. Iron oxide is used as a catalyst, as well as catalysts based on tin and molybdenum. During the war, approximately 1,400 tons of liquid fuel per day were obtained at 12 German factories using the Bergius process. Another process, Fischer–Tropsch, consists of two stages. First, the coal is gasified, i.e. carry out its reaction with water vapor and oxygen and get a mixture of hydrogen and carbon oxides. This mixture is converted into liquid fuel using catalysts containing iron or cobalt. With the end of the war, the production of synthetic fuel from coal in Germany was discontinued. As a result of the rise in oil prices that followed the oil embargo of 1973-1974, vigorous efforts were made to develop an economically viable method for producing gasoline from coal. Thus, direct liquefaction of coal can be carried out more efficiently using a two-stage process in which the coal is first contacted with an alumina-cobalt-molybdenum catalyst at a relatively low and then at a higher temperature. The cost of such synthetic gasoline is higher than that obtained from oil.

Ammonia. One of the simplest hydrogenation processes from a chemical point of view is the synthesis of ammonia from hydrogen and nitrogen. Nitrogen is a very inert substance. To break the N–N bond in its molecule, an energy of the order of 200 kcal/mol is required. However, nitrogen binds to the surface of the iron catalyst in the atomic state, and this requires only 20 kcal/mol. Hydrogen bonds with iron even more readily. The synthesis of ammonia proceeds as follows:

This example illustrates the ability of a catalyst to speed up both the forward and reverse reactions equally, i.e. the fact that the catalyst does not change the equilibrium position of the chemical reaction.

Hydrogenation of vegetable oil. One of the most important hydrogenation reactions in practice is the incomplete hydrogenation of vegetable oils to margarine, cooking oil, and other food products. Vegetable oils are obtained from soybeans, cotton seeds and other crops. They include esters, namely triglycerides of fatty acids with varying degrees of unsaturation. Oleic acid CH 3 (CH 2) 7 CH \u003d CH (CH 2) 7 COOH has one C \u003d C double bond, linoleic acid has two and linolenic acid has three. The addition of hydrogen to break this bond prevents the oils from oxidizing (rancidity). This raises their melting point. The hardness of most of the products obtained depends on the degree of hydrogenation. Hydrogenation is carried out in the presence of a finely dispersed nickel powder deposited on a substrate or nickel Raney catalyst in a highly purified hydrogen atmosphere.

Dehydrogenation. Dehydrogenation is also an industrially important catalytic reaction, although the scale of its application is incomparably smaller. With its help, for example, styrene, an important monomer, is obtained. To do this, dehydrogenate ethylbenzene in the presence of a catalyst containing iron oxide; potassium and some structural stabilizer also contribute to the reaction. IN industrial scale carry out the dehydrogenation of propane, butane and other alkanes. Dehydrogenation of butane in the presence of an alumina-chromium catalyst produces butenes and butadiene.

acid catalysis. The catalytic activity of a large class of catalysts is due to their acidic properties. According to I. Bronsted and T. Lowry An acid is a compound that can donate a proton. Strong acids easily donate their protons to bases. The concept of acidity received further development in works G. Lewis, who defined an acid as a substance capable of accepting an electron pair from a donor substance with the formation of a covalent bond due to the socialization of this electron pair.

These ideas, together with ideas about reactions with the formation of carbenium ions, helped to understand mechanism of various catalytic reactions, especially those involving hydrocarbons. The strength of an acid can be determined using a set of bases that change color when a proton is added. It turns out that some industrially important catalysts behave like very strong acids. These include the catalyst Friedel-Crafts process, such as HCl–AlCl 2 O 3 (or HAlCl 4), and aluminosilicates. Acid strength- this is a very important characteristic, since the rate of protonation, a key stage in the process of acid catalysis, depends on it. The activity of catalysts such as aluminosilicates used in oil cracking is determined by the presence of Bronsted and Lewis acids on their surface. Their structure is similar to the structure of silica (silicon dioxide), in which some of the Si 4+ atoms are replaced by Al 3+ atoms. The excess negative charge that arises in this case can be neutralized by the corresponding cations. If the cations are protons, then the aluminosilicate behaves like Bronsted acid:

Activity of acid catalysts conditioned their ability to react with hydrocarbons to form a carbenium ion as an intermediate. Alkylcarbenium ions contain a positively charged carbon atom bonded to three alkyl groups and/or hydrogen atoms. They play an important role as intermediates formed in many reactions involving organic compounds. The mechanism of action of acid catalysts can be illustrated by the example of the isomerization reaction of n-butane to isobutane in the presence of HCl–AlCl 3 or Pt–Cl–Al 2 O 3 . First, a small amount of C 4 H 8 olefin attaches the positively charged hydrogen ion of the acid catalyst to form a tertiary carbenium ion. Then the negatively charged hydride ion H - is split off from n-butane with the formation of isobutane and secondary butylcarbenium ion. The latter, as a result of the rearrangement, turns into a tertiary carbenium ion. This chain can continue with the elimination of the hydride ion from the next n-butane molecule, etc.:

Significantly, tertiary carbenium ions are more stable than primary or secondary ones. As a result, they are mainly present on the catalyst surface, and therefore the main product of butane isomerization is isobutane. Acid catalysts are widely used in oil refining - cracking, alkylation, polymerization and isomerization of hydrocarbons (see also CHEMISTRY AND METHODS OF OIL REFINING).

Installed mechanism of action of carbenium ions playing the role of catalysts in these processes. At the same time, they participate in a number of reactions, including the formation of small molecules by splitting large ones, the combination of molecules (olefin with olefin or olefin with isoparaffin), structural rearrangement by isomerization, the formation of paraffins and aromatic hydrocarbons by hydrogen transfer. One of the latest industrial applications of acid catalysis is the production of leaded fuels by the addition of alcohols to isobutylene or isoamylene. The addition of oxygenated compounds to gasoline reduces the concentration of carbon monoxide in the exhaust gases. Methyl tertiary butyl ether (MTBE) with a blending octane number of 109 also makes it possible to obtain the high-octane fuel needed to run a high-compression automobile engine without resorting to the introduction of tetraethyl lead into gasoline. The production of fuels with octane numbers 102 and 111 is also organized.

main catalysis. Catalyst activity conditioned their main properties. An old and well-known example of such catalysts is sodium hydroxide used to hydrolyze or saponify fats in the production of soap, and one recent example is the catalysts used in the production of polyurethane plastics and foams. Urethane is formed by the interaction of alcohol with isocyanate, and this reaction is accelerated in the presence of basic amines. During the reaction, the base is attached to the carbon atom in the isocyanate molecule, as a result of which a negative charge appears on the nitrogen atom and its activity with respect to alcohol increases. A particularly effective catalyst is triethylenediamine. Polyurethane plastics are obtained by reacting diisocyanates with polyols (polyalcohols). When the isocyanate reacts with water, the previously formed urethane decomposes to release CO 2 . When a mixture of polyalcohols and water reacts with diisocyanates, the resulting polyurethane foam foams with gaseous CO 2 .

Dual action catalysts. These catalysts speed up two types of reactions and give better results than passing the reactants in series through two reactors each containing only one type of catalyst. This is due to the fact that the active sites of the double acting catalyst are very close to each other, and the intermediate product formed on one of them immediately turns into final product on another. Combining a hydrogen activating catalyst with a hydrocarbon isomerization promoting catalyst gives a good result. Hydrogen activation carry out some metals, and the isomerization of hydrocarbons - acids. An effective dual-acting catalyst that is used in oil refining to convert naphtha to gasoline is finely dispersed platinum deposited on acid alumina. Conversion of naphtha components such as methylcyclopentane (ICP), into benzene increases the octane number of gasoline. At first ICP dehydrogenates on the platinum part of the catalyst to an olefin with the same carbon backbone; then the olefin passes to the acid part of the catalyst, where it isomerizes to cyclohexene. The latter passes to the platinum part and dehydrogenates to benzene and hydrogen. Dual action catalysts significantly accelerate oil reforming. They are used to isomerize normal paraffins to isoparaffins. The latter, boiling at the same temperatures as gasoline fractions, are valuable because they have a higher octane number compared to straight hydrocarbons. In addition, the conversion of n-butane to isobutane is accompanied by dehydrogenation, contributing to the production of MTBE.

Stereospecific polymerization. An important milestone in the history of catalysis was the discovery of the catalytic polymerization of a-olefins with the formation of stereoregular polymers. Stereospecific polymerization catalysts were discovered by K. Ziegler when he tried to explain the unusual properties of the polymers he obtained. Another chemist, J. Natta, suggested that the uniqueness of Ziegler polymers is determined by their stereoregularity. X-ray diffraction experiments have shown that polymers prepared from propylene in the presence of Ziegler catalysts are highly crystalline and indeed have a stereoregular structure. Natta introduced the terms "isotactic" and "syndiotactic" to describe such ordered structures. In the case where there is no order, the term "atactic" is used:

Stereospecific reaction occurs on the surface solid catalysts containing transition metals of groups IVA-VIII (such as Ti, V, Cr, Zr) in a partially oxidized state, and any compound containing carbon or hydrogen, which is associated with a metal from groups I-III. A classic example such a catalyst is a precipitate formed during the interaction of TiCl 4 and Al(C 2 H 5) 3 in heptane, where titanium is reduced to a trivalent state. This extremely active system catalyzes the polymerization of propylene at normal temperature and pressure.

catalytic oxidation. The use of catalysts to control the chemistry of oxidation processes is of great scientific and practical value. In some cases, oxidation must be complete, for example, when neutralizing CO and hydrocarbon contaminants in car exhaust gases. However, more often it is necessary that the oxidation be incomplete, for example, in many processes widely used in industry for the conversion of hydrocarbons into valuable intermediate products containing such functional groups as -CHO, -COOH, -C-CO, -CN. In this case, both homogeneous and heterogeneous catalysts are used. An example of a homogeneous catalyst is a transition metal complex, which is used to oxidize para-xylene to terephthalic acid, the esters of which are the basis for the production of polyester fibers.

Catalysts for heterogeneous oxidation. These catalysts are usually complex solid oxides. Catalytic oxidation takes place in two stages. First, the oxide oxygen is captured by a hydrocarbon molecule adsorbed on the oxide surface. The hydrocarbon is oxidized and the oxide is reduced. The reduced oxide reacts with oxygen and returns to its original state. Using a vanadium catalyst, phthalic anhydride is obtained by partial oxidation of naphthalene or butane.

Ethylene production by methane dehydrodimerization. The synthesis of ethylene through dehydrodimerization allows natural gas to be converted into more easily transportable hydrocarbons. reaction

2CH 4 + 2O 2 → C 2 H 4 + 2H 2 O

carried out at 850 °C using various catalysts; best results obtained with a Li-MgO catalyst. Presumably, the reaction proceeds through the formation of a methyl radical by splitting off a hydrogen atom from a methane molecule. Cleavage is carried out by incompletely reduced oxygen, for example, O 2 2–. Methyl radicals in the gas phase recombine to form an ethane molecule and are converted to ethylene during subsequent dehydrogenation. Another example of incomplete oxidation is the conversion of methanol to formaldehyde in the presence of a silver or iron-molybdenum catalyst.

Zeolites. Zeolites make up a special class of heterogeneous catalysts. These are aluminosilicates with an ordered honeycomb structure, the cell size of which is comparable to the size of many organic molecules. They are also called molecular sieves. Of greatest interest are zeolites, the pores of which are formed by rings consisting of 8–12 oxygen ions (Fig. 2). Sometimes the pores overlap, as in the ZSM-5 zeolite (Fig. 3), which is used for the highly specific conversion of methanol to gasoline fraction hydrocarbons. Gasoline contains significant amounts of aromatic hydrocarbons and therefore has a high octane number. In New Zealand, for example, one third of all gasoline consumed is obtained using this technology. Methanol is obtained from imported methane.

Picture 2 - The structure of zeolites with large and small pores.

Picture 3 - Zeolite ZSM-5. Schematic representation of the structure in the form of intersecting tubes.

Catalysts that make up the group of Y-zeolites significantly increase the efficiency of catalytic cracking due primarily to their unusual acidic properties. Replacing aluminosilicates with zeolites makes it possible to increase the yield of gasoline by more than 20%. In addition, zeolites are selective with respect to the size of the reacting molecules. Their selectivity is due to the size of the pores through which molecules can pass only certain sizes and forms. This applies to both starting materials and reaction products. For example, due to steric constraints, para-xylene is formed more easily than the bulkier ortho and meta isomers. The latter are "locked" in the pores of the zeolite (Fig. 4).

Figure 4 - Scheme explaining the selectivity of zeolites in relation to reagents (a) and products (b).

The use of zeolites has made a real revolution in some industrial technologies - dewaxing gas oil and engine oil, obtaining chemical intermediates for the production of plastics by aromatic alkylation, xylene isomerization, toluene disproportionation and catalytic cracking of oil. Zeolite ZSM-5 is especially effective here.

Dewaxing of petroleum products- extraction of paraffin and ceresin from petroleum products (diesel fuels, oils), as a result of which their quality improves, in particular, the pour point decreases.

Paraffin(German Paraffin, from lat. Parum - little and affinis - related), a mixture of saturated hydrocarbons C 18 -C 35, predominantly. normal structure with a mol. m. 300-400; colorless crystals with t pl. \u003d 45–65 o C, density 0.880–0.915 g / cm 3 (15 o C).

Ceresin(from lat. cera - wax), a mixture of solid hydrocarbons (mainly alkylcyclanes and alkanes), obtained after purification of ozocerite. By density, color (from white to brown), melting point (65-88 ° C) and viscosity, ceresin is similar to wax.

Catalysts and environmental protection. The use of catalysts to reduce air pollution began in the late 1940s. In 1952, A. Hagen-Smith found that hydrocarbons and nitrogen oxides, which are part of exhaust gases, react to light to form oxidants (in particular, ozone), which irritate the eyes and give other undesirable effects. Around the same time, Y. Houdry developed a method for the catalytic purification of exhaust gases by oxidizing CO and hydrocarbons to CO 2 and H 2 O. In 1970, the Clean Air Declaration was formulated (revised in 1977, expanded in 1990), according to which all new cars , starting with 1975 models, must be equipped with exhaust gas catalytic converters. Norms have been established for the composition of exhaust gases. Since lead compounds added to gasoline poison catalysts, a phase-out program has been adopted. Attention was also drawn to the need to reduce the content of nitrogen oxides. Especially for automobile catalytic converters, catalysts have been created in which active components are deposited on a ceramic substrate with a honeycomb structure, through the cells of which exhaust gases pass. The substrate is coated thin layer metal oxide, for example Al2O3, on which a catalyst is applied - platinum, palladium or rhodium. The content of nitrogen oxides formed during the combustion of natural fuels at thermal power plants can be reduced by adding small amounts of ammonia to the flue gases and passing them through a titanium-vanadium catalyst.

Enzymes. Enzymes are natural catalysts that regulate biochemical processes in a living cell. They participate in the processes of energy exchange, the breakdown of nutrients, biosynthesis reactions. Many complex organic reactions cannot proceed without them. Enzymes function at ordinary temperature and pressure, have very high selectivity and are able to increase the rate of reactions by eight orders of magnitude. Despite these advantages, only about 20 of the 15,000 known enzymes are used on a large scale. Man has been using enzymes for thousands of years to bake bread, produce alcoholic beverages, cheese and vinegar. Now enzymes are also used in industry: in the processing of sugar, in the production of synthetic antibiotics, amino acids and proteins. Proteolytic enzymes that accelerate hydrolysis processes are added to detergents. With the help of Clostridium acetobutylicum bacteria, H. Weizmann carried out the enzymatic conversion of starch into acetone and butyl alcohol. This method of obtaining acetone was widely used in England during the First World War, and during the Second World War, butadiene rubber was made with its help in the USSR. An exceptionally large role was played by the use of enzymes produced by microorganisms for the synthesis of penicillin, as well as streptomycin and vitamin B12. Enzymatically produced ethyl alcohol is widely used as an automotive fuel. In Brazil, more than a third of the approximately 10 million cars run on 96% ethyl alcohol derived from sugar cane, and the rest on a mixture of gasoline and ethyl alcohol (20%). The technology for the production of fuel, which is a mixture of gasoline and alcohol, is well developed in the United States. In 1987, about 4 billion liters of alcohol were obtained from corn kernels, of which approximately 3.2 billion liters were used as fuel. Various applications are also found in the so-called. immobilized enzymes. These enzymes are associated with a solid carrier, such as silica gel, over which the reagents are passed. The advantage of this method is that it ensures efficient contact of the substrates with the enzyme, separation of products and preservation of the enzyme. One example of the industrial use of immobilized enzymes is the isomerization of D-glucose to fructose.

Literature

1. Gates B.K. Chemistry of catalytic processes. M., 1981

2. Boreskov G.K. Catalysis. Questions of theory and practice. Novosibirsk, 1987

3. Gankin V.Yu., Gankin Yu.V. New general theory catalysis. L., 1991

4. Tokabe K. Catalysts and catalytic processes. M., 1993

5. Collier's Encyclopedia. - open society. 2000.

According to their composition, catalysts are subdivided into 1) modified; 2) on mixed and 3) on media.

1) Modified catalysts. A modifier is an addition to the catalyst of a small (up to 10 - 12 wt.%) amount of another substance that is not catalytically active for this reaction, but improves certain qualities of the catalyst (thermal stability, strength, poison resistance). If the modifier increases activity, it is a promoter. According to the nature of the action, promoters are divided into a) electronic, causing deformation of the crystal lattices of the catalyst or changing the work function of the electrons in the desired direction. For example, the addition of Cl - in a silver catalyst for the oxidation of methanol: CH 3 OH ® CH 2 O; b) stabilizing, preventing sintering of the dispersed structure of the catalyst. For example, the promoters of Al 2 O 3 and SiO 2 stabilize the primary crystals of the iron catalyst in the synthesis of ammonia: N 2 + 3H 2 ® 2NH 3 . On the first day of operation, the crystals are sintered, enlarged from 6 to 20 nm. The stock of free energy at the interface of crystals decreases and the activity falls. The introduced promoters, without being reduced, melt at the temperature of synthesis, the crystals are covered with a thin film, preventing their sintering. However, both additives have an acidic surface, on which the NH 3 molecule is strongly adsorbed, preventing the sorption of nitrogen molecules, and the catalyst activity decreases; V) structure-forming, neutralizing acid centers Al 2 O 3 and SiO 2 . For example, K 2 O, CaO and MgO, but their amount should be no more than 4-5 wt.%, since they have a mineralizing effect, i.e. contribute to the sintering of Fe crystals.

2) Mixed catalysts. Mixed catalysts are called catalysts containing several catalytically active components for a given reaction, taken in commensurate amounts. The activity of such catalysts is not additive, but takes on an extreme value due to the following reasons: the formation of mechanical mixtures with a larger phase boundary, i.e. with a large amount of free energy ( for example, for the reaction HCºHC + H 2 O ® CH 3 -CHO, the catalyst is a mixture of CdO + CaO / P 2 O 5 \u003d 3-4; at a molar ratio of £3, high selectivity is observed, but the strength of the catalyst granules is low; at ³4 - high strength of granules, but low selectivity); formation of spinel type solid solutions(for example, in the V 2 O 5 +MoO 3 oxidation catalyst, the Mo +6 cation is introduced into the vacant positions of the V 2 O 5 crystal lattice. Lattice deformation leads to an increase in the free energy of the system; formation under the reaction conditions of new more active catalysts(for example, for the synthesis of methanol CO + 2H 2 ® CH 3 OH, a chromium-zinc catalyst is used:

ZnO + CrO 3 + H 2 O ® ZnCrO 4 × H 2 O

2ZnCrO 4 × H 2 O + 3H 2 ® + 5H 2 O

Shown in square brackets is the active phase obtained after the reduction of the catalyst, which is essentially a new catalyst.

3) Supported catalysts. The carrier determines the shape and size of the granules, the optimal porous structure, strength, heat resistance, and cost reduction. Sometimes increases activity (see ligand field theory). Media classification: synthetic- silica gel, Activated carbon, aluminum oxide (g, a), ceramic; natural- pumice, diatomaceous earth; by pore volume- porous (more than 10%), non-porous (10% or less); by grain size- large (1-5 mm), small (0.1-1.0 mm), fine (less than 0.1 mm); according to the size of the specific surface- small (less than 1 m 2 /g), medium (1-50 m 2 /g), developed (more than 50 m 2 /g).

Catalysis is one of the most dynamically and rapidly developing areas of science and technology. New catalytic systems are constantly being developed and existing ones are being improved, new catalytic processes are being proposed, their instrumentation is changing, and new physicochemical methods for studying catalysts are being improved and appear. Most of the chemical processes involved in the enterprises of the petrochemical and oil refining complex are catalytic. The development of catalysis and catalytic technologies largely determine the competitiveness of petrochemical products in the market. Therefore, there is an acute issue of the need to train highly qualified specialists in the field of catalysis for petrochemistry.

Catalysis is a specific phenomenon. There are no substances that would have catalytic properties in a general form. Each reaction must use its own specific catalyst.

Application of catalysis in chemical industry . Catalytic processes are used to produce hydrogen, which serves as a raw material for the synthesis of ammonia and a number of other chemical technology industries. Methane conversion. The cheapest source of hydrogen is natural gas. The first stage of hydrogen production includes the interaction of methane with water vapor with the partial addition of oxygen or air at a temperature of 800–1000°C (reaction 2.1). Nickel supported on heat-resistant alumina carriers (corundum - a-Al 2 O 3) is used as a catalyst.

CH 4 + H 2 O ⇄ 3H 2 + CO (2.1)

CO + H 2 O ⇄ CO 2 + H 2 (2.2)

As a result of this reaction, along with hydrogen, carbon monoxide is formed in a significant amount.

CO conversion. The interaction of carbon monoxide with water vapor is carried out in two stages at decreasing temperature using oxide catalysts (reaction 2.2), while hydrogen is additionally formed. At the first stage, a medium-temperature (435-475°C) iron-chromium catalyst (Fe 3 O 4 with Cr 2 O 3 additives) was used; on the second, a low-temperature (230-280°C) catalyst (a mixture of oxides of aluminium, copper, chromium and zinc). The final content of carbon monoxide, the presence of which sharply reduces the activity of iron catalysts for the synthesis of ammonia, can be reduced to tenths of a percent.

To remove residual CO, it was necessary to apply complex washing of the gas mixture with an ammonia solution of Cu 2 O under high pressure 120-320 atm and low temperature 5-20°C.

In practice industrial production purification of gas emissions from CO is carried out by absorption with solutions of Cu-ammonia salts (copper formates and carbonates), which have the ability to form complex compounds with CO. Since formates are not very stable, preference is given to carbonate solutions.

The initial carbonate-ammonia complex of copper has the following composition (kmol / m 3): Cu + - 1.0 - 1.4; Cu 2+ - 0.08 - 0.12; NH 3 - 4.0 - 6.0; CO 2 - 2.4 - 2.6.

The absorption capacity with respect to CO is possessed by monovalent copper salts. Cu 2+ cations, as a rule, do not take part in absorption. However, the concentration of Cu 2+ must be maintained in the solution at least 10 wt. % of Cu + content. The latter helps to prevent the formation of elemental copper deposits, which can clog the pipelines and disrupt the operation of the absorber. The presence of copper carbonate-ammonia complex Cu 2+ in solution shifts the equilibrium of reaction (1) towards the formation of Cu + : Cu 2+ + Cu ⇄ 2 Cu + (1)

The solution of the carbonate-ammonia copper complex used for CO absorption contains 2 CO 3 ; CO 3 ; (NH 4) 2 CO 3; free NH 3 and CO 2 .

The process of absorption of CO by the carbonate-ammonia complex of copper proceeds according to the reaction: + + CO + NH 3 ⇄ + - DH (2)

Simultaneously with CO, CO2 is also absorbed according to the equation:

2 NH 3 + H 2 O + CO 2 ⇄ (NH 4) 2 CO 3 - DH 1 (3)

Metanization. In connection with the development of a new active nickel catalyst, the complex washing operation can be replaced at 250–350°C by a simpler process of converting the carbon monoxide residue into methane inert for the ammonia synthesis catalyst (reaction 2.3):

CO + 3H 2 ⇄ CH 4 + H 2 O (2.3)

Thus, the development of a more active catalyst made it possible to significantly simplify technological scheme and improve the efficiency of ammonia production.

Application of catalysis in the oil refining industry. The efficiency of the use of catalysis turned out to be so significant that in a few years a genuine technical revolution took place in the oil refining industry, which made it possible to dramatically increase both the yield and the quality of motor fuels obtained on the basis of the use of catalysts.

Currently, over 80% of oil is processed using catalytic processes: cracking, reforming, isomerization and hydrogenation of hydrocarbons, hydrotreatment of oil fractions from sulfur-containing compounds, hydrocracking. Table 2.1 lists the most important modern catalytic processes in oil refining.

Cracking. Catalytic cracking of oil or its fractions is a destructive process carried out at temperatures of 490-540°C on synthetic and natural aluminosilicate catalysts of acidic nature to produce high-quality gasoline with an octane rating of 98-92, a significant amount of gases containing saturated and unsaturated hydrocarbons C 3 - C 4 , kerosene-gas oil fractions, carbon black and coke.

Octane number (O.ch.) - a conditional indicator of the detonation resistance of light (gasoline, kerosene) motor fuels during combustion in carburetor engines. The reference fuel is isooctane (O.p. = 100), normal heptane (O.p. = 0). The octane number of gasoline is the percentage (by volume) of isooctane in such a mixture of it with n-heptane, which, under standard test conditions on a special single-cylinder engine, detonates in the same way as the tested gasoline.

In recent years, catalysts based on crystalline synthetic zeolites have received wide industrial use. The activity of these catalysts, especially those containing a mixture of oxides of rare earth elements (СеО 2 , La 2 O 3 , Ho 2 O 3 , Dy 2 O 3 and others), is much higher than that of amorphous aluminosilicate catalysts.

The use of catalysts made it possible not only to increase the rate of formation of hydrocarbons of lower molecular weight from naphthenes by 500-4000 times, but also to increase the yield of valuable fractions compared to thermal cracking.

Catalytic cracking is the most high-tonnage industrial catalytic process. It currently processes over 300 million tons of oil per year, which requires an annual consumption of about 300 thousand tons of catalysts.

Reforming. Catalytic reforming is carried out at a temperature of 470-520°C and a pressure of 0.8-1.5 MPa on Pt, Re-catalysts supported on aluminum oxide, treated with hydrogen chloride to increase the acid properties. Reforming is a method of processing petroleum products, mainly gasoline and naphtha fractions of oil (hydrocarbons C 6 -C 9 of three main classes: paraffin, naphthenic and aromatic) in order to obtain high-octane motor gasoline, aromatic hydrocarbons (benzene, toluene, xylene, ethylbenzene) and technical hydrogen. During the reforming process, the reactions of dehydrogenation of naphthenes to aromatic hydrocarbons, cyclization of paraffins and olefins, and isomerization of five-membered cyclic hydrocarbons into six-membered ones take place. Currently, catalytic reforming is used to process more than 200 million tons of oil per year. Its use allowed not only to improve the quality of motor fuel, but also to produce significant amounts of aromatic hydrocarbons for the chemical industry. By-products of catalytic reforming are fuel gas, consisting mainly of methane and ethane, as well as liquefied gas - propane-butane fraction

Hydrotreating of petroleum products. Hydrogen is a valuable by-product of catalytic reforming. The appearance of cheap hydrogen made it possible to widely use the catalytic hydrotreatment of petroleum products from sulfur-, nitrogen- and oxygen-containing compounds, with the formation of easily removable H 2 S, NH 3 and H 2 O, respectively (reactions 2.4 - 2.7):

CS 2 + 4H 2 ⇄ 2H 2 S + CH 4 (2.4)

RSH + H 2 ⇄ H 2 S + RH (2.5)

COS + 4H 2 ⇄ H 2 S + CH 4 + H 2 O (2.6)

RNH + 3/2H 2 ⇄ NH 3 + RH (2.7)

At the same time, hydrogenation of the dienes occurs, which increases the stability of the product. For this purpose, catalysts prepared from oxides of cobalt (2–5 wt.%) and molybdenum (10–19 wt.%) or oxides of nickel and molybdenum deposited on γ-aluminum oxide are most widely used.

Hydrotreating makes it possible to obtain up to 250-300 thousand tons of elemental sulfur per year. To do this, implement the Claus process:

2H 2 S + 3O 2 ⇄ 2SO 2 + 2H 2 O (2.8)

2H 2 S + SO 2 ⇄ 3S + 2H 2 O (2.9)

Part of H 2 S is oxidized by atmospheric oxygen to γ-Al 2 O 3 at 200-250°C (reaction 2.8); the other part of H 2 S reacts with sulfur dioxide to form sulfur (reaction 2.9).

The conditions for hydrotreatment depend on the properties of the raw material being purified, but most often lie within 330-410°C and 3-5 MPa. About 300 million tons of oil products (gasoline and kerosene fractions, diesel fuel, vacuum distillates, paraffins and oils) are hydrotreated annually. The implementation of the hydrotreatment stage in oil refining made it possible to prepare raw materials for catalytic reforming (gasolines) and cracking (vacuum distillates), to obtain low-sulphur lighting kerosene and fuel, to improve the quality of products (paraffins and oils), and also has a significant environmental effect, since atmospheric pollution with exhaust gases is reduced. gases from the combustion of motor fuels. The introduction of hydrotreatment made it possible to use high-sulfur oils to obtain petroleum products.

Hydrocracking. Recently, the hydrocracking process has received significant development, in which cracking, isomerization and hydrotreatment reactions are simultaneously carried out. Hydrocracking is a catalytic process of deep conversion of raw materials of various fractional composition in the presence of hydrogen in order to obtain light petroleum products: gasoline, jet and diesel fuel, liquefied gases C 3 -C 4 . The use of polyfunctional catalysts makes it possible to carry out this process at 400–450°C and a pressure of about 5–15 MPa. Tungsten sulfide, mixed tungsten-nickel sulfide catalysts on carriers, cobalt-molybdenum catalysts on alumina, with additions of Ni, Pt, Pd and other metals on amorphous or crystalline zeolites are used as catalysts.

Table 2.1 - Modern catalytic processes of oil refining

Isomerization. To improve the quality of gasoline, add 10-15 wt.% isomerizate with a high octane number. The isomerizate is a mixture of saturated aliphatic (there are no cycles in the molecules) hydrocarbons of isostructure (more than 65 wt.% 2-methylbutane; isohexanes) obtained by isomerization of alkanes (normal saturated paraffins). The raw material for isomerization is a light gasoline fraction of direct distillation of oil, boiling in the range of 62-85°C and containing mainly pentane and hexane, as well as a fraction (75-150°C) obtained by catalytic cracking. The processes of catalytic isomerization proceed in the presence of bifunctional catalysts: platinum or palladium on various acidic carriers (γ-Al 2 O 3 , zeolite) promoted by halogen (Cl, F). Isomerization is the transformation of organic substances into compounds of a different structure (structural isomerism) or with a different arrangement of atoms or groups in space (spatial isomerism) without changing the composition and molecular weight.

Thus, catalytic processes occupy a leading position in oil refining. Thanks to catalysis, the value of products obtained from oil has been increased several times.

A more promising possibility of catalytic methods in oil refining is the rejection of the inherent modern processes global transformation of all complex compounds found in oils. Thus, all sulfur compounds undergo hydrogenolysis with the release of hydrogen sulfide. Meanwhile, many of them are of considerable independent value. The same is true for nitrogen-containing, metal-complex, and many other compounds. It would be very important to isolate these substances or subject them to individual catalytic transformations to obtain valuable products. An example is the production of sulfur-containing extractants such as sulfoxides and sulfones, which are formed during the catalytic oxidation of sulfur compounds contained in oil and boiler fuel. Undoubtedly, this way of catalysis will significantly increase the efficiency of oil refining.

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Heterogeneous catalysts must meet certain requirements catalytic process technologies , the main ones being:

1) high catalytic activity;

2) sufficiently high selectivity (selectivity) in relation to the target reaction;

3) high mechanical strength to compression, impact and abrasion;

4) sufficient stability of all properties of the catalyst during its service life and the ability to restore them with a particular regeneration method;

5) ease of preparation, ensuring the reproducibility of all properties of the catalyst;

6) optimal shape and geometric dimensions, which determine the hydrodynamic characteristics of the reactor;

7) low economic costs for the production of the catalyst.

- Catalyst activity is determined by the specific rate of a given catalytic reaction, i.e., the amount of product formed per unit time per unit volume of the catalyst or reactor.

In the vast majority of cases, in the presence of this catalyst, in addition to the main reaction, a number of side parallel or sequential reactions proceed. The proportion of reacted starting substances with the formation of target products characterizes catalyst selectivity . It depends not only on the nature of the catalyst, but also on the parameters of the catalytic process; therefore, it should be attributed to certain reaction conditions. Selectivity also depends on thermodynamic equilibrium. In oil refining, sometimes selectivity is conditionally expressed as the ratio of the yields of the target and by-products, such as gasoline/gas, gasoline/coke, or gasoline/gas + coke.

- Stability is one of key indicators quality of the catalyst characterizes its ability to maintain its activity over time. It affects the stability of the installations, the duration of their overhaul run, technological design, catalyst consumption, material and economic costs, environmental issues and technical and economic indicators of the process, etc.

During long-term operation, catalysts undergo physicochemical changes with a certain intensity, leading to a decrease or loss of their catalytic activity (sometimes selectivity), i.e., catalysts undergo physical and chemical deactivation.

- Physical deactivation (sintering) of the catalyst occurs under the influence of high temperature (in some catalytic processes) and water vapor and during its transportation and circulation. This process is accompanied by a decrease in the specific surface of both the carrier (matrix) of the catalyst and the active component (as a result of recrystallization - coalescence of the deposited metal with loss of dispersity).

- Chemical deactivation of the catalyst due to:

1) poisoning of its active sites by some impurities contained in the raw material, called poison (for example, sulfur compounds in the case of alumina-platinum reforming catalysts);

2) blocking of its active centers with carbon deposits (coke) or organometallic compounds contained in the oil feedstock.

Depending on whether or not the catalytic activity is restored after catalyst regeneration, a distinction is made between reversible and irreversible deactivation, respectively. However, even in the case of reversible deactivation, the catalyst eventually "ages" and has to be unloaded from the reactor.

Heterogeneous catalysts are rarely used in the form of individual substances and, as a rule, contain a carrier and various additives, which are called modifiers. Their purposes are varied:

Increasing the activity of the catalyst (promoters),

Increasing its selectivity and stability,

Improvement of mechanical and structural properties.