Natural sources of hydrocarbons. Oil refining. Natural sources of hydrocarbons Natural sources of hydrocarbons gas oil coke

The most important sources of hydrocarbons are natural and associated petroleum gases, oil, and coal.

By reserves natural gas the first place in the world belongs to our country. Natural gas contains low molecular weight hydrocarbons. It has the following approximate composition (by volume): 80-98% methane, 2-3% of its closest homologues - ethane, propane, butane and a small amount of impurities - hydrogen sulfide H 2 S, nitrogen N 2 , noble gases, carbon monoxide (IV ) CO 2 and water vapor H 2 O . The composition of the gas is specific to each field. There is the following pattern: the higher the relative molecular weight of hydrocarbon, the less it is contained in natural gas.

Natural gas is widely used as a cheap fuel with high calorific value (combustion of 1m 3 releases up to 54,400 kJ). It is one of the best types of fuel for domestic and industrial needs. In addition, natural gas is a valuable raw material for the chemical industry: the production of acetylene, ethylene, hydrogen, soot, various plastics, acetic acid, dyes, medicines and other products.

Associated petroleum gases are in deposits together with oil: they are dissolved in it and are located above the oil, forming a gas “cap”. When extracting oil to the surface, gases are separated from it due to a sharp drop in pressure. Previously, associated gases were not used and were flared during oil production. Currently, they are captured and used as fuel and valuable chemical raw materials. Associated gases contain less methane than natural gas, but more ethane, propane, butane and higher hydrocarbons. In addition, they contain basically the same impurities as in natural gas: H 2 S, N 2, noble gases, H 2 O vapor, CO 2 . Individual hydrocarbons (ethane, propane, butane, etc.) are extracted from associated gases, their processing makes it possible to obtain unsaturated hydrocarbons by dehydrogenation - propylene, butylene, butadiene, from which rubbers and plastics are then synthesized. A mixture of propane and butane (liquefied gas) is used as a household fuel. Natural gasoline (a mixture of pentane and hexane) is used as an additive to gasoline for better ignition of the fuel when starting the engine. Oxidation of hydrocarbons produces organic acids, alcohols and other products.

Oil- oily flammable liquid of dark brown or almost black color with a characteristic odor. It is lighter than water (= 0.73–0.97 g / cm 3), practically insoluble in water. By composition, oil is a complex mixture of hydrocarbons of various molecular weights, so it does not have a specific boiling point.

Oil consists mainly of liquid hydrocarbons (solid and gaseous hydrocarbons are dissolved in them). Usually these are alkanes (mainly of a normal structure), cycloalkanes and arenes, the ratio of which in oils from various fields varies widely. Ural oil contains more arenes. In addition to hydrocarbons, oil contains oxygen, sulfur and nitrogenous organic compounds.

Crude oil is not normally used. To obtain technically valuable products from oil, it is subjected to processing.

Primary processing oil consists in its distillation. Distillation is carried out at refineries after the separation of associated gases. During the distillation of oil, light oil products are obtained:

gasoline ( t kip \u003d 40–200 ° С) contains hydrocarbons С 5 -С 11,

naphtha ( t kip \u003d 150–250 ° С) contains hydrocarbons С 8 -С 14,

kerosene ( t kip \u003d 180–300 ° С) contains hydrocarbons С 12 -С 18,

gas oil ( t kip > 275 °C),

and in the remainder - a viscous black liquid - fuel oil.

Oil is subjected to further processing. It is distilled under reduced pressure (to prevent decomposition) and lubricating oils are isolated: spindle, engine, cylinder, etc. Petroleum jelly and paraffin are isolated from fuel oil of some grades of oil. The residue of fuel oil after distillation - tar - after partial oxidation is used to produce asphalt. The main disadvantage of oil refining is the low yield of gasoline (no more than 20%).

Oil distillation products have various uses.

Petrol used in large quantities as aviation and automotive fuel. It usually consists of hydrocarbons containing an average of 5 to 9 C atoms in molecules. Naphtha It is used as a fuel for tractors, as well as a solvent in the paint and varnish industry. Large quantities are processed into gasoline. Kerosene It is used as a fuel for tractors, jet planes and rockets, as well as for domestic needs. solar oil - gas oil- used as a motor fuel, and lubricating oils- for lubricating mechanisms. Petrolatum used in medicine. It consists of a mixture of liquid and solid hydrocarbons. Paraffin used to obtain higher carboxylic acids, to impregnate wood in the production of matches and pencils, for the manufacture of candles, shoe polish, etc. It consists of a mixture of solid hydrocarbons. fuel oil in addition to processing into lubricating oils and gasoline, it is used as boiler liquid fuel.

At secondary processing methods oil is a change in the structure of the hydrocarbons that make up its composition. Among these methods, of great importance is the cracking of oil hydrocarbons, which is carried out in order to increase the yield of gasoline (up to 65–70%).

Cracking- the process of splitting hydrocarbons contained in oil, as a result of which hydrocarbons with a smaller number of C atoms in the molecule are formed. There are two main types of cracking: thermal and catalytic.

Thermal cracking is carried out by heating the feedstock (fuel oil, etc.) at a temperature of 470–550 °C and a pressure of 2–6 MPa. In this case, hydrocarbon molecules with a large number of C atoms are split into molecules with a smaller number of atoms of both saturated and unsaturated hydrocarbons. For example:

(radical mechanism),

In this way, mainly automobile gasoline is obtained. Its output from oil reaches 70%. Thermal cracking was discovered by Russian engineer V.G. Shukhov in 1891.

catalytic cracking is carried out in the presence of catalysts (usually aluminosilicates) at 450–500 °C and atmospheric pressure. In this way, aviation gasoline is obtained with a yield of up to 80%. This type of cracking is mainly subjected to kerosene and gas oil fractions of oil. In catalytic cracking, along with cleavage reactions, isomerization reactions occur. As a result of the latter, saturated hydrocarbons with a branched carbon skeleton of molecules are formed, which improves the quality of gasoline:

Catalytic cracked gasoline is of higher quality. The process of obtaining it proceeds much faster, with less consumption of thermal energy. In addition, relatively many branched-chain hydrocarbons (isocompounds) are formed during catalytic cracking, which are of great value for organic synthesis.

At t= 700 °C and above, pyrolysis occurs.

Pyrolysis- decomposition of organic substances without air access at high temperature. During oil pyrolysis, the main reaction products are unsaturated gaseous hydrocarbons (ethylene, acetylene) and aromatic hydrocarbons - benzene, toluene, etc. Since oil pyrolysis is one of the most important ways to obtain aromatic hydrocarbons, this process is often called oil aromatization.

Aromatization– transformation of alkanes and cycloalkanes into arenes. When heavy fractions of petroleum products are heated in the presence of a catalyst (Pt or Mo), hydrocarbons containing 6–8 C atoms per molecule are converted into aromatic hydrocarbons. These processes occur during reforming (upgrading of gasoline).

Reforming- this is the aromatization of gasolines, carried out as a result of heating them in the presence of a catalyst, for example, Pt. Under these conditions, alkanes and cycloalkanes are converted into aromatic hydrocarbons, as a result of which the octane number of gasoline also increases significantly. Aromatization is used to obtain individual aromatic hydrocarbons (benzene, toluene) from gasoline fractions of oil.

In recent years, petroleum hydrocarbons have been widely used as a source of chemical raw materials. Substances necessary for the production of plastics, synthetic textile fibers, synthetic rubber, alcohols, acids, synthetic detergents, explosives, pesticides, synthetic fats, etc. are obtained from them in various ways.

Coal just like natural gas and oil, it is a source of energy and a valuable chemical raw material.

The main method of coal processing is coking(dry distillation). During coking (heating up to 1000 °С - 1200 °С without air access), various products are obtained: coke, coal tar, tar water and coke oven gas (scheme).

Scheme

Coke is used as a reducing agent in the production of iron in metallurgical plants.

Coal tar serves as a source of aromatic hydrocarbons. It is subjected to rectification distillation and benzene, toluene, xylene, naphthalene, as well as phenols, nitrogen-containing compounds, etc. are obtained.

Ammonia, ammonium sulfate, phenol, etc. are obtained from tar water.

Coke oven gas is used to heat coke ovens (combustion of 1 m 3 releases about 18,000 kJ), but it is mainly subjected to chemical processing. So, hydrogen is extracted from it for the synthesis of ammonia, which is then used to produce nitrogen fertilizers, as well as methane, benzene, toluene, ammonium sulfate, and ethylene.

Oil refining

Oil is a multicomponent mixture of various substances, mainly hydrocarbons. These components differ from each other in boiling points. In this regard, if oil is heated, then the lightest-boiling components will first evaporate from it, then compounds with a higher boiling point, etc. Based on this phenomenon primary oil refining , consisting in distillation (rectification) oil. This process is called primary, since it is assumed that during its course chemical transformations of substances do not occur, and oil is only separated into fractions with different boiling points. Below is a schematic diagram of a distillation column with a brief description of the distillation process itself:

Before the rectification process, oil is prepared in a special way, namely, it is removed from impurity water with salts dissolved in it and from solid mechanical impurities. The oil prepared in this way enters the tubular furnace, where it is heated to a high temperature (320-350 o C). After being heated in a tubular furnace, high-temperature oil enters the lower part of the distillation column, where individual fractions evaporate and their vapors rise up the distillation column. The higher the section of the distillation column is, the lower its temperature. Thus, the following fractions are taken at different heights:

1) distillation gases (taken from the very top of the column, and therefore their boiling point does not exceed 40 ° C);

2) gasoline fraction (boiling point from 35 to 200 o C);

3) naphtha fraction (boiling points from 150 to 250 o C);

4) kerosene fraction (boiling points from 190 to 300 o C);

5) diesel fraction (boiling point from 200 to 300 o C);

6) fuel oil (boiling point over 350 o C).

It should be noted that the average fractions isolated during the rectification of oil do not meet the standards for fuel quality. In addition, as a result of oil distillation, a considerable amount of fuel oil is formed - far from being the most demanded product. In this regard, after the primary processing of oil, the task is to increase the yield of more expensive, in particular, gasoline fractions, as well as to improve the quality of these fractions. These tasks are solved using various processes. oil refining , such as cracking andreforming .

It should be noted that the number of processes used in the secondary processing of oil is much larger, and we touch on only some of the main ones. Let's now understand what is the meaning of these processes.

Cracking (thermal or catalytic)

This process is designed to increase the yield of the gasoline fraction. For this purpose, heavy fractions, such as fuel oil, are subjected to strong heating, most often in the presence of a catalyst. As a result of this action, long-chain molecules that are part of the heavy fractions are torn and hydrocarbons with a lower molecular weight are formed. In fact, this leads to an additional yield of a more valuable gasoline fraction than the original fuel oil. The chemical essence of this process is reflected by the equation:

Reforming

This process performs the task of improving the quality of the gasoline fraction, in particular, increasing its knock resistance (octane number). It is this characteristic of gasolines that is indicated at gas stations (92nd, 95th, 98th gasoline, etc.).

As a result of the reforming process, the proportion of aromatic hydrocarbons in the gasoline fraction increases, which among other hydrocarbons has one of the highest octane numbers. Such an increase in the proportion of aromatic hydrocarbons is achieved mainly as a result of the dehydrocyclization reactions occurring during the reforming process. For example, when heated sufficiently n-hexane in the presence of a platinum catalyst, it turns into benzene, and n-heptane in a similar way - into toluene:

Coal processing

The main method of coal processing is coking . Coal coking called the process in which coal is heated without access to air. At the same time, as a result of such heating, four main products are isolated from coal:

1) coke

A solid substance that is almost pure carbon.

2) Coal tar

Contains a large number of various predominantly aromatic compounds, such as benzene, its homologues, phenols, aromatic alcohols, naphthalene, naphthalene homologues, etc.;

3) Ammonia water

Despite its name, this fraction, in addition to ammonia and water, also contains phenol, hydrogen sulfide and some other compounds.

4) coke oven gas

The main components of coke oven gas are hydrogen, methane, carbon dioxide, nitrogen, ethylene, etc.

– consists (mainly) of methane and (in smaller quantities) of its closest homologues - ethane, propane, butane, pentane, hexane, etc.; observed in associated petroleum gas, i.e., natural gas that is in nature above oil or dissolved in it under pressure.

Oil

- it is an oily combustible liquid, consisting of alkanes, cycloalkanes, arenes (predominate), as well as oxygen-, nitrogen- and sulfur-containing compounds.

Coal

- solid fuel mineral of organic origin. It contains little graphite a and many complex cyclic compounds, including the elements C, H, O, N and S. There are anthracite (almost anhydrous), coal (-4% moisture) and brown coal (50-60% moisture). By coking coal is converted into hydrocarbons (gaseous, liquid and solid) and coke (rather pure graphite).

Coal coking

Heating coal without air access to 900-1050 ° C leads to its thermal decomposition with the formation of volatile products (coal tar, ammonia water and coke oven gas) and a solid residue - coke.

Main products: coke - 96-98% carbon; coke oven gas - 60% hydrogen, 25% methane, 7% carbon monoxide (II), etc.

By-products: coal tar (benzene, toluene), ammonia (from coke oven gas), etc.

Oil refining by rectification method

The pre-purified oil is subjected to atmospheric (or vacuum) distillation into fractions with certain boiling point ranges in continuous distillation columns.

Main products: light and heavy gasoline, kerosene, gas oil, lubricating oils, fuel oil, tar.

Oil refining by catalytic cracking

Raw materials: high-boiling oil fractions (kerosene, gas oil, etc.)

Auxiliary materials: catalysts (modified aluminosilicates).

The main chemical process: at a temperature of 500-600 ° C and a pressure of 5 10 5 Pa, hydrocarbon molecules are split into smaller molecules, catalytic cracking is accompanied by aromatization, isomerization, alkylation reactions.

Products: mixture of low-boiling hydrocarbons (fuel, feedstock for petrochemicals).

C 16. H 34 → C 8 H 18 + C 8 H 16
C 8 H 18 → C 4 H 10 + C 4 H 8
C 4 H 10 → C 2 H 6 + C 2 H 4

During the lesson, you will be able to study the topic “Natural sources of hydrocarbons. Oil refining". More than 90% of all energy currently consumed by mankind is extracted from fossil natural organic compounds. You will learn about natural resources (natural gas, oil, coal), what happens to oil after it is extracted.

Topic: Limit hydrocarbons

Lesson: Natural Sources of Hydrocarbons

About 90% of the energy consumed by modern civilization is generated by burning natural fossil fuels - natural gas, oil and coal.

Russia is a country rich in natural fossil fuels. There are large reserves of oil and natural gas in Western Siberia and the Urals. Hard coal is mined in the Kuznetsk, South Yakutsk basins and other regions.

Natural gas consists on average of 95% by volume of methane.

In addition to methane, natural gas from various fields contains nitrogen, carbon dioxide, helium, hydrogen sulfide, and other light alkanes - ethane, propane and butanes.

Natural gas is extracted from underground deposits, where it is under high pressure. Methane and other hydrocarbons are formed from organic substances of plant and animal origin during their decomposition without air access. Methane is produced constantly and currently as a result of the activity of microorganisms.

Methane is found on the planets of the solar system and their satellites.

Pure methane is odorless. However, the gas used in everyday life has a characteristic unpleasant odor. This is the smell of special additives - mercaptans. The smell of mercaptans allows you to detect a leak of domestic gas in time. Mixtures of methane with air are explosive in a wide range of ratios - from 5 to 15% of gas by volume. Therefore, if you smell gas in the room, you can not only light a fire, but also use electrical switches. The smallest spark can cause an explosion.

Rice. 1. Oil from different fields

Oil- a thick liquid like oil. Its color is from light yellow to brown and black.

Rice. 2. Oil fields

Oil from different fields varies greatly in composition. Rice. 1. The main part of oil is hydrocarbons containing 5 or more carbon atoms. Basically, these hydrocarbons are saturated, i.e. alkanes. Rice. 2.

The composition of oil also includes organic compounds containing sulfur, oxygen, nitrogen. Oil contains water and inorganic impurities.

Gases are dissolved in oil, which are released during its extraction - associated petroleum gases. These are methane, ethane, propane, butanes with impurities of nitrogen, carbon dioxide and hydrogen sulfide.

Coal, like oil, is a complex mixture. The share of carbon in it accounts for 80-90%. The rest is hydrogen, oxygen, sulfur, nitrogen and some other elements. In brown coal the proportion of carbon and organic matter is lower than in stone. Even less organic oil shale.

In industry, coal is heated to 900-1100 0 C without air. This process is called coking. The result is coke with a high carbon content, coke gas and coal tar, necessary for metallurgy. A lot of organic substances are released from the gas and tar. Rice. 3.

Rice. 3. The device of the coke oven

Natural gas and oil are the most important sources of raw materials for the chemical industry. Oil as it is produced, or "crude oil", is difficult to use even as a fuel. Therefore, crude oil is divided into fractions (from the English "fraction" - "part"), using differences in the boiling points of its constituent substances.

The method of separating oil, based on the different boiling points of its constituent hydrocarbons, is called distillation or distillation. Rice. 4.

Rice. 4. Products of oil refining

The fraction that is distilled from about 50 to 180 0 C is called gasoline.

Kerosene boils at temperatures of 180-300 0 C.

A thick black residue that does not contain volatile substances is called fuel oil.

There are also a number of intermediate fractions boiling in narrower ranges - petroleum ethers (40-70 0 C and 70-100 0 C), white spirit (149-204 ° C), and gas oil (200-500 0 C). They are used as solvents. Fuel oil can be distilled under reduced pressure, in this way lubricating oils and paraffin are obtained from it. Solid residue from the distillation of fuel oil - asphalt. It is used for the production of road surfaces.

Processing of associated petroleum gases is a separate industry and makes it possible to obtain a number of valuable products.

Summing up the lesson

During the lesson, you studied the topic “Natural sources of hydrocarbons. Oil refining". More than 90% of all energy currently consumed by mankind is extracted from fossil natural organic compounds. You learned about natural resources (natural gas, oil, coal), about what happens to oil after it is extracted.

Bibliography

1. Rudzitis G.E. Chemistry. Fundamentals of General Chemistry. Grade 10: textbook for educational institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. - M.: Education, 2012.

2. Chemistry. Grade 10. Profile level: textbook. for general education institutions / V.V. Eremin, N.E. Kuzmenko, V.V. Lunin and others - M.: Drofa, 2008. - 463 p.

3. Chemistry. Grade 11. Profile level: textbook. for general education institutions / V.V. Eremin, N.E. Kuzmenko, V.V. Lunin and others - M.: Drofa, 2010. - 462 p.

4. Khomchenko G.P., Khomchenko I.G. Collection of problems in chemistry for those entering the universities. - 4th ed. - M.: RIA "New Wave": Publisher Umerenkov, 2012. - 278 p.

Homework

1. Nos. 3, 6 (p. 74) Rudzitis G.E., Feldman F.G. Chemistry: Organic Chemistry. Grade 10: textbook for educational institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. - M.: Education, 2012.

2. What is the difference between associated petroleum gas and natural gas?

3. How is oil refining carried out?

Compounds containing only carbon and hydrogen atoms.

Hydrocarbons are divided into cyclic (carbocyclic compounds) and acyclic.

Cyclic (carbocyclic) compounds are called compounds that include one or more cycles consisting only of carbon atoms (as opposed to heterocyclic compounds containing heteroatoms - nitrogen, sulfur, oxygen, etc.). Carbocyclic compounds, in turn, are divided into aromatic and non-aromatic (alicyclic) compounds.

Acyclic hydrocarbons include organic compounds whose carbon skeleton of molecules is open chains.

These chains can be formed by single bonds (al-kanes), contain one double bond (alkenes), two or more double bonds (dienes or polyenes), one triple bond (alkynes).

As you know, carbon chains are part of most organic substances. Thus, the study of hydrocarbons is of particular importance, since these compounds are the structural basis of other classes of organic compounds.

In addition, hydrocarbons, especially alkanes, are the main natural sources of organic compounds and the basis of the most important industrial and laboratory syntheses (Scheme 1).

You already know that hydrocarbons are the most important feedstock for the chemical industry. In turn, hydrocarbons are quite widespread in nature and can be isolated from various natural sources: oil, associated petroleum and natural gas, coal. Let's consider them in more detail.

Oil- a natural complex mixture of hydrocarbons, mainly linear and branched alkanes, containing from 5 to 50 carbon atoms in molecules, with other organic substances. Its composition significantly depends on the place of its production (deposit), it can, in addition to alkanes, contain cycloalkanes and aromatic hydrocarbons.

Gaseous and solid components of oil are dissolved in its liquid components, which determines its state of aggregation. Oil is an oily liquid of dark (from brown to black) color with a characteristic odor, insoluble in water. Its density is less than that of water, therefore, getting into it, oil spreads over the surface, preventing the dissolution of oxygen and other air gases in water. Obviously, getting into natural water bodies, oil causes the death of microorganisms and animals, leading to environmental disasters and even catastrophes. There are bacteria that can use the components of oil as food, converting it into harmless products of their vital activity. It is clear that the use of cultures of these bacteria is the most environmentally safe and promising way to combat oil pollution in the process of its production, transportation and processing.

In nature, oil and associated petroleum gas, which will be discussed below, fill the cavities of the earth's interior. Being a mixture of various substances, oil does not have a constant boiling point. It is clear that each of its components retains its individual physical properties in the mixture, which makes it possible to separate the oil into its components. To do this, it is purified from mechanical impurities, sulfur-containing compounds and subjected to the so-called fractional distillation, or rectification.

Fractional distillation is a physical method for separating a mixture of components with different boiling points.

Distillation is carried out in special installations - distillation columns, in which the cycles of condensation and evaporation of liquid substances contained in oil are repeated (Fig. 9).

Vapors formed during the boiling of a mixture of substances are enriched with a lighter-boiling (i.e., having a lower temperature) component. These vapors are collected, condensed (cooled to below boiling point) and brought back to a boil. In this case, vapors are formed that are even more enriched with a low-boiling substance. By repeated repetition of these cycles, it is possible to achieve almost complete separation of the substances contained in the mixture.

The distillation column receives oil heated in a tubular furnace to a temperature of 320-350 °C. The distillation column has horizontal partitions with holes - the so-called plates, on which the oil fractions condense. Light-boiling fractions accumulate on the higher ones, high-boiling fractions on the lower ones.

In the process of rectification, oil is divided into the following fractions:

Rectification gases - a mixture of low molecular weight hydrocarbons, mainly propane and butane, with a boiling point of up to 40 ° C;

Gasoline fraction (gasoline) - hydrocarbons of composition from C 5 H 12 to C 11 H 24 (boiling point 40-200 ° C); with a finer separation of this fraction, gasoline (petroleum ether, 40-70 ° C) and gasoline (70-120 ° C) are obtained;

Naphtha fraction - hydrocarbons of composition from C8H18 to C14H30 (boiling point 150-250 ° C);

Kerosene fraction - hydrocarbons of composition from C12H26 to C18H38 (boiling point 180-300 ° C);

Diesel fuel - hydrocarbons of composition from C13H28 to C19H36 (boiling point 200-350 ° C).

Residue of oil distillation - fuel oil- contains hydrocarbons with the number of carbon atoms from 18 to 50. Distillation under reduced pressure from fuel oil produces solar oil (C18H28-C25H52), lubricating oils (C28H58-C38H78), vaseline and paraffin - fusible mixtures of solid hydrocarbons. The solid residue of fuel oil distillation - tar and its processing products - bitumen and asphalt are used for the manufacture of road surfaces.

The products obtained as a result of oil rectification are subjected to chemical processing, which includes a number of complex processes. One of them is the cracking of petroleum products. You already know that fuel oil is separated into components under reduced pressure. This is due to the fact that at atmospheric pressure, its components begin to decompose before reaching the boiling point. This is what underlies cracking.

Cracking - thermal decomposition of petroleum products, leading to the formation of hydrocarbons with a smaller number of carbon atoms in the molecule.

There are several types of cracking: thermal cracking, catalytic cracking, high pressure cracking, reduction cracking.

Thermal cracking consists in the splitting of hydrocarbon molecules with a long carbon chain into shorter ones under the influence of high temperature (470-550 ° C). In the process of this splitting, along with alkanes, alkenes are formed.

In general, this reaction can be written as follows:

C n H 2n+2 -> C n-k H 2(n-k)+2 + C k H 2k
alkane alkane alkene
long chain

The resulting hydrocarbons can again undergo cracking to form alkanes and alkenes with an even shorter chain of carbon atoms in the molecule:

During conventional thermal cracking, many low molecular weight gaseous hydrocarbons are formed, which can be used as raw materials for the production of alcohols, carboxylic acids, and high molecular weight compounds (for example, polyethylene).

catalytic cracking occurs in the presence of catalysts, which are used as natural aluminosilicates of the composition

The implementation of cracking using catalysts leads to the formation of hydrocarbons having a branched or closed chain of carbon atoms in the molecule. The content of hydrocarbons of such a structure in motor fuel significantly improves its quality, primarily knock resistance - the octane number of gasoline.

Cracking of petroleum products proceeds at high temperatures, so carbon deposits (soot) are often formed, polluting the surface of the catalyst, which sharply reduces its activity.

Cleaning the catalyst surface from carbon deposits - its regeneration - is the main condition for the practical implementation of catalytic cracking. The simplest and cheapest way to regenerate a catalyst is its roasting, during which carbon deposits are oxidized by atmospheric oxygen. Gaseous oxidation products (mainly carbon dioxide and sulfur dioxide) are removed from the catalyst surface.

Catalytic cracking is a heterogeneous process involving solid (catalyst) and gaseous (hydrocarbon vapor) substances. It is obvious that the regeneration of the catalyst - the interaction of solid deposits with atmospheric oxygen - is also a heterogeneous process.

heterogeneous reactions(gas - solid) flow faster as the surface area of ​​the solid increases. Therefore, the catalyst is crushed, and its regeneration and cracking of hydrocarbons are carried out in a "fluidized bed", familiar to you from the production of sulfuric acid.

The cracking feedstock, such as gas oil, enters the conical reactor. The lower part of the reactor has a smaller diameter, so the feed vapor flow rate is very high. The gas moving at high speed captures the catalyst particles and carries them to the upper part of the reactor, where, due to the increase in its diameter, the flow rate decreases. Under the action of gravity, the catalyst particles fall into the lower, narrower part of the reactor, from where they are again carried upwards. Thus, each grain of the catalyst is in constant motion and is washed from all sides by a gaseous reagent.

Some catalyst grains enter the outer, wider part of the reactor and, without encountering gas flow resistance, sink to the lower part, where they are picked up by the gas flow and carried away to the regenerator. There, too, in the "fluidized bed" mode, the catalyst is burned and returned to the reactor.

Thus, the catalyst circulates between the reactor and the regenerator, and the gaseous products of cracking and roasting are removed from them.

The use of cracking catalysts makes it possible to slightly increase the reaction rate, reduce its temperature, and improve the quality of cracked products.

The obtained hydrocarbons of the gasoline fraction mainly have a linear structure, which leads to a low knock resistance of the obtained gasoline.

We will consider the concept of “knock resistance” later, for now we only note that hydrocarbons with branched molecules have a much greater detonation resistance. It is possible to increase the proportion of isomeric branched hydrocarbons in the mixture formed during cracking by adding isomerization catalysts to the system.

Oil fields contain, as a rule, large accumulations of the so-called associated petroleum gas, which collects above the oil in the earth's crust and partially dissolves in it under the pressure of the overlying rocks. Like oil, associated petroleum gas is a valuable natural source of hydrocarbons. It contains mainly alkanes, which have from 1 to 6 carbon atoms in their molecules. Obviously, the composition of associated petroleum gas is much poorer than oil. However, despite this, it is also widely used both as a fuel and as a raw material for the chemical industry. Until a few decades ago, in most oil fields, associated petroleum gas was burned as a useless addition to oil. At present, for example, in Surgut, Russia's richest oil pantry, the world's cheapest electricity is generated using associated petroleum gas as fuel.

As already noted, associated petroleum gas is richer in composition in various hydrocarbons than natural gas. Dividing them into fractions, they get:

Natural gasoline - a highly volatile mixture consisting mainly of lentane and hexane;

Propane-butane mixture, consisting, as the name implies, of propane and butane and easily turns into a liquid state when pressure increases;

Dry gas - a mixture containing mainly methane and ethane.

Natural gasoline, being a mixture of volatile components with a small molecular weight, evaporates well even at low temperatures. This makes it possible to use gas gasoline as a fuel for internal combustion engines in the Far North and as an additive to motor fuel, which makes it easier to start engines in winter conditions.

A propane-butane mixture in the form of liquefied gas is used as household fuel (gas cylinders familiar to you in the country) and for filling lighters. The gradual transition of road transport to liquefied gas is one of the main ways to overcome the global fuel crisis and solve environmental problems.

Dry gas, close in composition to natural gas, is also widely used as a fuel.

However, the use of associated petroleum gas and its components as a fuel is far from the most promising way to use it.

It is much more efficient to use associated petroleum gas components as feedstock for chemical production. Hydrogen, acetylene, unsaturated and aromatic hydrocarbons and their derivatives are obtained from alkanes, which are part of associated petroleum gas.

Gaseous hydrocarbons can not only accompany oil in the earth's crust, but also form independent accumulations - natural gas deposits.

Natural gas - a mixture of gaseous saturated hydrocarbons with a small molecular weight. The main component of natural gas is methane, the share of which, depending on the field, ranges from 75 to 99% by volume. In addition to methane, natural gas contains ethane, propane, butane and isobutane, as well as nitrogen and carbon dioxide.

Like associated petroleum gas, natural gas is used both as a fuel and as a raw material for the production of various organic and inorganic substances. You already know that hydrogen, acetylene and methyl alcohol, formaldehyde and formic acid, and many other organic substances are obtained from methane, the main component of natural gas. As a fuel, natural gas is used in power plants, in boiler systems for water heating of residential buildings and industrial buildings, in blast furnace and open-hearth production. Striking a match and igniting gas in the kitchen gas stove of a city house, you "start" a chain reaction of oxidation of alkanes that are part of natural gas. In addition to oil, natural and associated petroleum gases, coal is a natural source of hydrocarbons. 0n forms powerful layers in the bowels of the earth, its explored reserves significantly exceed oil reserves. Like oil, coal contains a large amount of various organic substances. In addition to organic, it also includes inorganic substances, such as water, ammonia, hydrogen sulfide and, of course, carbon itself - coal. One of the main ways of coal processing is coking - calcination without air access. As a result of coking, which is carried out at a temperature of about 1000 ° C, the following are formed:

Coke oven gas, which includes hydrogen, methane, carbon monoxide and carbon dioxide, impurities of ammonia, nitrogen and other gases;
coal tar containing several hundred different organic substances, including benzene and its homologues, phenol and aromatic alcohols, naphthalene and various heterocyclic compounds;
supra-tar, or ammonia water, containing, as the name implies, dissolved ammonia, as well as phenol, hydrogen sulfide and other substances;
coke - solid residue of coking, almost pure carbon.

coke used in the production of iron and steel, ammonia - in the production of nitrogen and combined fertilizers, and the importance of organic coking products can hardly be overestimated.

Thus, associated petroleum and natural gases, coal are not only the most valuable sources of hydrocarbons, but also part of the unique pantry of irreplaceable natural resources, the careful and reasonable use of which is a necessary condition for the progressive development of human society.

1. List the main natural sources of hydrocarbons. What organic substances are included in each of them? What do they have in common?

2. Describe the physical properties of oil. Why doesn't it have a constant boiling point?

3. After summarizing the media reports, describe the environmental disasters caused by the oil spill and how to overcome their consequences.

4. What is rectification? What is this process based on? Name the fractions obtained as a result of oil rectification. How do they differ from each other?

5. What is cracking? Give the equations of three reactions corresponding to the cracking of petroleum products.

6. What types of cracking do you know? What do these processes have in common? How do they differ from each other? What is the fundamental difference between different types of cracked products?

7. Why is associated petroleum gas so named? What are its main components and their uses?

8. How does natural gas differ from associated petroleum gas? What do they have in common? Give the equations of combustion reactions of all components of associated petroleum gas known to you.

9. Give the reaction equations that can be used to obtain benzene from natural gas. Specify the conditions for these reactions.

10. What is coking? What are its products and their composition? Give the equations of the reactions typical for the products of coal coking known to you.

11. Explain why burning oil, coal and associated petroleum gas is far from being the most rational way to use them.