Natural sources of hydrocarbons and their use. Natural sources of hydrocarbons
– consists (mainly) of methane and (in smaller quantities) its closest homologues - ethane, propane, butane, pentane, hexane, etc.; observed in associated petroleum gas, i.e. natural gas found in nature above oil or dissolved in it under pressure.
Oil
is an oily flammable liquid consisting of alkanes, cycloalkanes, arenes (predominant), as well as oxygen-, nitrogen- and sulfur-containing compounds.
Coal
– solid fuel mineral of organic origin. It contains little graphite and many complex cyclic compounds, including the elements C, H, O, N and S. Anthracite (almost anhydrous), coal (-4% moisture) and brown coal (50-60% moisture) are found. Using the coking method, coal is converted into hydrocarbons (gaseous, liquid and solid) and coke (fairly pure graphite).
Coking of coal
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 using rectification method
Pre-refined 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).
Basic 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, and alkylation reactions.
Products: mixture of low-boiling hydrocarbons (fuels, raw materials 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
The most important natural sources of hydrocarbons are oil , natural gas And coal . They form rich deposits in various regions of the Earth.
Previously, extracted natural products were used exclusively as fuel. Currently, methods for their processing have been developed and are widely used, making it possible to isolate valuable hydrocarbons, which are used both as high-quality fuel and as raw materials for various organic syntheses. Processes natural sources of raw materials petrochemical industry . Let's look at the main methods of processing natural hydrocarbons.
The most valuable source of natural raw materials is oil . It is an oily liquid of dark brown or black color with a characteristic odor, practically insoluble in water. Oil density is 0.73–0.97 g/cm3. Oil is a complex mixture of various liquid hydrocarbons in which gaseous and solid hydrocarbons are dissolved, and the composition of oil from different fields may differ. Alkanes, cycloalkanes, aromatic hydrocarbons, as well as oxygen-, sulfur- and nitrogen-containing organic compounds may be present in oil in varying proportions.
Crude oil is practically not used, but is processed.
Distinguish primary oil refining (distillation ), i.e. dividing it into fractions with different boiling points, and recycling (cracking ), during which the structure of hydrocarbons is changed
dovs included in its composition.
Primary oil refining is based on the fact that the higher the boiling point of hydrocarbons, the higher their molar mass. Oil contains compounds with boiling points from 30 to 550°C. As a result of distillation, oil is divided into fractions that boil at different temperatures and contain mixtures of hydrocarbons with different molar masses. These fractions have a variety of uses (see Table 10.2).
Table 10.2. Products of primary oil refining.
Fraction | Boiling point, °C | Compound | Application |
Liquefied gas | <30 | Hydrocarbons C 3 -C 4 | Gaseous fuels, raw materials for the chemical industry |
Gasoline | 40-200 | Hydrocarbons C 5 – C 9 | Aviation and automobile fuel, solvent |
Naphtha | 150-250 | Hydrocarbons C 9 – C 12 | Diesel fuel, solvent |
Kerosene | 180-300 | Hydrocarbons C 9 -C 16 | Fuel for diesel engines, household fuel, lighting fuel |
Gas oil | 250-360 | Hydrocarbons C 12 -C 35 | Diesel fuel, raw materials for catalytic cracking |
Fuel oil | > 360 | Higher hydrocarbons, O-, N-, S-, Me-containing substances | Fuel for boiler plants and industrial furnaces, raw materials for further distillation |
Fuel oil accounts for about half the mass of oil. Therefore, it is also subjected to thermal processing. To prevent decomposition, fuel oil is distilled under reduced pressure. In this case, several fractions are obtained: liquid hydrocarbons, which are used as lubricating oils ; mixture of liquid and solid hydrocarbons – petrolatum , used in the preparation of ointments; mixture of solid hydrocarbons – paraffin , used for the production of shoe polish, candles, matches and pencils, as well as for impregnating wood; non-volatile residue - tar , used to produce road, construction and roofing bitumen.
Oil recycling involves chemical reactions that change the composition and chemical structure of hydrocarbons. Its variety is
ty – thermal cracking, catalytic cracking, catalytic reforming.
Thermal cracking usually subjected to fuel oil and other heavy fractions of oil. At a temperature of 450-550°C and a pressure of 2–7 MPa, hydrocarbon molecules are split by the free radical mechanism into fragments with a smaller number of carbon atoms, and saturated and unsaturated compounds are formed:
S 16 H 34 ¾® S 8 H 18 + S 8 H 16
C 8 H 18 ¾®C 4 H 10 +C 4 H 8
This method is used to obtain motor gasoline.
Catalytic cracking carried out in the presence of catalysts (usually aluminosilicates) at atmospheric pressure and a temperature of 550 - 600°C. At the same time, aviation gasoline is produced from kerosene and gas oil fractions of oil.
The breakdown of hydrocarbons in the presence of aluminosilicates occurs according to the ionic mechanism and is accompanied by isomerization, i.e. the formation of a mixture of saturated and unsaturated hydrocarbons with a branched carbon skeleton, for example:
CH 3 CH 3 CH 3 CH 3 CH 3
cat., t||
C 16 H 34 ¾¾® CH 3 -C -C-CH 3 + CH 3 -C = C - CH-CH 3
Catalytic reforming carried out at a temperature of 470-540°C and a pressure of 1–5 MPa using platinum or platinum-rhenium catalysts deposited on an Al 2 O 3 base. Under these conditions, the transformation of paraffins and
cycloparaffins petroleum into aromatic hydrocarbons
cat., t, p
¾¾¾¾® + 3Н 2
cat., t, p
C 6 H 14 ¾¾¾¾® + 4H 2
Catalytic processes make it possible to obtain gasoline of improved quality due to its high content of branched and aromatic hydrocarbons. The quality of gasoline is characterized by its octane number. The more the mixture of fuel and air is compressed by the pistons, the greater the engine power. However, compression can only be carried out to a certain limit, above which detonation (explosion) occurs.
gas mixture, causing overheating and premature engine wear. Normal paraffins have the lowest resistance to detonation. With a decrease in chain length, an increase in its branching and the number of double
It increases in the number of connections; it is especially high in aromatic hydrocarbons
before giving birth. To assess the resistance to detonation of various types of gasoline, they are compared with similar indicators for the mixture isooctane And n-hep-tana with different ratios of components; The octane number is equal to the percentage of isooctane in this mixture. The higher it is, the higher the quality of gasoline. The octane number can also be increased by adding special anti-knock agents, for example, tetraethyl lead Pb(C 2 H 5) 4, however, such gasoline and its combustion products are toxic.
In addition to liquid fuel, catalytic processes produce lower gaseous hydrocarbons, which are then used as raw materials for organic synthesis.
Another important natural source of hydrocarbons, the importance of which is constantly increasing, is natural gas. It contains up to 98% vol. methane, 2–3% vol. its closest homologues, as well as impurities of hydrogen sulfide, nitrogen, carbon dioxide, noble gases and water. Gases released during oil production ( passing ), contain less methane, but more of its homologues.
Natural gas is used as fuel. In addition, individual saturated hydrocarbons are isolated from it by distillation, as well as synthesis gas , consisting mainly of CO and hydrogen; they are used as raw materials for various organic syntheses.
Mined in large quantities coal – heterogeneous solid material of black or gray-black color. It is a complex mixture of various high molecular weight compounds.
Coal is used as a solid fuel and is also subjected to coking – dry distillation without air access at 1000-1200°C. As a result of this process, the following are formed: coke , which is finely ground graphite and is used in metallurgy as a reducing agent; coal tar , which is distilled to produce aromatic hydrocarbons (benzene, toluene, xylene, phenol, etc.) and pitch used for the preparation of roofing felt; ammonia water And coke oven gas , containing about 60% hydrogen and 25% methane.
Thus, natural sources of hydrocarbons provide
the chemical industry with a variety of and relatively cheap raw materials for carrying out organic syntheses, which make it possible to obtain numerous organic compounds that are not found in nature, but are necessary for humans.
The general scheme of using natural raw materials for basic organic and petrochemical synthesis can be presented as follows.
Arenas Synthesis gas Acetylene AlkenesAlkanes
Basic organic and petrochemical synthesis
Test tasks.
1222. What is the difference between primary oil refining and secondary refining?
1223. What compounds determine high quality gasoline?
1224. Suggest a method that makes it possible to obtain ethyl alcohol from oil.
It should be noted that hydrocarbons are widespread in nature. Most organic substances are obtained from natural sources. In the process of synthesis of organic compounds, natural and accompanying gases, coal and brown coal, oil, peat, and products of animal and plant origin are used as raw materials.
Natural sources of hydrocarbons: natural gases.
Natural gases are natural mixtures of hydrocarbons of different structures and some gas impurities (hydrogen sulfide, hydrogen, carbon dioxide) that fill rocks in the earth's crust. These compounds are formed as a result of the hydrolysis of organic substances at great depths in the Earth. They are found in a free state in the form of huge accumulations - gas, gas condensate and oil and gas fields.
The main structural component of flammable natural gases is CH₄ (methane - 98%), C₂H₆ (ethane - 4.5%), propane (C₃H₈ - 1.7%), butane (C₄H₁₀ - 0.8%), pentane (C₅H₁₂ - 0 .6%). Associated petroleum gas is part of the oil in a dissolved state and is released from it due to a decrease in pressure when the oil rises to the surface. In gas and oil fields, one ton of oil contains from 30 to 300 sq. m of gas. Natural sources of hydrocarbons are valuable fuel and raw materials for the organic synthesis industry. Gas is supplied to gas processing plants, where it can be processed (oil, low-temperature adsorption, condensation and rectification). It is divided into separate components, each of which is used for specific purposes. For example, from methane synthesis gas, which is the basic raw material for the production of other hydrocarbons, acetylene, methanol, methanal, chloroform.
Natural sources of hydrocarbons: oil.
Oil is a complex mixture that consists primarily of naphthenic, paraffinic and aromatic hydrocarbons. The composition of oil includes asphalt-resinous substances, mono- and disulfides, mercaptans, thiophene, thiophane, hydrogen sulfide, piperidine, pyridine and its homologues, as well as other substances. Based on the products using petrochemical synthesis methods, more than 3000 different products are obtained, incl. ethylene, benzene, propylene, dichloroethane, vinyl chloride, styrene, ethanol, isopropanol, butylenes, various plastics, chemical fibers, dyes, detergents, medicines, explosives, etc.
Peat is a sedimentary rock of plant origin. This substance is used as fuel (mainly for thermal power plants), chemical raw materials (for the synthesis of many organic substances), antiseptic litter on farms, especially in poultry farms, and a component of fertilizers for gardening and field cultivation.
Natural sources of hydrocarbons: xylem or wood.
Xylem is the tissue of higher plants through which water and dissolved nutrients flow from the rhizome system to the leaves, as well as other plant organs. It consists of cells with a stiffened shell that have a vascular conduction system. Depending on the type of wood, it contains different amounts of pectin substances and mineral compounds (mainly calcium salts), lipids and essential oils. Wood is used as fuel; methyl alcohol, acetate acid, cellulose, and other substances can be synthesized from it. Some types of wood are used to produce dyes (sandalwood, logwood), tannins (oak), resins and balsams (cedar, pine, spruce), alkaloids (plants of the nightshade, poppy, ranunculaceae, and umbellaceae families). Some alkaloids are used as medicines (chitin, caffeine), herbicides (anabasine), insecticides (nicotine).
Natural source of hydrocarbons | Its main characteristics |
Oil | A multicomponent mixture consisting primarily of hydrocarbons. Hydrocarbons are mainly represented by alkanes, cycloalkanes and arenes. |
Associated petroleum gas | A mixture consisting almost exclusively of alkanes with a long carbon chain of 1 to 6 carbon atoms is formed as a by-product of oil production, hence the origin of the name. There is such a tendency: the lower the molecular weight of the alkane, the higher its percentage in associated petroleum gas. |
Natural gas | A mixture consisting predominantly of low molecular weight alkanes. The main component of natural gas is methane. Its percentage, depending on the gas field, can be from 75 to 99%. In second place in terms of concentration by a large margin is ethane, propane contains even less, etc. The fundamental difference between natural gas and associated petroleum gas is that the proportion of propane and isomeric butanes in associated petroleum gas is much higher. |
Coal | A multicomponent mixture of various compounds of carbon, hydrogen, oxygen, nitrogen and sulfur. Coal also contains a significant amount of inorganic substances, the proportion of which is significantly higher than in oil. |
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 you heat oil, the most easily boiling components will evaporate from it first, 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 no chemical transformations of substances occur, and the oil is only divided 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 a tubular furnace, where it is heated to a high temperature (320-350 o C). After heating 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 selected at different heights:
1) distillation gases (selected from the very top of the column, and therefore their boiling point does not exceed 40 o C);
2) gasoline fraction (boiling point from 35 to 200 o C);
3) naphtha fraction (boiling point from 150 to 250 o C);
4) kerosene fraction (boiling point from 190 to 300 o C);
5) diesel fraction (boiling point from 200 to 300 o C);
6) fuel oil (boiling point more than 350 o C).
It should be noted that the middle fractions released during oil rectification do not meet the standards for fuel quality. In addition, as a result of oil distillation, a considerable amount of fuel oil is formed - not the most popular product. In this regard, after primary oil refining, the task is to increase the yield of more expensive, in particular, gasoline fractions, as well as improve the quality of these fractions. These problems are solved using various processes oil refining , for example, such as cracking Andreforming .
It should be noted that the number of processes used in oil recycling is much larger, and we are only touching on some of the main ones. Let's now figure out what the meaning of these processes is.
Cracking (thermal or catalytic)
This process is designed to increase the yield of gasoline fraction. For this purpose, heavy fractions, for example, fuel oil, are subjected to strong heating, most often in the presence of a catalyst. As a result of this effect, the long-chain molecules that make up the heavy fractions are torn and hydrocarbons with a lower molecular weight are formed. In fact, this leads to an additional yield of a gasoline fraction that is more valuable than the original fuel oil. The chemical essence of this process is reflected by the equation:
Reforming
This process accomplishes the task of improving the quality of the gasoline fraction, in particular increasing its knock resistance (octane number). It is this characteristic of gasoline 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. This increase in the proportion of aromatic hydrocarbons is achieved mainly as a result of dehydrocyclization reactions occurring during the reforming process. For example, if the heating is strong enough 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 processing coal is coking . Coking of coal is a 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 gas
The main components of coke oven gas are hydrogen, methane, carbon dioxide, nitrogen, ethylene, etc.
Hydrocarbons are of great economic importance, since they serve as the most important type of raw material for the production of almost all products of the modern organic synthesis industry and are widely used for energy purposes. They seem to accumulate solar heat and energy, which are released when burned. Peat, coal, oil shale, oil, natural and associated petroleum gases contain carbon, the combination of which with oxygen during combustion is accompanied by the release of heat.
coal | peat | oil | natural gas |
solid | solid | liquid | gas |
without smell | without smell | Strong smell | without smell |
homogeneous composition | homogeneous composition | mixture of substances | mixture of substances |
a dark-colored rock with a high content of flammable substances resulting from the burial of accumulations of various plants in sedimentary strata | accumulation of half-rotted plant matter accumulated at the bottom of swamps and overgrown lakes | natural flammable oily liquid, consisting of a mixture of liquid and gaseous hydrocarbons | a mixture of gases formed in the bowels of the Earth during the anaerobic decomposition of organic substances, the gas belongs to the group of sedimentary rocks |
Calorific value - the number of calories released when burning 1 kg of fuel | |||
7 000 - 9 000 | 500 - 2 000 | 10000 - 15000 | ? |
Coal.
Coal has always been a promising raw material for producing energy and many chemical products.
The first major consumer of coal since the 19th century was transport, then coal began to be used for the production of electricity, metallurgical coke, the production of various products through chemical processing, carbon-graphite structural materials, plastics, rock wax, synthetic, liquid and gaseous high-calorie fuels, high-nitrous acids for the production fertilizers
Coal is a complex mixture of high-molecular compounds, which include the following elements: C, H, N, O, S. Coal, like oil, contains a large number of various organic substances, as well as inorganic substances, such as water, ammonia, hydrogen sulfide and of course carbon itself - coal.
Coal processing occurs in three main directions: coking, hydrogenation and incomplete combustion. One of the main methods of processing coal is coking– calcination without air access in coke ovens at a temperature of 1000–1200°C. At this temperature, without access to oxygen, coal undergoes complex chemical transformations, resulting in the formation of coke and volatile products:
1. coke oven gas (hydrogen, methane, carbon monoxide and carbon dioxide, admixtures of ammonia, nitrogen and other gases);
2. coal tar (several hundred different organic substances, including benzene and its homologues, phenol and aromatic alcohols, naphthalene and various heterocyclic compounds);
3. tar, or ammonia, water (dissolved ammonia, as well as phenol, hydrogen sulfide and other substances);
4. coke (solid coking residue, almost pure carbon).
The cooled coke is sent to metallurgical plants.
When volatile products (coke oven gas) are cooled, coal tar and ammonia water condense.
By passing non-condensed products (ammonia, benzene, hydrogen, methane, CO 2, nitrogen, ethylene, etc.) through a solution of sulfuric acid, ammonium sulfate is released, which is used as a mineral fertilizer. Benzene is absorbed into the solvent and distilled from the solution. After this, the coke oven gas is used as fuel or as a chemical raw material. Coal tar is obtained in small quantities (3%). But, given the scale of production, coal tar is considered as a raw material for the production of a number of organic substances. If you remove products boiling at 350°C from the resin, what remains is a solid mass - pitch. It is used to make varnishes.
Hydrogenation of coal is carried out at a temperature of 400–600°C under a hydrogen pressure of up to 25 MPa in the presence of a catalyst. This produces a mixture of liquid hydrocarbons, which can be used as motor fuel. Production of liquid fuel from coal. Liquid synthetic fuel is high-octane gasoline, diesel and boiler fuel. To obtain liquid fuel from coal, it is necessary to increase its hydrogen content through hydrogenation. Hydrogenation is carried out using multiple circulation, which allows you to convert the entire organic mass of coal into liquid and gases. The advantage of this method is the possibility of hydrogenating low-grade brown coal.
Coal gasification will make it possible to use low-quality brown and hard coal in thermal power plants without polluting the environment with sulfur compounds. This is the only method for producing concentrated carbon monoxide (carbon monoxide) CO. Incomplete combustion of coal produces carbon (II) monoxide. Using a catalyst (nickel, cobalt) at normal or increased pressure, gasoline containing saturated and unsaturated hydrocarbons can be obtained from hydrogen and CO:
nCO + (2n+1)H 2 → C n H 2n+2 + nH 2 O;
nCO + 2nH 2 → C n H 2n + nH 2 O.
If dry distillation of coal is carried out at 500–550°C, then tar is obtained, which, along with bitumen, is used in the construction industry as a binding material in the manufacture of roofing and waterproofing coatings (roofing felt, roofing felt, etc.).
In nature, hard coal is found in the following regions: Moscow Region, South Yakutsk Basin, Kuzbass, Donbass, Pechora Basin, Tunguska Basin, Lena Basin.
Natural gas.
Natural gas is a mixture of gases, the main component of which is methane CH 4 (from 75 to 98% depending on the field), the rest is ethane, propane, butane and a small amount of impurities - nitrogen, carbon monoxide (IV), hydrogen sulfide and vapors water, and, almost always, hydrogen sulfide and organic petroleum compounds - mercaptans. It is they that give the gas a specific unpleasant odor, and when burned, lead to the formation of toxic sulfur dioxide SO 2 .
Typically, the higher the molecular weight of a hydrocarbon, the less of it is found in natural gas. The composition of natural gas from different fields is not the same. Its average composition in percentage by volume is as follows:
CH 4 | C 2 H 6 | C 3 H 8 | C 4 H 10 | N 2 and other gases |
75-98 | 0,5 - 4 | 0,2 – 1,5 | 0,1 – 1 | 1-12 |
Methane is formed during anaerobic (without access to air) fermentation of plant and animal residues, therefore it is formed in bottom sediments and is called “swamp” gas.
Deposits of methane in hydrated crystalline form, the so-called methane hydrate discovered under a layer of permafrost and at great depths in the oceans. At low temperatures (−800ºC) and high pressures, methane molecules are located in the voids of the crystal lattice of water ice. In the ice voids of one cubic meter of methane hydrate, 164 cubic meters of gas are “canned.”
Chunks of methane hydrate look like dirty ice, but in air they burn with a yellow-blue flame. It is estimated that the planet stores between 10,000 and 15,000 gigatons of carbon in the form of methane hydrate (“giga” equals 1 billion). Such volumes are many times greater than all currently known natural gas reserves.
Natural gas is a renewable natural resource, as it is synthesized in nature continuously. It is also called "biogas". Therefore, many environmental scientists today associate the prospects for the prosperous existence of mankind with the use of gas as an alternative fuel.
As a fuel, natural gas has great advantages over solid and liquid fuels. Its heat of combustion is much higher, when burned it does not leave ash, and the combustion products are much cleaner in environmental terms. Therefore, about 90% of the total volume of extracted natural gas is burned as fuel in thermal power plants and boiler houses, in thermal processes in industrial enterprises and in everyday life. About 10% of natural gas is used as a valuable raw material for the chemical industry: for the production of hydrogen, acetylene, soot, various plastics, and medicines. Methane, ethane, propane and butane are separated from natural gas. Products that can be obtained from methane are of great industrial importance. Methane is used for the synthesis of many organic substances - synthesis gas and further synthesis of alcohols based on it; solvents (carbon tetrachloride, methylene chloride, etc.); formaldehyde; acetylene and soot.
Natural gas forms independent deposits. The main deposits of natural combustible gases are located in Northern and Western Siberia, the Volga-Ural basin, the North Caucasus (Stavropol), the Komi Republic, the Astrakhan region, and the Barents Sea.