Enterprises were forced to burn liquid methane using flares, as they were unable to transfer condensate for subsequent petrochemical processing. Now they have learned how to transport it and use it in many areas of industry. At the same time, it is well stored and does not form harmful impurities during combustion.

Physical and chemical properties of methane

Methane belongs to the simplest hydrocarbons. It is lighter than air, non-toxic, poorly soluble in water, and has no perceptible odor. It is believed that methane is not dangerous to humans, but there are cases of its effects on the central and autonomic nervous system. Accumulating indoors, at a concentration in the air from 4% to 17% it becomes explosive. Therefore, in order to detect it by a person (without instruments), special substances are often added to methane that resemble the smell of gas. Refers to In methane, weak narcotic properties are manifested, which are weakened by low solubility in water.

By origin, as a result of compounds with various substances and chemical reactions, it is divided into:

• biogenic (organic);
• abiogenic (inorganic);
• bacterial (life activity of microorganisms);
• thermogenic (thermochemical processes).

This gas is also obtained in the laboratory by heating soda lime or anhydrous sodium hydroxide with frozen acetic acid.

Methane in the liquid state occupies a volume 600 times less than in the gaseous state. Therefore, for ease of transportation and storage, it is subjected to liquefaction. Liquid methane is a colorless, odorless liquid. It retains almost all properties of the gas. liquid methane is 4.58 MPa (the minimum at which it turns into a liquid).

Existence in nature

Methane is part of and is the main constituent of the following gases:

• natural (up to 98%);
• oil (40-90%);
• marsh (99%);
• mine (35-50%);
• mud volcanoes (more than 94%).

It is also found in the composition of the water of the oceans, lakes, seas. It is present in the atmosphere of such planets as Earth, Saturn, Jupiter, Uranus, and in the surface gases of the Moon. A large amount is found in coal seams. This makes underground mining an explosive activity.

Natural gas liquefaction technology

Pure methane is obtained from removing other components from it: ethane, propane, butane and nitrogen. To obtain liquid methane, the gas is compressed and then cooled. The liquefaction process is carried out in cycles. At each stage, the volume will decrease up to 12 times. It turns into a liquid in the last cycle. Various types of installations are used for liquefaction, among them:

• throttle;
• turbine-vortex;
• turbo-expander.

In this case, the following schemes can be used:

• cascading;
• expansion.

The cascade scheme uses three cooling agents. In this case, the temperature of liquid methane decreases in stages. This technology requires large capital expenditures. Currently, this process has been improved and a mixture of refrigerants (ethane and propane) has been used immediately. Such a scheme has become self-cooling, since these substances are obtained from liquefied natural gas. Costs have come down slightly, but are still high.

When using an expansion scheme, more economical centrifugal machines are used. The mixture is preliminarily cleaned from water and other contaminants and liquefied under pressure due to heat exchange with a cold expanded gas stream. However, this process requires more energy than with a cascade scheme (by 25-35%). But at the same time capital costs for compressors and equipment operation are saved.

The temperature of liquid methane obtained as a result of the above process averages 162 degrees.

Methane application

The scope of methane, both in gaseous and liquid state, is very extensive. It is used as a fuel, in the form of raw materials for industry, in everyday life, as anabolic steroids for building muscle mass.

With incomplete combustion, soot is obtained from methane, which is widely used in industry: in the production of rubber, stamp paint, shoe polish, etc. They are also used for the production of hydrocyanic and acetic acid, methanol, acetylene, ammonia, carbon disulfide, as (eternal flame) .

Liquid methane is used as motor fuel for cars. It has an octane rating 15% higher than that of gasoline, as well as high calorific value and anti-knock properties. According to reviews, liquid methane burns out almost completely, and with the correct installation of the appropriate equipment on a car, quite significant savings occur compared to gasoline (when traveling long distances).

This gas is actively used for the production of drugs that increase muscle mass. On its basis, such products as Dianoged, Danabol, Nerobol are produced, which are in the greatest demand. It is believed that these drugs have a positive effect on the human body:

• strengthen bones;
• stimulate the formation of sexual characteristics;
• burn fatty layers;
• increase endurance;
• accelerate protein synthesis.

However, it is important to remember that all drugs have side effects, so they should be taken under the supervision of a doctor.

Based on the foregoing, we can conclude that the production of liquid methane is a very promising area of ​​modern industry.

Methane burning in the air bluish flame, while the energy of about 39 MJ per 1 m 3 is released. Forms with air explosive mixtures. Of particular danger is methane released during underground mining of mineral deposits into mine workings, as well as at coal processing and briquette factories, at screening plants. So, at a content of up to 5-6% in air, methane burns near a heat source (ignition temperature 650-750 ° C), from 5-6% to 14-16% it explodes, more than 16% can burn with an influx of oxygen from outside. A decrease in the concentration of methane in this case can lead to an explosion. In addition, a significant increase in the concentration of methane in the air causes asphyxiation (for example, a methane concentration of 43% corresponds to 12% O 2).

Explosive combustion spreads at a speed of 500-700 m/s; gas pressure during an explosion in a closed volume is 1 Mn/m 2 . After contact with a heat source, the ignition of methane occurs with some delay. The creation of safety explosives and explosion-proof electrical equipment is based on this property. At sites that are dangerous due to the presence of methane (mainly coal mines), the so-called. gas mode.

At 150–200 °C and a pressure of 30–90 atm, methane is oxidized to formic acid.

Methane forms inclusion compounds - gas hydrates, widely distributed in nature.

Methane application

Methane is the most thermally stable saturated hydrocarbon. It is widely used as a household and industrial fuel and as a raw material for industry. . So, by chlorination of methane, methyl chloride, methylene chloride, chloroform, carbon tetrachloride are produced.

Incomplete combustion of methane results in soot , in catalytic oxidation - formaldehyde , when interacting with sulfur - carbon disulfide .

Thermal-oxidative cracking and electrocracking of methane are important industrial methods for the production of acetylene .

Catalytic oxidation of a mixture of methane with ammonia underlies the industrial production of hydrocyanic acid . Methane is used as a source of hydrogen in the production of ammonia, as well as to produce water gas (the so-called synthesis gas): CH 4 + H 2 O → CO + 3H 2, used for the industrial synthesis of hydrocarbons, alcohols, aldehydes, etc. Important methane derivative - nitromethane .

Methane and the greenhouse effect

Methane is greenhouse gas. If the degree of carbon dioxide impact on the climate is conditionally taken as one, then the greenhouse activity of methane will be 23 units. The content of methane in the atmosphere has grown very rapidly over the past two centuries.

Now the average content of methane CH 4 in the modern atmosphere is estimated at 1.8 ppm ( parts per million, parts per million). And, although this is 200 times less than the content of carbon dioxide (CO 2) in it, per molecule of gas, the greenhouse effect of methane - that is, its contribution to the dissipation and retention of heat radiated by the Earth heated by the sun - is significantly higher than from CO 2 . In addition, methane absorbs the Earth's radiation in those "windows" of the spectrum that are transparent to other greenhouse gases. Without greenhouse gases - CO 2 , water vapor, methane and some other impurities, the average temperature on the Earth's surface would be only -23°C, and now it is about +15°C.

Methane seeps out at the bottom of the ocean through cracks in the earth's crust, and is released in considerable quantities during mining and when forests are burned. Recently, a new, completely unexpected source of methane has been discovered - higher plants, but the mechanisms of formation and the significance of this process for the plants themselves have not yet been elucidated.

Methane is the first representative of a number of alkanes with the formula CH 4. It is a colorless, odorless natural gas. Due to its physical and chemical properties, methane is used as a fuel.

Structure

The methane molecule is a tetrahedron, in the middle of which there is carbon connected by simple (single) σ-bonds with hydrogen atoms. The structure and properties of the methane molecule are important for understanding all organic chemistry, since most organic compounds contain methyl groups -CH 2 .

Rice. 1. The structure of the methane molecule.

Methane forms a homologous series of alkanes. Each subsequent homologue differs from the previous one by one -CH 2 group.

Due to the tetrahedral configuration, long alkane molecules look like curved chains.

Receipt

Methane is a common gas in the universe. It is found in natural and associated gas, is formed at the bottom of the seas, and is released as the end product of the vital activity of intestinal bacteria. Methane is part of the atmosphere of the giant planets. On the surface of Titan - Saturn's moon - there are ethane-methane lakes and rivers.

Rice. 2. Satellite Titan.

In industry, methane is isolated from natural gas and obtained by coking (calcining) coal.

In the laboratory, methane is formed by heating dry sodium hydroxide with acetic acid, and also by melting acetate with sodium hydroxide:

• 2NaOH + CH 3 COOH → Na 2 CO 3 + H 2 O + CH 4;
• CH 3 COONa + NaOH → CH 4 + Na 2 CO 3.

Methane was first discovered in swamps by physicist Alessandro Volta in 1776. Two years later, he isolated pure methane from swamp gas.

Properties

Main physical properties:

• lighter than air;
• odorless and tasteless;
• poorly soluble in water;
• molecular weight - 16;
• melting point - -182.49°C;
• boiling point - -161.56 ° C;
• flash point - 87.8°C;
• self-ignition temperature - 537.8 ° C.

Methane determines the physicochemical properties of the homologous series of alkanes. Under normal conditions, methane and its homologues are inactive and react under the action of high temperature and a catalyst. Additional conditions are necessary for C-H bond cleavage.

Main reactions of methane:

• nitration:

  CH 4 + HONO 2 → CH 3 -NO 2 + H 2 O;

• halogenation:

  CH 4 + Cl 2 → CH 3 Cl + HCl;

• sulphochlorination:

  CH 4 + SO 2 + Cl 2 → CH 3 -SO 2 Cl + HCl;

• catalytic oxidation under the action of copper and manganese salts:

  2CH 4 + O 2 → 2CH 3 OH;

• complete oxidation (combustion):

  CH 4 + 2O 2 → CO 2 + 2H 2 O + Q;

• steam oxidation:

  CH 4 + H 2 O → CO + 3H 2;

• cracking (petroleum refining method):

  2CH 4 → HC≡CH + 3H 2 .

Rice. 3. Combustion of methane.

The concentration of methane in the air is more than 4% explosive. Therefore, methane is specially given a smell by mixing the gas with thiols containing sulfur. This helps to control the leakage of household gas.

What have we learned?

Methane is the simplest representative of the alkane class, forming a homologous series. It is a colorless combustible gas derived from natural gas and produced by coal coking. Methane is used as fuel. Self-ignites at high temperatures. The gas is subject to nitration, halogenation, sulphochlorination, oxidation under the action of a catalyst, steam, combustion, as well as cracking used in oil refining.

Combustion - a fast-flowing chemical reaction of the combination of combustible components with oxygen, accompanied by an intense release of heat and a sharp increase in the temperature of the combustion products.

Combustion reaction of pure methane:

CH4 + 2O2 = CO2 + 2H2O + Heat generation

Since methane makes up a larger volume, it is customary to express the general formula of natural gas by the formula of methane itself. So, it turns out that the chemical formula of natural gas is methane -CH4.

The remaining components have the following empirical formulas in chemistry:

ethane - C2H6;

propane - C3H8;

butane - C4H10;

carbon dioxide - CO2;

hydrogen - H2;

hydrogen sulfide - H2S.

A mixture of these substances is natural gas.

More often natural gas cleaning occurs directly during the extraction of raw materials. Depending on the composition and concentration of impurities, one or another purification method is chosen. In world practice, the most commonly used chemisorption cleaning methods, where the main active ingredients are Alkacolamine solutions with water or Benfield(potassium carbonate and water with additives). The next most popular are combined methods, combining chemical and physical processes, with the presence of sulfinol as an active agent. If necessary fine cleaning of raw materials, use solid adsorbents and the oxidation of sulfur to a solid precipitate.

Obtaining in laboratory and industry

In addition to natural places of gas formation, there are a number of ways to get it in the laboratory. However, these methods, of course, are used only for small portions of the product, since it is not economically profitable to carry out the synthesis of natural gas in the laboratory.

Laboratory methods:

Hydrolysis of a low molecular weight compound - aluminum carbide: AL4C3 + 12H2O = 3CH4 + 4AL(OH)3.

From sodium acetate in the presence of alkali: CH3COOH + NaOH = CH4 + Na2CO3.

From syngas: CO+ 3H2 = CH4 + H2O.

From simple substances - hydrogen and carbon - at elevated temperature and pressure.

The chemical formula of natural gas is reflected by the formula of methane, therefore, all reactions characteristic of alkanes are also characteristic of this gas.

City gas = Natural gas + Smell additives

Pure natural gas is colorless and odorless. In order to be able to determine the leak by smell, a small amount of substances with a strong unpleasant odor (rotten cabbage, rotten hay) (the so-called odorants) is added to the gas. The most commonly used odorant is ethyl mercaptan (С2H5SH) (16 g per 1000 cubic meters of natural gas).

C3H8 - Propane

Types of reaction classifications.

Physical and chemical properties of methane.

Hazardous impurities in mine air

Toxic impurities in mine air include carbon monoxide, nitrogen oxides, sulfur dioxide and hydrogen sulfide.

Carbon monoxide (CO) - colorless, tasteless and odorless gas with a specific gravity of 0.97. Burns and explodes at a concentration of 12.5 to 75%. Ignition temperature, at a concentration of 30%, 630-810 0 C. Very toxic. Lethal concentration - 0.4%. Permissible concentration in mine workings - 0.0017%. The main help in case of poisoning is artificial respiration in the working with fresh air.

Sources of carbon monoxide are blasting, internal combustion engines, mine fires, and methane and coal dust explosions.

Nitrogen oxides (NO) They are brown in color and have a characteristic pungent odour. Very poisonous, cause irritation of the mucous membranes of the respiratory tract and eyes, pulmonary edema. Lethal concentration, with short-term inhalation, is 0.025%. The limiting content of nitrogen oxides in mine air should not exceed 0.00025% (in terms of dioxide - NO 2). For nitrogen dioxide - 0.0001%.

Sulfur dioxide (SO 2)- colorless, with a strong irritating odor and sour taste. Heavier than air 2.3 times. Very toxic: irritates the mucous membranes of the respiratory tract and eyes, causes inflammation of the bronchi, swelling of the larynx and bronchi.

Sulfur dioxide is formed during blasting (in sulfurous rocks), fires, and is released from rocks.

The limiting content in the mine air is 0.00038%. A concentration of 0.05% is life-threatening.

Hydrogen sulfide (H 2 S)- gas without color, with a sweetish taste and the smell of rotten eggs. The specific gravity is 1.19. Hydrogen sulfide burns, and at a concentration of 6% it explodes. Very toxic, irritates the mucous membranes of the respiratory tract and eyes. Lethal concentration - 0.1%. First aid in case of poisoning - artificial respiration on a fresh stream, inhalation of chlorine (using a handkerchief moistened with bleach).

Hydrogen sulfide is released from rocks and mineral springs. It is formed during the decay of organic matter, mine fires and blasting.

Hydrogen sulfide is highly soluble in water. This must be taken into account when moving people along abandoned workings.

The permissible content of H 2 S in mine air should not exceed 0.00071%.

Lecture 2

Methane and its properties

Methane is the main, most common part of firedamp. In the literature and in practice, methane is most often identified with firedamp. In mine ventilation, this gas receives the most attention due to its explosive properties.

Physical and chemical properties of methane.

Methane (CH 4) is a colorless, tasteless and odorless gas. Density - 0.0057. Methane is inert, but by displacing oxygen (displacement occurs in the following proportion: 5 volume units of methane replace 1 volume unit of oxygen, i.e. 5:1), it can be dangerous to people. It ignites at a temperature of 650-750 0 C. Methane forms combustible and explosive mixtures with air. When the content in the air is up to 5-6%, it burns at a heat source, from 5-6% to 14-16% - explodes, more than 14-16% - does not explode. The greatest force of the explosion at a concentration of 9.5%.

One of the properties of methane is the flash delay after contact with an ignition source. The flash delay time is called induction period. The presence of this period creates conditions for the prevention of outbreaks during blasting, using safety explosives (BB).

The gas pressure at the site of the explosion is about 9 times higher than the initial pressure of the gas-air mixture before the explosion. In this case, pressure up to 30 at and higher. Various obstacles in the workings (narrowings, protrusions, etc.) contribute to an increase in pressure and increase the speed of propagation of the blast wave in the mine workings.