Physical and chemical properties of methane. Physical Properties

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.

Biogas from sewers, sewage gas, sewer gas. Density. Compound. Danger.

physical properties. Density.

Biogas is the collective designation of gases and volatile components that are released in sewage and natural processes associated with the fermentation and decomposition of organic substances and materials. Main components: nitrogen (N 2), hydrogen sulfide (H 2 S), carbon dioxide (CO 2), methane (CH 4), ammonia (NH 3), biological organisms, water vapor, and other substances. The composition and concentration of these components are highly dependent on time, the composition of the sewage or biomass mixture, temperature, and .

• Nitrogen makes up about 78% of the earth's atmosphere and, in general, does not usually occur as a result of biological decomposition reactions, but its concentration increases dramatically in biogas due to the active consumption of atmospheric oxygen in the process.
• hydrogen sulfide is formed by biological and chemical processes in the biomass and enters the volume above the liquid; its concentration in biogas depends on its concentration in the liquid phase and the equilibrium conditions of the system. At non-toxic concentrations, H 2 S has the familiar rotten egg smell. In dangerous concentrations, H 2 S quickly paralyzes a person's ability to smell this pungent odor and then renders the victim helpless. H 2 S is explosive at concentrations well above the toxicity level (Minimum explosive concentration 4.35%, Maximum explosive concentration 46%).
• carbon dioxide and methane practically odorless and have a density: 1.5 times greater than air (CO 2) and 0.6 times that of air (methane). The relative densities of these gases can cause significant stratification of gases in stagnation conditions. Since both gases are actively produced in the biomass, their concentration on the liquid/air surface can be significantly higher than the volume average.
• Methane extremely combustible, has a very wide explosive range and a low flash point. Methane can also react with some oxidizing agents quite by accident, but with sad consequences. Other combustible gases in the composition of biogas appear as a result of the evaporation of combustible substances that accidentally got into the sewer.
• Ammonia it has a sharp strong smell of ammonia, which is a good warning about the possible achievement of toxic levels. Above a certain level, ammonia can damage the mucous membrane of the eyes and cause eye burns. Reaching toxic concentrations under normal bioreactor and sewer conditions is unlikely.

All of the above gases are colorless (colourless) at biogas concentrations.

The maximum expected concentrations of components in the composition of biogas are as follows:

• Methane 40-70%;
• Carbon dioxide 30-60%;
• Hydrogen sulfide 0-3%;
• Hydrogen 0-1 percent;
• Other gases, incl. ammonia 1-5 percent.

Natural, incl. pathogenic microorganisms can get into the air when the biomass is agitated, but usually their lifetime outside the biomass is short.

Findings:
Substances that may exist in such places as sewers can be both toxic and explosive and flammable, while they may be odorless, colorless, etc.

Possible harm to health: The main risks are:

1. H 2 S poisoning, asphyxiation due to lack of oxygen
2. Decreased concentration and attention, fatigue due to reduced oxygen levels (from CO 2 and CH 4),
3. biological contamination
4. Fires and explosions from methane, H 2 S and other combustible gases

• hydrogen sulfide is the leading cause of sudden death in the workplace when working with biogas. At air concentrations of approximately 300 ppm, H 2 S causes immediate death. It mainly enters the body through the lungs, but a limited amount can penetrate the skin and cornea of ​​the eye. No chronic damage found due to repeated exposure. The main symptoms are eye irritation, fatigue, headache and dizziness.
• Carbon dioxide is only a suffocating agent (replaces oxygen) and also an irritant of the respiratory system. A concentration of 5% may cause headache and shortness of breath. Background content in the atmosphere: 300-400 ppm (0.3-0.4%).
• Methane is only a suffocating agent (replaces oxygen), but by itself does not noticeably affect the body.

Table 1 - Some properties of sewer gas (biogas)

Table 2 - Some of the main diseases and viruses living in the sewer

Findings:
Substantial levels of biogas may present a hazard due to toxicity, reduction in total oxygen levels, and potential explosion and fire hazards. Some components of biogas have a distinct smell, which, however, does not allow an unambiguous assessment of the level of danger. Biological materials and organisms can quite successfully exist in biomass particles above the liquid surface (airborne suspensions).

Chemical properties / formation

• hydrogen sulfide formed from sulfates contained in water; in the process of decomposition of organics containing sulfur in the absence of oxygen (anaerobic decomposition processes), as well as in the reactions of metal sulfides and strong acids. Hydrogen sulfide will not form if there is enough dissolved oxygen. There is a possibility of additional oxidation of hydrogen sulfide to low concentrations of sulfuric acid (H 2 SO 4) and the formation of iron sulfide (FeS) - in the presence of iron - in the form of a solid black precipitate.
• Carbon dioxide natural product of respiration, incl. microorganisms and its harm is determined by the replacement of free oxygen in the air (as well as the consumption of free oxygen for the formation of CO 2). Under certain parameters, this gas is formed in the reactions of certain acids and concrete structures - but in limited quantities. There are also types of soil mineral waters that contain this gas in dissolved form and release it when the pressure is reduced.
• Methane in sewers and similar systems is produced in biological and chemical reactions. Usually, its concentration is below the explosive level (but it happens, and fart:!). Methane can be supplemented by vapors of other flammable and explosive substances discharged into the system. The presence of elevated levels of nitrogen and carbon dioxide can slightly alter the normal flammability limits of methane in air.

The formation of these and other gases is highly dependent on the composition of the mixture, changes in temperature pH. The process greatly affects the final composition of the gas.

Findings:
There are many processes that determine the kinetics of chemical reactions and mass transfer processes in the processes taking place in sewage and biomass, and so on. biogas composition.

Sources:

1. J.B. Barsky et al., "Simultaneous Multi-Instrumental Monitoring of Vapors in Sewer Headspaces by Several Direct-Reading Instruments," environmental research v. 39#2 (April 1986): 307-320.
2. "Characteristics of Common Gases Found in Sewers," in Operation of Wastewater Treatment Plants, Manual of Practice No. eleven. Alexandria, VA, Water Pollution Control Federation, 1976, Table 27-1.
3. R. Garrison and M. Erig, "Ventilation to Eliminate Oxygen Deficiency in Confined Space - Part III: Heavier-than-Air Characteristics," Applied Occupational and Environmental Hygiene v. 6 #2 (February 1991): 131-140.
4. "Criteria for a Recommended Standard - Occupational Exposure to Hydrogen Sulfide," DHEW Pub. no. 77-158; NTIS PB 274-196. Cincinnati, National Institute for Occupational Safety and Health, 1977.
5. Permissible Exposure Limit (29 CFR 1910.1000 Tables Z-1 and Z-2).
6. Short-Term Exposure Limit (29 CFR 1910.1000 Table Z-2).
7. Biological Hazards at Wastewater Treatment Facilities. Alexandria, VA, Water Pollution Control Federation, 1991.
8. J. Chwirka and T. Satchell, "A 1990 Guide for Treating HydrogenSulfide in Sewers," Water Engineering and Management v. 137 #1 (January 1990): 32-35.
9. John Holum, Fundamentals of General, Organic and Biological Chemistry. New York, John Wiley & Sons, 1978, p. 215.
10. J. Chwirka and T. Satchell, "1990 Guide for Treating Hydrogen Sulfide" in Sewers, Water Engineering and Management v. 137 #1 (January 1990): 32.
11. V. Snoeyink and D. Jenkins, water chemistry. New York, John Wiley & Sons, 1980, p. 156.
12. M. Zabetakis, "Biological Formation of Flammable Atmospheres," US. Bureau of Mines Report #6127, 1962.

Many aspects of combustion chemistry are taken into account when fire professionals carry out categorization of premises by explosion hazard. First of all, in this process it is necessary to know the nature of combustible gases that create an explosion threat. We bring to the attention of colleagues an excerpt from the textbook Chemistry of Combustion by the founders of the science of combustion processes - Boris Genrikhovich Tiedeman and Dmitry Borisovich Stsiborsky

hydrogen sulfide and methane.

hydrogen sulfide(H 2 S) somewhat heavier than air. Its density is 1.192. Compared to other gases, hydrogen sulfide is less dangerous, since its presence in the air is easy to notice due to its smell (smells like rotten eggs), and it does not explode as much.

Hydrogen sulfide is formed during the decay of many organic substances, especially in sewers, cesspools, it is released during the processing of sulfurous metals, during the storage of soda residues and gas cleaning mass; occurs naturally in volcanic gases and in mineral springs.

Laffitt and Bare (199), determining the self-ignition temperature of a mixture of hydrogen sulfide with air, found that the lowest temperature, namely 292°, is observed at an H 2 S concentration in air of approximately 13-14%. At a given temperature, the flame does not appear immediately, but with some delay, and before the appearance of the flame, the entire mixture begins to glow. At higher temperatures, the glow disappears, since the interval between the appearance of the glow of the mixture and ignition decreases with increasing temperature.

This work is presented to your attention by the team of the site "Categorization of premises by explosion hazard"

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Methane(CH 4) lighter than air; its density is 0.559. It is sometimes incorrectly referred to as marsh or firedamp. True, these gases mainly consist of methane, but they are not a purely chemical compound, but a mixture of various gases. Let us give an approximate composition of natural gas in the Baku and Grozny regions, as well as the composition of mine gas (Table 2).

table 2

Mine gas ……………… Surakhany ………………….. Shubans - "Eternal Lights" ... Starogroznensky IV……...	CH 4	About 2	air	CO 2		C 2 H 6	C 3 H 8	Higher carbohydrate.
	in percent
	76,2 76,3 92,9 57,6			19,5	19,7	16,8		10,2

Methane with oxygen and air forms explosive mixtures that ignite at a temperature of 650-750 °, as well as from flames, sparks and under the influence of various catalysts. During an explosion in the mines, sometimes sulfur pyrite (FeS 2), which constantly accompanies fossil coals, plays the role of a catalyst.

The strongest explosive mixture consists of one volume of methane and two volumes of oxygen, or 9.6 volumes of air. The reaction occurs according to the equation:

CH 4 + 2O 2 \u003d CO 2 + 2H 2 O + 192 cal.

Methane forms the following flammable mixtures with air (41)

From 0 to 4% methane ……………………………….. no explosion

» 4 » 6 % » ……………………………... weak explosion

» 6 » 9 % » ……………………………... strong explosion

» 9 » 10 % » ……………………………... very strong explosion

» 10 » 13 % » ……………………………... strong explosion

» 13 » 16 % » ……………………………... weak explosion

Above 16% » ……………………………… combustible mixture

This work is presented to your attention by the team of the site " Categorization of premises by explosion hazard»

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The explosive properties of these mixtures are reduced in the presence of carbon dioxide; on the contrary, they rise from the presence of coal dust. The ignition temperature is relatively high; methane is difficult to ignite, so safety bulbs, arranged according to the Davy principle, protect the mixture well from an explosion.

There are cases of self-ignition of methane, which are explained by the presence of traces of hydrogen phosphide, resulting from the decay of organic matter. With chlorine, methane gives a mixture that explodes from light.

Methane is formed in coal mines, in coal warehouses, in the coal pits of ships from the slow decomposition of coal, in stagnant waters, canals, cesspools, swamps, ponds, due to the decay of organic matter. In reservoirs, it forms bubbles under the ice, which sometimes self-ignite when breaking through the ice. It constitutes the main part of natural combustible gases. There have been cases of explosions in cellars and basements of methane released from the soil.

Diagnosis of poisoning with hydrogen sulfide and methane.

N.P. Varshavets, S.N. Abramova, A.G. Karchenov
Krasnodar city

In January 1997, during repair work at the sewerage station, in violation of the existing regulations, fecal effluents were discharged from the pipeline into the machine room.
The bodies of five workers were found in fecal waters, the height of which at the bottom of the machine room did not exceed 0.7 m. Two more workers were found unconscious on a flight of stairs in the same room. When removing the latter, two rescuers who used filter gas masks felt unwell, weak, dizzy, short of breath, impaired consciousness. These phenomena intensified and both rescuers, as well as the extracted victims, were taken to the hospital, where they were treated with hyperbaric oxygen in a pressure chamber.
The corpses of 5 dead were removed by other rescuers who were already using insulating gas masks. Studies of the air of the working room, where the victims were found for the presence of gases, including methane, carried out by the Sanitary and Epidemiological Supervision Service, gave a negative result.
Examination of the corpses the next day revealed the presence of a cap of persistent fine bubble foam at the openings of the nose and mouth, Rasskazov-Lukomsky spots under the visceral pleura, pulmonary edema, and acute circulatory disorder. The foregoing gave grounds to believe that the death of all the victims was caused by drowning.
Material was taken for forensic chemical research: part of the substance of the brain, lung, stomach with contents, kidney, water sample from the room. Valves of diatom plankton were not found either in fecal effluents or in the internal organs of the dead. Earlier, during other forensic examinations related to drowning in hydrogen sulfide sources, we also did not detect diatom plankton. This gives reason to believe that plankton does not inhabit water containing hydrogen sulfide.
Based on the available data on survivors who received effective medical care, evidence that when trying to remove the victims, people felt short of breath, weakness and impaired consciousness, it was suggested that poisoning by a mixture of unidentified gases, possibly a mixture of methane and hydrogen sulfide, which could cause helpless people to get into sewage.
Water taken from the engine room, where the corpses were found, was subjected to a chemical study. From the water there was a sharp smell of hydrogen sulfide, the presence of which was confirmed by chemical reactions. During the forensic chemical examination of the lung and the wall of the stomach, hydrogen sulfide was found from all the corpses. Chemical detection in the internal organs of the corpse of hydrogen sulfide, which caused poisoning, is difficult to assess due to its formation during the decomposition of proteins. In fresh cases (absence of ammonia), the presence of large amounts of hydrogen sulfide is a characteristic sign indicating the possibility of poisoning by it.
In our case, ammonia was absent in the internal organs and a rare opportunity presented itself for determining hydrogen sulfide in the stomach and lungs using the M.D. Shvaykova (1975). As a result of fermentation, various gases are formed, the main of which is methane. The solubility of methane in water is 3.3 ml in 100 ml of water. The presence of organic suspension increases the concentration of dissolved methane.
A study was made of sewage water and internal organs for methane content by two methods: gas-liquid and gas-adsorption. In the first case, the study was carried out on a Tsvet-4 chromatograph with a flame ionization detector. The following conditions were chosen: 200 x 0.3 cm column, 25% dinonyl phthalate packing on an N-AW Chromatron. Column temperature 75°C, injector 130°C. Carrier gas consumption - nitrogen 40ml/min, hydrogen 30ml/min, air 300ml/min. In the second case, the study was carried out on a "Tsvet-100" chromatograph with DIP under the following conditions: column 100x0.3 cm, nozzle - Separon BD. Column temperature 50°C, injector 90°C. Carrier gas consumption - nitrogen 30ml/min, air 300ml/min. The measurement limit of the IMT-0.5 device is 2x10A. The registration was carried out using the ITs-26 integrator. Research methodology: 5 ml of the investigated water, as well as 5 g. chopped internal organs were placed in penicillin vials, hermetically sealed and heated in a boiling water bath for 10 minutes. From the flasks, 2 ml of vaporous samples were taken and injected into the injectors of the chromatographs. For control, household gas containing 94% methane was used. On the chromatograms in all objects (water, lung, stomach) there were peaks coinciding in retention time with the peak of methane. The retention time of methane in the first case is 31 seconds, in the second - 22 seconds. Thus, methane was found in sewage water, as well as in the lung and stomach of each corpse that was submitted for chemical research.
Our conclusions formed the basis of the departmental verification of the accident and were subsequently confirmed by the materials of the preliminary investigation.

Natural gases are represented mainly by methane - CH 4 (up to 90 - 95%). It is the simplest gas in terms of chemical formula, combustible, colorless, lighter than air. The composition of natural gas also includes ethane, propane, butane and their homologues. Combustible gases are an obligatory companion of oils, forming gas caps or dissolving in oils.

In addition, methane is also found in coal mines, where, due to its explosive nature, it poses a serious threat to miners. Methane is also known in the form of excretions in swamps - swamp gas.

Depending on the content of methane and other (heavy) hydrocarbon gases of the methane series, gases are divided into dry (poor) and fatty (rich).

• To dry gases are mainly methane composition (up to 95 - 96%), in which the content of other homologues (ethane, propane, butane and pentane) is insignificant (fractions of a percent). They are more characteristic of purely gas deposits, where there are no sources of enrichment in their heavy components that are part of the oil.
• fatty gases- These are gases with a high content of "heavy" gas compounds. In addition to methane, they contain tens of percent of ethane, propane and higher molecular weight compounds up to hexane. Fatty mixtures are more characteristic of associated gases accompanying oil deposits.

Combustible gases are common and natural companions of oil in almost all of its known deposits, i.e. oil and gas are inseparable due to their related chemical composition (hydrocarbon), common origin, conditions of migration and accumulation in natural traps of various types.

An exception is the so-called "dead" oils. These are oils close to the day surface, completely degassed due to evaporation (volatilization) of not only gases, but also light fractions of the oil itself.

Such oil is known in Russia at Ukhta. It is a heavy, viscous, oxidized, almost non-fluid oil that is produced by unconventional mining methods.

Purely gas deposits are widespread in the world, where there is no oil, and gas is underlain by formation waters. In Russia, super-giant gas fields have been discovered in Western Siberia: Urengoyskoye with reserves of 5 trillion cubic meters. m 3, Yamburgskoye - 4.4 trillion. m 3, Zapolyarnoye - 2.5 trillion. m 3, Bear - 1.5 trillion. m 3.

However, oil and gas and oil fields are the most widespread. Together with oil, gas occurs either in gas caps, i.e. over oil, or in a state dissolved in oil. Then it is called dissolved gas. At its core, oil with gas dissolved in it is similar to carbonated drinks. At high reservoir pressures, significant volumes of gas are dissolved in the oil, and when the pressure drops to atmospheric pressure during the production process, the oil is degassed, i.e. gas is rapidly released from the gas-oil mixture. Such gas is called associated gas.

The natural companions of hydrocarbons are carbon dioxide, hydrogen sulfide, nitrogen and inert gases (helium, argon, krypton, xenon) present in it as impurities.

Carbon dioxide and hydrogen sulfide

Carbon dioxide and hydrogen sulfide in the gas mixture appear mainly due to the oxidation of hydrocarbons under surface conditions with the help of oxygen and with the participation of aerobic bacteria.

At great depths, when hydrocarbons come into contact with natural sulfate formation waters, both carbon dioxide and hydrogen sulfide are formed.

For its part, hydrogen sulfide easily enters into oxidative reactions, especially under the influence of sulfur bacteria, and then pure sulfur is released.

Thus, hydrogen sulfide, sulfur and carbon dioxide constantly accompany hydrocarbon gases.

Nitrogen

Nitrogen - N - a frequent impurity in hydrocarbon gases. The origin of nitrogen in sedimentary strata is due to biogenic processes.

Nitrogen is an inert gas that hardly reacts in nature. It is poorly soluble in oil and water, so it accumulates either in the free state or as impurities. The content of nitrogen in natural gases is often small, but sometimes it accumulates in its pure form. For example, at the Ivanovskoye field in the Orenburg region, a nitrogen gas deposit was discovered in the Upper Permian deposits.

inert gases

Inert gases - helium, argon and others, like nitrogen, do not react and are found in hydrocarbon gases, as a rule, in small quantities.

The background values ​​of the helium content are 0.01 - 0.15%, but there are also up to 0.2 - 10%. An example of the industrial content of helium in natural hydrocarbon gas is the Orenburg field. To extract it, a helium plant was built next to the gas processing plant.