Methane (a system called “carbon alkyl,” but only in the introduction nomenclature system occurs when usually with customary name “methane”) is widely distributed in nature, Methane is the simplest organic, natural gas, methane, gas pit The main component of the class, commonly known as gas.

It is also the hydrocarbon with the smallest carbon content (the largest hydrogen content) and is also the main component of natural gas, biogas, oil field gas, and coal mine pit gas. It can be used as a fuel and as a raw material for the production of hydrogen, carbon black, carbon monoxide, acetylene, hydrocyanic acid, and formaldehyde.

methane

On April 2, 2018, researchers at the US Department of Energy’s Lawrence Berkeley National Laboratory demonstrated for the first time that methane has led to an increasing greenhouse effect on the Earth’s surface.

Introduction of Methane

Methane, the chemical formula CH4, is the simplest hydrocarbon consisting of one carbon and four hydrogen atoms by sp3 hybridization, so the structure of the methane molecule is a regular tetrahedral structure. The bond lengths of the four bonds are equal to each other. Methane is a colorless, odorless gas under standard conditions. The biogas produced when some organic matter is decomposed in the absence of oxygen is actually methane.

In theory, the bond line of methane can be expressed as a dot “·”, but it has not been seen in practice. The reason may be that the “·” sign can also represent electrons. So in the middle school stage, methane is considered to have no key line.

Methane is mainly used as a fuel, such as natural gas and gas, and is widely used in civil and industrial applications. As a chemical raw material, it can be used to produce acetylene, hydrogen, synthetic ammonia, carbon black, nitrochloromethane, carbon disulfide, methyl chloride, Dichloromethane, Chloroform, Carbon Tetrachloride, and Hydrocyanic Acid.

Methane Content Distribution

Methane and Hydrogen are also present in the atmosphere of Uranus. According to experiments conducted by scientists at the German Institute of Nuclear Physics, both plants and leaves produce methane, and the amount of production increases with temperature and sunshine.

In addition, plants produce 10 to 100 times more methane than decaying plants. They have estimated that the annual methane produced by plants accounts for 10% to 30% of the world’s methane production. Methane found in the planet According to foreign media reports, American astronomers announced on the 19th that they first discovered methane in the atmosphere of a planet outside the solar system.

This is the first time scientists have detected organic molecules in extrasolar planets, thus increasing the recognition of the solar system. There is hope for life. The team also confirmed the previous speculation that the planet named HD 189733b had water in the atmosphere.

methane

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Methane is an organic molecule that plays an important role in creating conditions that are suitable for life. Astronomers at NASA’s Jet Propulsion Laboratory used the Hubble Space Telescope, which orbited the orbit, to obtain an infrared spectroscopic spectrum of the planet’s atmosphere and found traces of methane.

Planet HD 189733b is located in the constellation of Fox, 63 light years from Earth. It is a large planet called “Hot Jupiter”. Its surface is hot and there is no liquid water. HD 189733b takes only two days to make a round around its star. Due to the proximity of the star, the surface temperature of the planet is as high as 900 ° C (1650 ° F), enough to melt the silver.

However, it is worth noting that methane is detected. This method can be used to surround other planets that operate around the lower temperature stars in the so-called “Goldilocks Zone”. The “habitable area” is neither cold nor hot, just right for life.

Physical Properties of Methane

 

Colour

Colorless

odorTasteless
Melting point-182.5 ° C
Boiling point-161.5 °C
Solubility (normal temperature and pressure)0.03
Molecular StructureA regular tetrahedral non-polar molecule
Molecular diameter0.414nm
Vapor pressure53.32kPa/-168.8°C
Saturated vapor pressure (kPa)53.32 (-168.8 ° C)
Relative density (water = 1)0.42 (-164 ° C)
Relative density (air = 1)0.5548 (273.15K, 101325Pa)
Critical temperature (°C)-82.6
Critical pressure (MPa)4.59
Upper explosion limit % (V/V)15.4
Lower explosion limit % (V/V)5.0
Flashpoint (°C)-188
Ignition temperature (°C)538
Heat of combustion890.31KJ/mol
Total calorific value (product liquid water)55900kJ/kg (40020kJ/m3)
Net calorific value (product gaseous water)50200kJ/kg (35900kJ/m3)
H—C—H bond angle109°28′
C-H key413kJ/mol
Crystal typeMolecular crystal
National standard number21007
IUPAC nameMethane
AliasNatural gas, biogas, biogas
CAS number74-82-8
SMILESC
InChI1/CH4/h1H4
Solubility (water)3.5 mg/100 mL (17 °C)
Molar mass16.0425 g·mol
Warning termR: R12
Security termS: S2-S9-S16-S33
Density (standard case)0.717g/L
Special natureExtremely difficult to dissolve in water

Chemical Properties and Reactions

Under normal circumstances, methane is relatively stable, does not react with strong oxidants such as potassium permanganate, and does not react with strong acids and bases. However, under certain conditions, some reactions occur in methane.

Substitution reaction

Among the halogenation of methane, there are mainly chlorination and bromination. The reaction between methane and fluorine is a large amount of exothermic. Once the reaction occurs, a large amount of heat is difficult to remove, destroying the generated fluoromethane, and only carbon and hydrogen fluoride are obtained.

Therefore, the direct fluorination reaction is difficult to achieve and needs to be diluted with a rare gas. Iodine and methane need to react.

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For higher activation energy, the reaction is difficult to carry out. Therefore, iodine cannot be directly substituted with methane to form methyl iodide. But its reverse reaction is easy to carry out.

Taking Chlorination as an Example: it can be seen that the yellow-green gas of chlorine in the test tube gradually fades, a white mist is formed, and oil droplets are formed on the inner wall of the test tube, which is the methyl chloride and dichloride formed by the reaction of methane and chlorine. A mixture of methane, chloroform (or chloroform), carbon tetrachloride (or tetrachloromethane), hydrogen chloride, and a small amount of ethane (impurities).

CH 4 +Cl 2 → (light) CH 3 Cl (gas) + HCl

CH 3 Cl+Cl 2 → (light) CH 2 Cl 2 (oil) + HCl

CH 2 Cl2+Cl 2 → (light) CHCl 3 (oil) + HCl

CHCl 3 +Cl 2 → (light) CCl 4 (oil) + HCl

The liquid level in the test tube rises, and white crystals in the saline solution are precipitated, which is because the hydrogen chloride generated in the reaction is dissolved in water.

Because hydrogen chloride is very soluble in water, it dissolves in water and increases the concentration of chloride ions in the water to precipitate sodium chloride crystals.

methane

Hold the tube mouth with your thumb, raise the liquid level, and press the tube up. Add purple pistil test solution or zinc particles to the test tube to verify that it is dilute hydrochloric acid.

If the amount of chlorine is controlled, a large amount of methane is used to obtain mainly methyl chloride, if a large amount of chlorine is used, carbon tetrachloride is mainly obtained. Industrially, the rectification is carried out to separate the mixtures one by one. The above several chlorinated products are important solvents and reagents.

Features:

1. does not react in the dark at room temperature;

2. reacted at 250 ° C;

3. can react under the action of light at room temperature;

4. using light to initiate the reaction, the absorption of a photon can produce thousands of molecules of methyl chloride;

5. If there is oxygen or some impurities that can capture free radicals, the reaction has an induction period, and the length of the induction period is related to the presence of these impurities.

According to the characteristics of the above facts, it can be judged that the chlorination of methane is a radical type substitution reaction.

Oxidation reaction

The most basic oxidation reaction of methane is combustion:

CH 4 +2O 2 →CO 2 +2H 2 O

The hydrogen content of methane is the highest among all hydrocarbons, reaching 25%, so the same quality of gaseous hydrocarbons is completely burned, and methane has the highest oxygen consumption.

Ignite pure methane, cover a dry beaker over the flame, and quickly see the condensation of water vapor on the beaker wall. Invert the beaker, add a small amount of clarified lime water, shake, and the lime water becomes cloudy. It indicates that methane is burned to produce water and carbon dioxide.

Collect methane gas in a high glass cylinder, stand upright on the table, remove the glass piece, and quickly put the burning spoon with the burning candle into the tube, the candle will be extinguished immediately, but the methane is burning in the bottle mouth.

Light blue flame. This means that methane can burn quietly in the air but does not support combustion. In a large test tube with a draining process to start the oxygen storage cylinders in 2/3 volume of oxygen input, and then pass into 1/3 volume methane. Plug it with a rubber stopper and take out the water.

The tube was inverted several times to allow the gas to mix thoroughly. Use a cloth to bake the tube outside, let the tube mouth tilt down slightly, remove the stopper, and quickly ignite the tube with the burning small wooden strip, that is, a sharp popping sound occurs.

Although this experiment is simple, it is easy to fail. The methane released from the glass conduit is ignited and placed in a bottle filled with chlorine. The methane will continue to burn, emitting a red-yellow flame while seeing black smoke and white mist. Black smoke is carbon black, and white mist is a hydrochloric acid mist formed by hydrogen chloride gas and water vapor.

Heat Decomposition

Methane decomposes to form carbon black and hydrogen under the condition of insulating air and heating to 1000 °C.

CH 4 = (1000 ° C) = C + 2H 2

Hydrogen is a raw material for industries such as ammonia and gasoline; carbon black is a raw material for the rubber industry.

Hydrate Formation

Methane can form caged hydrates, and methane is encased in “cage“. This is the flammable ice we often say. It is an ice-like, non- stoichiometric, composed of water and natural gas mixed under medium and high-pressure conditions under certain conditions (suitable temperature, pressure, gas saturation, water salinity, pH, etc.) Cage-like crystal compound (carbon has a large electronegativity, and under high pressure, it can attract hydrogen atoms similar to each other to form a hydrogen bond to form a cage structure). It can be represented by m CH4 ·nH2Om represents a gas molecule in the hydrate, and n is a hydration index (ie, the number of water molecules).

Combustible ice is mainly stored in the permafrost zone on the seabed or in cold regions and is difficult to find and explore. The newly developed highly sensitive instrument can instantly measure the accurate content of various ultra-methane, ethane, propane, and hydrogen in the seabed soil and rock, and judge the existence and resources of combustible ice resources and resources.

Natural gas hydrates having a methane content of more than 99% are also referred to as methane hydrates.

Greenhouse effect

On April 2, 2018, researchers at the US Department of Energy’s Lawrence Berkeley National Laboratory used the comprehensive observations of the Earth’s atmosphere obtained from the Observatory of the Great Southern Plains of Oklahoma for the first time to directly prove that methane causes the earth’s surface greenhouse. The effect continues to increase.

Researchers say that at the beginning of the 21st century, the concentration of methane in the atmosphere stagnated, and the greenhouse effect followed the same pattern; but since 2007, when the concentration of methane began to rise, the greenhouse effect caused by it also rose.

Methane Preparation

Methane is a flammable gas and can be manufactured by hand so methane will become an important energy source after the oil is used up.

Its main sources are:

  1. Decomposition of organic waste.
  2. Natural source (such as swamp) 23%.
  3. Extracted from fossil fuels20%.
  4. The digestion process of animals (such as cattle): 17%.
  5. Bacteria in rice fields: 12%.
  6. The biomass is heated or burned by anoxic conditions.

The main methods of methane artificial products are as follows:

Bacterial Decomposition

The organic matter into biogas tank, control the temperature and humidity, the methane bacteria multiply rapidly, the decomposition of organic matter to methane, carbon dioxide, hydrogen, hydrogen sulfide, carbon monoxide, methane, wherein 60% -70%. After low-temperature liquefaction, methane is raised to produce cheap methane.

Synthetic Method

Carbon dioxide and hydrogen are generated under the action of a catalyst to form methane and oxygen, which are then purified.

CO 2 +2H 2 =CH 4 +O 2 directly reacts carbon vapor with hydrogen, and high purity methane can also be obtained.

Laboratory method

Anhydrous sodium acetate (CH 3 COONa) and soda lime (NaOH and CaO as a desiccant)

Reaction equation: CH 3 COONa + NaOH ===Na 2 CO 3 +CH 4 ↑

Collection: Drainage method (cannot be collected by the downward air method)

Features and precautions:

  1. Methane must be prepared by reacting anhydrous sodium acetate with dry soda lime. If sodium acetate crystals or lime are not dried, methane gas is hardly produced.
  2. The operational considerations and collection methods for this experiment are identical to those for oxygen.

Transformation Pathway

In July 2018, the Zuo Zhiwei team of the School of Physical Science and Technology of Shanghai University of Science and Technology found a low-cost, high-efficiency catalyst combination that can convert methane at room temperature.

This provides a new scheme for the conversion of methane into high value-added chemical products such as rocket propellant fuel, which provides a new idea for the efficient use of unique rare earth metal resources in China. Relevant research results have been published in the international academic journal Science.

Safety

Health Hazard

Methane is basically non-toxic to humans, but when the concentration is too high, the oxygen content in the air is significantly reduced, causing suffocation. When methane in the air reaches 25%-30%, it can cause headache, dizziness, fatigue, inattention, breathing and heartbeat, and ataxia. If you do not stay away in time, you can die of suffocation. Skin contact with liquefied methane can cause frostbite.

Environmental Impact

Methane is also a greenhouse gas. Analysis of GWP shows that the greenhouse effect of methane is 25 times greater than that of carbon dioxide in terms of the number of molecules per unit.

This is because there is already a lot of carbon dioxide in the atmosphere so that many bands of radiation have already been absorbed; therefore, most of the newly added carbon dioxide can only exert its absorption effect at the edge of the original absorption band.

Conversely, some of the smaller amounts of greenhouse gases (including methane) absorb the bands that have not been effectively intercepted, so each additional molecule provides new absorption capacity.

Toxicological Information

Toxicity: Acute poisoning, methane toxicity is very low, “methane poisoning” caused by exposure to high concentrations of methane is actually anoxic asphyxiation caused by relatively low air oxygen content.

Allow gas to diffuse safely into the atmosphere or as a fuel. It has a simple asphyxiating effect and causes poisoning due to hypoxia and asphyxia at high concentrations. Dizziness, respiratory acceleration, and movement disorders occur in 25 to 30% of the air.

Acute toxicity: mice inhaled 2% concentration × 60 minutes, anesthesia; rabbit inhalation 2% concentration × 60 minutes, anesthesia. This product produces suffocation only when the air is replaced at a very high concentration and the partial pressure of oxygen is lowered.

anesthesia

The air concentration of methane in the air caused the mice to suffocate and the breathing stopped at 90%. A mixture of 80% methane and 20% oxygen can cause headaches.

When methane in the air reaches 25% to 30%, people have pre-suffocation symptoms such as dizziness, accelerated breathing, increased heart rate, and lack of concentration, fatigue, ataxia, and even suffocation.

Skin contact with liquefied methane can cause frostbite. Methane enters the body mainly through the respiratory tract. Most of it is exhaled in its original form, and a small amount can be oxidized to carbon dioxide and water in the body. Because of its extremely low ability to bind to proteins, the anesthetic effect is rather weak.

A series of clinical manifestations of hypoxia can occur in people with methane concentrations of 25% to 30%, such as dizziness, headache, inattention, shortness of breath, weakness, ataxia, asphyxia, etc. the patient can die quickly.

It has been observed that patients with methane poisoning have varying degrees of toxic encephalopathy, and patients with severe poisoning may have neurological sequelae. The biggest hazard of methane in coal mine production is the fire and explosion after mixing with air.

Methane Poisoning

When the skin comes into contact with liquid methane, it can cause frostbite due to its rapid evaporation.

There is no clinical data on chronic methane poisoning in chronic poisoning.

Diagnosis and differential diagnosis According to the presence of a high concentration of methane on the site, the patient has clinical manifestations of significant hypoxia and asphyxia. After identification with other similar gas poisoning or diseases, acute methane poisoning can be diagnosed.

There is less real acute methane poisoning, especially in the diagnosis and other gas poisonings.

First-aid and treatment of acute methane poisoning, no specific antidote, can be treated according to the principle of hypoxia treatment, such as immediately moving the patient to fresh air, lying down, keeping warm, keeping the airway open and oxygen.

What Methane is Dangerous

Morphine and barbiturates have respiratory depression and should be avoided. Cardiopulmonary cerebral resuscitation should be performed immediately when breathing or heartbeat is stopped. Pay attention to the prevention of possible brain edema and, if necessary, hyperbaric oxygen therapy.

When liquefied methane contaminates the skin, it can cause frostbite. If the skin of the frostbite is still not thawed, it can be dipped in warm water at about 42 °C and treated according to surgical principles.

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Hazardous characteristics: Flammable, mixed with air can form an explosive mixture, and there is a danger of burning and exploding in case of heat and open flame. With bromine pentafluoride, chlorine, hypochlorous acid, nitrogen trifluoride, oxygen, oxygen difluoride, and other strong oxidants contact reaction vigorously.

Combustion (decomposition) products: carbon (very incomplete combustion), carbon monoxide (incomplete combustion, harmful), carbon dioxide and water (complete combustion).