Methane, preparation, properties, and chemical reactions.
Methane, CH4, is the simplest in composition limiting hydrocarbon, organic substance class alkanes. In nature, found in natural gas extracted from gas and gas condensate fields in oil and gas, in mining and swamp gases. Dissolved in oil at reservoir and surface waters. In the solid state is found in the form of gas hydrates.
Methane (lat. methanum) is a simple composition of ultimate hydrocarbon, organic substance class alkanesof one carbon atom and four hydrogen atoms.
Chemical formula of methane is CH4, the rational formula of CH4. Isomers has not.
The structure of the molecule:
Methane – under normal conditions a light colorless gas, without taste and smell. However, in methane, used as a technical gas that can be added odorants — substances with a sharp odor to prevent its leakage.
Methane is the main component of natural gas.
Is one of the greenhouse gases. Its contribution to the greenhouse effect is around 4-9 %.
In nature, found in natural gasextracted from gas and gas condensate fields in oil and gas. For the isolation of natural and associated petroleum gas produced by cleaning and separation of gas. Also contained in the mine and marsh gas (hence the other name of methane – marsh gas or fire-damp), landfill gas.
Under anaerobic conditions (in bogs, waterlogged soils at the bottom of ponds and stagnant waters, where it is formed during the decomposition of plant residues without access of air, in the intestines of ruminant animals, bioreactors, biogas plants, etc.) is formed nutrient in the result of the activity of some microorganisms.
In dissolved form is contained in the oil, formation and surface waters. Oil refining methane release separately for further use.
In addition to gaseous state in nature, occurs also in the solid state on the bottom of seas, oceans and in the permafrost zone in the form of methanehydrates (natural gas hydrates), referred to as “flammable ice.”
Also contained in shale oil, shale gas and liquefied gas (liquefied natural gas).
Flammable and explosive.
Almost insoluble in water and other polar solvents. But soluble in some nonpolar organic substances (methanol, acetone, benzene, carbon tetrachloride, diethyl ether, etc.).
Low toxicity, but adverse effects in humans – has a narcotic effect. The fourth class of danger.
|Aggregate state (at 20 °C and atmospheric pressure of 1 ATM.)||gas|
|Density (at 20 °C and atmospheric pressure of 1 ATM.) kg/m3||0,6682|
|Density (at 0 °C and atmospheric pressure of 1 ATM.) kg/m3||0,7168|
|Density (at -164,6 °C and atmospheric pressure of 1 ATM.) kg/m3||415|
|Melting point, °C||-182,49|
|Boiling point, °C||-161,58|
|The auto-ignition temperature, °C||537,8|
|Critical temperature*, °C||-82,4|
|Critical pressure, MPa||4,58|
|Critical specific volume, m3/kg||0,0062|
|Explosive concentration of the mixture of gas with air, % by volume||from 4.4 to 17.0|
|Specific heat of combustion, MJ/kg||50,1|
|Coefficient of thermal conductivity (at 0 °C and atmospheric pressure of 1 ATM.) W/(m·K)||0,0302|
|Coefficient of thermal conductivity (at 50 °C and atmospheric pressure of 1 ATM.) W/(m·K)||0,0361|
|Molar mass, g/mol||16,04|
|Solubility in water, g/kg||0,02|
* at temperatures above the critical temperature the gas cannot be condensed at any pressure.
Methane is difficult chemical reactions. In normal conditions does not react with concentrated acids, melted and concentrated alkalis, alkali metals, Halogens (except fluorine), potassium permanganate and potassium dichromate in an acidic medium.
Chemical properties of methane are similar to properties of other representatives of a number of alkanes. So it is characterized by the following chemical reactions:
1. conversion of methane to synthesis gas:
CH4 + H2O → CO + 3H2 (kat = Ni/Al2O3 at to = 800-900 OS or without catalyst at to = 1400-1600 OS).
Formed in the reaction, synthesis gas can be used for further syntheses of methanol, hydrocarbons, acetic acid, acetaldehyde and other products.
2. galogenirovannami methane:
CH4 + Br2 → CH3Br + HBr (hv or increased to);
CH4 + I2 → CH3I + HI (hv or increased to).
The reaction is self-perpetuating. A molecule of bromine or iodine under the action of light decomposes to the radicals, then they attack molecules of methane, taking from them an atom of hydrogen, this produces free of methyl CH3·, which collide with molecules of bromine (iodine), destroying them and forming new radicals of iodine or bromine:
Br2 → Br·+ Br· (hv); – initiation reactions of halogenation;
CH4 + Br· → CH3· + HBr; – the chain growth reactions of halogenation;
CH3· + Br2 → CH3Br + Br·;
CH3· + Br· → CH3Br; – open circuit reactions of halogenation.
Galogenirovannami is one of the substitution reactions. First halogenides least gidrirovanny carbon atom (atom is tertiary, then secondary, primary atoms halogenide least). Galogenirovannami of methane takes place in stages – one stage is replaced by one hydrogen atom.
CH4 + Br2 → CH3Br + HBr (hv or increased to);
CH3Br + Br2 → CH2Br2 + HBr (hv or increased to);
Galogenirovannami will happen next while will not be replaced by atoms of hydrogen.
CH2Br2 + Br2 → CHBr3 + HBr (hv or increased to);
CHBr3 + Br2 → CBr4 + HBr (hv or increased to).
3. nitration of methane:
Cm. nitration of ethane.
4. the oxidation (combustion) of methane:
With excess oxygen:
CH4 + 2O2 → CO2 + 2H2O.
Burns with a bluish flame.
If there is insufficient oxygen instead of carbon dioxide (CO2) is a carbon monoxide (co), with still less oxygen is released and fine carbon (soot in various forms, including in the form of graphene, fullerenes , etc.) or a mixture thereof.
5. sulfochlorinated methane:
CH4 + SO2 + Cl2 → CH3-SO2Cl + … (hv).
6. sulfookislenie methane:
2CH4 + 2SO2 + O2 → 2CH3-ЅО2ОН (increased to).
7. the decomposition of methane:
CH4 → C + 2H2 (subject to > 1000 oC).
8. the dehydrogenation of methane:
2CH4 → C2H2 + 3H2 (subject to > 1500 OC).
9. catalytic oxidation of methane:
In reactions of catalytic oxidation of methane can form alcohols, aldehydes, carboxylic acids.
2CH4 + O2 → 2СН3ОН (at to = 200 OS, kat); – methanol is formed;
CH4 + O2 → SNO + H2O (when to = 200 OS, kat); – to form formaldehyde;
2CH4 + 3O2 → 2НСООН + H2O (when to = 200 OS, kat); – formed formic acid.
The production of methane in industry and in the laboratory. The chemical reaction equation for methane production:
Methane in large quantities is found in nature. For example, contained in natural gas, casinghead gas and stands out from the cracking of petroleum products, it usually don’t get artificially. It is isolated in the purification and separation of natural gas, associated gas and oil by distillation. In addition, it is derived from methanehydrates (natural gas hydrates) in the process of operation of biogas plants , etc.
Methane in industrial and laboratory conditions is the result of the following chemical reactions:
1. gasification of solid fuels:
C + 2H2 → CH4 + H2O (high blood pressure and to kat = Ni, Mo or without a catalyst).
2. synthesis Fischer-Tropsch:
CO + 3H2 → CH4 (kat = Ni, to = 200-300 oC);
3. the reaction of carbon oxide (IV) and hydrogen:
CO2 + 4H2 → CH4 + 2H2O (kat, to = 200-300 oC);
4. hydrolysis of aluminium carbide:
Al4C3 + 12H2O → CH4 + 4Al(OH)3.
5. alkaline melting of salts of monobasic organic acids
CH3-COONa + NaOH → CH4 + Na2CO3 (increased to).
– as fuel for vehicles, vessels, gas stoves, furnaces, blowtorches, lighters, etc. household appliances;
– as a raw material in chemical industry for carrying out organic synthesis reactions.
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