Natural sources of hydrocarbons. Natural gas and coal
Natural gas is 90–98 % methane by volume, the rest being ethane, propane, butane and small amounts of nitrogen, CO₂ and hydrogen sulfide. Associated gases come out with petroleum and contain less methane and more ethane, propane and butane; low-temperature distillation separates individual hydrocarbons, gas gasoline and the propane–butane mixture (liquefied gas). Natural gas is one of the cleanest fuels: CH₄ + 2O₂ → CO₂ + 2H₂O + Q; it also yields acetylene (2CH₄ → C₂H₂ + 3H₂) and synthesis gas (CH₄ + H₂O → CO + 3H₂), from which ammonia and alcohols are made. Heating coal without air (coking) gives coke, coal tar, ammoniacal water and coke-oven gas. Coke is used in metallurgy to produce iron; benzene, toluene, phenol and naphthalene are isolated from the tar; ammoniacal water is used for nitrogen fertilizers; coke-oven gas contains H₂, CH₄ and benzene vapour. Uzbekistan has large gas fields and gas-processing enterprises (Shurtan, Mubarek) as well as brown coal at Angren.
In class make a table “natural gas vs liquefied propane–butane”: composition, uses and precautions (if gas smells: no flame or switch, ventilate). No experiments with gas.