Petroleum and its refining

Petroleum is an oily mixture of gaseous, liquid and solid hydrocarbons; its colour ranges from yellow to black, it is lighter than water and insoluble in it, and it has no sharp boiling point because it is a mixture. Besides hydrocarbons it contains sulfur, oxygen and nitrogen compounds. By fractional distillation it is separated by boiling range: up to about 150 °C gasoline (petrol, C₅–C₉), 150–300 °C kerosene (about C₉–C₁₆), above 300 °C fuel oil (mazut); mazut gives lubricating oils, petroleum jelly and paraffin, and the residue tar gives asphalt. Straight-run distillation yields little petrol, so heavy fractions are cracked: C₁₆H₃₄ → C₈H₁₈ + C₈H₁₆, C₈H₁₈ → C₄H₁₀ + C₄H₈. Thermal cracking uses high temperature and pressure; catalytic cracking uses a catalyst and gives more branched alkanes. Burning petroleum products releases CO₂ and SO₂ and pollutes the air, so economy and cleaner fuels matter. Uzbekistan has petroleum refineries, for example in the Fergana and Bukhara regions.