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Unit 24

Unit 24. Demand for different fractions of petroleum. Demand for different fractions of petroleum. Demand for different fractions. The lighter, low boiling fractions – made up of small hydrocarbon molecules. Can be sold in a higher price (of higher economic value). More demanded by us.

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Unit 24

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  1. Unit 24 Demand for different fractions of petroleum

  2. Demand for different fractions of petroleum

  3. Demand for different fractions • The lighter, low boiling fractions – made up of small hydrocarbon molecules. • Can be sold in a higher price (of higher economic value). • More demanded by us.

  4. Demand for different fractions • Heavier, high boiling fractions – made up of large hydrocarbon molecules. • Supply is more than demand. • Cracking is a process in which large hydrocarbon molecules are broken down into small molecules. • A way to meet our demand for petrol.

  5. Cracking of petroleum • When hydrocarbon molecules are heated, they move and vibrate faster. Their more frequent collisions lead to the breaking up of large molecules into smaller ones.

  6. Methods of cracking • Thermal cracking – heating hydrocarbons up to 500oC and 30 atmospheres. • Cracking cracking – vapours of large hydrocarbons are passed over red hot catalyst (aluminium oxide and silicon(IV) oxide) at 500oC and 1 atmosphere.

  7. Catalyst • A substance that can speed up the rate of reaction, but itself is not used up at the end of reaction (remains unchanged at the end of the reaction). • Compare with enzyme! • Enzymes would be denatured.

  8. Cracking in the laboratory

  9. Cracking in the laboratory • Broken porous pot (unglazed porcelain pieces) or alumina (aluminium oxide) – used as catalyst. • Products of cracking (differing from case to case). Why? • Carbon soot, hydrogen, small alkanes and small alkenes.

  10. Importance of cracking • Producing extra petrol • High boiling fractions of C13 to C25 are cracked into small molecules which are fuels for motor-cars. • As a source of alkenes (raw materials for plastics) • Alkenes – by products of cracking and raw materials for making plastics, polymers and detergents.

  11. Town gas • Made from the reforming of naphtha. • Naphtha vapour and steam were passed over red-hot nickel catalyst at 700oC. • C6H14 + 5H2O → 5CO + CH4 + 10H2 • C6H14 + 8H2O → 2CO2 + 4CO + 15H2 • An odorant is added to alert people if there is a leakage of town gas.

  12. Composition of town gas • Hydrogen (49%) • Methane (28.5%) • Carbon dioxide (19.5%) • Carbon monoxide (3%)

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