2 Petrol and Crude OilCrude oil is separated by fractional distillationworks because the molecules have different boiling/condensation pointsmany of these hydrocarbons are alkanes, and are sorted into fractionseach fraction has a range of boiling points in the distillationnarrow boiling ranges of limited carbon number (eg light gasoline is C5 to C7 boiling point 25C -75C)Gasoline and gas oil fractions are sources of petrol componentsNaptha used for high grade petrol and chemical feedstocks
3 Fractionation of Crude Oil Fractions and their uses Refinery Gas (LPG)Light Gasoline (Petrol)Naphtha (Petrol)Kerosene (Jet Fuel)Gas Oil (Diesel Fuel)Residue Fractions (Bitumen)
4 Natural GasNatural gas is an extremely fuel both for domestic and industrial use.It is a mixture consisting mostly of methane, CH4, (at least 85%), ethane, C2H6, (up to 10%) and small amounts of propane, C3H8, and butane, C4H10.
5 Liquid Petroleum Gas (LPG) The gases in the refinery gas fraction are bottled and sold for domestic use.Propane and butane from this fraction can be readily liquefied under pressure and are referred to as liquid petroleum gas (LPG).
6 MercaptansVery smelly, organic sulfur compounds called mercaptans are added to natural gas and LPG so that leaks can be detected
7 Petrol Composition Complex mixture of compounds Mainly Hydrocarbons Branched – chain alkanesAromatic Compounds
8 Petrol in the Internal Combustion Engine VaporisedMixed with airCompressedIgnited and burnedGases produced expandKinetic Energy
9 Premature Ignition Problem: Auto-ignition (i.e. knocking or pinking) Effects: a) Loss of powerb) Engine damagePrevention: a) Additivesb) Use suitable mixtures of high-octane compounds
10 Octane Rating Measure of tendency to resist auto-ignite or Measure of tendency to cause knockingLow octane rating makes auto-ignition more likely
11 Octane Rating 2,2,4-tri-methylpentane Octane Number =100 Heptane
12 Additives Lead compounds e.g. tetra ethyl lead Prevents reactions Harmful environmental effectsPhased out in 2000Oxygenates e.g. ROR orROR1 MTBERaise octane numberCause less pollution
13 Mixture of compounds with high octane numbers Molecular features:Degree of branching – the more the betterChain length – the shorter the betterPresence of rings – highly desirable
14 High octane numbers can be obtained from low by: IsomerisationDehydrocyclisationCatalytic crackingAll three methods involve the use of catalysts
15 Isomerisation Take a straight chain alkane e.g. pentane (O.N.62) C ─ C ─ C ─ C ─ CHeat in the presence of a catalystChain breaksBits rejoin to form a branched compound e.g.2-methylbutane (O.N.93)C ─ C ─ C ─ C│C
16 Dehydrocyclisation Take a straight chain alkane e.g. hexane (O.N. 25) Catalyst causes change to a cycloalkane (O.N. 83)C6H14 → (CH2)6 + H2Catalyst causes the cycloalkane to change to an aromatic compound e.g. benzene (O.N. >100)(CH2)6 → 3H C6H6Benzene
17 Catalytic Cracking Heavy oil e.g. kerosine or diesel High temperature and catalystMolecule breaks into several smaller moleculesUnsaturated products are used as feedstock for the polymer industrySaturated products are usually high octane branched chain alkanes suitable for making petrol