21(a) Oil Refining and its Products

Crude Oil Distillation columns Oil rig Photo - Chris Grossman Oil rig Distillation columns http://www.festanks.com.au/crude-oil-refining-in-australia-infographic/img/oil-distillation.gif

Fractional Distillation of Crude Oil

Fractional Distillation of Crude Oil Small molecules Low boiling point Large molecules High boiling point

Fractional Distillation of Crude Oil Crude oil is separated by fractional distillation Molecules have different boiling/condensation points Many of these hydrocarbons are alkanes, and are sorted into fractions They are separated as groups of compounds with similar boiling points The temperature of the fractionating column is maintained at a high level at the bottom and decreases up the column Substances with higher boiling points condense in the lower part of the fractionating column and those with lower boiling points condense at the higher part of the column.

The Fractions Fraction Length of C Chain Uses Refinery Gas C1 – C4 Bottled and sold for domestic use (cooking etc) LPG: Liquified Petroleum Gas Petrol (light gasoline) C5 – C10 Motor fuel Naptha C7 – C10 Petrochemical industry: production of plastics, medicines, synthetic fibres, detergents Kerosene (paraffin) C10 – C14 Domestic heating oil Aircraft fuel Diesel oil (gas oil) C14 – C19 Fuel for buses, trucks, trains and cars Lubricating oil C14 – C35 Lubricant to reduce wear and tear Waxes and polishes Fuel oil C30 – C40 Fuel for ships and power stations Bitumen > C35 Tar for roads and roofing

Mercaptans Very smelly, organic sulfur compounds that are added to natural gas and LPG so that leaks can be detected

Combustion Engine Air drawn in Petrol injected → air-fuel mixture created Spark ignites petrol-air Atomised diesel spontaneously combusts in high temp https://www.youtube.com/watch?v=bZUoLo5t7kg https://www.youtube.com/watch?v=fTAUq6G9apg

Auto-ignition / Knocking The premature ignition of the petrol-air mixture before normal ignition of the mixture by a spark Effects: a) Loss of power b) Engine damage Prevention: a) Additives b) Use suitable mixtures of high-octane compounds

Octane Number A measure of the tendency of a fuel to resist knocking * A low octane number makes auto-ignition (knocking) more likely → the lower the octane number, the less efficient the fuel

Octane Number 2,2,4-trimethylpentane Octane # = 100 Heptane →These are reference hydrocarbons

Factors that Affect Octane Number Length of Chain Degree of branching Straight chain or cyclic structure

Factors that Affect Octane Number Length of Chain The shorter the chain, the higher the octane number Butane Octane # = 94 Heptane Octane # = 0

Factors that Affect Octane Number 2. Degree of Branching The more branched the chain, the higher the octane number 3-methylhexane Octane # = 65 2,3-dimethylpentane Octane # = 91

Factors that Affect Octane Number 3. Straight Chain or Cyclic Structure Cyclic compounds have a higher octane number than straight chain compounds Hexane Octane # = 25 Cyclohexane Octane # = 83

Methods to Increase Octane Number Isomerisation Catalytic Cracking Dehydrocyclisation Adding Oxygenates

Isomerisation Changing straight chain alkanes into their isomers Heated in the presence of a catalyst Chain breaks Bits rejoin to form a branched compound E.g: Pentane Octane # = 62 2-methylbutane Octane # = 93

Catalytic Cracking The breaking down of long-chain hydrocarbon molecules into short chain-molecules using heat and catalysts E.g: Cracking C12H26 2,4-dimethylpentane 2-methylbut-1-ene

Catalytic Cracking Unsaturated products (alkenes) are used as feedstock for the polymer industry Saturated products (alkanes)are usually high octane branched chain alkanes suitable for making petrol

Dehydrocyclisation Using catalysts To form ring compounds from straight-chain alkanes E.g: Hexane Octane # = 25 Cyclohexane Octane # = 83

Methyl tertiary-butyl ether Adding Oxygenates Need to know all 3! Oxygen containing compounds: *Oxygenates also give rise to very little pollution MTBE Methyl tertiary-butyl ether Methanol Ethanol

Adding Oxygenates Lead compounds e.g. tetra ethyl lead Prevents reactions Harmful environmental effects Phased out in 2000

Manufacture of Hydrogen Steam Reforming of Natural Gas CH4 + H2O = 3 H2 + CO In presence of a suitable catalyst

Manufacture of Hydrogen Electrolysis of Water using dilute H2SO4 forms at cathode [negative electrode] Overall H2O = H2 + 1/2 O2 Too expensive in most parts of world

Uses of Hydrogen Fuel - about 10% of worlds production of hydrogen is used as fuel Environmentally friendly Water is the only product of combustion H2 + 1/2 O2 = H2O It is explosive with air Difficulties with storage and transport

Uses of Hydrogen Haber Process for producing ammonia N2 + 3 H2 = 2 NH3 Hydrogenating vegetable oils

Fuel Cell