2 Fractional distillation ContentsUseful OilCrude oilFractional distillationPhysical properties of fractionsUses of fractionsSummary activities
3 Hydrocarbons are molecules that contain carbon and hydrogen only. Crude oilCrude oil is a mixture.It contains hundreds of different compounds. Some are small but most are large.Nearly all of these compounds contain carbon and hydrogen only.They are called hydrocarbons.Hydrocarbons are molecules that contain carbon and hydrogen only.
5 HydrocarbonsCrude oil is a mixture of different sized hydrocarbons. The exact composition depends upon where the oil comes from but typically it contains a lot of big molecules.Small moleculesBig moleculesMedium molecules
7 Making oil usefulAlthough we can get useful substances from oil, crude oil itself has no uses.In order to make crude oil into useful substances we first have to separate the mixture into molecules of similar size.This is done in an oil refinery.
9 Fractional distillation ContentsUseful OilCrude oilFractional distillationPhysical properties of fractionsUses of fractionsSummary activities
10 Fractional distillation coolhotCrude oil is split into fractions containing similar sized molecules using fractional distillation.The oil is heated until it vaporises.It then passes up a tall tower that is hot at the bottom but cool at the top.As the vapour passes up this tower the molecules cool and condense back to liquid.
11 Fractions and boiling points coolhotCopy the column and arrange the fractions in the right order next to the arrows.Fuel gasPetroleumFractionBoiling Range(oC)KerosineDiesel220 – 275PetrolBitumen>350Fuel gasBelow 40Lubricating oilKerosineDieselLub. OilBitumen
13 Fractional distillation ContentsUseful OilCrude oilFractional distillationPhysical properties of fractionsUses of fractionsSummary activities
14 The boiling point of hydrocarbons We have already said that, in general, the bigger the molecule the higher the boiling point.No. Carbon atoms B.Pt(oC)
15 Boiling point and fraction size Here are the boiling ranges of some fractions obtained from distillation of petroleum.Using the previous graph, estimate the size range of the molecules present in each fraction.FractionBoiling Range(oC)Number of carbonsFuel gasBelow 40PetrolKerosineDiesel1-55-109-1413-17
16 Flammability of hydrocarbons When hydrocarbons burn they are reacting with oxygen in the air.In general, the smaller the molecule the better it will mix and then react with the air.
17 Flash points Substance Flash Point Kerosine <23 Petrol 85 - 150 Flash points are (roughly) the temperature below which you cannot ignite the substance.Here is some flash points data for oil fractions. Link the molecule to the flash point.SubstanceFlash PointKerosine<23PetrolFuel Oil
18 Viscosity of hydrocarbons When we pour a liquid the molecules have to pass each other. The easier they do this, the runnier the liquid is.The molecules in fuel oil and bitumen may contain up to 400 carbon atoms in long chain structures.These chains easily become entangled reducing the runniness of the liquid and so those made up of big molecules tend to be viscous (treacly) not runny.
19 Viscosity of hydrocarbons In contrast, small molecules are more spherical and tend not to get tangled.They are therefore likely to have a low viscosity (be runny).Bigger moleculesHigher viscosity“Treacly”Smaller moleculesLower viscosity“Runny”
20 Matching hydrocarbons to their viscosity Here are the viscosities of 5 hydrocarbons.The higher the value the less runny the hydrocarbon is. Draw arrows joining the hydrocarbon with the appropriate value.HydrocarbonViscosity (cP)Pentane - C5H120.40Hexane - C6H120.52Heptane - C7H160.24Octane - C8H180.92Decane - C10H220.70
21 Colour of hydrocarbons Small hydrocarbon molecules are gases or transparent liquids.As the molecules get larger the colour becomes increasingly yellow through to the brown/black colour of bitumen used on roads and roof repairs.Increasing size of molecules
22 Composition of fractions We already know that each petroleum fraction consist of hydrocarbon molecules falling within a particular size range.The proportions of the different hydrocarbons present in oil can vary greatly across the world.It is therefore not surprising that the exact nature of the fractions collected will vary both in amount and detailed composition.Nonetheless most crude oil will give rise to some quantity of each type of fraction.
23 Viscosity of different crude oil Using viscosity data for crude oil from different areas of the world, arrange the oils putting those with the smallest molecules first.CrudeOrderViscosity (cSt)Saudi Arabia47.7UK (Brent)6.13Norway (Gulifaks)16.5Alaskan31.5Malaysian3.4352341
24 Fractional distillation ContentsUseful OilCrude oilFractional distillationPhysical properties of fractionsUses of fractionsSummary activities
25 Uses of different fractions Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gasFuel gasPetrol/ gasolineFuel for cars and motorcycles, also used to make chemicals.NaphthaUsed to make chemicals.Paraffin /kerosineFuel for greenhouse heaters and jet engines, manufacture of chemicals.Diesel fuelFuel for lorries, trains.Fuel andlubricatingoilFuel for the heating systems of large buildings, fuel for ships, lubricating oil.BitumenRoofing, and road surfaces.
26 Burning hydrocarbonsThe apparatus below is used to test the products of combustion of a hydrocarbon.Suctionpumpice-waterLime waterCandle wax is thehydrocarbon hereLiquid collectedcan be tested withanhydrous cobalt chloridepaper (bluepink).any hydrocarbon + oxygen water + carbon dioxide
27 Fractional distillation ContentsUseful OilCrude oilFractional distillationPhysical properties of fractionsUses of fractionsSummary activities
28 Glossarycombustion – A rapid reaction between a substance and oxygen that produces heat and light energy.crude oil – A naturally-occurring mixture of hydrocarbons and other substances.flammable – A substance that easily catches fire and burns rapidly.fractional distillation – The process used to separate crude oil into different fractions.hydrocarbon – A molecule containing only hydrogen and carbon.viscosity – A measure of how easily a liquid flows.