Organic Chemistry for IGCSE Chemistry

Crude Oil

Crude Oil ProcessingCrude Oil is a mixture of hydrocarbons. These are simple covalently bonded molecules, with weak intermolecular forces.Fractional distillation is used to separate crude oil into useful components (fractions). The more carbon atoms the molecule contains, the stronger the intermolecular forces and the higher its boiling point. The crude oil is heated to around 350°C in a furnace, and the compounds in the oil enter the bottom of the fractional distillation tower as a mixture of gases. They rise up the tower, and as they do so, they cool down. When a molecule reaches a temperature below its boiling point, it condenses, turns to a liquid and falls down the tower, to be collected in a series of trays. The compounds with a similar boiling point condense in the same area, and are removed as part of the same fraction. The compounds with the lowest boiling points reach the top of the tower without condensing, and are removed as part of the refinery gases section.There are many types of hydrocarbon – straight chain, branched chain, and ring molecules – but the carbon always forms four bonds, and the hydrogen one. Crude oil consists of mostly alkanes.

CrackingIf alkane vapour is passed over a heated catalyst, it thermally decomposes. The alkane is broken down into two smaller molecules, an alkane and an alkene, or an alkene and hydrogen. If an alkane and an alkene are produced, the alkene is usually smaller. The hydrogen can be burned as a fuel to power the refinery. The catalyst is a mixture of silicon dioxide and aluminium oxide, and this is done as 500 degrees centigrade. Cracking is very useful, as it breaks down the longer, less useful alkanes found in crude oil such as diesel and naptha into shorter alkanes like petrol, which is in high demand, and into alkenes, which are more reactive than alkanes, and are can be used to make plastics.

Polymerisation

AdditionAlkenes can add to other alkenes, and the monomers join to form polymers.

The chain above shows three repeat units, with one repeat unit being a length of polymer made from a single monomer.Polymers:Name Monomer Repeat Unit Notes, Uses, and

PropertiesPoly(ethene) Ethene Also called

polythene, and is used to make plastic bags, carrier bottles and packaging.

Poly(propene) Propene Commonly called polypropylene, it is used to make ropes, crates, and many other items.

Poly(chloroethene) Chloroethene Commonly called PVC, it is the strong

rigid material used to make doors, window frames and drainpipes.

Drawing PolymersTo draw a polymer, draw out a monomer so that the C=C bond is horizontal, and all the other groups are vertical. Then break the C=C double bond, and draw the new bonds at the side, then add the brackets.

To find the monomer from which a polymer is made, isolate two adjacent carbon atoms, and then replace the C=C double bond.

The name of a polymer is always poly followed by the name of monomer in brackets e.g. ethene goes to poly(ethene)

Condensation PolymerisationA condensation reaction can be used to join many monomers to form a polymer, and this reaction differs from addition reactions as different monomers are used. If one monomer contains an –OH group, and the other contains an –H, these combine to form water. The remainders of the monomers join to form the condensation polymer.

PolyamidesOne of the most important condensation polymers is nylon, which is used in ropes, carpets and clothing. Nylon is a polyamide, which is made from a carboxylic acid (-COOH) and an amine (-NH2). Each of the monomers is double ended, which lets them join together alternately by forming an amide link (-CONH-) to make the polymer. This can be seen below, with the central portion of the monomers being represented by a block:

PolyestersPolyesters are condensation polymers, which are like polyamides, but are formed from a carboxylic acid (-COOH), and an alcohol (-OH), and both monomers are double ended. This results in the formation of an ester link (-COO-), with water being produced as a side product.

Polyesters such as terylene are used to manufacture material for clothing.