Fractional distillation of crude oil Industrial cracking and catalytic cracking By Craig Wilson

What is fractional distillation? Fractional distillation is the separation of a material into its separate fractions. The main use of this is in the distillation of crude oil into various substances such as petrol and diesel.

What are the products? The products of crude oil (and their boiling points) are as follows: Gases(310 degrees) Petrol ( ) Naphtha ( ) Kerosene ( ) Gas oil ( ) Fuel oil and wax (above 620)

Uses of the products Petrol- fuel for cars Gases- keeping houses warm Naphtha- making plastics Kerosene- aeroplane fuel

Industrial cracking This is when longer chain fractions of crude oil are broken down into more useful, shorter fractions. This has 2 useful results: Shorter, more useful, chains are produced, especially petrol. Some of the products are alkenes, which are more reactive than alkanes.

Uses of industrial cracking The alkenes which are created are used as chemical feedstock. This means they supply industry with starting materials to make other useful materials. They are also made into other compounds such as polymers, paint and drugs. The most important of the alkenes is ethene which is the starting material for polythene and a wide range of other everyday materials.

Cracking alkanes As alkanes are very unreactive, harsh conditions are needed to break them down. There are 2 main ways of doing this thermal and catalytic.

Thermal cracking This reaction involves heating alkanes to K and 7000kPa. This breaks carbon-carbon double bonds so that one electron from each pair goes to each carbon atom. These are called free radicals. Free radicals are highly reactive intermediates and they react to form a variety of short chain molecules.

Catalytic cracking This takes place at about 720K and a slightly lower pressure than thermal cracking and uses a zeolite catalyst, which consists of silicon dioxide and aluminium oxide. This type of cracking is used mainly to make motor fuels. In this type of cracking the products are separated using fractional distillation.