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Uses of the components of crude oil as fuels

Refinery gas:

1-2% of crude oil C1 C4 length carbon chain Mainly used as a gaseous fuel or it can be liquefied under pressure to produce liquefied

petroleum gas (LPG).

Gasoline & naphtha:

15 30% of crude oil It is distilled off and used as motor fuel for internal combustion engines.

Kerosene:

10 15% of crude oil Is used as jet fuel as well as for domestic heating Can be broken down to produce gasoline

Gas oil:

15 10% of crude oil Used as fuel in diesel engines and industrial furnaces

Residue:

40 50% or crude oil Used as fuel for ships and power stations.

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Fractional distillation:

The way the distillation works is by becoming progressively cooler from the base to thetop. All the hydrocarbon fractions start off in gas form, as they have been heated to that

point. The gases then rise up the tower.

The gas mixture then encounters a barrier through which there are only openings called bubble

caps. The gas mixture is then forced to go through a liquid before

continuing upwards. The liquid in the first tray is at a cool enough

temperature to get the heaviest gas fractions to condense into

liquid form, while the lighter fractions stay gaseous.

In this way the heaviest hydrocarbon fractions are separated out from the mixed gas.The remaining gas continues its journey up the tower until it reaches another barrier.

Here the bubble cap process is repeated but at a lower temperature than before, which

then filters out the next lightest set of fractions.

This process continues until only the very lightest fractions, those of 1-4 carbon atoms,are left. These stay in gas form and are collected at the top of the tower.

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Some fractions are in heavier demand than other, for example the fractions diesel andpetrol are required in extremely large amounts while the heavier fraction are not in such

high demand. A process called cracking is then used to fragment the large molecules

into smaller molecules (forming even more diesel and petrol fractions).

Catalytic cracking:

Catalytic cracking involves the use of a catalyst at lower temperatures to break thebonds on the hydrocarbon molecules.

Catalytic cracking is used to crack the distilled fractions such as diesel oil and keroseneinto

The reaction is usually catalysed by a powdered mixture of alumina and silica(Al2O3/SiO2) at about 500oC.

The C-C bond undergoes hererolytic fission which results in a mechanism involvingcarbocations.

This tends to produce large amounts of branched chain alkanes which are useful asgasoline.

Branched chain alkanes give gasoline a higher octane number.

Reforming:

Reforming is a process which converts straight chain hyrocarbons into aromatic andmore highly brancged hydrocarbons.

This process converts low value naphtha fractions into high greade gaselinecomponents.

Higher grade gasoline contains a higher proportion of branched alkanes and aromatichydrocarbons.

The gasoline produced then undergoes reforming techniques to improve its octanerating. Iso-octane or 2,2,4-trimethylpentane is the standard used to determine octanerating i.e. octane is reformed into 2,2,4-trimethylpentane. In the final stages blending

of fuels with different octane ratings occurs to produce the retail gasoline for selling to

customers to meet certain specifications.

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Refineries also produce pure chemicals, called feedstocks, from crude oil. These feedstocks are

sold to the petrochemical industries, where a great variety of products are made.

Feedstock Products

Methane (Natural Gas) Fertilizers Polyethylene

Ethylene Plastics Explosives

Propylene Rayon Synthetic Rubber

Butylene Vinyl Polystyrene

Naphthene Nylon Dyes

Dacron Drugs

Teflon Antifreeze

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Past paper question I found online:

The other past paper questions are : 2007 U2 P2 #8, 2006 U2 P2 #9, 2004 U2 P2 #9

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