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Petroleum chemistry

Hydrocarbons as a source of energy

Hydrocarbons are energy-rich because of their high carbon content. They are burned in oxygen (combustion) to release their energy.

Crude oil, or petroleum, is the main source of liquid hydrocarbons. Crude oil is a mixture of various hydrocarbons, which can be separated via fractional distillation.

These components have distinct uses, from providing energy for cooking to lubricating machine parts.

Extraction of crude oil from deep oil wells is aided by large machines known as pumpjacks.

Natural gas mainly contains methane, which is the smallest hydrocarbon.

Crude oil and natural gas formed over the course of millions of years from decomposed plants and animals buried underground.

Oil, natural gas and coal (which consists of carbon and various other elements) are fossil fuels.

Fractional distillation

Fractional distillation is a physical process used to separate the mixture of hydrocarbons in crude oil. The method relies on the differences in boiling points among different hydrocarbons.

The crude oil is heated until all components of the crude oil turn gaseous. The gas is then piped into the bottom of a tall column that gets cooler with height.

Smaller molecules have lower boiling points and so condense at lower temperatures. As a result, they are collected in liquid form higher up in the column than the larger molecules.

Products of fractional distillation of crude oil

The substances separated by the fractional distillation column are called fractions.

Important fractions and their uses are shown in the table below.

Fraction Use Boiling Point $(^{\circ}\text{C})$
Petrol/gasoline Fuel for petrol engines in cars 30-60
Naphtha Industrial use, chemical feedstock 60-180
Paraffin/kerosene Aviation fuel, cooking and heating 180-220
Diesel Fuel for diesel engines (e.g. cars, trucks and ships) 220 - 300
Lubricating Oil Lubricant, polishes 300-340

The fractions at the bottom (with the highest boiling points) have the lowest economic value.

For instance, bitumen (or asphalt) can only be used as road tar.

Cracking, the process of breaking down hydrocarbons, is used to obtain a greater amount of more valuable smaller hydrocarbons.

Crude oil use and social issues

Crude oil is a finite resource. It was slowly created over millions of years but is now rapidly being used.

Global oil reserves will eventually run out but the timing is highly uncertain.

New oil deposits are still being discovered. Technological improvements allow for the access of oil deposits that were previously too costly to exploit.

Supply stability is another concern. Most oil reserves are concentrated in a small number of countries. Many of these, particularly in the Middle East, are politically unstable.

Biofuels are an alternative to crude oil but they also have disadvantages.

Most biofuels are produced from plants grown on farm land. Producing more biofuel reduces the land available for food production.

Corn is one of the crops used to produce biofuel..