Chemistry - Fuels from Oils

This is for an AQA GCSE paper and has five sub - sub topics which are:

Alkanes          Separating Crude Oil          Burning Fuels          Promblem Fuels          Better Fuels

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Crude oil is a fossil fuel. They form from an ancient single-clled plant or animal that live in the sea. When they died they sank and were buried in sediment. The deeper they were the more compressed and heated converting the remains into oil.

Crude oil is a mixture of componds which are mostly hydrocarbons, most of these are alkanes.

The bonds in an alkane are covelant, hydrogen can only have one bond but carbon have four. Alkanes are saturated meaning the are made up of single bonds.

Alkanes are full, so have no spare bonds and are a homoglobus series meaning they have a general formula which is CnH2n+2.

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Separating Crude Oil - Fractional Distillation

A mixture consists of two or more elements or compounds not chemically bonded. The chemical properties in a substance are unchanged so can be separated by filtration or distillation.

Fractional distillation is used to separate a liquid from a mixture of liquids by heating up the mixture, the liquid with the lowest boiling point will evaporate the liquid and then condense it through a condensing tube.

Crude oil is heated strongly to evaporate it. The vapours are led up a fractionating column which is hottest at the bottom and coldest at the top. The hydrocarbons with the highest boiling point will condense at the bottom and flow off as a liquid.

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Separating Crude Oil - Properties and Uses

A long alkane will:

1. Condense at the bottom of a fractionating column.          2. Have a higher boiling point.          3. Have higher viscosity.          4. Have lower flammability.          5.Have lower volatility. 

An alkane with a melting point of:

350+ will be used as bitumen          300-350 will be used as lubricating oil       250-300 will be used for fuel oil          220-250 will be used for diesel          180-220 will be used for paraffin            60-180 will be used for naphtha           25-60 will be used for petrol           -25 will be used for liquefied petroleum gas    

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Burning Fuels

Fuels can be used as a store of energy. An example of this is coal which is made of of mostly carbon. When there is complete combustion, the product of coal being burned are, CO2.

However when there is incomplete combustion the product can be CO, which is a toxic gas that attaches to your haemoglobin reducing space for oxygen.

The burning of alkanes can have the same products but with water vapour.

Particulates are solid particles of unburned fuels, soot. High levels of particulates can lead to early deaths and extra cases of respiratory diseases.

When sulphur is burned it can also form sulphur dioxide. This is acidic and can cause acid rain.

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Problem Fuels

Sunlight that reaches the Earth's surface is emitted as infrared radiation. Greenhouse gases absorb this energy and trapping it in our atmosphere, without these gases the earth would be much colder.

Carbon dioxide is  emitted through the combustion of fuels and the concentration of it in our atmosphere has increase by 22%. This has caused global warming.

Global dimming occurs when solid particles are released from fuels. These particles reflect the sunlight back into space and water vapour condenses around them making more reflective clouds. Global dimming has decreased global warming but has also caused droughts.

Sulphuric acid is produced when fuels burn and causes acid rain. Acid rain can kill or harm plants and animals or destroy rocks.

Sulphuric acid can react with calcium carbonate to produce a less harmful product, calcium sulphate

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Better Fuels

We are running out of fuels rapidly and our only supply are in unconventional places. Crude oil, coal and natural gases are not renewable sources.

Ethanol is used in alcohol and antiseptics and formed through fermentation which uses renewable resources, crops. Modern vehicles can run with 5% ethanol and 95% petrol.

The burning of ethanol produce water vapour and carbon dioxide, if there is complete combustion. A proportion of carbon dioxide released is balanced by the carbon dioxide taken in by plants. However, these plant could be used to feed people, other than used for fuelling cars.

Hydrogen gas can be formed by performing electrolysis on water. Hydrogen is a renewable source for electricity and when burnt, produces water vapour which does not cause pollution problems.This is a promising method as the electricity power electric motors.

But the hydrogen is explosive and usually stored as a liquid at high temperature and low pressure which is expensive.

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