Chemistry-Crude oil and fuels

Fuels from crude oil

• Crude oil is a mixture of many different compounds
• Distillation can be used to separate mixtures of liquids
• Most of the compounds in crude oil are hydrocarbons-they contain only hydrogen and carbon
• Alkanes are saturated hydrocarbon. They contain as many hydrogen atoms as possible in their molecules
• A molecular formula shows the number of each type of atom in each molecule, e.g. C2H6 represents a molecule of ethane. We can also represent molecules by a displayed formula that shows how the atoms are bonded together
• H     H

H---C---C---H         Ethane

     H   H

Fractional distillation

• Crude oil is separated into fractions using fractional distillation
• The properties of each fraction depend on the size of the hydrocarbon molecules
• Fractions with lower boiling points are less viscous and burn more easily
• The crude oil is vaporised and fed into a fractionating column. This is a tall tower that is hot at the bottom and gets cooler going up the column
• Inside the colum there are many trays with holes to allow gases through. The vapours move up the column getting cooler as they go up. The hydrocarbons condense to liquids when they reach the level that is at their boiling point. Different liquids collect on the trays at different levels and there are outlets to collect the fractions 
• Hydrocarbons wih the smallest molecule have the lowest boiling points and so are collected at the top of the column. The fractions collected at the bottom of the column contain hyrdrocarbons with the highest boiling points
• Fractions with low boiling ranges have low viscosity so they are runny liquids., They are very flammable so they ignite easily. They also burn with clean flames, producing little smoke. This makes them very useful as fuels

Burning fuels

• Burning hydorcarbons in plenty of air produces carbon dioxide and water
• Burning hydrocarbons in a limited supply of air may produce carbon monoxide and solid particles
• Any sulfur compounds in the fuel burn to produce sulfur dioxide
• Oxide of nitrogen can be formed when fuels burn under extreme conditions 

Cleaner fuels

• Many scientists believe that carbon dioxide from burning fuels causes global warming
• Sulfur dioxide and nitrogen oxides cause acid rain
• Particulates cause global dimming
• Pollutants can be removed from waste gases after the fuel is burned
• Sulfur can be removed from fuels before they are burned so less sulfer dioxide is given off

Alternative fuels

• Biodiesel can be made from vegetable oils
• Biofuels are a renewable source of energy that could be used instead of fossil fuels
• There are advantages and disadvantages of using biodiesal
• Ethanol made from sugar is a biofuel
• Hydrogen is a potential fuel for the future