Fuels from crude oil
· Crude Oil is a mixture of many different compounds.
· A mixture contains two or more elements or compounds that are not chemically bonded together.
· Crude oil straight out of the ground is not much use. It has too many substances in it, with all different boiling points.
· We use distillation to separate the mixtures in crude oil.
· Crude oil mainly contains carbon and hydrogen. These are known as hydrocarbons. Most hydrocarbons in crude oil are alkanes.
· Formula = CnH2n+2
· We describe alkanes as being saturated hydrocarbons. This means they contain as many hydrogen atoms as possible in each molecule. We cannot add anymore.
· The smaller a hydrocarbon the more useful it is.
· The smaller chain of hydrocarbon has a lower boiling point.
· The smaller chain of hydrocarbon is more runny. It isn’t as viscous as the longer chains of hydrocarbon.
· The smaller chain of hydrocarbon is more flammable.
· At room temperature, small hydrocarbons are gases, the ones in with between five or twelve carbon atoms are liquids, and large hydrocarbons are solids.
· We separate crude oil into fractions using fractional distillation.
· It is fed into a tall tower (fractionating tower) as hot vapour. The tower is kept very hot at the bottom and much cooler at the top, so the temperature decreases going up the column. The gases in the column condense when they reach their boiling points, and the different fractions are collected at different levels.
Burning fuels and Cleaner fuel
· When fuels burn they all produce carbon dioxide and water. Carbon dioxide is a greenhouse gas and it causes global warming. As well as producing these hydrocarbons they produce other substances as well. These include Sulfur Dioxide, Nitrous Oxide, Carbon Dioxide and Carbon Monoxide.
· Sulfur dioxide is the substance that has caused us major problems. This is because this gas is poisonous and it causes acidic rain.
· Sulfur dioxide can also cause engine corrosion.
· Changing the conditions in which we burn fuels may change the products that are made. For example when a car engine does not have enough oxygen to burn the fuel we get incomplete combustion. Instead of all the carbon in the fuel turning to carbon dioxide we get carbon monoxide as well.
· Carbon monoxide is a poisonous gas which is bad for your health. It is bad for you because it replaces the oxygen in your blood.
· Also high temperatures in a car engine make nitrogen and oxygen to react together. This makes nitrogen oxides which are also poisonous and can trigger a person’s asthma to start. It also makes acid rain.
· Burning fuels in cars also produces pollutants These are tiny particles made up of unburnt hydrocarbons, which scientists believe are very harmful to little children. Particulates also cause global dimming.
· As well as any global warming we get global dimming. This is when the amount of light reaching the earth’s surface decreases.
· We can reduce the effects of burning fossils fuels in several ways. For example cars are fitted with catalytic converters. Catalytic converters reduce the gases that a car gives out and changes them into gases that are less harmful to the environment.
· Another example is in power stations sulfur dioxide is removed from the flue gases by reacting it with quicklime. This is called flue gas desulfurisation or FGD for short.