Crude oil is a mixture of hydrocarbons.
- A mixture consists of two (or more) elements or compounds that are not chemically bonded to each other.
- Hydrocarbons are basically fuels such as petrol and diesel. They're made of just carbon and hydrogen. They are not chemicallly bonded to one another.
- This means that they all keep their original properties, such as condensing points.
- The parts of the mixture can be seperated out by physical methods - crude oil can be split up into its seperate fractions by fractional distillation. Each molecule contains molecules with a similar number of carbon atoms to each other.
Fractional Distillation- Process
- Crude oil is heated. It evaporates.
- Fractions rise up the column.
- Each fraction cools and condenses at different temperatures.
- The different fractions are collected through pipes.
Crude Oil is mostly Alkanes
- All the fractions of crude oil are hydrocarbons called alkanes.
- Alkanes are made up of chains of carbon atoms surrounded by hydrogen atoms.
- Different alkanes have chains of different lengths.
- The first four alkanes are: Methane, Ethane, Propane, Butane (Monkey's eat peanut butter)
- Carbon atoms form four bondsand hydrogen atoms only form one bond.
- If a atom has formed bonds with as many other atoms as it can it is saturated.
- Alkanes have a general formula CnH2n+2
- The shorter the molecules, the more runny the hydrocarbon is- less viscous
- The shorter the molecules, the more volatile they are - turn into a gas at a lower temperature. So the shorter the molecules, the lower the temperature at which that fraction vaporises or condenses- and the lower its boiling point.
- Also, the shorter the molecules, the more flammable (easier to ignite) the hydrocarbon is.
The Uses of Hydrocarbons
- The volatility helps decide what the fraction is used for. The refinery gas fraction has the shortest molecules, so it has the lowest boiling point- this makes it ideal for using as bottled gas. It is stored under pressure as liquid. When the tap on the bottle is opened, the fuel vaporises and flows to the burner where it is ignited.
- The petrol fraction has longer molecules, so it has a higher boiling point. Petrol is a liquid which is ideal for storing in the fuel tank of a car. It can flow to the engine where it is easily vaporised to mix with the air before it is ignited.
- The viscosity also helps decide how the hydrocarbons are used. The really gloopy, viscous hydrocarbons are used for lubricating engine parts and for covering roads.
Using crude oil as a fuel
Crude Oil fractions burn cleanly so they make good fuels.
- Most modern transport is fuelled by crude oil fraction, e.g, cars, boats, trains and planes.
- Parts of crude oil is burned in central heating systems in homes and power stations to generate electricity.
- Crude oil also provides the raw materials for making various chemicals, including plastics.
- Alternatives to using crude oil fractions as fuel are possible. Electricity can be generated by nuclear power, wind power, and ethanol can power cars.
- Things are set up for using oil fractions. For example, cars are designed for petrol or diesel and it's readily available, There are filling stations all over the country, with storage facilities and pumps specifically designed for these crude oil fractions. So crude oil fractions are often easiest and cheapest thing to use.
- Crude oil fractions are more reliable too. Solar and wind power won't work withought the right weather conditions.
Crude oil may run out
- Most scientists think that oil will run out- it is a non-renewable fuel
- New oil reserves are discovered from time to time and technology is constantly improving, so it is now possible to extract oil that was once too difficult or expensive to extract.
- Some people think we should immediately stop using oil for things like transport, for which there are altrernatives, and keep it for things that is essential for, e.g chemicals and medicenes.
- It will take time to develop alternative fuels that will satisfy all our energy needs. It'll also take time to adapt things so that the fuels can be used on a wide scale.
- One alternative is to generate energy from renewable sources- these sources will not run out.
- It is a good idea to start conserving crude oil and finding alternatives now.
- Oil spills can happen as the oil is being transported by tanker. Birds get covered in oil and are poisoned as they try to clean themselves.
- You have to burn oil to release the energy from it. But burning it is thought to be a major cause of global warming, acid rain and global dimming.
Release of Gases and Particles
- Power stations burn huge amounts of fossil fuels to make electricity.
- Most fuels, such as crude oil and coal, contain carbon and hydrogen. During combustion, the carbon and hydrogen are oxidised so that carbon dioxide and water vapour are released into the atmosphere. Hydrocarbon +oxygen -----> carbon dioxide + water vapour
- If the fuel contains sulfur impurities, the sulfur will be released as sulfur dioxide when the fuelis burnt.
- Oxides of nitogen will also form if the fuel burns at a high temperature.
- When they're plenty of oxygen, all the fuel burns- this is called complete combustion.
- If there's not enough oxygen, some of the fuel doesn't burn - this is called partial combustion. Under these conditions, solid particles (called particulates) of soot (carbon) and unburnt fuel are release. Carbon Monoxide is also released.
- Sulfur dioxide is one of the gases that causes acid rain.
- When the sulfur dioxide mixes with the clouds it forms dilute sulfuric acid. This then falls as acid rain.
- In the same way, oxides of nitrogen cause acid rain by forming dilute nitric acid in clouds.
- Acid rain causes lakes to become acidic and many plants and animals die as a result.
- Acid rain kills trees and damages limestone buildings and ruins stone statue.
- Links between acid rain and human health problems have been suggested.
- International agreements have been put in place to reduce emissions of air pollutants such as sulfur dioxide.
Reducing sulfur emissions
- Most of the sulfur can be removed from fuels before they're burnt, but it costs more to do it.
- Removinf sulfur from fuels takes more energy. This usually comes from burning more fuel, which releases more of the greenhouse gas carbon dioxide.
- Petrol and Diesel are starting to be replaced by low-sulfur versions.
- Power stations now have Acid Gas Scrubber to take the harmful gases out before they release their fumes into the atmosphere.
- The other way of reducing acid rain is simply to reduce our usage of fossil fuels.
- The level of carbon dioxide in the atmosphere is increasing because of the large amounts of fossil fuels humans burn.
- There's a scientific consensus that the extra carbon dioxide has caused the average temperature of the earth to increase- global warming
- Global warming is a type of climate change and causes other types of cimate change e.g changing rainfall patterns
- Scientists have founs that in some areas nearly 25% less sunlight has been reaching the surface.
- They think that it is caused by particles of soot and ash that are produced when fossil fuels are burnt. These particles reflect sunlight back into space, or they can help to produce more clouds that reflect sunlight back into space.
ETHANOL- Can be produced from plant materal so is lnown as a biofuel. It's made by fermentation of plants and is used to power cars in some places. It's often mixed with petrol to make a better fuel.
pros- The CO2 released when it;s burnt was taken in by the plant as it gre, so it's carbon neutral. cons-Engines need to be converted before they'll work with ethanol fuels. And ethanol fuel isn't widely avaliable. There are worries that farmers will switch from growing food crops to make ethanol- which will increase food prices.
BIODIESEL- It can be produced from vegetable oils such as rapeseed oil and soybean oil. Biodiesel can be mixed with ordinary fuel and used to run a diesel engine.
pros- Biodiesel is carbon neutral. Engines do not need to be converted. It produces much less sulfr dioxide and particulates than ordinary diesel and petrol. cons- We cannot make enough to completely replace diesel. It is expensive to make
HYDROGEN GAS- Can also be used to power vehicles. You get the hydrogen from the electrolysis of water. This energy can come from a renewable source, e.g. solar.
pros- Hydrogen combines with oxygen in the air to form just water - so it is very clean. cons- You need a special, expensive engine and hydrogen is not widely available. You still need to use energy from another source to make it. It is hard to store.