Crude oil and fractional distillation

What do I need to know? Must Recall that crude oil is a mixture of a large number of compounds Should Define the term hydrocarbon Could Explain how the compounds in crude oil can be separated using physical methods including fractional distillation

Crude oil Crude oil is a mixture of a very large number of compounds and is made from the the bodies of plants and animals that have decayed many millions of years ago. A mixture is two or more substances NOT chemically combined together (such as a mixture of sand and water that can be separated by filtration).

Hydrocarbons Most of the compounds in crude oil consist of molecules made up of hydrogen and carbon atoms only. We call these HYDROCARBONS We can separate the different unchanged hydrocarbons from crude oil by FRACTIONAL DISTILLATION.

Fractional distillation Fractional distillation separates a mixture into a number of different parts, called fractions. A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top. Fractional distillation works because the different substances in the mixture have different boiling points.

Key points for exam questions To explain fractional distillation [3 marks] Heat crude oil to make it a gas/vapour Cool to condense Hydrocarbons condense at different temperatures (boiling points).

Different hydrocarbon – different BP Different hydrocarbons have different numbers of carbon atoms. The higher the number of carbon atoms the higher its boiling point.

Key points for exam questions A fraction is a set of hydrocarbon molecules of similar size and similar boiling points Different fractions have different uses. Lighter fractions are more useful as fuels than heavier fractions. The petrol fraction and diesel fraction are key fractions for the oil industry.

C1.4 Crude oil Alkanes

Objectives Must Recall that most of the compounds in crude oil consist of hydrocarbons called alkanes. Should Describe the general formula of an alkane and draw the structure. Could Explain the naming of alkanes up to a chain length of four carbon atoms.

Carbon chains Alkanes are chains of carbon atoms with hydrogen atoms attached to them. There is an alkane with one carbon atom, two carbon atoms, three, four, five and so on. The chains can be massive with hundreds of carbon atoms. You need be able to name and draw the first four and recognise some larger ones.

Methane One carbon atom bonded to four hydrogen atoms. Each line represents a single covalent bond.

Two carbon atoms six hydrogen atoms Ethane Two carbon atoms six hydrogen atoms

Three carbon atoms eight hydrogen atoms Propane Three carbon atoms eight hydrogen atoms

Four carbon atoms ten hydrogen atoms Butane Four carbon atoms ten hydrogen atoms

CnH2n+2 Can you spot a pattern? Every time we increase the number of carbons what happens to the number of hydrogens? We can work out a general formula for any alkane it is: CnH2n+2 where n is the number of carbon atoms and 2n+2 is the number of hydrogen atoms

Counting in chemistry Rather than the numbers 1,2,3 and 4 when we are counting in chemistry we use the terms: meth_ = 1 eth_ = 2 prop_ = 3 but_ = 4 The first four alkanes are therefore called methane, ethane, propane and butane.

Properties of hydrocarbons C1.4 Crude Oil Properties of hydrocarbons

What do I need to know? Must recall the term alkane and the names for the first four alkanes in the series. State that these substances are commonly used as fuels. Should describe the difference between a saturated and an unsaturated hydrocarbon Could explain the boiling points, flammability and viscosity of hydrocarbon fuels.

Saturated and unsaturated Ethane Ethene All single bonds Full of hydrogen Saturated Has double bond Fewer hydrogens Unsaturated

Liquid/Gas For this list of substance state whether liquid or gas at room temperature? The temperature when something boils is also the temperature when it condenses eg water boils at 100°C it also condenses at 100°C Hydrocarbon Boiling point in °C Solid/Liquid/Gas methane, CH4 -162 butane, C4H10 pentane, C5H12 +36 decane, C10H22 +175

Viscosity This simply means thickness of solution. For example water has a lower viscosity than treacle Generally the higher the molecular weight (longer carbon chain) the more viscous the substance is. Bitumen has very long chain molecules and is very viscous and stick (tar).

Boiling points

C1.4 Crude oil Burning fuels

Objectives Recall that most fuels contain carbon and/or hydrogen and may contain sulfur. Describe how, when a fuel burns gases are released into the atmosphere. Explain how the combustion of a fuel releases energy.

Hydrocarbon fuels We burn hydrocarbon fuels to release energy. Methane Propane Butane Petrol Diesel Kerosene Fuel oil + many more

Combustion Complete combustion occurs when there is enough oxygen – for example when the hole is open on a Bunsen burner. The products of complete combustion are carbon dioxide and water. CH4 + 2O2  CO2 + 2H2O

Test your understanding

Incomplete combustion Incomplete combustion occurs when there is not enough oxygen – for example when the hole is closed on a Bunsen burner. The products of incomplete combustion include carbon monoxide and carbon (soot). It is often called a sooty flame.

AfL – incomplete combustion

Carbon dioxide Carbon dioxide is a greenhouse gas. This means it causes global warming by trapping heat from the sun within the Earth’s atmosphere.

Carbon monoxide Carbon monoxide is an odourless and tasteless poisonous gas. If produced in an enclosed space it can be deadly.

Soot/smoke particles Particles of carbon from incomplete combustion can be released into the atmosphere. This contributes to GLOBAL DIMMING

Other pollutants Sulphur present in fuels burns to produce sulphur dioxide. At high temperatures oxides of nitrogen may also be formed from nitrogen in the atmosphere. These react with water in the atmosphere to form ACID RAIN

Cleaning up Undesirable combustion products can be cleaned from emissions before they leave the chimney by using a filter or catalytic converter (cars).

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C1.4 Crude Oil Biofuels

What do I need to know? Recall that biofuels are produced from plant material Describe the fuels that can be produced from plant material Evaluate the advantages and disadvantages of making fuel from renewable sources.

The problem with crude Crude oil is a limited resource that will eventually run out. Alternatives are needed and some are already under development.

Ethical and environmental issues Clearance of rainforests to plant fuel crops Using land formerly used for food crop (causing hardship) Not replacing crops with sufficient crops after harvest for the process to remain carbon neutral Erosion – replacing trees with crops with shallow roots

Carbon neutral – bioethanol, biodiesel and biomass Plants photosynthesise using carbon (dioxide) from the air Biodiesel/biothanol releases carbon (dioxide) from plants Plants are replanted and photosynthesise, removing the carbon (dioxide) again. By contrast (fossil) diesel from crude oil releases ‘locked up’ carbon (dioxide) and doesn’t absorb any CO2

Different types of biofuels Ethanol – produced by fermentation of sugars in sugarcane rather than from aalkanes. Biodiesel – produced from hydrolysis of vegetable oils

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