IGCSE Coordinated Science: Fuels Fuels Recall coal, natural gas and petroleum as fossil fuels that producecarbon dioxide on combustion. Fossil Fuels are: ● Petroleum ● Coal ● Natural Gas The reason these are called fossils are because they are the remains of plantsand animals that lived a few million years ago. ○ Petroleum: These are formed from the remains of dead organismsthat fell to the ocean ﬂoor and were then buried by the thicksediment. The high pressure in which the dead organisms areburied eventually converts the dead organisms into petroleum,but this is a process that takes millions of years. ○ Natural Gas: This is composed mainly of methaneand is often found with petroleum. Hightemperatures and pressure causes thecompounds to break down into gas. ○ Coal: This is the remain of lush vegetation thatgrew in ancient swamps. Over the millions ofyears, high pressure and heat eventuallyconverted the vegetation into coal. Understand the essential principle of fractional distillation in termsof differing boiling points (ranges) of fractions related to molecularsize and intermolecular attractiveforces.
● Petroleum is a mixture of hundreds and hundreds of differenthydrocarbons. ● Putting all these mixtures together isn’t really productive. ● In order to solve this problem, we have to reﬁne the petroleum in theprocess of Fractional Distillation. We will go into more detail about this in a second. However, in this point weonly need to acknowledge fractional distillation in terms of differing boilingpoints of fractions related to molecular size and attractive forces. Thecompounds with large molecules are likely to have a higher boiling point, sotherefore condense faster and are collected on a lower position in thefractionating column. Name methane as the main constituent of natural gas Natural gas is composed mostly out of methane. Describe petroleum as a mixture of hydrocarbons and its separationinto useful fractions by fractional distillation We already mentioned what fractional distillation is but now we’re going to godeeper in how a fractionating column works. The image below shows an apparatus that can be used for fractionaldistillation.
Steps involved: ● When you heat the petroleum, the compounds start to evaporate asparticles will more Kinetic Energy and therefore will more likely be ableto break bonds. The compounds which are smaller and lighter evaporateﬁrst as it takes less energy to evaporate these. ● The hot vapour rises and the vapour then condenses in the cool testtube. ● when the thermometer reaches 100 degrees, the ﬁrst test tube is thenreplaced with an empty one. The liquid in the ﬁrst test tube is the ﬁrstfraction from the distillation. ● Repeat, replacing the test tube at 150 degrees, 200 degrees, and 250degrees. However, industrially, the process is often done in a tower which has a very hot base, something like the one below.
Sorry I couldn’t get a more accurate diagram, but if you look in your textbook,you should be able to ﬁnd one, or simply google it. Here is what happens in the Fractionating Tower: ● Petroleum is pumped in at the base. ● The compounds start to evaporate. ● Those with the smallest molecules evaporate off ﬁrst, and rise to the topof the tower. ● Others rise only part of the way, this is entirely dependent on theirboiling points, and then condenses.
● The compounds are collected in their respective levels before theycondense. State the use of: ● Reﬁnery gas Used for bottled gas for heating and cooking, ● Gasoline fraction Used for fuel (petrol) in cars. ● Diesel oil/gas oil Used for fuel in diesel engines.