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C9- Crude Oils and Fuels - Coggle Diagram
C9- Crude Oils and Fuels
Crude Oil:
A finite rescource found in rocks. Fossils of tiny sea animals and plants, layer upon layer of rock is on top. Makes the conditions (high pressuree and temperature, in the absence of oxygen) to make crude oil.
A mixture of many different carbon compounds. Nearly all of the compounds in crude oil are compounds containing only Hydrogen and Carbon atoms. Called hydrocarbons.
There are too many substances in crude oil, they all have differnet boiling points. Before it can be used, it must be seperated into different substances with similiar boiling points (known as fractions). As properties of substances do not change when they are mixed, substances cna be seperated by distillation. It seperates liquids wit different boiling points.
Alkanes:
Most of the hydrocarbons in crude oil are alkanes.Alkanes are saturated hydrocarbons. These means that all the carbon-carbon bonds are single covalent bonds. This means that they contain as many hydrogen atoms as possible in each molecule. No more can be added.
The first four are: CH4 (Methane), C2H6 (Ethane), C3H8 ( Propane), C4 H10 (Butane).
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Fractional distillation:
This proicess works becuase each hydrocarbon fraction contains molecules with similiar numbers of carbona toms. Each of these fractions boils at a different temperature range becuase of the different sizes of molecules.
Crude oil is heated and fed in near the bottom of a fractionating column as hot vapor. The column is kept very hot at the bottom and much cooler at the top, so the temperature decreases going up the column. The gases move up the column and hydrocarbons condense when they reach the temperature of their different boiling points. The different fractions are collected as liquids at different levels. Hydrocarbons with the smallest molecules have the lowest boiling points. They are piped out of the cooler top of the column as gases. At the bottom of the column, the fractions have high boiling points. They cool to form very thick liquids or solids at room temperature.
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Cracking hydrocarbons:
Why crack hydrocarbons?
Some of the heavier fractions from fractional distillation crude oils sre not in high demand. The hydrocarbons in them are made up of large molecules. They are thick liquids or solids with high boiling points. They are difficult to burn and do not vaporise eaily, so they are bad fuels. The larger less useful hydrocarbon molecules cna be broken down into more useful ones in cracking.
How does it work?
The process take splace at an oil refinery in steel vessels called crackers. In the cracker, a heavy fraction distilled from crude oil is heated to vaporise the hydrocarbons. The vapour is then either:
Passed over a hot catalyst, or
mixed with steam and heated to a very high temperature.
Alkenes:
The different ending tells us that these moolecules are unsaturated. This means they contain at least one double bond between carbona toms. Carbon atoms form four covalent bonds, this means that he unsaturatedd alkene molecules have two fewer hydrogen atoms in their molecules.
Alkenes burn in air.
They react with bromine waster, which is orange in colour, decolouring it.
A positive test for an unsaturated hydrocarbon is that it turns orange bromine water colourless.