C09) Crude Oil and Fuels
Crude oil, hydrocarbons and alkanes
Carbon compounds as fuels and feedstock
Crude oil | A finite resource | Consisting mainly of plankton that was buried in the mud, crude oil is the remains of ancient biomass. |
Hydrocarbons | These make up the majority of the compounds in crude oil | Most of these hydrocarbons are called alkanes. |
General formula for alkanes | CnH2n+2 | For example: C2H6 C6H14 |
Carbon compounds as fuels and feedstock
Fractional distillation and petrochemicals
Properties of hydrocarbons
Cracking and alkenes
Display formula for first four alkanes
Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
Butane (C4H10)
Fractions | The hydrocarbons in crude oil can be split into fractions | Each fraction contains molecules with a similar number of carbon atoms in them. The process used to do this is called fractional distillation. |
Using fractions | Fractions can be processed to produce fuels and feedstock for petrochemical industry | We depend on many of these fuels; petrol, diesel and kerosene. Many useful materials are made by the petrochemical industry; solvents, lubricants and polymers. |
Boiling point (temperature at which liquid boils) | As the hydrocarbon chain length increases, boiling point increases. |
Viscosity (how easily it flows) | As the hydrocarbon chain length increases, viscosity increases. |
Flammability (how easily it burns) | As the hydrocarbon chain length increases, flammability decreases. |
Complete combustion of methane:
Methane + oxygen 🡪 carbon dioxide + water + energy
CH4 (g) + 2O2 (g) 🡪 CO2 (g) + 2 H2O (l)
Cracking | The breaking down of long chain hydrocarbons into smaller chains | The smaller chains are more useful. Cracking can be done by various methods including catalytic cracking and steam cracking. |
Catalytic cracking | The heavy fraction is heated until vaporised | After vaporisation, the vapour is passed over a hot catalyst forming smaller, more useful hydrocarbons. |
Steam cracking | The heavy fraction is heated until vaporised | After vaporisation, the vapour is mixed with steam and heated to a very high temperature forming smaller, more useful hydrocarbons. |
Alkanes to alkenes | Long chain alkanes are cracked into short chain alkenes. |
Alkenes | Alkenes are hydrocarbons with a double bond (some are formed during the cracking process). |
Properties of alkenes | Alkenes are more reactive that alkanes and react with bromine water. Bromine water changes from orange to colourless in the presence of alkenes. |
Decane 🡪 pentane + propene + ethane
C10H22 🡪 C5H12 + C3H6 + C2H4
Combustion | During the complete combustion of hydrocarbons, the carbon and hydrogen in the fuels are oxidised, releasing carbon dioxide, water and energy. |
Alkenes and uses as polymers | Used to produce polymers. They are also used as the starting materials of many other chemicals, such as alcohol, plastics and detergents. |
Why do we crack long chains? | Without cracking, many of the long hydrocarbons would be wasted as there is not much demand for these as for the shorter chains. |
Hydrocarbon chains | In oil | Hydrocarbon chains in crude oil come in lots of different lengths. |
Boiling points | The boiling point of the chain depends on its length. During fractional distillation, they boil and separate at different temperatures due to this. |