3.2 Alkanes
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What is petroleum?
A mixture made up of alkane hydrocarbons.
How do you separate petroleum?
Fractional distillation.
Outline the steps of fractional distillation.
• Crude oil is vaporised. • It is passed into a fractioning column. • The mixture of hydrocarbons will condense at different fractions in the column, as it is cooler at the top and hotter at the bottom of the column. • Shorter hydrocarbon chains condense at the top, whereas longer ones condense at the bottom.
What is the order of hydrocarbons from shortest to longest in petroleum?
• Gases • Gasoline • Kerosene • Waxes • Fuel Oil • Bitumen
What is the cracking of alkanes?
When long-chain hydrocarbons are broken down into shorter chain hydrocarbons.
Why do we crack alkanes?
Shorter chain alkanes and alkenes are more useful than long-chain alkanes, so they are broken down for economic benefits.
What are the two methods of cracking?
• Catalytic cracking 2. Thermal cracking
What are the conditions of catalytic cracking?
• 720K lower temp. - Lower pressure (>1atm).
What is the yield of catalytic cracking?
• Aromatic compound - Cycloalkanes
Which catalysts are used in catalytic cracking?
Zeolites (silicon dioxide)
What are the features of zeolites?
• Big surface area • Acidic • Honeycomb structure
What are the conditions of thermal cracking?
• A high temp (1200K) - A high pressure (7000kPa)
What is the yield of thermal cracking?
• High % of alkanes - Produces some alkenes
What is formed by the complete combustion of alkanes?
Carbon dioxide & water
What is formed by the incomplete combustion of alkanes?
• Carbon monoxide & water 2. Carbon particulates & water
What do catalytic converters do?
Reduce the release of pollutants from internal combustion engines in cars.
How do catalytic converters work?
The pollutants are passed over a catalyst and react together to make less harmful gases that are then released.
Which catalysts are used in catalytic conversion?
Platinum or Rhodium metal
How does carbon monoxide react with NO in catalytic conversion? (equation)
2CO + 2NO ⇌ N₂ + 2CO₂ Makes carbon dioxide.
What are some examples of pollutants? (4)
• CO, poisonous gases. • NOˣ, contributes to acid rain. • SO₂, contributes to acid rain. • CO₂, a greenhouse gas.
What are flue gases?
Gases are produced after fossil fuels and crude oils are burned, containing sulfur.
Why do you need to remove sulfur from flue gases?
The sulfur released in the flue gases produces sulfur dioxide, which leads to acid rain.
What is flue gas desulfurisation?
The removal of sulfur dioxide from flue gases.
What is used to facilitate flue gas desulfurisation?
CaO & H₂O