18 — fuels and crude oil Flashcards
Natural gas
A gaseous fossil fuel consisting mainly of methane. Natural gas is colourless and odourless.
Crude oil
Crude oil, or petroleum, is a finite and non-renewable resource that contains a mixture of hydrocarbons which have a range of boiling points. Separation of crude oil into useful fractions are done through fractional distillation. There are competing uses for crude oil such as the use as fuel to generate heat and electricity, chemical feedstock for the manufacture of petrochemicals and plastics.
Explain why larger hydrocarbons have higher boiling points
Hydrocarbons that contain more carbon atoms have higher boiling points as the molecule size is bigger so they have stronger intermolecular forces of attraction, and hence more energy is required to overcome the stronger intermolecular forces of attraction. Hydrocarbons w lower boiling points r less viscous and burn more easily.
Fractions of crude oil
- Petroleum gas | fuel for cooking + heating
- Petrol (gasoline) | fuel for car engines in vehicles
- Naphtha | feedstock (raw material) for the petrochemical industry
- Paraffin (kerosene) | fuel for aircraft engines, cooking n heating
- Diesel oil | fuel for diesel engines in buses, lorries and trains
- Lubricating oil | for lubricating machines, making waxes and polishes
- Bitumen | for paving road surfaces; for roofing
Issues due to competing uses of crude oil
- crude oil acts as a fuel that generates heat and electricity
- crude oil fractions r impt as a chemical feedstock for the manufacture of daily products thus is a waste to burn crude oil away
- conservation of crude oil to ensure continuous supply of crude oil
Ways to conserve crude oil
- Reduce the use of crude oil
- Use alternative energy sources (biofuels, solar and nuclear energy)
- Improve the design of power stations and vehicles to use crude oil more efficiently
Biofuels
Eg ethanol obtained from fermentation of sugar in sugar cane plants
Ethanol is burnt in excess oxygen, CO2 and H2O formed.
C2H5OH + 3O2 -> 2CO2 + 3H2O
— Sugarcane plant takes in CO2 during photosynthesis as it grows, which offsets the CO2 produced when bio ethanol is burnt during combustion. Hence, there is no net change in the amount of CO2 in the atmosphere.
Other examples:
1. Biodiesel from vegetable oils and liquid animal fats
2. Green diesel from algae and other plant sources
3. Biogas from methane in decomposed organic waste
Explain why cracking of naptha is an important process in an oil refinery. [2]
Cracking breaks down larger alkanes in crude oil into short-chain hydrocarbons that are more useful and in higher demand such as the manufacture of ethanol and plastics and as a fuel for vehicles.
Hydrogen is produced from the cracking of crude oil and acts as a reactant in the manufacture of ammonia in Haber Process.
Describe and explain how the process of fractional distillation separates crude oil into fractions [5]
Crude oil is a mixture of hydrocarbons with different boiling points. Crude oil mixture is heated until they completely vaporise.
Crude oil vapour rises up the fractionating column, as the vapour cool and condense at different temperatures.
Temperature of the fractionating column gets progressively cooler higher up the column.
Shorter and lighter hydrocarbons that contain lesser number of C atoms with lower boiling points condense and exit at higher sections of the fractionating column
Longer and heavier hydrocarbons that contain higher number of C atoms with higher boiling points condense at lower fractions.
Discuss whether hydrazine is a better fuel compared to H2 gas. [2]
Hydrazine is a BETTER fuel than H2 as it is a liquid at rtp which is EASIER TO STORE AND TRANSPORT compared to H2 which is a GAS.
However, hydrazine releases less energy per gram of fuel burnt.
Explain why propane and butane leave the column in the same fraction. [1]
They have similar boiling points.
Describe and explain the source of nitrogen gas in the furnace [1]
Nitrogen is found in hot air that is unreacted in the extraction process as air contains 78% nitrogen.
