Crude Oil and Fuels Flashcards
Why does crude oil need to be seperated?
It contains many different compounds that boil at different temperatures. These burn under different conditions so crude oil needs to be seperated to make useful fuels.
What process can be used to seperate a mixture of liquids?
Distillation
What does simple distillation of crude oil produce?
Liquids that boil within different temperature ranges. These are called fractions.
What are most of the compounds in crude oil (and what are these)?
Hydrocarbons - molecules containing only hydrogen and carbon. Many of these hydrocarbons are alkanes.
What is the general formula for alkanes?
Cn+H2n+2
What are alkanes?
Saturated hydrocarbons - they contain as many hydrogen atoms as possible in each molecule (i.e. bonded to each carbon atom). They do not contain a double bond.
What is a displayed formula?
A represntation of molecules that shows how the atoms are bonded together
What is a molecular formula?
A formula showing the number of each type of atom in each molecule.
E.g. C2H6 - ethane
How is crude oil separated at refineries?
Using fractional distillation
Describe the process of fractional distillation.
- The boiling point of each hydrocarbon depends on the size of the molecule. The larger the molecule, the higher the boiling point.
- Crude oil is vapourised and fed into the fractionating column. It is hotter at the bottom and cooler further up the column.
- The vapours travel up the column, cooling as they do so. The hydrocarbons condense to liquids when they reach the level that is at their boiling point and are collected on one of the trays at the different levels and siphoned off.
- The smallest molecules have the lowest boiling points so are collected at the top of the column. The fractions collected at the bottom have the highest boiling point.
- A very thick residue is left at the bottom of the column due to the fact that it has a boiling point higher than that of the bottom of the fractionating column.
What are the properties of fractions with low boiling ranges?
- Low viscocity, so are runny liquids
- Very flamable and ignite easily
- Burn with clean flames, producing little smoke
This makes them very useful as fuels
What are the properties of fractions with high boiling ranges?
- Very thick and sticky - very viscous
- Extremely high boiling points
- Can’t be seperated easily
- Not as flammable
Used in making roads and flat roofs
What happens when pure hydrocarbons are burnt completely?
They are oxidised to produce CO2 and water
What is produced by incomplete combustion?
Carbon monoxide may be produced
Carbon/soot may be produced
Some hydrocarbons may not burn
The latter two are what form particulates
What are particulates?
Small solid particles given off by motor vehicles etc. after incomplete combustion
What do most fossil fuels contain and what happens when this is burnt?
Sulfur compounds - produces sulfur dioxide when burnt.
Sulfur dioxide causes acid rain
What might also happen at the high temperatures produced when fuels burn?
Oxygen and nitrogen in the air may combine, producing nitrogen oxides
These also cause acid rain
What is global dimming?
The reduction in the amount of sunlight that reaches the Earth’s surface caused by particulates in the atmosphere reflecting sunlight away
How is acid rain produced?
Sulfur dioxide and nitrogen oxides dissolve in water droplets and react with oxygen in the air
How can we remove harmful substances from waste gasses before they are released into the atmosphere?
- Sulfur dioxide can be removed from the waste gasses produced by power stations before these enter the atmosphere.
- Sulfur can also be removed from fuels before they are burnt
- Exhaust systems of cars are fitted with catalytic converters to remove carbon monoxide + nitrogen oxides
- Filters can remove particulates
What is smog and what causes it?
A mixture of SMoke and fOg
Caused by lots of cars in a small area and the right weather conditions
What are biofuels?
Renewable fuels made from plant or animal products
What is biodiesel?
A biofuels made from vegetable oils extracted from plants.
It is used to power cars (as an alternative to diesel)
State an advantages of using biodiesel
It’s carbon neutral
State a disadvantage of using biodiesel
The plants that are grown for biodiesel use large areas of farmland
Give an example of another biofuel and how it can be used + produced
Ethanol made from sugar cane or sugar beet
It is a liquid so can be stored and distributed like other liquid fuels
It can also be mixed with petrol
What are the advantages and disadvantages of using hydrogen as a fuel?
- It only produces water when it is burned
- However, it is a gas so takes up a large volume. This makes it difficult to store in the quantities needed for combustion in engines
- It can be produced from water by electrolysis, but this requires large amounts of energy
