C.2 Fossil Fuels

Question 1

How are fossil fuels produced?

Answer 1

Reduction of biological molecules within dead organisms.
Carbon, hydrogen, nitrogen, sulphur and oxygen.
Result is a carbon rich fuel.

Question 2

What is crude oil?

Answer 2

A complex mixture of different hydrocarbons

Question 3

What happens during crude oil refining?

Answer 3

Mixture undergoes fractional distillation, physical process, separates on their boiling point.

Question 4

What happens during fractional distillation?

Answer 4

1 - crude oil heated until it boils
2 - vapour passes into the fractionating column
3 - temperature is higher at bottom of column than top
4 - different fractions condense and drawn off at different heights
5 - highest boiling points condense towards bottom of tower
6 - smaller hydrocarbons travel up the column until they condense and are drawn off

Question 5

What is the refinery gases fraction used for?

Answer 5

Fuel for cooking and heating, bottled gas, fuel in the refinery.

Question 6

What is the gasoline fraction used for?

Answer 6

Fuel for cars.

Question 7

What is the naphtha fraction used for?

Answer 7

Feedstock for petrochemical industry, converted by catalytic reforming into gasoline, used as a solvent.

Question 8

What is the kerosene (paraffin) fraction used for?

Answer 8

Jet fuel, household heaters and lamps, cracked to produce more gasoline.

Question 9

What is the diesel oil (gas oil) fraction used for?

Answer 9

Diesel fuel for cars, lorries etc. cracked to produce more gasoline.

Question 10

What is the fuel oil fraction used for?

Answer 10

Fuel for ships and industry, fuel for home central heating systems.

Question 11

What is the lubricating oil fraction used for?

Answer 11

Lubricant in engines and machinery, may be cracked.

Question 12

What is the wax fraction used for?

Answer 12

Candles, petroleum jelly, waxed paper and cardboard in the food industry.

Question 13

What is the bitumen/asphalt fraction used for?

Answer 13

Tarmac for roads and waterproofing roofs.

Question 14

What is volatility?

Answer 14

How readily a substance evaporates.

Question 15

How does the carbon chain length change over the fractions?

Answer 15

It increases as you move down the fraction from refinery gas to asphalt.

Question 16

How does volatility change over the fractions?

Answer 16

It decreases as chain length increases, (from refinery gases to asphalt).

Question 17

How does mean boiling temperature change over the fractions?

Answer 17

It increases from refinery gas down the fractions to asphalt

Question 18

What is auto ignition?

Answer 18

Occurs when fuel in the cylinder of an engine burns instantly (explodes), leads to knocking which can cause excessive engine wear and damage.

Question 19

What is an octane number?

Answer 19

An experimentally derived value provides a measure of the tendency of a fuel to auto ignite. HIGHER octane number LOWER tendency of fuel to auto ignite.

Question 20

What are octane numbers dependent on and why?

Answer 20

Carbon chain length - LONGER the chain the LOWER the octane number
Chain branching - branching INCREASES the octane number for the same number of carbon atoms
Cyclisation - cyclisation INCREASES the octane number for the same number of carbon atoms
Unsaturation - alkenes tend to have a HIGHER octane number than alkane equivalents.

Question 21

How can octane numbers be increased?

Answer 21

By cracking or catalytic reforming.

Question 22

What is cracking?

Answer 22

Long chain alkanes are passed over an aluminosilicate catalyst heated to 500 degrees Celsius under pressure. Resulting in a shorter chain alkane and one or more alkene molecules. Alkane molecules may also cyclise or become branched during the process.

Question 23

What is catalytic reforming?

Answer 23

Hydrocarbons are passed over a platinum catalyst at 500 degrees celsius. The molecules become branched, cyclised or aromatised.

Question 24

What is coal gasification?

Answer 24

Solid coal converted into a gaseous fuel (syngas a mixture of CO and hydrogen). Heating coal to temperature above 1000 degrees Celsius in the presence of oxygen and steam.
The main reaction occurring is:
C(s) + H20(g) —-> CO(g) + H2(g)
Syngas can be converted to methane by heating it with additional hydrogen:
CO(g) + 3H2(g) —-> CH4(g) + H20(g)

Question 25

What is coal liquefaction?

Answer 25

Coal converted to liquid hydrocarbons. One method involves mixing coal with solvent and hydrogen and heating to about 400 degrees celsius at high pressure and in the presence of a catalyst such as red mud (from bauxite purification).

Question 26

How else can coal liquefaction occur?

Answer 26

Produce liquid hydrocarbon from syngas using Fischer Tropsch process. At temperature of 300 degrees Celsius higher pressure and presence of ruthenium catalyst, the CO reactions with H2 to form liquid alkanes.

Question 27

What is a carbon footprint?

Answer 27

Total amount of greenhouse gas produced during the course of a human activity. Expressed in equivalent tonnes of carbon dioxide (CO2e).