Fractional Distillation and Thermal/Catalytic Cracking

Question 1

What are alkanes?

Answer 1

saturated hydrocarbons
C2nH2n+2

Question 2

How does fractional distillation work?

Answer 2

1. Mixture is vaporised and fed into fractionating column.
2. Vapours rise, cool and condense.
3. Products are siphoned off for different uses.

Products with short carbon chains = low boiling point = they rise, cool and condense higher up the column compared to products with longer carbon chains.

Collect all products –> can be broken down further via thermal/catalytic cracking.

Question 3

What is cracking?

Answer 3

Cracking involves breaking C–C bonds in alkanes.

Question 4

What is thermal cracking?

Answer 4

conditions: high temp (1200K) and high pressure(7000kPa)

produce: a high percentage of alkanes.

Question 5

What is catalytic cracking?

Answer 5

conditions: high temp, slight pressure, with a zeolite catalyst.

produces: aromatic compounds and motor fuels

Question 6

explain the economic reasons for cracking alkanes.

Answer 6

Petroleum fractions with shorter chains are more in demand and economically more valuable than those with longer chains.

To increase usefulness of longer chain hydrocarbons and to supply for demand for short chain hydrocarbons, longer hydrocarbons are cracked.