Matching supply to demand
Fractional distillation gives fractions containing hydrocarbons of different chain lengths. The amounts obtained do not match how strongly the different fractions are demanded.
1
Surplus
There is more of the longer-chain fractions than is needed.
2
Demand
Shorter-chain hydrocarbons are more sought after for fuels and as starting materials for useful chemicals.
3
Crack
Cracking converts larger, less useful molecules into smaller products with greater demand.
- Low-relative-mass alkanes are useful fuels.
- Alkenes are useful feedstocks, including for making polymers.
Exam Tip: An economic explanation should make both points clear: longer-chain fractions are in surplus, while shorter-chain products are in greater demand.