2 - Modification of alkanes by cracking Flashcards
1
Q
What is cracking?
A
The conversion of large hydrocarbons to smaller hydrocarbon molecules by the breakage of C-C bonds
2
Q
What are the products of cracking?
A
High Mr alkanes → smaller Mr alkanes + alkenes + (hydrogen)
3
Q
What are the two main types of cracking?
A
- Thermal cracking
- Catalytic cracking
4
Q
What are the conditions for thermal cracking?
A
High pressures (7000kPa)
High temperatures (400°C - 900°C)
5
Q
What are the products of thermal cracking?
A
- Alkenes
- Sometimes hydrogen
6
Q
What are the conditions for catalytic cracking?
A
- Slight / moderate pressure
- High temperature (450°C)
- Zeolite catalyst
7
Q
What are the products of catalytic cracking?
A
- Branched alkanes
- Cyclic alkanes
- Aromatic hydrocarbons
8
Q
Why is catalytic cracking cheaper than thermal cracking?
A
Catalytic cracking saves energy as lower temperatures and pressures are used
9
Q
What are 3 economic reasons for cracking?
A
- Petroleum fractions with shorter C chains are more in demand than larger fractions
- To make use of excess larger hydrocarbons and to supply demand for shorter ones
- The products of cracking are more valuable than starting products
