fractional distillation and cracking

Question 1

Describe the process of fractional distillation

Answer 1

• Crude oil is heated and enters bottom of column
• Fractions/ HCs have different bpts
• Bpt depends on Mr/chain length
• Negative temp gradient in column
• Fractions condense at points according to their bpt
• Higher bpts condense closer to bottom

Question 2

What are the financial advantages of cracking?

Answer 2

Higher demand for shorter chain HCs

Alkenes are more useful for initiating chemical reactions

Question 3

What is the reactive intermediate of thermal cracking?

Answer 3

Free radical

Question 4

What is the reactive intermediate of catalytic cracking?

Answer 4

carbocation

Question 5

What conditions are required for thermal cracking?

Answer 5

High temp (400-900°C)

High pressure (10atm - 1MPa)

Question 6

What are the products of thermal cracking?

Answer 6

Many alkenes

Fewer branches alkanes

Question 7

How many fractions can thermal cracking be used on?

Answer 7

All fractions

Question 8

What conditions are required for catalytic cracking?

Answer 8

Lower temp (400°C)

Lower pressure (>1atm)

Zeolite catalyst

Question 9

What are the products of catalytic cracking mainly used for?

Answer 9

Motor fuels

The alkanes produced have a low bpt so burn easily, making them good for fules such as petrol

Question 10

What are the products of catalytic cracking?

Answer 10

Fewer alkenes than thermal

Many branched alkanes/cycloalkanes

Many arenes (chemical feedstock)