DF5 Cracking

Question 1

What is cracking?

Answer 1

A reaction where larger molecules are made into smaller ones.

Question 2

What is cracking used?

Answer 2

To get highly branched shorter alkanes and alkenes which are used in petrol.

Question 3

What is a benefit from cracking?

Answer 3

It solves the supply and demand problem.

Question 4

What is an unsaturated alkane?

Answer 4

An alkane that doesn’t have as many hydrogen atoms as it could and has a double or triple bond between carbon atoms.

Question 5

What is catalytic cracking?

Answer 5

Cracking done by heating heavy oils in the presence of a catalyst to produce petrol.

Question 6

What can you crack alkanes into?

Answer 6

Branched alkanes and branched alkenes, or smaller alkanes and cycloalkanes.

Question 7

What can you crack cycloalkanes into?

Answer 7

Alkenes and branched alkenes.

Question 8

What can you crack alkenes into?

Answer 8

Smaller alkenes.

Question 9

What are alkenes important for?

Answer 9

Starting materials for other parts of the petrochemical industry.

Question 10

What does catalytic cracking take place in?

Answer 10

A riser reactor.

Question 11

What catalyst is involved in catalytic cracking?

Answer 11

Zeolite.

Question 12

Why is it called a riser reactor?

Answer 12

The hot vaporised hydrocarbons and zeolite catalyst are fed into the bottom of the tube and forced up by steam.

Question 13

How long does it take the mixture to flow up the riser reactor?

Answer 13

Two seconds.

Question 14

What is one problem with catalytic cracking?

Answer 14

Coke forms on the catalyst surface so that the catalyst eventually becomes inactive.

Question 15

What is coke?

Answer 15

Carbon from decomposition of hydrocarbon molecules.

Question 16

How do you overcome coke forming on a catalyst surface?

Answer 16

The powdery catalyst needs to be regenerated.

Question 17

Where does the mixture go once it leaves the riser reactor?

Answer 17

A separator.

Question 18

What happens in the separator?

Answer 18

Steam carries away the cracked products leaving behind solid catalyst.

Question 19

What happens to the catalyst in the separator?

Answer 19

It goes into the regenerator where the coke is burnt off with hot air that is blown through.

Question 20

What happens to the catalyst after the regenerator?

Answer 20

It’s reintroduced into the base of the reactor ready to repeat the cycle.

Question 21

What does the energy released from the burning coke do?

Answer 21

Heats up the catalyst.

Question 22

Where does the catalyst transfer its energy to?

Answer 22

The feedstock.

Question 23

Why does the catalyst transfer its energy to the feedstock?

Answer 23

So that cracking can occur without additional heating.

Question 24

What is a catalyst?

Answer 24

A substance that speeds up a reaction but is chemically unchanged.

Question 25

What is catalysis?

Answer 25

The process of speeding up a chemical reaction using a catalyst.

Question 26

How can catalysts undergo change?

Answer 26

Physically but not chemically.

Question 27

What does a catalyst being unchanged chemically but changed physically suggest?

Answer 27

That the catalyst is taking some part in the reaction but is being regenerated.

Question 28

How much of a catalyst is needed?

Answer 28

Only a small amount.

Question 29

What does the catalyst not effect?

Answer 29

The amount of product formed.

Question 30

Where does a catalyst not appear in?

Answer 30

As a reactant.

Question 31

What is homogeneous catalysis?

Answer 31

Catalysis where the reactants and catalysts are in the same physical state.

Question 32

What is an example of homogenous catalysis?

Answer 32

Enzyme catalysed reactions in cells.

Question 33

What is heterogeneous catalysis?

Answer 33

Catalysis where the reactants and catalyst are in different physical states.

Question 34

What does heterogeneous catalysis usually involve?

Answer 34

A mixture of gases and liquid reacting with a solid catalyst.

Question 35

Where does the reaction occur when a solid catalyst is reacted with gases or liquids?

Answer 35

On the surface of the solid.

Question 36

What do the reactant gases and liquids do with the surface of the catalyst?

Answer 36

Form bonds with the atoms on the surface and are adsorbed.

Question 37

What happens as a result of adsorption?

Answer 37

Bonds in the reactant molecules are weakened and break and new bonds form between the reactants and surface of the catalyst to form products.

Question 38

What does forming products on a catalyst do?

Answer 38

Weakens the bonds to the catalyst surface and the product molecules are released.

Question 39

What must a catalyst have for contact with the reactants?

Answer 39

A large surface area.

Question 40

What are most heterogeneous catalysts in industrial processes.

Answer 40

Transition metals.

Question 41

What does a catalyst poison do?

Answer 41

Block an enzyme catalysed reaction so that they no longer function properly.

Question 42

What happens with poison molecules in heterogeneous catalysis?

Answer 42

The poison molecules are adsorbed more strongly to the catalyst surface then the reactants.

Question 43

Why does the catalyst become inactive when the poison is adsorbed?

Answer 43

Because the catalyst can’t catalyse a reaction of the poison.

Question 44

How do the poison molecules inactivate the catalyst?

Answer 44

They block the active sites on its surface.