DF5

Cracking

• Any reaction in which a larger molecule is made into smaller molecules

• Solves supply and demand issues

Catalytic Cracking of Crude Oil

• Zeolite Catalyst

• Hot, vaporised hydrocarbons

• Moving fluidised bed where solids can flow like a liquid

• Catalyst must be regenerated to avoid poisoning

• Typical feedstock has 30-40 carbon atoms

Catalysts

• A substance which speeds up a reaction but can be recovered chemically unchanged at the end

• Catalysis is the process of speeding up a chemical reaction with a catalyst

Homogeneous Catalysis

• Reactants and catalyst in the same physical state

Heterogenous Catalysis

• Reactants and catalyst in different physical states

A model for heterogeneous catalysis:

1. Reactants adsorbed onto surface of catalyst, weakening the bonds

2. Bonds of reactant molecules break

3. New bonds form between the reactants

4. Bonds break and product desorbs and diffuses

• Large surface area required for contact

  • Catalyst can be used on fine wire mesh

  • Catalyst can be finely divided

  • Catalyst can be supported by a porous material (platforming)

• Often transition metals

Catalyst Poisoning

• Stops catalyst functioning properly

• Poison molecules more readily adsorbed to catalyst

• Blocks active site

• Prevents catalyst regeneration

• Reason for use of expensive catalysts

  • Cheap exhaust catalysts would be vulnerable to sulfur dioxide