1. CH EN 5253 – Process Design II Dealing with Impurities in Processes and Process Simulators
February 09, 2018

2. Books
There is not chapter in the book on this subject

3. Impurity Effects Heat Exchange Reactors Separation Systems
Recycle Loops

4. Impurities in Reactors
Point 1: Poisons for Catalysts
Kill Catalyst with time
Point 2: Impurities can cause side reactions altering
Reactor conversion
Generating additional undesirable products
Point 3: Impurities Impact Equilibrium Conversion
Point 4: Impurities Impact Reaction Rates
Lower concentrations
Point 5: Impurities have Reaction Heat Effects
Lower Cp of feed

5. Point 1: Poisons for Catalysts
Kill Catalyst with time
Lead, Sulfur, Manganese in Gasoline kill Catalytic Converter
Platinum, Palladium, Rhodium
Note: Vehicles equipped with catalytic converters can run only on unleaded fuel

6. Catalytic Reactors Various Mechanisms depending on rate limiting step
Surface Reaction Limiting
Surface Adsorption Limiting
Surface Desorption Limiting
Combinations
Langmuir-Hinschelwood Mechanism (Surface Reaction Limiting)
H2 + C7H8 (T) CH4 + C6H6(B)
Impurities decrease the Cv concentration of active sites due to Impurity Adsorption

7. Point 2: Side reactions altering
Reactor conversion
Generating additional undesirable products
Reactions

8. Point 3: Impurities Impact Equilibrium Conversion
Temperature Effects
Single Equilibrium
aA +bB  rR + sS
Van’t Hoff eq.

9. Unfavorable Equilibrium
Increasing Temperature Increases the Rate
Equilibrium Limits Conversion
Equilibrium line is repositioned and rate curves are repositioned due to impurities

10. Point 4: Impurities Impact Reaction Rates
Effect of Inert Addition Similar to Impurity Effects

11. Point 5: Reaction Heat Effects
Heat Balance over Reactor
Q = UA ΔTlm
Adiabatic
Adiabatic
Cooling

12. Impact on Reactor Design

13. Kinetic Reactors - CSTR & PFR – Temperature Effects
Used to Size the Reactor
Used to determine the reactor dynamics
Reaction Kinetics
Ci is lower with Impurities

14. PFR – no backmixing Used to Size the Reactor Space Time = Vol./Q
Outlet Conversion is used for flow sheet mass and heat balances
rK is smaller and V is larger due to impurities.

15. CSTR – complete backmixing
Used to Size the Reactor
Outlet Conversion is used for flow sheet mass and heat balances
rK is smaller and V is larger due to impurities.

16. Temperature Profiles in a Reactor
Exothermic Reaction
Impurities effect these curves and areas under these curves=size of reactor

17. Managing Heat Effects Reaction Run Away Reaction Dies
Exothermic
Reaction Dies
Endothermic
Preventing Explosions
Preventing Stalling

18. Costs Higher capital cost for Higher operating cost for
Bigger reactors
Cooling and heating systems
Bigger Separation System
Higher operating cost for
Utility – hot and cold water
Pumping
Separation