1. CHE 354 Chemical Reactor Design
The General Mole Balance
& Ideal Reactors

2. Example of Reactor Design
FA0 FA
In – Out + Generation = Accumulation
What do we do with this term?

3. As DV goes to zero and M goes to infinity:
The Generation Term
FA0 FA
Divide reactor into little regions, small enough that intensive variables (CA, T, P) do not vary within.
As DV goes to zero and M goes to infinity:

4. The General Mole Balance
Let’s apply it to the three ideal reactors!

5. Batch Reactor
Perfectly mixed
No flow in or out

6. Batch Reactor
Perfectly mixed
No flow in
No flow out

7. And if the volume is not a function of time (constant)
Batch Reactor
And if the volume is not a function of time (constant)

8. Team Exercise
What does design equation (mole balance) look like for a semi-batch reactor - continuous flow of Reactant A, Reactant B, or Product P?

9. Continuous Stirred Tank Reactor CSTR
Perfectly mixed
Steady state

10. CSTR
Perfectly mixed
Steady state

11. CSTR
What would the design equation look like at startup and with some spatial variations?

12. Plug Flow Reactor PFR
No radial gradients – only axial
Steady state

13. PFR
Steady state
This is the integral form. Often the differential form is more useful. Take the derivative with respect to volume of each term.

14. Derivative of a constant is just 0
PFR
Derivative of a constant is just 0 rA

15. Here is where some complication sets in:
PFR
Here is where some complication sets in:

16. Example 1-1 Assume isomerization is first order with k = 0.23 min-1
What volume PFR and CSTR are required for 90% conversion and 10 L/min?