Non-ideal reactors

Question 1

Ideal vs real PFR?

Answer 1

Ideal = plug flow, all reactant and product molecules move at the same rate in direction of bulk liquid flow
Real PFR: flow dist. -> fluid velocity profiles and turbulent mixing. Molecular diffusion -> molecules move with changing speeds and in different directions.

Question 2

Ideak CSTR vs real CSTR?

Answer 2

In an ideal CSTR, there would be uniform conc throughout, however in a real CSTR, there would be relatively high reactant conc at the feed entrance, and relatively low reactant conc in the stagnant regions (usually corners and behind baffles).

Question 3

Ideal PBR vs real PBR?

Answer 3

Ideal PBR = PFR, real PBR: In addition to phenomena observed in PFR, there would be channelling and dead zones.

Question 4

What is residence time distribution? How are they measured?

Answer 4

The distribution of how long fluid elements reside within the reactor. Measured using tracer experiments.

Question 5

Tracer requirements?

Answer 5

Tracer needs to be inert, easily detectable (often through colour or radioactivity), have similar properties to the reacting mixture, be soluble in the reacting mixture.

Question 6

How can we use RTD to predict conversion in a real reactor?

Answer 6

Reactor models:

1. Zero adjustment parameters:
   - segregation model
   - maximum mixedness model
2. One adjustable parameter:
   - reactor dead volume
   - fraction bypassing the reactor
   - tanks in series model
   - dispersion model
3. Two adjustable parameters:
   - reactor modelled as a combination of ideal reactors