Page 91 - Elements of Chemical Reaction Engineering 3rd Edition

Chap. 2 Questions and Problems 63

There are three ways you can arrange your system:
(1) Reactors in series: CSTR followed by PFR
(2) Reactors in series: PFR followed by CSTR
(3) Reactors in parallel with half the feed rate going to each reactor after
which the exit streams are mixed
(a) If possible, state which system will give the highest overall conversion.
(b) If possible, state which system will give the lowest overall conversion.
(c) If in one or more of the cases above it is not possible to obtain an
answer, explain why. ($nul exam, winter 1496)
(d) Comment on whether or not this is a reasonable final exam problem
P2-6s The exothermic reaction

A __+ B+C
was carried out adiabatically and the following data recorded:

X I 0 0.2 0.4 0.5 0.6 0.8 0.9
-rA(mol/am3.min) I 10 14.67 50 50 50 12.5 909
The entering molar flow rate of A was 300 mol/min.
(a) What are the PFR and CSTR volumes necessary to achieve 40% conver-
sion? (V,,, = 7.2 dm3, V,,, = 2.4 dm3)
(b) Over what range of conversions would the CSTR and PFR reactor vol-
umes be identical?
(c) What is the maximum conversion that can be achieved in a 10.5-dm3
CSTI??
(d) Whan conversion can be achieved if a 7.2-dm3 PFR is followed in series
by a 2.4-dm3 CSTR?
(e) Whaf conversion can be achieved if z 2.4-dm3 CSTR is followed in a
series by a 7.2-dm’ PFR?
(f) Plot ihe conversion and rate of reaction as a function of PFR reactor vol-
ume up to a volume of 10 dm3.
P2-7c Sgt. Nigel Ambercromby. Worthless Chemical has been making tirene (B) from
butalane (A) (both dark liquids) using a 8.0 ft3 CSTR followed by a 3.1 ft3 PFR.
The entering flow rate is 1 ft3/min. A conversion of approximately 81% is
achieved using this arrangement. The rate is shown as a function of conversion
in Figure P2-8(a). The CSTR is identical to the one of the battery of CS’rRs
shown in Figure 1-1 1. There is a preheater upstream of the CSTR that heats
the feed to 60°C. One morning the plant manager, iDr. Pakbed, arrived and found
that the clonversion had dropped to approximately 24%. After inspecting the
reactors, the PFR was found to be working perfectly, but a dent was found in
the CSTR that may have been caused by something like a fork lift truck. He
also notes the CSTR, which aormally makes a “woosh” sound is not as noisy
as it was yesterday. The manager suspects foul play and calls in Sgt. Nligel
Ambercromby from Scotland Yard. What are the first four questions Sgt.
Ambercromby asks? Make a list of all the things that could cause the drop in
conversian. Quantify the possible explanations with numerical calculations
where possible. Dr. Pakbed tells Sgt. Ambercromby that he must achieve a con-
version greater than 50% to meet production schedules downstream. Sgt.
Ambercromby says, “I think I know how you could do this immediately.” What
does Ambercromby have in mind? [with Dan Dixon, ChE 344 W’971