Page 573 - Elements of Chemical Reaction Engineering Ebook

Sec. 9.2 Unsteady Operation of CSTRs and Semibatch Reactors 543

A management 2. The reaction is normally carried out isothermally at 175°C over a 24-h period.
decision was made Approximately 45 min after the reaction was started, cooling to the reactor
to triple production was halted, but only for 10 min. Cooling may have been halted for 10 min or
so on previous occasions when the normal charge of 3.17 kmol of ONCB was
used and no ill effects occurred.
The reactor had a safety relief valve whose disk would rupture when the pres-
sure exceeded approximately 700 psi. Once the disk ruptures, the water would
vaporize, and i.he reaction would be cooled (quenched) by the release of the latent
heat of vaporization.
Plot the temperature-time trajectory up to a period of 120 min after the reac-
tants were mixed and brought up to 175°C. Show that the following three conditions
had to have been present for the explosion to occur: (1) increased ONCB charge,
(2) reactor stopped for 10 min, and (3) relief system failure.

Additional Information: The rate law is

with k = 0.00017 m3 at 188°C
kmol * min
The reaction volume for the charge of 9.044 kmol of ONCB:
V = 3.265 m3 ONCB/NH3 + 1.854 m3 II,O = 5.119 m3

The reaction volume for the charge of 3.17 kmol of ONCB:
V = 3.26 m3
AH,, = -5.9 X IO5 kcallkg mol
E = 11,273 cal/mol
CpONCB CPA = 40 cal/mol. K
=
CPHZo = Cpw = 18 cal/mol.K CNHl = CPB = 8.38 cal/mol.K
Assume that Akp=O :

Solution
A+2B __j C+D
Mole balance:

(E9-2.1)

Rate law:
-rA = kC,C, (E9-2.2)
Stoichiometry (liquid phase):
CA = cAO(1 -x) (E9--2.3)