Page 531 - Elements of Chemical Reaction Engineering Ebook

Sec. 8.7 Nonisothermal Multiple Chemical Reactions 501

The heat of reaction for reaction i must be referenced to the same species in the
rate, rG, by which AHRxrl is multiplied, that is,

moles of j reacted in reaction i joules "released" in reaction i
[-rrqIZ-AHRxr/l =
volume - time ] [aes of j reacted in reactiz]

= poules "released" in reaction i 1
volume. time
where the subscript j refers to the species, the subscript i to the particular reac-
tion, q is the number of independent reactions, and m is the number of species.
Consider the following reaction sequence carried out in a PFR:

Reaction 1: A k1 ,B (8-88)
Reilction 2: B '>C (8-89)

The PFR energy balance becomes

where AHRxlA = [kJ/mol of A reacted in reaction 13 and = kJ/mol
of B reacted in reaction 21.

Example 8-11 Parallel Reactions in a PFR with Heat Effects

The following gas-phase reactions occur in a PFR:
k
Reaction 1: A 1_) B -IlA = k1,CA (E8-1 I .l)
Rewtion 2: 2A k2 > C -r2, = k,,Ci (E8- 1 1.2)

Pure A is fed a1 a rate of 100 molls, a temperature of 150°C and a concentration of 0.1
moll dm3 . Determine the temperature and flow rate profiles down the reactor.

Additional information:
AH,,,, = J/mol of A reacted in reaction 1 = -20,000 J/mol
AHRx2A .= J/mol of A reacted in reaction 2 = -60,000 J/mol

CpA = 90 J/mol. "C k,, = 10 expb [& - i)] s-1

Cp, = 90 J/mol- "C E, = 8000 cal/mol

A)]
Cpc = 180 J/mol. "C k2* = 0.09 exp [ E! (1 dm3
-
R 300 T mo1.s
Ua=4000J/m3.s."C E,= 18,00Ocal/mal
T, = I0CI"C