Page 205 - Elements of Chemical Reaction Engineering 3rd Edition

Sec. 4.6 Using C, (liquid) and FA (gas) in the Mole Balances and Rate Laws 177

we have
- - - - - - __
-
'E
- 'C - rD
'A
- a -b c d (2-20)
Reaction (2-2) will be used together with the generic rate law

to develop the algoritms when Ci (liquids) and Fi (gases) are used as the sys-
tem variables.

4.6.1 CSTRs, PFRs, PBRs, and Batch Reactors

Liquid Phase. For liquid-phase reactions in which there is no volume
change, concentration is 'the preferred variable. The mole balances are shown
in Table 4-5 in terms of concentration for the four reactor types we have been
discussing. We see from Table 4-5 that we have only to specify the parameter
values for the system (CAo,u,,etc.) and for the rate law (Le., kA,w,f3) to solve
the coupled ordinary differential equations for either PFR, PBR, or batchi reac-
tors or to solve the coupled algebraic equations for a CSTR.

TABLE 4-5. MOLE BALANCES FOR LIQUID-PHASE REACTIONS

b
-
-
-
dt a'"
- -
Batch dCA - and ~CB
dt 'A
LIQUIDS
I'FR uo- dCA = and
dV

WR ug- dCA - and
Slw 'a
-

Gas Phase. For gas-phase reactions, the mole balances are given identically
in Table4-6. Consequently, the concentrations in the rate laws need ito be
expressed in terms of the molar flow rates: for example,
rj = kCj
2

Rate law We start by recalling and combining Equations (3-40) and (3-41),

(13-40)