Reaction Engineering EP 319/EP 327: Chapter 4 (Part Ii) Multiple Reactions
Reaction Engineering EP 319/EP 327: Chapter 4 (Part Ii) Multiple Reactions
Reaction Engineering EP 319/EP 327: Chapter 4 (Part Ii) Multiple Reactions
EP 319/EP 327
CHAPTER 4 (PART II)
MULTIPLE REACTIONS
A. Series
B. Parallel
C. Independent
TYPES OF REACTIONS
C. INDEPENDENT REACTIONS
Independent reactions are of the type
A α is the order
Reactor of the reaction
Undesired
7.1: Condition for maximizing yields and selectivity
for parallel reactions
1. We want the formation of D, rD to be high with respect to
the rate of formation of U, rU.
CASE 1: α1 > α2
(REACTION ORDER OF DESIRED GREATER THEN UNDESIRED
a
rD k D 1 2 k DCA
SDU CA
ru ku ku
rD kD 1 2 kD
SDU CA a
ru ku kuCA
1. Let the reaction order be positive number, difference
between these reaction orders. Therefore (α1 – α2 = -a).
2. For SD/U to be high, the concentration of A should be as
low as possible
A.Diluting the feed with inert and that running the reactor
at low concentration of A
3. Hence, a CSTR should be used because concentration of
reactant are maintained at low level
7.1: Condition for maximizing yields and selectivity
for parallel reactions
a
rD kDCA
SDU b
r U kUCB
7.1: Condition for maximizing yields and selectivity for
parallel reactions
MAXIMIZING THE DESIRED PRODUCT FOR TWO REACTANT
CASE 2: α1 > α2 (+), β1< β2 (-)
2. To maximize the ratio, concentration of A should be high &
concentration of B should be low. To achieve this, use
A. Semi batch reactor in which B is fed slowly into large
amount of A
B. Tubular reactor with side streams of B continually fed to
reactor
C. Series of small CSTRs with A fed only to the first
reactor and small amount of B fed to each reactor.
7.1: Condition for maximizing yields and selectivity for
parallel reactions
MAXIMIZING THE DESIRED PRODUCT FOR TWO REACTANT
CASE 3: α1 < α2 (-), β1< β2 (-)
kD α1 α 2 β1 β 2
SDU CA CB
kU
1. Let -a = α1 – α2 and -b = β1- β2, where a and b are
negative constants.
rD kD
S DU a b
r U k U C A CB
7.1: Condition for maximizing yields and selectivity for
parallel reactions
MAXIMIZING THE DESIRED PRODUCT FOR TWO REACTANT
CASE 3: α1 < α2 (-), β1< β2 (-)
2. To maximize the ratio, the reaction should be carried out at
low concentration of A and B. To achieve this, use
A. CSTR (For CSTR, the reactant concentration is always
at its lowest value)
B. Tubular reactor in which there is a large recycle ratio
C. Feed diluted with inerts
D. Low pressure (if gas phase)
7.1: Condition for maximizing yields and selectivity for
parallel reactions
MAXIMIZING THE DESIRED PRODUCT FOR TWO REACTANT
CASE 4: α1 < α2 (-), β1> β2(+)
kD α1 α 2 β1 β 2
SDU CA CB
kU