CHBE 550: Deriving Rate Expressions
S.A. Baldwin
September 16, 2013
1
Reversible reactions
Deriving the rate expression for a rst order reaction:
A
k1
Q
k2
The stoichiometric coecient is one in each case. If the working volume of the reactor
is constant:
Heterogeneous reactors
More than one phase: gas, liquid and/or solid
Commonly a solid catalyst provides a surface on which reactions take place
bulk phase is a uid (liquid or gas)
Considerations that impact assumptions that can be used to simplify the
CHBE 550
S.A. Baldwin
September 9, 2013
1
Systematic reactor design: stoichiometry
Mathematical formulation of the stoichiometric equation:
N
i,j Aj = 0
j=1
where is the stoichiometric coecient for chemical species j in reaction i. Sometimes
the symbol i,
37
Dispersion in a tubular reactor with laminar flow
The Text considers the situation where both axial and radial
diffusion can occur in a tubular reactor with laminar flow (i.e. a
parabolic velocity profile). Section 14.4.4.
When terms for both axial and
26
Axial Dispersion Model
The other common model for intermediate degrees of mixing
between PF and perfect mixing is the axial dispersion model.
This model considers the mixing to be analogous to molecular
diffusion, i.e. random-walk dispersion as in ma
1
Non-Ideal Mixing in Reactors
So far we have considered continuous flow reactors to be in
either (a) plug flow (no mixing: all elements spend identical
times in reactor) or (b) perfect mixing (CSTR: all elements
have equal probability of leaving reactor