Page 175 - Elements of Chemical Reaction Engineering 3rd Edition

Sec. 4.3 Tubular Reactors 1 47

click on “Dow Chemical USA’ and scroll the Reactivity Data, we would find
that ethylene glycol will ignite in air at 413°C.

4.3 Tubular Reactors

Gas-phase reactions are carried out primarily in tubular reactors where the flow
is generally turbulent. By assuming that there is no dispersion and there are no
radial gradients in either temperature, velocity, or concentration, we can model
the flow in the reactor as plug-flow. Laminar reactors are discussed in Chapter
13 artd dispersion effects in Chapter 14. The differential form of the dlesign
equation
PFR mole
dX -
balance FA0 - - -rA
dW
must be used when there is a pressure drop in the reactor or heat exchange
between the PFR and the surroundings. In the absence of pressure drop or heat
exchange the integral form of the plug JEow design equation is used,
PFR design
equation

Substituting the rate law for the special case of a second-order reaction gives
us

dX
Rate law

For constant-temperature and constant-pressure gas-phase reactions, the con-
centration is expressed as a function of conversion:
Stoichiometry
(gas-phase)

and then substituted into the design equation:

Combine

The entering concentration CAO can be taken outside the integral sign since it
is not a function of conversion. Since the reaction is carried out isothermally,
the specific reaction rate constant, k, can also be taken outside the integral
sign.
For an isothermal
reaction, k ir
constant
From the integral equations in Appendix A. 1, we find that