Page 190 - Principles of Catalyst Development

178 CHAPTER 7
extended experimental runs to return to some standard experimental condi-
tion at the end of the run. If results are the same, this ensures that no
deactivation has taken place. If activity has declined, then measured rates
may be "corrected" back to the fresh state.

7.5.2.2. Gradientless Reactors

These are reactors that operate in a well-mixed condition. For catalytic
systems this is achieved with Carberry or Berty reactors as shown in Fig. 7.33.
Concentrations remain constant throughout the reactor volume, and
mixing helps in temperature control. Conversions may be quite large, so
that rate precision is good, but interpretation is a simple application of
equation (7.25). Another advantage is that pelleted or extruded particles
can be used directly. Figure 7.34 demonstrates results with commercial-sized
particles.
Checks are necessary to ensure no external diffusion problems occur
and that well-mixed conditions prevail. This can be done by changing the
speed of the mixer.
Similar effects are achieved with recirculation reactors, in which at
least 9()(~o of the product is recirculated to the reactant so as to maintain
essentially constant concentrations over the bed. These reactors are,

CATALYST GAS THERMOCOUPLE
THERMOCOUPLE (.
~""II SHAFT REACTOR
11 GA~ IN BODY
" I'

~INSERT

BASKET
BAFFLE
CATALYST

Figure 7.33. A well-mixed basket reactor.