Page 192 - Principles of Catalyst Development

180 CHAPTER 7
7.5.3. Practical Activities

Practical activities are used when catalyst comparisons only are
required. Measurements are faster and less demanding. The same types of
reactor discussed above are used or larger units may be required. The
principal function of pilot unit operations is to explore real feeds, process
conditions, and deactivation, but practical activities are usually measured
as these change. Three types are encountered; measurement of (I) conver-
sion at fixed space velocity, (2) space velocity for a fixed conversion, and
(3) temperature for a fixed conversion.

7.5.3.1. Conversion at Fixed Space Velocity

Catalysts are compared by measuring the conversion at a fixed space
time. Consider the conversion space time curves in Fig. 7.35. At the selected
space velocity, catalyst A is better than B because the conversion is higher.
Feed composition, temperature, pressure, and process time should be con-
stant for the test to be meaningful. The best way to ensure this is to run
the samples in parallel reactors with the same feed. Figure 7.36 shows a
system designed for this purpose. Three catalysts are measured simul-
taneously, with microprocessor control to ensure identical and reproducible
conditions. One of the samples could be a standard against which the others
are checked.
This approach is relative only and has no kinetic meaning. Indeed, the
absolute ratio between two activities depends on the space velocity used
and has no meaning at other values.

CATALYST A
z
o
(/l
a:
w
>
z
o
()

CONTACT TIME. 1/s
Figure 7.35. Conversion versus space time tests.