Page 59 - Principles of Catalyst Development

46 CHAPTER 3
not provide guidance on parameters such as concentration of the active
component, method of preparation, and temperature of calcination. These
factors, outlined in detail in Chapter 6, must be determined empirically.
Careful planning using statistical strategy is necessary, since there are many
significant variables.

3.6. CATALYST TESTING

Allied with design and preparation, catalyst testing is the exploratory
screening of candidate catalysts. This phase does not yield either kinetics
or process variables but merely ranks performance. Bench reactors used
should be as simple and rapid as possible, for many samples are usually
tested.(86) For ease in operation and interpretation, model compound reac-
tions are helpful. Thus, for example, cumene dealkylation is a model for
catalytic cracking, and thiophene hydrogenolysis for hydrodesulfurization.
Care must be taken to ensure that the model system does indeed parallel
process performance.
Design, preparation, and testing should be treated as a unit with
continuous feedback, leading to optimized performance. Characterization
is important since proper evaluation of catalyst parameters is necessary.
These methods and procedures are discussed in Chapter 7.

3.7. PILOT UNIT TESTING

This stage is reached when one or more successful candidates emerge
from the catalyst design. It involves testing under simulated process condi-
tions, using pilot or semi commercial units. The principal objectives in using
pilot units are the following:
1. To test commercial-like formulations under process conditions to
ensure that design requirements are achieved. These include activity, selec-
tivity, diffusional, and mechanical properties.
2. To optimize process variables, such as space velocity, temperature,
and pressure. If activation (for example, reduction or sulfiding) is required,
proper procedures are developed at this time.
3. To carry out long-term lifetime tests. The catalyst encounters com-
ponents of the feed for the first time. Although the designer may have
anticipated the effect of substances such as poisons, sensitivity of the catalyst
formulation can only be checked with experiment. For well-behaved proces-
ses, lifetime tests of several hundred hours are necessary before long-term