Page 56 - Principles of Catalyst Development
P. 56
CATALYST DEVELOPMENT 43
feedstocks, products, processing routes, or conditions from those normally
used. Direct liquefaction of coal is a recent example; low-density polyethyl-
ene is another.
Modification of an existing process involves a change either in conver-
sion, selectivity, lifetime, or operating conditions. The need may come from
changes in economics, feedstocks, products and energy supplies or from
problems encountered in established units. For example, steam reforming,
as practiced until the 1960s, was a fairly low-pressure process. In order to
take advantage of more economical centrifugal compressors, it was desirable
to raise pressure in the reformer.(l) Higher pressures required more active
and robust catalysts. It is interesting that the solution to this problem was
to increase silica in the support, thereby generating a new problem. At
higher steam pressures, silica, which is volatile, leaves the catalyst, and
deposits on lower-temperature equipment downstream. Thus a second-
generation solution was needed.(49)
Whether new or existing, it is desirable at this point to make a detailed
analysis of similar processes. This helps to focus upon potential problems
and also define the direction of the development. For example, in direct
coal liquefaction, comparison with hydrotreating of heavy petroleum frac-
tions was useful to establish similarities and differences.(78)
Detailed comparisons are time consuming and tedious, but well worth
the effort. It is wise to follow a systematic procedure such as the "check
list" in Appendix 4. Only in this way is it certain that all relevant data are
included and nothing overlooked. If conscientiously carried out, the exercise
is not only informative but often generates creative and innovative ideas.
3.3. DEFINE PROBLEM AND OBJECTIVES
Catalyst problems vary from case to case. Increased activity or improved
selectivity may be called for, or decreased deactivation. Perhaps it is a
question of devising satisfactory regeneration procedures. In some cases
cost and availability of catalyst components may be the factor. Analyses of
similar processes are helpful in establishing reasonable levels and limits.
Just how much activity is required? What selectivity is sufficient? What is
the minimum regeneration cycle?
Next, we must define the precise objectives necessary to solve these
problems, and this can be very critical. For example, activity, selectivity,
and deactivation problems may exist because of either chemical or
diffusional factors. Which is it? The answer determines the route of future
development. If chemical properties are to be adjusted, then modification
of surface composition is necessary. On the other hand, correction for