Page 20 - Principles of Catalyst Development
P. 20
6 CHAPTER 1
Although the importance of increasing selectivity is different for each
process, in the case of industrial operations with large throughputs, small
improvements may lead to large benefits. For example, a 1 % increase in
gasoline yield in catalytic cracking amounts to an extra one million gallons
a day for the United States, thereby lowering dependence on imports.(9)
Deactivation rates enter significantly into process design. Not only are
yield-time relationships established, but also type of reaction and mode of
operation (e.g., fixed or fluidized bed).(lO) Lifetime decline can have a
profound effect on the engineering and economics of a process. Small
changes that improve lifetime can have a large payoff. An example is the
introduction of bimetallics in catalytic reforming. Adding rhenium to
platinum on alumina greatly decreased the deactivation rate from both
coking and sintering. Not only did the catalyst last longer and require less
regeneration (thus vastly simplifying process configurations), but lower
pressure operations were possible, giving improved selectivity to high-octane
aromatics. (II)
Priorities in today's industry emphasize more efficient utilization of
feedstocks and energy. Most effort is placed on improving existing processes
rather than developing new ones. With this in mind and with an awareness
of the direction of current research, it is the author's opinion that the relative
order of importance is selectivity> deactivation> activity.
1.2. ORGANIZATION OF CATALYSIS
Before proceeding with our discussion, we should perhaps briefly
acknowledge the different but complementary divisions of catalysis now
existing within industrial and academic fields. They are homogeneous,
heterogeneous, and enzyme catalysis. Each has its own structure and disci-
plines, involving researchers from varying backgrounds. There are special-
ized journals and meetings catering to each. Unfortunately, attempts at
cross-fertilization have not been too successful, which is regrettable since
each has much to learn from the others.
1.2.1. Homogeneous Catalysis
The catalyst is the same phase as the reactants and products.(12)
Examples are hydrolysis of esters by acids (liquid-liquid), oxidation of S02
by N0 2 (vapor-vapor), and decomposition of potassium chlorate by Mn02
(solid-solid). Usually, the liquid phase is most common, with both catalyst
and reactants in solution.