The industrial uses of clay minerals as catalysts date
from the early 'thirties. The application of catalysis to the thermal
cracking of oil started in about 1931; pre-heated oil was passed
downwards through fixed beds of granular catalyst, often attapulgite,
under pressure (80 lb. per sq. in.) and at about 900~ as in the
Houdry and Hydroforming systems. The catalyst had to be periodi-
cally burned off to regenrrate it, and was reintroduced at the top of
the reaction column. An improvement on this static process came
when the granulated catalyst was kept moving counter current to the
pre-heated oil. This led about 1939 to the fluid-flow method of
catalysis in which powdered catalysts are used in a fluid, free-flowing
condition, circulated by the air-rift method well-known in the move-
ment of liquids. The motive power for the circulation of the fluid is
obtained from the static head of gas-solid columns and by the intro-
duction under pressure of oil vapours to the oil-cracking reactor, and
of air to the catalyst reactivator. An up-flow system has recently
given way to a down-flow technique, which gives greater efficiency
and accuracy of control. Clay minerals have played an important
part in these petroleum techniques, and it is with this astonishingly
rapid development of new catalytic techniques in our minds that we
may review this morning the part which clay minerals have played
and may play.in catalysis.