Page 119 - Fluid Catalytic Cracking Handbook

96 Fluid Catalytic Cracking Handbook

vanadium and nitrogen attacks. But a matrix containing very small
pores can suppress strippablity of the spent catalyst and increase
hydrogen yield in the presence of nickel. Clay and binder provide
physical integrity and mechanical strength.

The manufacturing process of modern FCC catalyst is divided into
two general groups—incorporation and "in-situ" processes. All catalyst
suppliers manufacture catalyst by an incorporation process that requires
making zeolite and matrix independently and using a binder to hold
them together. In addition to the incorporation process, Engelhard also
manufactures FCC catalyst using an "in-situ" process in which the
zeolite component is grown within the pre-formed miscrospheres. The
following sections provide a general description of zeolite synthesis.

Conventional Zeolite (KEY, REHY, HY)

NaY zeolite is produced by digesting a mixture of silica, alumina,
and caustic for several hours at a prescribed temperature until crystal-
lization occurs (Figure 3-8). Typical sources of silica and alumina are
sodium silicate and sodium aluminate. Crystallization of Y-zeolite
typically takes 10 hours at about 210°F (100°C). Production of a
quality zeolite requires proper control of temperature, time, and pH
of the crystallization solution. NaY zeolite is separated after filtering
and water-washing of the crystalline solution.
A typical NaY zeolite contains approximately 13 wt% Na 2O. To
enhance activity and thermal and hydrothermal stability of NaY, the
sodium level must be reduced. This is normally done by the ion
exchanging of NaY with a medium containing rare earth cations and/
or hydrogen ions. Ammonium sulfate solutions are frequently employed
as a source for hydrogen ions.
At this state of the catalyst synthesis there are two approaches for
further treatment of NaY. Depending on the particular catalyst and the
catalyst supplier, further treatment (rare earth exchanged) of NaY can
be accomplished either before or after its incorporation into the matrix.
Post-treatment of the NaY zeolite is simpler, but may reduce ion
exchange efficiency.