Page 124 - Fluid Catalytic Cracking Handbook

100 Fluid Catalytic Cracking Handbook

The particle size distribution (PSD), sodium (Na), rare earth (RE), and
surface area (SA) are some of the parameters in the inspection sheet
that require close attention.

Particle Size Distribution (PSD)

The PSD is an indicator of the fluidization properties of the catalyst,
In general, fluidization improves as the fraction of the 0-40 micron
particles is increased; however, a higher percentage of 0-40 micron
particles will also result in greater catalyst losses.
The fluidization characteristics of an FCC catalyst largely depend on
the unit's mechanical configuration. The percentage of less than 40
microns in the circulating inventory is a function of cyclone efficiency.
In units with good catalyst circulation, it may be economical to minimize
the fraction of less than 40-micron particles. This is because after a few
cycles, most of the 0-40 microns will escape the unit via the cyclones,
The catalyst manufacturers control PSD of the fresh catalyst, mainly
through the spray-drying cycle. In the spray dryer, the catalyst slurry
must be effectively atomized to achieve proper distribution. As illu-
strated in Figure 3-10, the PSD does not have a normal distribution
shape. The average particle size (APS) is not actually the average size
of the catalyst particles, but rather the median value.

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Surface Area (SA), M /g

The reported surface area is the combined surface area of zeolite
and matrix. In zeolite manufacturing, the measurement of the zeolite
surface area is one of the procedures used by catalyst suppliers to
control quality. The surface area is commonly determined by the
amount of nitrogen adsorbed by the catalyst.
The surface area correlates fairly well with the fresh catalyst activity.
Upon request, catalyst suppliers can also report the zeolite surface area.
This data is useful in that it is proportional to the zeolite content of
the catalyst.

Sodium (Na), wt%

Sodium plays an intrinsic part in the manufacturing of FCC catalysts.
Its effects are well known and, because it deactivates the