Page 129 - Fluid Catalytic Cracking Handbook

104 Fluid Catalytic Cracking Handbook

Catalytic Properties

The activity, coke, and gas factors are the tests that reflect the
relative catalytic behavior of the catalyst.

Conversion (Activity)
The first step in E-cat testing is to burn the carbon off the sample.
The sample is then placed in a MAT unit (Figure 3-13), the heart of
which is a fixed bed reactor. A certain amount of a standard gas oil
feedstock is injected into the hot bed of catalyst. The activity is
reported as the conversion to 430°F (221°C) material. The feedstock's
quality, reactor temperature, catalyst-to-oil ratio, and space velocity are
four variables affecting MAT results. Each catalyst vendor uses slightly
different operating variables to conduct microactivity testing, as
indicated in Table 3-2.
In commercial operations, catalyst activity is affected by operating
conditions, feedstock quality, and catalyst characteristics. The MAT
separates catalyst effects from feed and process changes. Feed con-
taminants, such as vanadium and sodium, reduce catalyst activity.
E-cat activity is also affected by fresh catalyst makeup rate and
regenerator conditions.

Coke Factor (CF), Gas Factor (GF)
The CF and GF represent the coke- and gas-forming tendencies of an
E-cat compared to a standard steam-aged catalyst sample at the same
conversion. The CF and GF are influenced by the type of fresh catalyst
and the level of metals deposited on the E-cat. Both the coke and gas
factors can be indicative of the dehydrogenation activity of the metals on
the catalyst. The addition of amorphous alumina to the catalyst will tend
to increase the nonselective cracking, which forms coke and gas.

Physical Properties

The tests that reflect physical properties of the catalyst are surface
area, average bulk density, pore volume, and particle size distribution.

2
Surface Area (SA), M /g
For an identical fresh catalyst, the surface area of an E-cat is an
indirect measurement of its activity. The SA is the sum of zeolite and