81
• Chemisorption of metallic impurities in the pores of the catalyst. Such pore
blockage, contrary to conventional coking, is irreversible.
• Fouling or excess coking due to the presence of resinous or asphaltic hydrocarbons in the feed [36].
Modern catalysts are manufactured to be sufficiently stable to withstand these
above mechanisms in the usual range of operations. They can preserve their activity
for several weeks while cracking heavily contaminated feeds. Fresh catalyst needs
to be added periodically to make up for the lost catalyst activity. Coke gets deposited on the catalyst due to undesired side reactions taking place in FCC and affects
the intrinsic activity by covering sites and blocking pores. This loss of activity due
to coke deposition is very fast but is reversible, and the catalyst can be regenerated
easily by burning off the coke deposited on the catalyst surface. Due to the cyclic
nature of the process, the catalyst particles may undergo attrition, producing fines
that will result in particulate emissions and loss of catalyst as fines. The age distribution of catalyst particles also affects the activity of the catalyst in cracking reactions [37, 38]. At any instant of time, the catalyst in the reactor is composed of a
mixture of new low metal concentration, high-activity and old high metal concentration, low-activity catalyst particles. This mixture of new and old catalysts from an
industrial FCC unit is collectively called equilibrium catalyst [46][39].
5 The FCC Catalyst
The FCC catalyst is a fine mixture of four main components: zeolite, matrix, binder,
and clay having an average particle size (APS) of 75 μm [72] (Fig. 11).
Artificially crystallized zeolites are commercially synthesized by digesting a
mixture of sodium silicate, sodium aluminate, and caustic for several hours.
Crystallization is a slow process; hence, some seeds are added so that the process
takes about 10 h at 100 °C. Manufacturing a quality zeolite having the intended
textural properties requires fine control over temperature, pH of solution, and retention time. The crystalline powder obtained is termed NaY, and it contains approximately 13 wt% Na 2 O. Such a high amount of Na 2 O is the reason for the inherent
stability issues faced by zeolites in the regenerator. To improve its hydrothermal
stability, its sodium content is reduced by the de-alumination process (discussed
earlier) to obtain ultra-stable Y-zeolite (US-Y) or by ion exchange with ammonium
or rare-earth ions (La or Ce) followed by calcination to obtain (RE-Y).
To manufacture FCC catalyst, zeolite, clay, alumina, and binders are mixed into
a slurry. The slurry is then spray dried into fine microspheres using atomizers and
hot air. The textural properties of the final product catalyst depend heavily on the
spray-drying conditions and the constituents of the slurry.
Recent Developments in FCC Process and Catalysts
• Chemisorption of metallic impurities in the pores of the catalyst. Such pore
blockage, contrary to conventional coking, is irreversible.
• Fouling or excess coking due to the presence of resinous or asphaltic hydrocarbons in the feed [36].
Modern catalysts are manufactured to be sufficiently stable to withstand these
above mechanisms in the usual range of operations. They can preserve their activity
for several weeks while cracking heavily contaminated feeds. Fresh catalyst needs
to be added periodically to make up for the lost catalyst activity. Coke gets deposited on the catalyst due to undesired side reactions taking place in FCC and affects
the intrinsic activity by covering sites and blocking pores. This loss of activity due
to coke deposition is very fast but is reversible, and the catalyst can be regenerated
easily by burning off the coke deposited on the catalyst surface. Due to the cyclic
nature of the process, the catalyst particles may undergo attrition, producing fines
that will result in particulate emissions and loss of catalyst as fines. The age distribution of catalyst particles also affects the activity of the catalyst in cracking reactions [37, 38]. At any instant of time, the catalyst in the reactor is composed of a
mixture of new low metal concentration, high-activity and old high metal concentration, low-activity catalyst particles. This mixture of new and old catalysts from an
industrial FCC unit is collectively called equilibrium catalyst [46][39].
5 The FCC Catalyst
The FCC catalyst is a fine mixture of four main components: zeolite, matrix, binder,
and clay having an average particle size (APS) of 75 μm [72] (Fig. 11).
Artificially crystallized zeolites are commercially synthesized by digesting a
mixture of sodium silicate, sodium aluminate, and caustic for several hours.
Crystallization is a slow process; hence, some seeds are added so that the process
takes about 10 h at 100 °C. Manufacturing a quality zeolite having the intended
textural properties requires fine control over temperature, pH of solution, and retention time. The crystalline powder obtained is termed NaY, and it contains approximately 13 wt% Na 2 O. Such a high amount of Na 2 O is the reason for the inherent
stability issues faced by zeolites in the regenerator. To improve its hydrothermal
stability, its sodium content is reduced by the de-alumination process (discussed
earlier) to obtain ultra-stable Y-zeolite (US-Y) or by ion exchange with ammonium
or rare-earth ions (La or Ce) followed by calcination to obtain (RE-Y).
To manufacture FCC catalyst, zeolite, clay, alumina, and binders are mixed into
a slurry. The slurry is then spray dried into fine microspheres using atomizers and
hot air. The textural properties of the final product catalyst depend heavily on the
spray-drying conditions and the constituents of the slurry.
Recent Developments in FCC Process and Catalysts