94
Type I reactions are driven by matrix design and FCC hardware design. As
described above, mesopores in the 100–600 Å range are needed for effective bottom
cracking. Increasing the catalyst pore volume in this range will enhance bottom
cracking. The second type of bottom-cracking reaction is the conversion of alkylaromatics in which zeolite activity is much more effective than matrix for this dealkylation reaction. Increasing the zeolite activity resulted in increased conversion
and reduced bottom yield. The third type of bottom-cracking reaction is the conversion of naphthenoaromatic compounds. Conversion of polynuclear aromatics (PNA)
is known to be very difficult. However, it is possible to selectively crack saturated
naphthenic rings attached to the aromatic cores of these PNAs with an appropriately
designed catalyst. Since typical naphthenoaromatic molecules are too large to fit
into the zeolite pores, it is expected that cracking of the naphthenic rings will take
place on matrix sites or the external surface of the zeolite [85].
6 Chemistry
There are a multitude of reactions that occur when hydrocarbon feed is introduced
to a hot regenerated catalyst. As we previously discussed, the unit cell of the FCC
catalyst is a tetrahedron with either silicon or aluminum atoms at its center. These
silicon ions are at a +4 and aluminium ions are in a +3 oxidation state. Hence, an
extra charge of −1 is required to establish neutrality. These sites are of acidic nature
since they donate proton or cations. The catalyst’s acid sites are of both Bronsted
(proton donor) and Lewis (electron pair acceptor) type.
0.04
2
3
4
5
6
7
8
0.06
Catalyst Mesopore Volume (100-600Å), cc/g
Kinetic Conversion of Bottoms
0.08
0.1
0.12
0.14
0.16
Fig. 20 Improvement in bottom cracking with mesopore volume [85]
A. R. Khande et al.
Type I reactions are driven by matrix design and FCC hardware design. As
described above, mesopores in the 100–600 Å range are needed for effective bottom
cracking. Increasing the catalyst pore volume in this range will enhance bottom
cracking. The second type of bottom-cracking reaction is the conversion of alkylaromatics in which zeolite activity is much more effective than matrix for this dealkylation reaction. Increasing the zeolite activity resulted in increased conversion
and reduced bottom yield. The third type of bottom-cracking reaction is the conversion of naphthenoaromatic compounds. Conversion of polynuclear aromatics (PNA)
is known to be very difficult. However, it is possible to selectively crack saturated
naphthenic rings attached to the aromatic cores of these PNAs with an appropriately
designed catalyst. Since typical naphthenoaromatic molecules are too large to fit
into the zeolite pores, it is expected that cracking of the naphthenic rings will take
place on matrix sites or the external surface of the zeolite [85].
6 Chemistry
There are a multitude of reactions that occur when hydrocarbon feed is introduced
to a hot regenerated catalyst. As we previously discussed, the unit cell of the FCC
catalyst is a tetrahedron with either silicon or aluminum atoms at its center. These
silicon ions are at a +4 and aluminium ions are in a +3 oxidation state. Hence, an
extra charge of −1 is required to establish neutrality. These sites are of acidic nature
since they donate proton or cations. The catalyst’s acid sites are of both Bronsted
(proton donor) and Lewis (electron pair acceptor) type.
0.04
2
3
4
5
6
7
8
0.06
Catalyst Mesopore Volume (100-600Å), cc/g
Kinetic Conversion of Bottoms
0.08
0.1
0.12
0.14
0.16
Fig. 20 Improvement in bottom cracking with mesopore volume [85]
A. R. Khande et al.