The Influence of Alumina on the Performance of FCC Catalysts ...

Performance <strong>of</strong> FCC Catalysts Energy & Fuels, Vol. 17, No. 1, 2003 63
more coke, dry gas, and less gasoline than inactive
matrix. 16-18 <strong>The</strong> effect <strong>of</strong> alumina addition to FCC
catalyst matrix on processing different kinds <strong>of</strong> VGO
feedstock was studied by Otterstedt et al. 17 <strong>The</strong>y
observed that alumina addition to the catalyst matrix
had increased the conversion <strong>of</strong> the heavier feed oil but
at the same time increased coke selectivity and decreased
gasoline selectivity. However, alumina addition
did not have a significant effect during lighter feed oil
processing. Coke and gasoline selectivities were found
to have similar behavior to those <strong>of</strong> heavier feed oil.
It has been reported that the olefin/paraffin ratio
decreases by increasing zeolitic content and decreasing
matrix activity. 19 Moreover, Scherzer 15 claimed that
increasing matrix activity (by adding alumina) would
increase both olefin/paraffin ratio and gasoline octane.
This was attributed to lower hydrogen transfer reaction
rate versus cracking reaction rate over amorphous
matrix component.
Thus, it is clearly known that alumina addition to a
FCC catalyst matrix can influence the catalyst performance
by increasing catalyst acidity and surface area.
Consequently, the VGO catalytic cracking might be
enhanced by alumina addition to the matrix without
changing the USY-zeolite structure.
In the present study, a thorough investigation for the
role <strong>of</strong> active matrix on catalytic cracking <strong>of</strong> hydrotreated
VGO has been conducted. Systematic addition
<strong>of</strong> alumina to both matrix samples and FCC catalysts
containing USY-zeolite has been studied. Testing both
catalyst systems under standard MAT conditions has
been carried out. <strong>The</strong> activity <strong>of</strong> matrix with alumina
and catalyst containing alumina is determined. Furthermore,
the effect <strong>of</strong> alumina addition on product
selectivity is highlighted.
2. Experimental Section
2.1. Catalyst Preparation. USY-zeolite was mixed with
kaolin clay and stabilized silica sol (SI-550) supplied by
Catalyst and Chemicals Industries Co. <strong>The</strong> resulting slurry
was heated over a sand bath with continuous stirring. <strong>The</strong>
dried product was crushed and sieved to the proper particle
size (520-710 µm). <strong>The</strong> base catalyst, the one with inactive
matrix (CAT0), contained 30% zeolite, 50% kaolin, and 20%
silica sol binder. <strong>The</strong> prepared catalysts were calcined in air
at 600 °C for 2 h. Finally the catalysts were treated with 100%
steam at 810 °C for 6 h.
<strong>The</strong> series <strong>of</strong> catalysts containing the active matrices were
prepared in the same manner as the one containing inactive
matrix with the exception that part <strong>of</strong> the kaolin was replaced
by boehmite. <strong>The</strong> amount <strong>of</strong> boehmite used in these preparations
corresponded to 5 wt % (CAT5), 10 wt % (CAT10), and
20 wt % (CAT20). <strong>The</strong> three catalysts CAT5, CAT10 and
CAT20 all contained 30 wt % USY-zeolite and 20 wt % silica
sol. <strong>The</strong> other component is the kaolin as shown Table 1.
<strong>The</strong> series <strong>of</strong> matrix samples are prepared as follows;
inactive matrix contains only kaolin (M0). Active matrices were
prepared in the same manner as the FCC catalysts with active
matrix except that in these series no zeolite is present. Part
(16) Van de Gander, P.; Penslay, R. M.; Chuang, K. C.; Cormier,
W. E.; Walterman, G. M.; Boldingh, E. P. Advanced Fluid Catalytic
Cracking Technology; AIChE Symposium Series vol. 88, no. 291;
AIChE: New York; pp 21-29.
(17) Otterstedt, J. E.; Zhu, Y.; Sterte, J. Appl. Catal. 1988, 38, 143.
(18) Sterte, J.; Otterstedt, J. E. Appl. Catal. 1988, 38, 131.
(19) de Jong, J. I. Ketjen Catalysis. Symposium 1986, Scheveningen,
<strong>The</strong> Netherlands, Paper F-2.
catalyst
Table 1. Catalyst Composition Content
Y-zeolite
(wt %)
silica sol
(wt %)
kaolin
(wt %)
alumina
(wt %)
CAT0 30 20 50 0
CAT5 30 20 45 5
CAT10 30 20 40 10
CAT20 30 20 30 20
M0 0 0 100 0
M5 0 20 75 5
M10 0 20 70 10
M20 0 20 60 20
Table 2. Treatment and Characterization <strong>of</strong> Catalysts
catalyst treatment
unit cell
size (Å)
surface
area
(m 2 /g)
Al
(wt %)
acidity
(mmol/g)
CAT0 steaming, 810 °C 24.206 123 0 0.0190
CAT5 steaming, 810 °C 24.206 177 5 0.0296
CAT10 steaming, 810 °C 24.206 180 10 0.0311
CAT20 steaming, 810 °C 24.206 196 20 0.0377
M0 steaming, 810 °C - 22 0 0.006
M5 steaming, 810°C - 25 5 0.0088
M10 steaming, 810 °C - 31.7 10 0.0114
M20 steaming, 810 °C - 60 20 0.0227
<strong>of</strong> kaolin was substituted by boehmite. <strong>The</strong> amount <strong>of</strong> boehmite
used in these preparations corresponded to 5 wt % (M5), 10
wt % (M10), and 20 wt % (M20) see Table 1. All matrices were
calcined in air at 600 °C for 2 h. <strong>The</strong>n they were treated with
100% steam at 810 °C for 6 h (see Table 2).
2.2. Catalyst Characterization. <strong>The</strong> unit cell size was
determined by X-ray diffraction following ASTM D-3942-80.
High purity silicon powder (99.999%) was used as the calibration
standard. Surface area <strong>of</strong> the sample catalyst were
measured by nitrogen adsorption at -196 °C. <strong>The</strong> zeolite used
has 75.9 m 2 /g surface area (this surface area is for the zeolite
which is steamed at 810 °C for 8 h) and negligible Na content.
Moreover, the unit cell size is 24.206 Å. Hence its silica/
alumina ratio can be found from this unit cell size.
<strong>The</strong> acid property <strong>of</strong> the catalyst was characterized by
pyridine temperature programmed desorption (TPD). In all
experiments, 50 mg <strong>of</strong> sample was charged in a tubular cell.
Prior to obtaining TPD spectra, the sample was outgassed at
400 °C for 30 min in flowing helium and then cooled to 150
°C. At that temperature, pyridine was adsorbed on the sample
by injecting pulses <strong>of</strong> pyridine (2ul/ pulse). <strong>The</strong> injection <strong>of</strong>
pyridine was repeated until the amount <strong>of</strong> pyridine detected
was the same for the last two injections. After the adsorption
<strong>of</strong> pyridine was saturated, the sample was flushed at 150 °C
for 1 h with helium to remove excess pyridine and then
temperature programmed at 30 °C/min to 1000 °C in flowing
helium at 30 mL/min. An FID detector was used to monitor
the desorbed pyridine. <strong>The</strong> properties <strong>of</strong> the catalysts used in
the present study are presented in Table 2.
2.3. Catalyst Evaluation. Catalytic experiments were
carried out in a microactivity test (MAT) unit (fixed bed), which
had been designed according to the ASTM D-3907 method with
minor modifications. <strong>The</strong> reactor was operated at atmospheric
pressure and 520 °C. For a given catalyst, the conversion was
varied by varying the catalyst-to-oil ratio (C/O) in the range
<strong>of</strong> 0.5-3.0. <strong>The</strong> C/O ratio is defined as the amount <strong>of</strong> catalyst
divided by the total amount <strong>of</strong> oil fed in a given time on stream
and was varied by changing the weight <strong>of</strong> the catalyst while
the total amount <strong>of</strong> oil fed and the time were kept constant,
i.e., 1g<strong>of</strong>theoilwascharged to the reactor in 30 s (see Table
3). <strong>The</strong>rmal effects and changes in the bed volume were
minimized by diluting the catalyst with kaolin particles
(having the same size as the catalyst particle), and the total
weight <strong>of</strong> the catalyst bed was kept at 3 g. <strong>The</strong> distribution <strong>of</strong>
gaseous products was analyzed by gas chromatographies. <strong>The</strong>
boiling point range <strong>of</strong> the liquid products was determined by