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

Performance <strong>of</strong> FCC Catalysts Energy & Fuels, Vol. 17, No. 1, 2003 67
Table 6. MAT Products Yields for VGO Cracking at C/O ) 3 for Catalyst CAT0, CAT5, CAT10, and CAT20
compound name CAT0 yield (wt %) CAT5 yield (wt %) CAT10 yield (wt %) CAT20 yield (wt %)
H2 0.02 0.03 0.06 0.09
C1 0.22 0.34 0.36 0.42
C2 0.18 0.27 0.28 0.3
C2 ) 0.34 0.45 0.42 0.45
dry gas (H2+C1+C2+C2 ) ) 0.76 1.09 1.12 1.26
C3 0.51 0.74 0.73 0.76
C3 ) 4.96 5.91 5.63 5.63
i-C4 3.91 5.13 4.77 4.85
n-C4 0.57 0.78 0.75 0.78
t2-C4 ) 2.08 2.34 2.23 2.18
1-C4 ) 1.58 1.77 1.71 1.66
i-C4 ) 2.02 1.94 1.94 1.88
c2-C4 ) 1.57 1.77 1.69 1.65
total C4 ) 7.25 7.82 7.56 7.37
total C4 (olefins + paraffins) 11.73 13.74 13.08 13
LPG (total C3 +total C4) 17.2 20.39 19.44 19.38
gasoline 50.8 52.29 50.82 51.63
LCO 18.57 16.04 17.79 17.09
HCO 11.33 8.2 9.06 8.39
coke 1.34 1.93 1.77 2.24
total 100 99.94 100 100
conversion) 100 - (LCO wt % + HCO wt %) 70.1 75.8 73.2 74.5
Figure 7. <strong>The</strong> effect <strong>of</strong> alumina addition on dry gas selectivity.
9 0 wt % alumina (CAT0). 0 5 wt % alumina (CAT5), 4
10 wt % alumina (CAT10), and × 20 wt % alumina (CAT20).
in processes such as FCC. 17 <strong>The</strong> present results agree
with above arguments (see Figures 6 and 7). Table 6
reports the product distribution for FCC catalysts.
<strong>The</strong> effect <strong>of</strong> alumina addition on light olefin selectivity
is shown in Figure 8. Light olefin selectivity is
defined as the total gas olefin (C2-C4) yield divided by
VGO conversion. It can be seen that alumina addition
has contributed to a mild increase in the product
olefinicity. <strong>The</strong>se results are in agreements with the
argument that alumina addition might increase olefin/
paraffin ratio due to the increased cracking over hydrogen
transfer reaction ratio. 16
Taking the role <strong>of</strong> coke in FCC unit into consideration,
Mott 20 introduced the concept <strong>of</strong> “dynamic activity”
which is defined as the second-order conversion [conversion/(100
- conversion)] divided by coke yield (wt %).
It was found that a plot <strong>of</strong> coke wt % versus the second
order conversion gives a straight line with a slope equal
to the reciprocal <strong>of</strong> catalyst dynamic activity (the specific
coke) as shown in Figure 9. Catalysts with high dynamic
activity have better performance at commercial conditions.
For each catalyst, (with different alumina content)
the graphs were plotted and a slope (reciprocal <strong>of</strong>
Figure 8. <strong>The</strong> effect <strong>of</strong> alumina addition on light olefin (C2-
C4) selectivity. 9 0 wt % alumina (CAT0). 0 5 wt % alumina
(CAT5), 4 10 wt % alumina (CAT10), and × 20 wt % alumina
(CAT20).
dynamic activity) was obtained for each alumina content.
It is extremely important that the relationship
between the VGO second-order conversion and coke
yield is linear at FCC conditions. 20 For the base catalyst
(CAT0), the dynamic activity was 1/(0.391) ) 2.56 while
for those catalysts containing alumina was 1/(0.5771)
) 1.73. Thus although alumina addition to FCC catalyst
matrix has increased the catalyst activity as shown in
Figure 2, it decreased its dynamic activity. Usually
dynamic activity parameter is more important than
activity parameter. 20
Figure 9 shows that CAT0 with inactive matrix has
higher dynamic activity than CAT20 with active matrix.
This result is expected, since alumina increases coke
formation. Thus it can be concluded that FCC catalyst
acidity can be increased by incorporating alumina or by
increasing Y-zeolite unit cell size. 6,7 Increasing these
factors leads to a decrease in the catalyst dynamic
activity. 6,7 However, increasing alumina has better