Abstract:Progress in understanding the nature of cracking catalysts has led from the early recognition of the carbonium ion intermediate to the current view which ascribes cracking activity to the acidic nature of active sites. Here we develop the concept of acid catalysis to include the specific effects of Bronsted and Lewis acid sites on gas oil cracking. It is shown that these two types of sites react with specific substrates and that each has a characteristic kinetic behaviour. This leads us to suggest that careful… Show more
“…Table II gives the complete set of the n-heptane conversion results that were obtained with the zeolite catalysts. With these data and the kinetic equation (Wojciechowski, 1968;Corma et al, 1982)…”
A serles of REHY zeolites (RE, rare earths) with differing RE/NH4+ ratios was prepared and the influence of composition and pretreatments (deep-bed calcination and steaming) on their structural stability and acid characteristics reported, n -Heptane cracking activity and the decay of the REHY samples were studied by using a plug flow tubular reactor at atmospheric pressure and at temperatures of up to 470 °C. With the deep-bed-calcined samples containing 15% RES+ exchanged, a maximum in the activity/decay ratio was observed, while in the steamed samples this maximum was obtained with the zeolite containing 40-60% RE3+ exchanged. For the samples containing a Si/AI framework ratio =¿6.0 a maximum in activity was observed independent of the treatment conditions. Catalytic activity depends on strong acid sites related to isolated aluminum tetrahedron and alumina tetrahedra having one nearest aluminum neighbor. With the sample containing 80% RE3"1" exchanged an optimum in selectivity and hydrothermal stability was observed.
“…Table II gives the complete set of the n-heptane conversion results that were obtained with the zeolite catalysts. With these data and the kinetic equation (Wojciechowski, 1968;Corma et al, 1982)…”
A serles of REHY zeolites (RE, rare earths) with differing RE/NH4+ ratios was prepared and the influence of composition and pretreatments (deep-bed calcination and steaming) on their structural stability and acid characteristics reported, n -Heptane cracking activity and the decay of the REHY samples were studied by using a plug flow tubular reactor at atmospheric pressure and at temperatures of up to 470 °C. With the deep-bed-calcined samples containing 15% RES+ exchanged, a maximum in the activity/decay ratio was observed, while in the steamed samples this maximum was obtained with the zeolite containing 40-60% RE3+ exchanged. For the samples containing a Si/AI framework ratio =¿6.0 a maximum in activity was observed independent of the treatment conditions. Catalytic activity depends on strong acid sites related to isolated aluminum tetrahedron and alumina tetrahedra having one nearest aluminum neighbor. With the sample containing 80% RE3"1" exchanged an optimum in selectivity and hydrothermal stability was observed.
“…Furthermore, the catalyst/oil ratio is the parameter with the largest influence on the cracking reaction. The temperature effect is surprisingly low in the measured range of 698−798 K. The calculated value of C in eq 4 corresponds to an appearent overall activation energy for the cracking reaction of 25 kJ, which does not agree with a doubling of the rate constant per 20 °C temperature increase as measured by Corma et al We have no explanation of this discrepancy, but the catalytic cracking is a complex reaction and the MAT test may be influenced by experimental artifacts. 4 Fit between measured and modeled values for the gas yield ( G y ). 5 Fit between measured and modeled values for (C 1 + C 2 )/(C 3 + C 4 ).…”
The effect of hydrotreating of a vacuum gas oil (VGO) feed on the
activity, product composition,
and quality in a microactivity test (MAT) has been studied.
Reduced gas and coke yields and
increased gasoline production were observed at constant ASTM conversion
after hydrotreating
of the VGO feed. Correlations of the activity, gas and coke yield,
butene/(total C4), and (C1 +
C2)/(C3 + C4) ratios are
presented as functions of the H/C ratio in the feed (degree of
hydrogenation)
and operation parameters. In the activity correlation a new
measure of the degree of cracking
is introduced: N
100C = the number of
molecules per 100 C atoms of the cracking products.
The
cracking ability increases with increasing hydrotreating. At
constant temperature and catalyst/oil ratio the gas yield increases and the coke yield decreases with
increasing hydrotreating. Both
the (C1 + C2)/(C3 +
C4) and the butenes/(total C4) ratios are
decreasing at increasing H/C ratio
and constant operation parameters. The total product value
increases as the H/C ratio in the
VGO feed increases from 1.56 to 1.73 at constant
N
100C.
“…Using the procedures described above, initial selectivities in cumene cracking were determined at a variety of temperatures on various catalysts [56][57][58]2]. Table VI shows a set of selectivlties obtained on LaY and HY at three temperatures, together with product-type identification.…”
Section: The Reactions In Ciymene Crackingmentioning
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