0000000000175592
AUTHOR
A.v. Orchilles
The role of pore topology on the behaviour of FCC zeolite additives
Abstract A large variety of zeolite topologies including: large pore tridirectional (Beta), large pore unidirectional (Mordenite, SSZ-24), bidirectional 10 member ring pores (MRP) (ZSM-5), bidirectional 10 × 8 MRP (Ferrierite), tridirectional with connected 12 and 10 MRP (CIT-1), bidirectional with 12 MRP connected by 10 MRP (NU-87), tridirectional with 10 × 11 × 12 MRP (NU-86), and finally 10 MRP, and independent 12 MR cavities connected by 10 MR windows (MCM-22), have been studied as catalysts for the cracking of a gasoline range model molecule ( n -heptane). Kinetic and decay constants as well as selectivity parameters such as paraffin/olefin, i -C 4 / n -C 4 , i -C 5 / n -C 5 , C 3 /C 4…
Can Macroscopic Parameters, Such as Conversion and Selectivity, Distinguish between Different Cracking Mechanisms on Acid Catalysts?
n-heptane cracking has been carried out for very short time periods on an established reaction mechanism which includes the following group of stream reactions on different zeolites: Initiation reactions (protolytic cracking), charge isomerization, chain isomerization, hydride transfer, β-scission–alkylation, desorption–adsorption, and hydrogen transfer–cyclization. It has been observed that a given experimental distribution of products can be explained by more than just one reaction scheme. This does not allow one to clearly distinguish the fraction of reactant which disappears via monomolecular initiation reactions with respect to bimolecular hydride transfer reactions.
Cracking Activity and Hydrothermal Stability of MCM-41 and Its Comparison with Amorphous Silica-Alumina and a USY Zeolite
It has been found that the cracking activity of MCM-41 for a reaction catalyzed by strong acids site, such asn-heptane cracking, is much lower than that of a USY zeolite, and similar to that of amorphous silica-alumina. The higher activity of USY is due to the presence of stronger Bronsted acid sites in the zeolite. In the case of gas oil cracking, the greater accessibility of the large molecules to acid sites in MCM-41 relative to USY makes the difference in activity between these two catalysts much smaller than for the pure hydrocarbon. In the calcined state MCM-41 is more active and gives more gasoline and less gases and coke than amorphous silica-alumina. However, when the catalysts wer…
Cracking of n-heptane on a hzsm-5 zeolite. The influence of acidity and pore structure
Abstract The crackino of n-heptane on a HZSM-5 zeolite has been studied in a continuous qlass flow reactor, at atmospheric pressure, up to 470°C. The initial selectivities to the different reaction products, kinetic rate constants, activation energies and decay parameters have been calculated and compared with those obtained using a large pore zeolite (HYUS). A different product distribution is obtained with the two zeolites. In that way, and considering initial selectivities, different C 6 /C 1 , C 5 /C 2 , C 4 /C3, i-C 4 /n-C 4 , ethylene/ethane, propylene/propane ratios have been found on the two zeolite catalysts. The results have been quantitatively explained by considerinq a direct cr…
Catalytic activity of large-pore high Si/Al zeolites: Cracking of heptane on H-Beta and dealuminated HY zeolites
Abstract The catalytic activity, selectivity, catalyst decay, thermal and hydrothermal stability, and acidity of H-Beta and HY zeolites with Si Al ratios of 7.5 and 10, respectively, have been studied during cracking of n-heptane at 450 °C and atmospheric pressure. It has been found that the H-Beta zeolite is more active and decays more slowly than HY. H-Beta presents a higher steric hindrance for dibranched molecules and therefore its open structure should be smaller than that of HY. A lower hydrogen transfer activity and hydrothermal stability is observed for H-Beta in comparison with the corresponding HY.
Formation of products responsible for motor and research octane of gasolines produced by cracking The implication of framework Si/Al ratio and operation variables
Abstract An alkane in the range of gasoline fraction ( n -heptane) has been used as a reactant to study the influence of zeolite Y catalyst and process variables (i.e., framework Si Al ratio and procedure of dealumination, time on stream, and contact time) on the formation of products responsible for motor and research octane of gasoline during cracking, namely branched, aromatics, and olefins. It is found that the branched isomers in the C 5 and C 6 fractions appear as primary products and are partly produced by disproportionation, since the ratio of iso to normal compounds is above equilibrium. The ratio of branched to linear products strongly decreases when the number of carbon atoms of …
Influence of the process variables on the product distribution and catalyst decay during cracking of paraffins
Abstract The influence of the partial pressure of the hydrocarbon, reaction temperature, time on stream and the presence of olefins on the product distribution and the kinetics and decay during the cracking of n-heptane on an REHY zeolite were studied. It was found that the isomerization to cracking ratio depends on the hydrocarbon partial pressure. The active sites for cracking and isomerization are not the same and those for cracking decay faster, the selectivity changing with the degree of decay of the zeolite. The protolytic to β-cracking ratio, and therefore the paraffin to olefin ratio, are a function of the partial pressure of n-heptane. Both reactants and products have a marked infl…
Cracking behavior of zeolites with connected 12- and 10-member ring channels: The influence of pore structure on product distribution
n-Heptane has been cracked on a CIT-1 zeolite which has connected 12- and 10-member ring (MR) channels, and its behavior was compared with that of MCM-22 with nonconnected 12- and 10-MR channels, and SSZ-24 and BETA with unidirectional and tridirectional 12-MR channels, respectively. The kinetic rate constant is highest for CIT-1, and the decay constant is lowest. From the selectivity point of view, its behavior can be better represented by a system with large cavities (the intersections between the 12- and 10-MR) connected by windows. This gives a behavior typical of that of large pore zeolites. CIT-1 produces a remarkably high selectivity toi-C4, and specially to isobutane. This zeolite s…
ChemInform Abstract: Catalytic Activity of Large-Pore High Si/Al Zeolites: Cracking of Heptane on H-Beta and Dealuminated HY Zeolites
Abstract The catalytic activity, selectivity, catalyst decay, thermal and hydrothermal stability, and acidity of H-Beta and HY zeolites with Si Al ratios of 7.5 and 10, respectively, have been studied during cracking of n-heptane at 450 °C and atmospheric pressure. It has been found that the H-Beta zeolite is more active and decays more slowly than HY. H-Beta presents a higher steric hindrance for dibranched molecules and therefore its open structure should be smaller than that of HY. A lower hydrogen transfer activity and hydrothermal stability is observed for H-Beta in comparison with the corresponding HY.
Decalin and Tetralin as Probe Molecules for Cracking and Hydrotreating the Light Cycle Oil
Abstract Cracking of tetralin and decalin was carried out over several zeolites to establish the effect of the pore topology of the catalyst on product distribution. These molecules were chosen as probe molecules, because they indicate which catalyst is the best for cracking or hydrotreating the light cycle oil (LCO) fraction, which is obtained directly from fluid catalytic cracking units. A set of zeolites with medium-sized (ZSM-5, MCM-22, ITQ-2), large (USY, Beta), and ultralarge pores (UTD-1), as well as a mesoporous MCM-41, were used as catalysts at 723 K. The results demonstrate that pore size and topology have a strong influence on diffusion, and consequently, on activity and selectiv…
Comparison of the activity, selectivity and decay properties of lay and hyultrastable zeolites during the cracking of alkanes
Abstract The cracking of n-heptane on LaY ultrastable zeolite has been studied in a continuous glass flow reactor, at atmospheric pressure, up to 470°C. The initial selectivity to cracking, isomerization and disproportionation, kinetic rate constants, activation energies and decay parameters have been calculated and compared with those obtained using a HY ultrastable zeolite as a catalyst. It has been found that the HY ultrastable zeolite is about 7 times more active for cracking, and about 10 times more active for isomerization and disproportionation than the LaY ultrastable zeolite. The protolytic to β-cracking ratio is higher for the HY ultrastable zeolite. The deactivation takes place b…