A.V. Orchillés

Catalytic activity of large-pore high Si/Al zeolites: cracking of heptane on H-Beta and dealuminated HY zeolites

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/sup 0/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.

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 cracking of heptanes as well as a condensation-cracking process of some of the products formed. From the kinetic parameters it has been seen that the HYUS is three times more active for cracking but decays some eight times faster than the HZSM-5 zeolite.

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 the product fraction increases. It goes through a maximum for samples with unit cell size in the range 24.30–24.40 A. The selectivity to aromatics is strongly dependent on total conversion and increases with time on stream, while dealumination decreases the selectivity to aromatics. The saturation of olefins, via hydrogen transfer, decreases with increasing dealumination, increasing temperature and decreasing time on stream. These observations are explained not only on the basis of site density and strength but also on the basis of the adsorption characteristics of the samples. Finally, methane and ethane can be formed by a protolytic cracking of branched products. Part of these two gases and most of the ethylene are formed by a radical type of cracking, in which extraframework aluminium plays an important role.

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 influence on catalyst decay.

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 by both a chemical poisoning of the active sites (second order) and by pore blocking, the decay by pore blocking being higher for the LaY ultrastable zeolite.