Juan B. Montón

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.

Densities, refractive indices, and derived excess properties of the binary systems tert-butyl alcohol+toluene, +methylcyclohexane, and +isooctane and toluene+methylcyclohexane, and the ternary system tert-butyl alcohol+toluene+methylcyclohexane at 298.15 K

Abstract This paper reports experimental densities and refractive indices of the binary systems tert -butyl alcohol (TBA)+toluene, +isooctane, and +methylcyclohexane, and toluene+methylcyclohexane, and the ternary system TBA+toluene+methylcyclohexane, over the entire range of composition at 298.15 K. Excess molar volumes and changes of refractive indices were evaluated from the experimental data obtained. These derived properties were fitted to variable-degree polynomials. The experimental values of physical properties were compared with the values estimated by different methods of prediction.

Comparison of models in heterogeneous catalysis for ideal and non-ideal surfaces

Abstract A generalized multicomponent adsorption isotherm is used to derive rate equations for kinetic models which, from an energetic point of view, assume adsorption sites that are: (a) all identical (Langmuir), (b) have a linear distribution of adsorption energies (Temkin), or (c) have a logarithmic distribution of adsorption energies (Freundlich). A comparison is then made of the goodness of fit, for each of these rate equations, for 19 studies reported in the literature in which detailed kinetic data are available. In general, the same level of fitting is obtained for all three isotherm equations, indicating that the effect of distribution of site energies on the global kinetics is weak.

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.

On the Mechanism of Xylene Isomerization and its Limitations as Reaction Test for Solid Acid Catalysts

The kinetics of the gas-phase isomerization of m-xylene, over a series of ultraestable Y zeolites, has been studied in a fixed-bed flow reactor under initial conditions. Using deuterated p-xylene as reactant it has been seen that more than 20% of the m- and o-xylene obtained, are formed via a bimolecular mechanism. The relative proportion of uni- to bimolecular mechanism depends on the zeolite composition. The relation between the turnover number, calculated from the kinetic rate constant for the unimolecular mechanism, and the framework Al content of the zeolite, was coincident with the topological zeolite model. Besides, the values of the adsorption constants indicate that dealumination has an influence on the adsorption capacity of the zeolite for m-xylene, specially visible at high Si/Al ratios, coincident with the result of direct adsorption experiments of m-xylene, which in turn could explain the observed changes in the ratio uni- to bimolecular xylene isomerization upon dealumination.