Francisco J. Llopis

A New Aluminosilicate Molecular Sieve with a System of Pores between Those of ZSM-5 and Beta Zeolite

A new aluminosilicate zeolite (ITQ-39) has been synthesized. This is an extensively faulted structure with very small domains that makes the structure elucidation very difficult. However, a combination of adsorption spectroscopy and reactivity studies with selected probe molecules suggests that the pore structure of ITQ-39 is related to that of Beta zeolite, with a three-directional channel system with large pores (12-MR), but with an effective pore diameter between those of Beta and ZSM-5, or a three-directional channel system with interconnected large (12-MR) and medium pores (10-MR). The pore topology of ITQ-39 is very attractive for catalysis and shows excellent results for the preparation of cumene by alkylation of benzene, while it can be a promising additive for FCC.

Non-oxidative dehydroaromatization of methane: an effective reaction–regeneration cyclic operation for catalyst life extension

Non-oxidative methane aromatization is an attractive direct route for producing higher hydrocarbons. It is highly selective to benzene despite the low conversion due to thermodynamic limitations, and Mo/H-ZSM-5, the first catalyst proposed for this reaction, is still considered as one of the most adequate. The major problem of this process is the severe catalyst deactivation due to the rapid build-up of carbonaceous deposits on the catalysts. Here we present an effective regeneration procedure that extends the life of Mo/zeolite based catalysts by combining reaction periods of 1.5 h with 0.5 h regeneration steps in a continuous cyclic mode and methane activation after each regeneration stage. Benzene productivity obtained with Mo/ZSM-5 is shown to be almost constant for increasing TOS ranges when applying this new cyclic protocol, and threefold values are achieved for an 18 h on stream period by limiting the reaction steps to the first 1.5 h of maximum benzene selectivity (97 vs. 33 g benzene per kg cat h) compared to a conventional single run.

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.

Isobaric vapor-liquid equilibrium of binary mixtures of 1-propanol + chlorobenzene and 2-propanol + chlorobenzene

Abstract Isobaric vapor-liquid equilibria were obtained for the system 1-propanol + chlorobenzene at 20 and 100 kPa and for the system 2-propanol + chlorobenzene at 100 kPa using a dynamic still. The experimental error in temperature was ±0.1 K, in pressure ±0.01 kPa and ±0.1 kPa for the experiments carried out at 20 and 100 kPa, respectively, and in the liquid and vapor mole fraction 0.001. The two systems satisfy the point-to-point thermodynamic consistency test. Both systems show a positive deviation from ideality. The data were well correlated with the Margules, Van Laar, Wilson, NRTL and UNIQUAC equations.

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.

Phase equilibria and variation of the azeotropic composition with pressure for binary mixtures of 1-propanol + chlorobenzene and 1-butanol + chlorobenzene

Abstract Isobaric vapor-liquid equilibria were obtained for the systems 1-propanol + chlorobenzene and 1-butanol + chlorobenzene at 200 and 300 kPa using a dynamic still. The mole fraction of the alcohol in the azeotropic point increases with pressure and for the 1-propanol + chlorobenzene system at 300 kPa, the azeotrope has disappeared. The two systems satisfy the point-to-point thermodynamic consistency test. Both systems show a positive deviation from ideality. The data were well correlated with the Margules, van Laar, Wilson. NRTL and UNIQUAC equations.

Vapor–liquid equilibrium of binary mixtures of trichloroethylene with 1-pentanol, 2-methyl-1-butanol and 3-methyl-1-butanol at 100 kPa

Abstract Isobaric vapor–liquid equilibria (VLE) have been obtained for the systems trichloroethylene+1-pentanol, trichloroethylene+2-methyl-1-butanol and trichloroethylene+3-methyl-1-butanol at 100 kPa using a dynamic still. The experimental error in temperature is ±0.1 K, in pressure ±0.1 kPa, and in the liquid and vapor mole fraction ±0.001. The three systems satisfy the point-to-point thermodynamic consistency test. All the systems show positive deviations from ideality. The data have been correlated with the Margules, van Laar, Wilson, NRTL and UNIQUAC equations.

Vapor–liquid equilibrium of binary mixtures of chlorobenzene with 3-methyl-1-butanol, 3-methyl-2-butanol and 2-methyl-2-butanol, at 100 kPa

Abstract Isobaric vapor–liquid equilibria have been obtained for the systems 3-methyl-1-butanol+chlorobenzene, 3-methyl-2-butanol+chlorobenzene and 2-methyl-2-butanol+chlorobenzene at 100 kPa, using a dynamic still. The experimental error in temperature is ±0.1 K, in pressure ±0.1 kPa, and in the liquid and vapor mole fraction ±0.001. The three systems satisfy the point-to-point thermodynamic consistency test. All the systems show positive deviations from ideality. The data have been correlated with the Margules, Van Laar, Wilson, NRTL and UNIQUAC equations.