Pedro L. Benito

Effect of Si/Al ratio and of acidity of H-ZSM5 zeolites on the primary products of methanol to gasoline conversion

From experiments in a chromatographic reactor, under conditions of incipient reaction, the effect of the Si/Al ratio of H-ZSM5 zeolites on the nature of the primary products has been proven in the transformation of methanol into gasoline. It has been determined that alkenes (ethene, propene and butenes) are the first reaction products, the proportion of heavier alkenes being greater as the Bronsted/Lewis ratio increases and as total acidity decreases (decrease in acidic site density). By in-situ FTIR analysis of the adsorbed phase, the presence of surface methoxy groups has been determined. By virtue of the results, a mechanism of propagation–decomposition of oxonium ions has been proposed. This mechanism basically occurs in a phase adsorbed on the zeolite and explains the formation of the first CC bond and the presence in the gas phase of the first products according to a reaction–diffusion compromise for each one of the intermediate products of the mechanism.

Relationship between surface acidity and activity of catalysts in the transformation of methanol into hydrocarbons

The effect of Si/A1 ratio of HZSM5 zeolite-based catalysts on surface acidity and on selectivity in the transformation of methanol into hydrocarbons has been studied. The acidic strength distribution (measured by combining the differential scanning calorimetry and the chromatographic analysis) and the total acidity (measured by calorimetry and temperature programmed desorption), using ammonia and tert-butylamine, have been studied as acidity measurements. The nature of the acidic sites has been determined by FTIR analysis of both the surface OH groups and the interaction of Bronsted and Lewis sites with pyridine. The increase in light olefin selectivity and the decrease in methanol conversion with increasing Si/Al ratio are a consequence of the kinetic scheme of the reaction, which has steps in series, and can be explained by the decrease in total acidity. The same acidic sites are responsible for the formation of light olefins and for the transformation of these olefins into higher hydrocarbons.

Acidity deterioration and coke deposition in a HZSM5 zeolite in the MTG process

Summary The total acidity deterioration and the acidity strength distribution of a catalyst prepared from a H-ZSM-5 zeolite has been studied in the MTG process carried out in catalytic chamber and in an isothermal fixed bed integral reactor. The acidity deterioration has been related to coke deposition. The evolution of the acidic structure and of coke deposition has been analysed in situ by diffuse reflectance FTIR in a catalytic chamber. The effect of operating conditions (time on stream and temperature) on acidity deterioration, coke deposition and coke nature has been studied from experiments in a fixed integral reactor. The technique for studying acidity yields a reproducible measurement of total acidity and acidity strength distribution of the catalyst deactivated by coke. The NH3 adsorption-desorption is measured by combination of scanning differential calorimetry and the FTIR analysis of the products desorbed.

Kinetic model of the MTG process taking into account the catalyst deactivation. Reactor simulation

Abstract A kinetic model for the deactivation of catalyst (based on a HZSM5 zeolite) in the transformation of methanol into gasoline is proposed from results obtained in an isothermal fixed bed integral reactor. The kinetic model takes into account the effect of the composition of the lumps of oxygenates, light olefins and rest of products on the catalyst deactivation along the reactor. The model allows for simulating the integral reactor and for studying the influence of the operating conditions on selectivity towards different lumps in the MTG process. The resukts have been experimentally proven in an isothermal integral reactor and are in agreement with the results of coke deposition along the reactor.

The role of water on the attenuation of coke deactivation of a SAPO-34 catalyst in the transformation of methanol into olefins

The effect of water concentration on the reaction medium in order to attenuate coke formation on a SAPO-34 has been studied in the transformation of methanol into olefins. From the results obtained in an integral reactor for different values of space time and water concentration in the feed, a kinetic model for deactivation by coking on a SAPO-34 in the 623–748 K range has been proposed. The model takes into account the effect on the deactivation of organic components and water in the reaction medium.

Analysis of kinetic models of the methanol-to-gasoline (MTG) process in an integral reactor

Abstract From experimental results obtained in a wide range of operating conditions (temperature and contact time) in an isothermal fixed bed integral reactor, the validity both of the kinetic models proposed in the literature as well as their modifications, for the methanol-to-gasoline (MTG) process at zero time on-stream, has been studied. The kinetic parameters for the various models have been calculated by solving the equation of mass conservation in the reactor for the lumps of the kinetic models. The usefulness of the model of Schipper and Krambeck for simulating the operation in the isothermal fixed bed integral reactor has been proven in the 573–648 K range.