Andrés T. Aguayo

Pressure drop in conical spouted beds

Abstract The limitations of the few correlations in the literature for the design of conical spouted beds and the non-validity of these conventional correlations proposed for cylindrical spouted beds have been proven. Consequently, original hydrodynamic correlations for spouting and jet spouting, corresponding to conical contactors, have been proposed for the calculation of the maximum pressure drop and of the pressure drop in stable operational conditions. The hydrodynamic study has been carried out with different geometries of the contactor—inlet system (different angles and diameters of inlet) and with solids of different particle sizes, densities and shape factors, so that the correlations obtained are of general applicability.

Deactivation by coke of a catalyst based on a SAPO-34 in the transformation of methanol into olefins

When methanol is converted to olefins on a SAPO-34 catalyst between 350 and 425°C, there is a rapid initial formation of coke, followed by a slower rate of coke deposition. The rate of coke formation decreases with increasing temperature, and with progression through the catalyst bed. The coke completely blocks the internal channels of the SAPO-34 crystals and subsequently blocks the mesopores (intercrystalline and those of the bentonite). Coke deposition mainly blocks sites of acidic strength above 175 kJ/mol. The presence of water in the feed lessens coke formation, either by converting Lewis to Bronsted sites or by competing for surface sites with coke precursors.

Catalyst deactivation by coking in the MTG process in fixed and fluidized bed reactors

Abstract The validity of a kinetic model for describing the deactivation of a catalyst based on a HZSM5 zeolite has been studied by carrying out reaction in fixed and fluidized bed reactors. The kinetic model takes into account that activity is dependent on the concentration of the lumps of oxygenates, of light olefins and of the remaining products and shows that coke formation capability follows this order. The difference between the deactivation kinetic constants calculated for the fixed and fluidized bed reactors is explained by the effect of the steam produced in the reaction, where coke stripping attenuates deactivation. Future improvements in the deactivation kinetic model must take into account coke stripping by the steam produced in the reaction.

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.

Expansion of spouted beds in conical contactors

Abstract The expansion of conical spouted beds has been studied on a wide experimental base (using contactors of different geometries and solids of different diameters and sphericities). The correlation obtained for calculating the global voidage from the operation conditions is of a more general application than those previously proposed in the literature, which are generally centred on the study of voidage in the spout. The global incipient voidages are delimited for both stable regimes corresponding to two voidage ranges: spouting and jet spouting. While the correlation for calculation of expansion can be applied for the calculation of global minimum jet spouting voidage, a correlation is proposed for the calculation of the global minimum spouting voidage. This equation is applicable in a wide range of operation conditions.

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.

Hydrodynamics of nearly flat base spouted beds

Abstract The hydrodynamic behaviour of a nearly flat base spouted bed (angle 150▿) was studied in a pilot plant unit,using solids of different densities and particle diameters and with different values of the contactor inlet diameter. It was determined that the equation of Mathur and Gishler with an exponent of 0.10 for the (D0/Dc) modulus is suitable for calculation of the minimum spouting velocity. Original correlations for prediction of the maximum pressure drop, of the pressure drop for stable operation and of bed viodage in the bed expansion are proposed. It is proved that the maximum spoutable bed height can be calculated using the equation proposed by Morgan et al. for conventional spouted beds. For small particle diameters the equation of Malek and Lu is also valid.

Regeneration of a catalyst based on a SAPO-34 used in the transformation of methanol into olefins

The regeneration by coke combustion of a catalyst based on a SAPO-34 used in the transformation of methanol into olefins (ethene and propene) has been studied. It has been observed that coke combustion kinetics are strongly dependent on the nature of the coke (H/C ratio), which in turn is a consequence of the reaction conditions (especially of the water content in the feed) and of the ageing level of the coke prior to its combustion. A severe ageing treatment is needed in order for combustion kinetics to be reproducible. Combustion is delayed due to the fact that coke is not an inert material but is bound to the acid sites. © 1999 Society of Chemical Industry

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.

Porous supramolecular compound based on paddle-wheel shaped copper(II)–adenine dinuclear entities

The reaction between CuCl2 and adenine in a non-aqueous solvent provides a 3D porous structure based on paddle-wheel [Cu2(µ-adenine)4Cl2]2+ cations and Cl− anions that are held together by a robust supramolecular hydrogen bonding network. The desolvated compound is able to host different guest molecules within the ∼6 A diameter 1D channels.