Ana G. Gayubo

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.

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.

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.

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.

Calculation of the kinetics of deactivation by coke in an integral reactor for a triangular scheme reaction

Abstract The kinetics of deactivation by coke deposition has been studied for a SiO2-Al2O3 catalyst in the isomerization of n-butenes in the 150-240°C temperature range. The kinetic model is a separable one, with a kinetic equation of the Langmuir—Hinshelwood—Hougen—Watson type for each one of the steps of the main reaction and of the deactivation reaction. The deactivation corresponds to the blockage of active sites by coke coming from degradation of cis-butene and trans-butene. The experimentation has been carried out in an isothermal integral reactor by working with a linear sequence of temperature—time. The treatment of the deactivation data for kinetic parameter calculation consists in rigorously solving the design equation for plug flow reactor; this method takes into account the effect of the composition of all the components on deactivation. The kinetic model has been verified by comparing the experimental results with those foreseen in the simulation of the isothermal operation and with different sequences of temperature-time. The procedure for both obtaining and analysing the deactivation kinetics data is particularly useful for complex reaction systems. In these systems, simplified methods for experimentation and calculation used to isolate the effect of composition on deactivation are not applicable.

Spatial Distribution of Zeolite ZSM‐5 within Catalyst Bodies Affects Selectivity and Stability of Methanol‐to‐Hydrocarbons Conversion

Solid acids, such as zeolites, are used as catalyst materials in a wide variety of important crude oil refinery, bulk chemical synthesis, and green processes. Examples include fluid catalytic cracking (FCC),[1] methanol-to-hydrocarbons (MTH) conversion,[ 2] plastic waste valorization,[3] and biomass catalysis.[4] Industrially, these solid acid catalysts are used as composite materials with the zeolite particles as active components heterogeneously dispersed within a matrix of binders and fillers (alumina or porous solids) then shaped into micro- or millimetersized catalyst bodies.[5] It is known that these matrix materials extend the lifetime of the active zeolite component by providing mechanical strength and protection against poisoning as well as by enhancing heat dissipation and mass transport.

Compositional Insights and Valorization Pathways for Carbonaceous Material Deposited During Bio-Oil Thermal Treatment

This work analyses the composition, morphology, and thermal behavior of the carbonaceous materials deposited during the thermal treatment of bio-oil (thermal pyrolytic lignin-TPL). The bio-oil was obtained by flash pyrolysis of lignocellulosic biomass (pine sawdust), and the TPLs were obtained in the 400-700 °C range. The TPLs were characterized by performing elemental analysis; (13)C NMR, Raman, FTIR, and X-ray photoelectron spectroscopy; SEM; and temperature-programmed oxidation analyzed by differential thermogravimetry and differential scanning calorimetry. The results are compared to a commercial lignin (CL). The TPLs have lower oxygen and hydrogen contents and a greater aromaticity and structural order than the CL material. Based on these features, different valorization routes are proposed: the TPL obtained at 500 °C is suitable for use as a fuel, and the TPL obtained at 700 °C has a suitable morphology and composition for use as an adsorbent or catalyst support.