It is possible to say that zeolites are the most widely used catalysts in industry They are crystalline microporous materials which have become extremely successful as catalysts for oil refining, petrochemistry, and organic synthesis in the production of fine and speciality chemicals, particularly when dealing with molecules having kinetic diameters below 10 A The reason for their success in catalysis is related to the following specific features of these materials:1 (1) They have very high surface area and adsorption capacity (2) The adsorption properties of the zeolites can be controlled, and they can be varied from hydrophobic to hydrophilic type materials (3) Active sites, such as acid sites for instance, can be generated in the framework and their strength and concentration can be tailored for a particular application (4) The sizes of their channels and cavities are in the range typical for many molecules of interest (5-12 A), and the strong electric fields2 existing in those micropores together with an electronic confinement of the guest molecules3 are responsible for a preactivation of the reactants (5) Their intricate channel structure allows the zeolites to present different types of shape selectivity, ie, product, reactant, and transition state, which can be used to direct a given catalytic reaction toward the desired product avoiding undesired side reactions (6) All of these properties of zeolites, which are of paramount importance in catalysis and make them attractive choices for the types of processes listed above, are ultimately dependent on the thermal and hydrothermal stability of these materials In the case of zeolites, they can be activated to produce very stable materials not just resistant to heat and steam but also to chemical attacks Avelino Corma Canos was born in Moncofar, Spain, in 1951 He studied chemistry at the Universidad de Valencia (1967−1973) and received his PhD at the Universidad Complutense de Madrid in 1976 He became director of the Instituto de Tecnologia Quimica (UPV-CSIC) at the Universidad Politecnica de Valencia in 1990 His current research field is zeolites as catalysts, covering aspects of synthesis, characterization and reactivity in acid−base and redox catalysis A Corma has written about 250 articles on these subjects in international journals, three books, and a number of reviews and book chapters He is a member of the Editorial Board of Zeolites, Catalysis Review Science and Engineering, Catalysis Letters, Applied Catalysis, Journal of Molecular Catalysis, Research Trends, CaTTech, and Journal of the Chemical Society, Chemical Communications A Corma is coauthor of 20 patents, five of them being for commercial applications He has been awarded with the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) 2373 Chem Rev 1997, 97, 2373−2419

From Microporous to Mesoporous Molecular-Sieve Materials and Their Use in Catalysis

This study describes the development and validation of Computational Fluid Dynamics (CFD) methodology for the simulation of dispersed two-phase flows. A two-fluid (Euler-Euler) methodology previously developed at Imperial College is adapted to high phase fractions. It employs averaged mass and momentum conservation equations to describe the time-dependent motion of both phases and, due to the averaging process, requires additional models for the inter-phase momentum transfer and turbulence for closure. The continuous phase turbulence is represented using a two-equation k − ε−turbulence model which contains additional terms to account for the effects of the dispersed on the continuous phase turbulence. The Reynolds stresses of the dispersed phase are calculated by relating them to those of the continuous phase through a turbulence response function. The inter-phase momentum transfer is determined from the instantaneous forces acting on the dispersed phase, comprising drag, lift and virtual mass. These forces are phase fraction dependent and in this work revised modelling is put forward in order to capture the phase fraction dependency of drag and lift. Furthermore, a correlation for the effect of the phase fraction on the turbulence response function is proposed. The revised modelling is based on an extensive survey of the existing literature. The conservation equations are discretised using the finite-volume method and solved in a solution procedure, which is loosely based on the PISO algorithm, adapted to the solution of the two-fluid model. Special techniques are employed to ensure the stability of the procedure when the phase fraction is high or changing rapidely. Finally, assessment of the methodology is made with reference to experimental data for gas-liquid bubbly flow in a sudden enlargement of a circular pipe and in a plane mixing layer. Additionally, Direct Numerical Simulations (DNS) are performed using an interface-capturing methodology in order to gain insight into the dynamics of free rising bubbles, with a view towards use in the longer term as an aid in the development of inter-phase momentum transfer models for the two-fluid methodology. The direct numerical simulation employs the mass and momentum conservation equations in their unaveraged form and the topology of the interface between the two phases is determined as part of the solution. A novel solution procedure, similar to that used for the two-fluid model, is used for the interface-capturing methodology, which allows calculation of air bubbles in water. Two situations are investigated: bubbles rising in a stagnant liquid and in a shear flow. Again, experimental data are used to verify the computational results.

Computational fluid dynamics of dispersed two-phase flows at high phase fractions

Supercritical fluids posses properties that make them attractive as media for chemical reactions. Conducting chemical reactions at supercritical conditions affords opportunities to manipulate the reaction environment (solvent properties) by manipulating pressure, to enhance the solubilities of reactants and products, to eliminate interphase transport limitations on reaction rates, and to integrate reaction and separation unit operations. Supercritical conditions may be advantageous for reactions involved in fuels processing, biomass conversion, biocatalysis, homogeneous and heterogeneous catalysis, environmental control, polymerization, materials synthesis, and chemical synthesis. Moreover, supercritical fluids can be used profitably in fundamental chemical investigations of intermolecular interactions and their influence on chemical processes. Work on chemical reactions in and with supercritical fluids is reviewed. We discuss both fundamental studies and applications of reactions at supercritical conditions, with focus on work published after 1985.

/pdf/reactions-at-supercritical-conditions-applications-and-1qoeqkmmtb.pdf

Reactions at supercritical conditions: Applications and fundamentals

Application of membrane separation processes in petrochemical industry: a review

This review focuses on the use of layered and porous aluminosilicates and layered double hydroxides as catalysts for the Fenton reaction. In the general sections of this review we present the elementary equations leading to the generation of hydroxyl radicals from H2O2 and the subsequent reactivity of this highly aggressive species. After justifying the advantages of using insoluble solids as heterogeneous catalysts, replacing soluble iron salts, we discuss the desirable features that should have an ideal Fenton catalyst and which are the parameters to be considered when ranking the efficiency of the materials. The main part of this review is focused on presenting the results reported up to late 2009 obtained using layered and porous aluminosilicates as heterogeneous catalysts. The structure of these materials is briefly presented to highlight the benefits and advantages of each type of solid with respect to their use as catalysts. When presenting the catalytic data, special emphasis is made on the missing data that would be useful to clarify, the relative efficiency and performance of the materials. In the final concluding remarks we stress again that the present situation needs to be clarified to draw solid conclusions on the relative performance and efficiency of the tested catalysts.

Heterogeneous Fenton catalysts based on clays, silicas and zeolites

Untersuchungen zum Oxidationsgrad eines CO-Tieftemperatur-Konvertierungs-kontaktes mit Hilfe dynamischer Experimente

Summary The main reaction pathways of the oxidative coupling of CH 4 to C 2 H 6 , C 2 H 4 , CO and CO 2 were determined using a Ce/Li/MgO catalyst at 750 ° C. In non-catalytic runs it was found that homogeneous oxidation of CH 4 as well as of CO is neglegible, but the conversion of C 2 H 6 to C 2 H 4 and further oxidation of C 2 H 4 into CO occure as homogeneous gas phase reactions. In the presence of the catalyst CH 4 is oxidized selectively to C 2 H 6 as well as unselectively to CO 2 , which is partly produced also from C 2 H 6 . C 2 H 6 is converted to C 2 H 4 by oxidative dehydrogenation as well as by dehydrogenation. CO is oxidized to CO 2 . The rates of all these reactions were described by power law equations.

Kinetic Studies of the Oxidative Coupling of Methane Over a Ce/Li/Mgo Catalyst

The rational design, simulation and optimization of an industrial reactor has to be based on accurate, reliable data for mass, energy and momentum transport as well as chemical kinetics. For this purpose specially designed laboratory or pilot experiments are needed, as only in very rare cases is a theoretical evaluation possible. The aim of any kinetic data analysis in reaction engineering is to find adequate reaction model equations and to arrive at reliable parameter estimates dependent on the operating variables of the reactor, like pressure, temperature, flow conditions etc. These parameters then will be used in a reactor model, i.e., a set of equations that describe the behavior of a reactor with sufficient accuracy.

Kinetic Data Analysis and Parameter Estimation

Kinetik der Absorption von Stickstoff(IV)-oxid bei kleinen Partialdrücken

A body-centred cubic lattice has been used to represent the packing in a model of a trickle bed. Liquid distribution has been simulated by a percolation process in this lattice. The liquid flow distribution is governed by a single parameter p which describes the static properties of the packing independent of the liquid load. Simulations of different packings and flow rates describe the experimental results in the low-interaction regime satisfactorily. The simulation results may also be used for the successful estimation of the experimentally determined dynamic liquid hold-up.

Some experiences with the application of the percolation concept for modelling trickle-bed fluid dynamics

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