Computing the correlation between catalyst composition and its performance in the catalysed process

The methodology for computing correlations between continuous descriptors of catalytic materials and their performance in the catalysed process is addressed. Continuous descriptors are typically molar fractions of individual components of the catalyst, whereas the performance is represented most frequently by yield or selectivity of reaction products or conversion of key feed components. Measures of various kinds of correlation are recalled, and their descriptor-wise application to catalytic data for computing correlations between the composition and performance of catalysts is presented. The paper also compares the application of correlation measures to catalytic data on the one hand with the analysis of variance, on the other hand with the application of regression trees. As a case study, the presented approaches are applied to data from high-temperature synthesis of hydrocyanic acid

Studies on Biodiesel Synthesis Using Nanosilica Immobilised Lipase in Inverse Fluidized Bed Bioreactors

Biodiesel synthesis from neem oil and methyl acetate using lipase catalyst immobilised in nanosilica particles in a continuous inverse fluidised bed bioreactor of modified design has been analysed. The process has been simulated mathematically by developing a multiparameter software package and subsequently verified through pilot plant tests(experiments).The improved performance characteristics of the bioreactor of proposed design have been highlighted. Graphical data have been presented to illustrate the dependence of reactor performance on system/operating parameters such as substrate flow rate, catalyst loading and molar ratio of oil to acetate in the blend(substrate solution).The downflow mode of operation is an added advantage of these bioreactors which tends to reduce their operating cost. Due to the use of nanoparticles, the effectiveness factor is close to unity and consequently, the global rate of transesterification is more or less equal to the intrinsic rate. This enhances the performance efficiency of the bioreactor

Study of Confinement and Catalysis Effects of the Reaction of Methylation of Benzene by Methanol in H-Beta and H-ZSM-5 Zeolites by Topological Analysis of Electron Density

In this work we studied the host-guest interactions between confined molecules and zeolites and their relationship with the energies involved in the reaction of methylation of benzene by methanol in H-ZSM-5 and H-Beta zeolites employing density functional theory (DFT) methods and the quantum theory of atoms in molecules. Results show that the strength of the interactions related to adsorption and coadsorption processes is higher in the catalyst with the larger cavity; however, the confinement effects are higher in the smaller zeolite, explaining, from an electronic viewpoint, the reason why the stabilization energy is higher in H-ZSM-5 than in H-Beta. The confinement effects of the catalyst on the confined species for methanol adsorption, benzene coadsorption, and the formed intermediates dominate this stabilization. For the transition state (TS), the stability of the TS is achieved due to the stabilizing effect of the surrounding zeolite framework on the formed carbocationic species (CH3+) which is higher in H-ZSM-5 than in H-Beta. In both TSs the methyl cation is multicoordinated forming the following H2O···CH3+···CB concerted bonds. It is demonstrated that, through the electron density analysis, the criteria can be defined to discriminate between interactions related to the confinement effects and the reaction itself (adsorption, coadsorption, and bond-breaking and bond-forming processes) and, thus, to discriminate the relative contributions of the degree of confinement to the reaction energies for two zeolite catalysts with different topologies.Fil: Zalazar, Maria Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Química Básica y Aplicada del Nordeste Argentino. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Química Básica y Aplicada del Nordeste Argentino; ArgentinaFil: Paredes, Esteban Nadal. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Química. Laboratorio de Estructura Molecular y Propiedades; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; ArgentinaFil: Romero, Gonzalo David. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Química. Laboratorio de Estructura Molecular y Propiedades; ArgentinaFil: Cabral, Néstor Damián. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Química. Laboratorio de Estructura Molecular y Propiedades; ArgentinaFil: Peruchena, Nelida Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Química Básica y Aplicada del Nordeste Argentino. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Química Básica y Aplicada del Nordeste Argentino; Argentin

Cynara cardunculus as an alternative crop for biodiesel production.

Biodiesel is a renewable fuel obtained from vegetable oils or animal fats, with similar propertiesto fossil diesel fuel. It is obtained from the transesterification of the triglycerides with a shortchain alcohol in the presence of a catalyst, giving biodiesel and glycerol in two separated phases.Traditional raw materials for biodiesel production are the oils of rapeseed, sunflower, soybeanand palm. However, some alternative raw materials such as animal fats, recycled oils and nonconventional crops, are also used.This thesis is focused on the use of Cynara cardunculus oil for the production of biodiesel. Cynaracardunculus is a wild cardoon from the family of artichoke that is well adapted to theMediterranean weather. The maximum production reaches 2 tons/ha per year of seeds thatcontain up to 25 % oil, with a similar composition to sunflower oil. Thus, Cynara cardunculuscultivation may represent an alternative for abandoned cropland and a good candidate asrenewable energy source and biodiesel production.In the first part of the work, the reaction conditions where optimised for the transesterificationof unrefined Cynara cardunculus oil. The product obtained was characterised. The acid value of theoriginal oil (11.8 mgKOH/g) was higher than the values recommended for alkalinetransesterification (1-2 mgKOH/g) resulting in the formation of soaps and gels. For some of thereaction conditions, the ester and glycerol phases were not clearly separated, reflecting the needof a preesterification step in order to reduce the acid value of the oil. The preesterification stepwas optimised using different reaction temperatures, catalyst and methanol concentrations andreaction times. The best results were obtained for the reactions conducted at 60ºC, using a 6:1methanol to oil molar ratio and 0.5% sulphuric acid as catalyst. Finally, the oil was pre-treatedusing the best conditions for the preesterification, with an additional degumming step. Thetransesterification of the pre-treated oil was optimised and the results were compared to theprevious ones. The ester yield increased with the pre-treatment and the ester and glycerol phaseswere clearly separated in most of the cases, showing the advantages of the degumming andpreesterification steps.The second part of the work was the characterisation of the mixtures of biodiesel and diesel fuel.European specific normatives for both biodiesel (EN 14214) and fossil diesel fuel (EN 590) weredetailed, together with their requirements and test methods. Mixtures of both fuels at differentproportions, were analysed according to EN 590. Correlations for the mixtures were determinedwith experiments or mass balances, according to each case. There are some properties than canlimit the amount of biodiesel allowed in the mixture in order to satisfy the specifications fordiesel fuel, such as density, viscosity, distillation, oxidative stability and cold weather properties. Itwas detected the need of specific analytical methods and requirements for some of the properties.The third part of the work was the analysis of the biodegradability of mixtures of biodiesel andfossil derived fuels, such as heavy fuel oil, diesel fuel and gasoline. The CO2 evolution test wasused to analyse the biodegradation behaviour of the mixtures. In all the cases cometabolicbiodegradation was observed demonstrating that biodiesel enhances the degradation of the threefossil derived fuels analysed. The physical properties of the mixtures were also analysed.UNIVERSITAT ROVIRA I VIRGILICYNARA CARDUNCULUS AS AN ALTERNATIVE CROP FOR BIODIESEL PRODUCTION.Jorgelina Cecilia PasqualinoEl biodiesel es un combustible de origen renovable que se obtiene a partir de aceites vegetales ygrasas animales y posee propiedades similares a las del gasoil. Se produce mediante latransesterificación de los triglicéridos con un alcohol de cadena corta, en presencia de uncatalizador, obteniendo biodiesel y glicerol en dos fases separadas. Los aceites más utilizados en laproducción de biodiesel son los de soja, colza, girasol y palma, aunque existen alternativas comolos aceites de fritura reciclados, las grasas animales y algunos cultivos no convencionales.En este trabajo se utilizó el aceite de Cynara cardunculus para producir biodiesel. Cynaracardunculus es un cardo silvestre de la familia de la alcachofa, que se encuentra adaptado al climaMediterráneo. Su producción máxima alcanza las 2 toneladas de semilla por hectárea al año, quecontienen hasta un 25 % de aceite, con una composición similar al aceite de girasol. De estemodo, el Cynara cardunculus puede representar un cultivo alternativo para la producción debiodiesel, pudiéndose cultivar en tierras abandonadas.En la primera parte del trabajo se optimizaron las condiciones para la transesterificación de aceitede Cynara cardunculus sin refinar y se caracterizó el producto obtenido. El índice de acidez delaceite original (11.8 mgKOH/g) fue mayor al recomendado para la transesterificación alcalina (1-2 mgKOH/g), resultando en la formación de gel y jabón. En algunos casos no se produjo unaseparación clara de las fases, reflejando la necesidad de una etapa de preesterificación para reducirel índice de acidez. La preesterificación fue optimizada utilizando diferentes temperaturas,concentraciones de metanol y catalizador, y tiempos finales de reacción. Las mejores condicionesde operación se obtuvieron para la reacción realizada a 60ºC, utilizando metanol en una relaciónmolar de 6:1 con respecto al aceite, y un 0.5% de H2SO4 como catalizador. Finalmente, el aceitefue pre-tratado bajo las condiciones óptimas de preesterificación, con una etapa adicional dedegomado. La reacción de transesterificación del aceite pre-tratado fue optimizada y losresultados comparados con los de la reacción del aceite crudo. El contenido en metilésteres fuesuperior al utilizar aceite pre-tratado, y las fases de metilésteres y glicerol se separaron confacilidad en la mayoría de los casos, demostrando la utilidad de las etapas de pretratamiento.La segunda parte fue la caracterización de las mezclas de biodiesel con gasoil. Las normativaseuropeas para el biodiesel (EN 14214) y para el gasoil (EN 590) fueron detalladas junto con susrequisitos y métodos de ensayo. Las mezclas de ambos combustibles en diferentes proporcionesse analizaron de acuerdo a la norma EN 590. Las correlaciones para el comportamiento de lasmezclas se determinaron mediante experimentación y balances de materia, según el caso. Sedeterminó que algunas propiedades como la densidad, la viscosidad, la destilación, la estabilidad ala oxidación y las propiedades en frío pueden limitar la cantidad de biodiesel permitida en lamezcla para que esta cumpla con la normativa vigente para el gasoil. Se detectó la necesidad demétodos específicos de análisis y requisitos para algunas de las propiedades.La tercera parte de este trabajo consistió en el análisis de la biodegradabilidad de las mezclas debiodiesel con combustibles de origen fósil, como fuel pesado, gasoil y gasolina. Labiodegradación se determinó mediante el método de evolución de CO2. En todos los casos seobservó la presencia de cometabolismo, demostrando que el biodiesel incrementa labiodegradabilidad de los tres combustibles fósiles examinados. Se analizaron además laspropiedades físicas de las mezclas.UNIVERSITAT ROVIRA I VIRGILICYNARA CARDUNCULUS AS AN ALTERNATIVE CROP FOR BIODIESEL PRODUCTION.Jorgelina Cecilia Pasqualin

Computational Ligand Descriptors for Catalyst Design

Ligands, especially phosphines and carbenes, can play a key role in modifying and controlling homogeneous organometallic catalysts, and they often provide a convenient approach to fine-tuning the performance of known catalysts. The measurable outcomes of such catalyst modifications (yields, rates, selectivity) can be set into context by establishing their relationship to steric and electronic descriptors of ligand properties, and such models can guide the discovery, optimization, and design of catalysts. In this review we present a survey of calculated ligand descriptors, with a particular focus on homogeneous organometallic catalysis. A range of different approaches to calculating steric and electronic parameters are set out and compared, and we have collected descriptors for a range of representative ligand sets, including 30 monodentate phosphorus­(III) donor ligands, 23 bidentate P,P-donor ligands, and 30 carbenes, with a view to providing a useful resource for analysis to practitioners. In addition, several case studies of applications of such descriptors, covering both maps and models, have been reviewed, illustrating how descriptor-led studies of catalysis can inform experiments and highlighting good practice for model comparison and evaluation

Concepts, models, and methods in computational heterogeneous catalysis illustrated through CO2 conversion

Theoretical investigations and computational studies have notoriously contributed to the development of our understanding of heterogeneous catalysis during the last decades, when powerful computers have become generally available and efficient codes have been written that can make use of the new highly parallel architectures. The outcomes of these studies have shown not only a predictive character of theory but also provide inputs to experimentalists to rationalize their experimental observations and even to design new and improved catalysts. In this review, we critically describe the advances in computational heterogeneous catalysis from different viewpoints. We firstly focus on modeling because it constitutes the first key step in heterogenous catalysis where the systems involved are tremendously complex. A realistic description of the active sites needs to be accurately achieved to produce trustable results. Secondly, we review the techniques used to explore the potential energy landscape and how the information thus obtained can be used to bridge the gap between atomistic insight and macroscale experimental observations. This leads to the description of methods that can describe the kinetic aspects of catalysis, which essentially encompass microkinetic modeling and kinetic Monte Carlo simulations. The puissance of computer simulations in heterogeneous catalysis is further illustrated by choosing CO2 conversion catalyzed by different materials for most of which a comparison between computational information and experimental data is available. Finally, remaining challenges and a near future outlook of computational heterogeneous catalysis are provided.publishe

Kinetic Monte Carlo simulation of the water gas shift reaction on Cu(111) from density functional theory based calculations

A systematic first-principles kinetic Monte Carlo study of the water gas shift reaction taking place on the Cu(111) surface is presented including adsorption/desorption, diffusion and other elementary chemical reactions, totalling 34 elementary steps with all reaction rates obtained from periodic density functional theory based calculations. The kinetic Monte Carlo simulations were carried out at different partial pressures and temperatures. The results show that the diffusion processes cannot be neglected and that the reaction proceeds predominantly through an associative mechanism via a carboxyl intermediate. The analysis of temperature dependence shows an Arrhenius behaviour with an apparent activation energy of 0.5-0.8 eV in agreement with experiments and with previous microkinetic studies. The effect of H2O/CO ratio on this reaction shows that mixtures with higher CO proportion enhance the reactivity, also in accordance to previous studies. The present work allows one to ascertain the relative importance of the different steps in the mechanism of water gas shift reaction over Cu(111) at several conditions as well as to see the coverage evolution of the surface