Kinetics of Aqueous Phase Dehydration of Xylose into Furfural Catalyzed by ZSM-5 Zeolite

ZSM-5 zeolite in H+ form with an average pore size of 1.2 nm was used for aqueous phase dehydration of xylose to furfural at low temperatures;, that is, from 413 to 493 K. The selectivity in furfural increased with the temperature to a value of 473 K. Beyond this temperature, condensation reactions were significant and facilitated by the intrinsic structure of ZSM-5. A reaction mechanism that included isomerization of xylose to lyxose, dehydration of lyxose and xylose to furfural, fragmentation of furfural to organic acids, oligomerization of furfural to bi- and tridimensional furilic species, and complete dehydration of organic acids to carbonaceous deposits was developed, and the associated kinetic parameters were estimated. The rate of furfural production was found to be more sensitive to temperature than the rates of side reactions, with an estimated activation energy of 32.1 kcal/mol. This value correlated well with data in the literature obtained by homogeneous catalytic dehydration.

Experimental validation of the performance of a microreactor for the high-throughput screening of catalytic coatings

In this paper, the results of computational fluid dynamics simulations of flow, temperature, and concentration distributions used in the design of a microreactor for the high-throughput screening of catalytic coatings (Mies et al., Chem. Eng. J. 2004, 101, 225) are compared with experimental data, and good agreement is obtained in all cases. The experimental results on flow distribution were obtained from laser Doppler anemometry measurements in the range of Reynolds numbers from 6 to 113. The measured flow nonuniformity in the separate reactor compartments was below 2%. The temperature distribution was obtained from thermocouple measurements. The temperature nonuniformity between the reactor compartments was below 3 K at a maximum heat production rate of 1.3 W in ethylene oxidation at 425 degrees C over CuO/Al2O3/Al coatings. With respect to concentration gradients, a deviation from the average rate of reaction of only 2.3% was obtained at realistic process conditions in the ethylene ammoxidation process over identical Co-ZSM-5 coatings in all reactor compartments. The cross talking noise between separate compartments does not exceed 0.1% when the reactor parts have a smooth surface finish. This illustrates the importance of ultraprecision machining of surfaces in microtechnology, when interfaces cannot be avoided.

On the solubility of three disperse anthraquinone dyes in supercritical carbon dioxide: new experimental data and correlation

Solubility measurements of quinizarin. (1,4-dihydroxyanthraquinone), disperse red 9 (1-(methylamino) anthraquinone), and disperse blue 14 (1,4-bis(methylamino)anthraquinone) in supercritical carbon dioxide (SC CO2) were carried out in a flow type apparatus, at a temperature range from (333.2 to 393.2) K and at pressures from (12.0 to 40.0) MPa. Mole fraction solubility of the three dyes decreases in the order quinizarin (2.9 x 10(-6) to 2.9.10(-4)), red 9 (1.4 x 10(-6) to 3.2 x 10(-4)), and blue 14 (7.8 x 10(-8) to 2.2 x 10(-5)). Four semiempirical density based models were used to correlatethe solubility of the dyes in the SC CO2. From the correlation results, the total heat of reaction, heat of vaporization plus the heat of solvation of the solute, were calculated and compared with the results presented in the literature. The solubilities of the three dyes were correlated also applying the Soave-Redlich-Kwong cubic equation of state (SRK CEoS) with classical mixing rules, and the physical properties required for the modeling were estimated and reported.

Using SysML in systems design

System of systems involves several secondary systems working together with its creation gathering the knowledge of several distinct disciplines and teams, each one with their own background and methods, leading to a difficult communication between them. SysML, a language originated from UML, enables that communication, without background interference, with the use of a rich notation for systems design. This paper analyzes its use through the experience gained in the design of a chemical system with SysML.

Software de gestão de manutenção como ferramenta de apoio à melhoria da eficiência da gestão de infraestruturas

Este trabalho académico surge no âmbito da realização da dissertação do Mestrado em Engenharia e Gestão Industrial. Tem como objetivo a melhoria da gestão do Departamento de Infraestruturas, numa empresa de produção de motores elétricos para a indústria automóvel, através da análise, implementação e melhoria de um software de gestão de manutenção, de forma a aumentar a eficiência do Departamento. Este estudo foi desenvolvido durante um estágio curricular na empresa Globe Motors Portugal Lda, localizada em Vila do Conde. Para sua sustentação, foi efetuada uma análise funcional, suportada por um Software de gestão de manutenção, de forma a perceber qual a importância que o mesmo tem no funcionamento do Departamento de Infraestruturas. Pretendeu-se compreender quais as vantagens e desvantagens da sua utilização. Posteriormente, implementou-se uma nova versão deste software, analisando-se os pontos fortes e as oportunidades de melhoria, de forma a tornar o Departamento de infraestruturas mais eficiente, através da utilização desta renovada ferramenta de trabalho. Como objetivo último, pretendeu-se à melhoria da organização e gestão do Departamento de infraestruturas, contribuindo para um desenvolvimento de toda a empresa, uma vez que comungamos a ideia de que só é possível ser competitivo, num mercado altamente exigente, através de processos eficientes, possibilitando a redução de custos a todos os níveis.

Heuristic solution methods for multi-attribute vehicle routing problems

Le Problème de Tournées de Véhicules (PTV) est une clé importante pour gérér efficacement des systèmes logistiques, ce qui peut entraîner une amélioration du niveau de satisfaction de la clientèle. Ceci est fait en servant plus de clients dans un temps plus court. En terme général, il implique la planification des tournées d'une flotte de véhicules de capacité donnée basée à un ou plusieurs dépôts. Le but est de livrer ou collecter une certain quantité de marchandises à un ensemble des clients géographiquement dispersés, tout en respectant les contraintes de capacité des véhicules. Le PTV, comme classe de problèmes d'optimisation discrète et de grande complexité, a été étudié par de nombreux au cours des dernières décennies. Étant donné son importance pratique, des chercheurs dans les domaines de l'informatique, de la recherche opérationnelle et du génie industrielle ont mis au point des algorithmes très efficaces, de nature exacte ou heuristique, pour faire face aux différents types du PTV. Toutefois, les approches proposées pour le PTV ont souvent été accusées d'être trop concentrées sur des versions simplistes des problèmes de tournées de véhicules rencontrés dans des applications réelles. Par conséquent, les chercheurs sont récemment tournés vers des variantes du PTV qui auparavant étaient considérées trop difficiles à résoudre. Ces variantes incluent les attributs et les contraintes complexes observés dans les cas réels et fournissent des solutions qui sont exécutables dans la pratique. Ces extensions du PTV s'appellent Problème de Tournées de Véhicules Multi-Attributs (PTVMA). Le but principal de cette thèse est d'étudier les différents aspects pratiques de trois types de problèmes de tournées de véhicules multi-attributs qui seront modélisés dans celle-ci. En plus, puisque pour le PTV, comme pour la plupart des problèmes NP-complets, il est difficile de résoudre des instances de grande taille de façon optimale et dans un temps d'exécution raisonnable, nous nous tournons vers des méthodes approcheés à base d’heuristiques.

El Outsourcing en la dinámica de sistemas hacia mercados extranjeros

Este trabajo recopila literatura académica relevante sobre estrategias de entrada y metodologías para la toma de decisión sobre la contratación de servicios de Outsourcing para el caso de empresas que planean expandirse hacia mercados extranjeros. La manera en que una empresa planifica su entrada a un mercado extranjero, y realiza la consideración y evaluación de información relevante y el diseño de la estrategia, determina el éxito o no de la misma. De otro lado, las metodologías consideradas se concentran en el nivel estratégico de la pirámide organizacional. Se parte de métodos simples para llegar a aquellos basados en la Teoría de Decisión Multicriterio, tanto individuales como híbridos. Finalmente, se presenta la Dinámica de Sistemas como herramienta valiosa en el proceso, por cuanto puede combinarse con métodos multicriterio.

Las prácticas de recursos humanos y su incidencia en el bienestar laboral de los empleados

El objetivo del presente trabajo es formular, mediante una profunda revisión documental, bibliográfica y empírica, una fundamentación teórica sobre si existe o no incidencia de las prácticas de recursos humanos sobre el bienestar laboral de los empleados, y el que grado en que esta se presenta sobre aspecto como el engagement y la satisfacción laboral. Se realizó la revisión de múltiples estudios empíricos que aportaran evidencia sobre la relación que se presenta entre las principales prácticas de recursos humanos – provisión de personal, formación y desarrollo, promoción de personal, evaluación de desempeño, compensación y pago, y balance trabajo-familia – y el bienestar laboral, representado en el engagement y satisfacción en el trabajo de los empleados. Los resultados de este trabajo indican la existencia de una relación e incidencia de las prácticas de recursos humanos, el bienestar laboral, el engagement y la satisfacción laboral. De igual forma se encontró que estas relaciones son principalmente de carácter positivo, lo cual indica que las organizaciones que desarrollan este tipo de prácticas en su interior, fomentan tanto el desarrollo y la presencia de bienestar laboral en sus empleados, como su perdurabilidad.

Gestión de la cadena de suministros desde la dinámica de sistemas. Aproximación al mejoramiento de la toma de decisiones

El objetivo de este trabajo es hacer un estudio sobre la cadena de suministros en organizaciones empresariales desde la Dinámica de Sistemas y como esta puede aportar al desempeño y el control de las cadenas de suministros. Se buscará Abordar el cocimiento sobre tres perspectivas de Supply Chain y su relación con la dinámica de sistemas. También se buscará identificar los tipos de integración en las actividades de la gestión en la cadena de suministros y sus horizontes de planeación. Por último, se pretende analizar las aplicaciones de Supply Chain Management que se han basado en el uso de la metodología de dinámica de sistemas. Para esto, la investigación empezará por definir la problemática alrededor de unir estas dos áreas y definirá el marco teórico que fundan estas dos disciplinas. Luego se abordará la metodología usada por la Dinámica de Sistemas y los diferentes aspectos de la cadena de suministros. Se Ahondará en el acercamiento de las dos disciplinas y como convergen ayudando la SD a la SCM (Supply Chain Management). En este punto también se describirán los trabajos en los diferentes enfoques que se han hecho a partir de uso de la dinámica de sistemas. Por último, presentaremos las correspondientes conclusiones y comentarios acerca de este campo de investigación y su pertinencia en el campo de la Supply Chain. Esta investigación abarca dos grandes corrientes de pensamiento, una sistémica, a través de la metodología de dinámica de sistemas y la otra, lógico analítica la cual es usada en Supply Chain. Se realizó una revisión de la literatura sobre las aplicaciones de dinámica de sistemas (SD) en el área de Supply Chain, sus puntos en común y se documentaron importantes empleos de esta metodología que se han hecho en la gestión de la cadena de suministros.

Low-temperature sol-gel preparation of ordered nanoparticles of tungsten carbide/oxide

Tungsten carbide/oxide particles have been prepared by the gel precipitation of tungstic acid in the presence of an organic gelling agent [10% ammonium poly(acrylic acid) in water, supplied by Ciba Specialty Chemicals]. The feed solution; a homogeneous mixture of sodium tungstate and ammonium poly(acrylic acid) in water, was dropped from a 1-mm jet into hydrochloric acid saturated hexanol/concentrated hydrochloric acid to give particles of a mixture of tungstic acid and poly(acrylic acid), which, after drying in air at 100 degrees C and heating to 900 degrees C in argon for 2 h, followed by heating in carbon dioxide for a further 2 h and cooling, gives a mixture of WO, WC, and a trace of NaxWO3, with the carbon for the formation of WC being provided by the thermal carbonization of poly(acrylic acid). The pyrolyzed product is friable and easily broken down in a pestle and mortar to a fine powder or by ultrasonics, in water, to form a stable colloid. The temperature of carbide formation by this process is significantly lower (900 degrees C) than that reported for the commercial preparation of tungsten carbide, typically > 1400 degrees C. In addition, the need for prolonged grinding of the constituents is obviated because the reacting moieties are already in intimate contact on a molecular basis. X-ray diffraction, particle sizing, transmission electron microscopy, surface area, and pore size distribution studies have been carried out, and possible uses are suggested. A flow diagram for the process is described.

Pyrolysis of polymer-derived carbons in the formation of graphitizing carbons and nanoparticles of zirconia

Carbons have been prepared by the low-temperature pyrolysis, under argon, of a number of long-chain polymers. We have found that the resistivity (Omega cm(-1)) varies considerably with the temperature of pyrolysis; thus, for ammonium polyacrylate, the resistivity of that pyrolyzed at 600 degrees C is 9.7 x 10(4) Omega cm(-1) whereas that pyrolyzed at 1000 degrees C is ca. 3 Omega cm(-1). A similar situation arises for the other polymers studied (including radiolyzed cross-linked polyacrylamide). All those pyrolyzed at 600 degrees C had a resistivity of > 1 x 10(6) Omega cm(-1), whereas those pyrolyzed at 1000 degrees C had a resistivity of ca. 3-5 Omega cm(-1). A notable exception was that of unirradiated polyacrylamide, where the resistivity remained at > 1 x 10(6) Omega cm(-1) over the range of temperatures studied. The decrease of resistivity with increase of temperature of pyrolysis has been related to the formation of glassy carbon. Nanoparticles (4 nm) of tetragonal zirconia were formed when zirconium polyacrylate was pyrolyzed under similar conditions.