Search

espanolMateriales fotoactivos tipo Pt/S-TiO2 fueron obtenidos por fotodeposicion de Pt sobre el fotocatalizador S-TiO2 sintetizado a partir de oxisulfato de titanio (TiOSO4) usando el metodo integrado sol-gel/solvotermal a bajas temperaturas (250 °C). La fotodeposicion se realizo variando la concentracion de platino en 0.2% y 0.5% en peso empleando dos tiempos de residencia de 60 min y 120 min. Las propiedades de los materiales fueron determinadas a traves de analisis de DRX, Raman, XRF, FTIR-ATR, XPS, UV-vis/DRS, SEM, EDX, TEM, area superficial y porosidad. Los materiales obtenidos fueron mesoporosos y cristalizaron en fase anatasa, con incorporaciones de 0.31% en peso de S y 85% del valor nominal de Pt, presentando absorcion y fotoactividad tanto en radiacion ultravioleta como visible. El material preparado con mayor contenido de Pt y tiempo de fotodeposicion, 0.5/120 Pt/S-TiO2, alcanzo la mayor fotoactividad en UV y visible en la decoloracion de naranja de metilo en fase liquida. EnglishPhotoactive materials Pt/S-TiO2 were obtained by photodeposition of Pt on S-TiO2 photocatalyst synthesized from titanium oxysulfate (TiOSO4) using the integrated method sol-gel/solvothermal at low temperatures (250°C). The photodeposition was performed changing platinum concentration by 0.2% and 0.5% w/w and using two residence times of 60 min and 120 min. The properties of materials were determined by analysis of DRX, Raman, XRF, FTIR-ATR, XPS, UV-vis/DRS, SEM, EDX, TEM, surface area and porosity. The obtained materials were mesoporous and crystallized as anatase phase, incorporating 0.31% of S (by weight) and 85% of the nominal Pt value, showing absorption and photoactivity in both ultraviolet and visible radiation. The material prepared with higher Pt content and longer photodeposition time, 0.5/120 Pt/S-TiO2, reached the highest UV and visible photoactivities in the degradation of methyl orange in the liquid phase.

RESUMEN: Objetivos: El trasplante hepático es el tratamiento de elección para la falla hepática aguda y crónica, casos seleccionados de tumores y enfermedades por errores en el metabolismo. En este documento se reporta la experiencia de un centro en Latinoamérica. Métodos: Entre el 2004 y el 2010 se realizaron 305 trasplantes ortotópicos de hígado en 284 pacientes. De ellos, 241 corresponde a primer trasplante en adultos. Resultados: La edad promedio fue 52 años y el 62% eran hombres. La principal indicación fue cirrosis por alcohol. La supervivencia de los pacientes a 1 y 5 años fue de 82 y 72% respectivamente y del injerto hepático a 1 y 5 años fue de 78 y 68% respectivamente. La principal causa de muerte fue sepsis. Se documentaron complicaciones en la arteria hepática en el 5% y complicaciones en la vía biliar en el 14.5%. Se encontraron infecciones en el 41% de los pacientes. Rechazo agudo se presento en el 30% y rechazo crónico en el 3%. Conclusión: El trasplante hepático en nuestro centro en Colombia ofrece buenos resultados a mediano plazo, con una tasa de complicaciones similar a lo reportado en otros centros del mundo. ABSTRACT: Objectives: Liver transplantation is the treatment of choice for acute and chronic liver failure, for selected cases of tumors, and for conditions resulting from errors in metabolism. This paper reports the experience of a medical center in Latin America. Methods: Were conducted 305 orthotopic liver transplantations on 284 patients between 2004 and 2010. Of these patients, 241 were adults undergoing their first transplantation. Results: The average age of patients was 52 years old, and 62% of the individuals were male. The most common indication was alcoholic cirrhosis. The rate of patient survival after 1 and 5 years was 82 and 72% respectively. The rate of liver graft survival after 1 and 5 years was 78 and 68% respectively. The main cause of death was sepsis. Complications in the hepatic artery were documented for 5% of the patients. Additionally, 14.5% of the patients had complications in the biliary tract. Infections were found in 41% of the individuals. Acute rejection was observed in 30% of the subjects, and chronic rejection in 3%. Conclusion: In conclusion, liver transplantation at our medical center in Colombia offers good mid-term results, with a complication rate similar to that reported by other centers around the world. COL0024159 COL0004362

Cloud computing is an emerging paradigm to offer on-demand IT services to customers. The access control to resources located in the cloud is one of the critical aspects to enable business to shift into the cloud. Some recent works provide access control models suitable for the cloud; however there are important shortages that need to be addressed in this field. This work presents a step forward in the state-of-the-art of access control for cloud computing. We describe a high expressive authorization model that enables the management of advanced features such as role-based access control (RBAC), hierarchical RBAC (hRBAC), conditional RBAC (cRBAC) and hierarchical objects (HO). The access control model takes advantage of the logic formalism provided by the Semantic Web technologies to describe both the underlying infrastructure and the authorization model, as well as the rules employed to protect the access to resources in the cloud. The access control model has been specially designed taking into account the multi-tenancy nature of this kind of environment. Moreover, a trust model that allows a fine-grained definition of what information is available for each particular tenant has been described. This enables the establishment of business alliances among cloud tenants resulting in federation and coalition agreements. The proposed model has been validated by means of a proof of concept implementation of the access control system for OpenStack with promising performance results.

Cloud computing is revealing a new scenario where different cloud customers need to collaborate to meet client demands. The cloud stack must be able to support this situation by enabling collaborative agreements between cloud customers. However, these collaborations entail new security risks since participating entities should trust each other to share a set of resources. The management of trust relationships in the cloud is gaining importance as a key element to establish a secure environment where entities are given full control in the definition of which particular services or resources they are willing to share. Entities can cooperate at different levels of trust, according to their willingness of sharing information. This paper analyses these collaboration agreements defining a taxonomy of different levels of trust relationships among customers for the cloud. Privacy concerns, assumed risk, as well as easiness in the definition of the trust relationships have been taken into account. A set of different trust relationships have been identified and modeled, enabling entities to control the information they share with others in the cloud. The proposed model has been validated with a prototypical implementation. Likewise, some examples to illustrate the application of these trust models to common cloud collaboration scenarios are provided.

This article shows the results of a research on the production of solid waste generated by companies based in Antioquia. This Research was conducted by the University of San Buenaventura, University of Medellin and the University of Antioquia in the program called Antioquia Expedition 2013. For this purpose, we evaluated the production of waste generated by companies in economic activities such as agriculture, cattle ranching, hunting and forestry, mining and quarry exploitation, manufacturing and construction. The purpose of the study was to determine the type, quantity and environmental impact of the waste generated in Antioquia in the selected sectors, constituting itself into a basis for further investigations aimed in determining the potential use of waste for creating new products. The territory analyzed corresponds to 80.8% of the area belonging to the department of Antioquia, subregions, Bajo Cauca, North-east, North, East, South west, Urabá and Valle de Aburrá, where are concentrated the most significant industrial, mining and farming areas of the department, besides being highly populated subregions with growth in infrastructure, represented in a stronger construction sector. The methodology used was the development of databases of companies belonging to the selected sectors to subsequently get information on solid waste generation through surveys conducted by means of a web application, face-to-face or by telephone. Este artículo muestra los resultados de una investigación sobre la producción de residuos sólidos generados por las empresas Antioqueñas. Investigación que fue desarrollada por la Universidad de San Buenaventura, la Universidad de Medellín y la Universidad de Antioquia dentro del programa Expedición Antioquia 2013. Para lo cual, se evaluó la producción de residuos generados en empresas pertenecientes a las actividades económicas; agricultura, ganadería, caza y silvicultura; Explotación de minas y canteras; Industrias manufactureras y Construcción. El propósito del estudio fue conocer la tipología, cantidad e impacto ambiental de los residuos generados en el departamento en los sectores seleccionados, constituyéndose en una base para futuras investigaciones, orientadas a determinar el potencial aprovechamiento de los residuos para la elaboración de nuevos productos. La zona de estudio corresponde al 80,8% de la superficie del departamento de Antioquia, subregiones, Bajo Cauca, Nordeste, Norte, Oriente, Suroeste, Urabá y Valle de Aburrá; las cuales concentran las zonas industriales, mineras y agropecuarias más representativas del departamento, además de ser subregiones altamente pobladas con un crecimiento en infraestructura, representado en un sector de construcción fortalecido. La metodología utilizada fue la construcción de bases de datos de las empresas de los sectores seleccionados para posteriormente obtener información de la generación de residuos sólidos por medio de encuestas realizadas por un aplicativo web, personal o telefónicamente.

We review and analyze the major security features and concerns in deploying modern commodity operating systems such as Windows 7 and Linux 2.6.38 in a cloud computing environment. We identify the security weaknesses and open challenges of these two operating systems when deployed in the cloud environment. In particular, we examine and compare various operating system security features which are critical in providing a secure cloud. These security features include authentication, authorization and access control, physical memory protection, privacy and encryption of stored data, network access and firewalling capabilities, and virtual memory.

Headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry detection (HS/SPME-GC/MSD) was optimized for trihalomethane (THM) determination in drinking water. A 75 μm fiber coated with carboxen/polydimethylsiloxane (75-CAR.PDMS) was used. Experimental parameters such as sample volume, time and temperature of extraction, time and temperature of desorption, magnetic stirring, and addition of sodium chloride (NaCl) were studied to determine their influence on THM extraction. Furthermore, analytical parameters such as linearity and detection limit were also evaluated. High sensitivity with detection limits in the μg/L range as well as a good linearity and reproducibility were achieved. Therefore, the HS/SPME-GC/MSD method with 75-CAR.PDMS is suitable for monitoring THMs in drinking water.

Photoactive nano-titanium dioxide, as anatase phase, was obtained by the sol–gel method coupled with the solvothermal technique at short crystallization time (2 h) and low temperature (200 °C), using tetraisopropyl orthotitanate as Ti-precursor and 2-propanol as solvent. Precursor ratios were evaluated to determine their influence in the synthesis. Methyl orange was used as model molecule for the photocatalytic degradation. Highest anatase crystallinity was obtained when the water content is close to the stoichiometrically needed to hydrolyze a molecule of TIOT and these materials also showed the highest methyl orange photodegradation.

This study demonstrated a novel method used to coat polymeric pellets with titanium dioxide (TiO 2 ) using simple and flexible equipment. In this method, TiO 2 catalyst and polymeric pellets were dispersed in glycerine and heated to the melting point of the polymer, and then the system was cooled to room temperature, which resulted in the TiO 2 -embedded polymer. Degussa P-25 TiO 2 was used as the catalyst, and pellets of polypropylene (PP) and low-density polyethylene (PE) were used as the polymeric supporting substrates. The coating adhesion was analyzed using an erosion test, and the photodegradation of the coated polymers was assessed through a photo-degradation test. The characterization of the TiO 2 -embedded polymer was performed using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS), UV/Vis spectroscopy, diffuse reflectance UV–Vis spectra (DR/UV–Vis), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), Fourier transforms infrared spectroscopy (FTIR), and stereomicroscopy. The photocatalytic activity was determined by analyzing the degradation of the model compound, 4-chlorophenol. The results indicated that the controlled-temperature embedding method led to well-TiO 2 -coated polymeric pellets with a high activity and surface area. Thus, the controlled-temperature embedding method is a promising technique for surface engineering in the application of wastewater and drinking water treatment.

Non-photochemical advanced oxidation technologies, ozonation and electrochemical oxidation, as alternative technologies to treat wastewaters from biodiesel production were applied. The physicochemical characterization of the wastewaters showed high levels in biochemical and chemical oxygen demand, total organic carbon and residual methanol. Both technologies increased the wastewater biodegradability and showed similar efficiencies in the reduction of the organic loads, with chemical oxygen demand removal between 5 and 9 % and total organic carbon removal between 9 and 11 %. However the ozonation showed to be a more versatile technology to be implemented on a larger scale as a system for treatment alone or coupled to biological processes that are typically used in treating waters with high organic load.

Much research has been undertaken on the photocatalytic degradation of humic substances with titanium dioxide using commercial humic acids (HA), which are extracts from either peat or coal. Most of the research has been focused on the changes in dissolved organic carbon (DOC) and UV254 absorption. These parameters only give a general assessment. This work studies the changes in the physical and structural properties of a commercial humic acid by size exclusion chromatography with DOC and UV254 absorption detection (SEC-DOC, SEC-UV254), and the evolution of halogenated organic compounds (AOX) and trihalomethanes (THMs) during the photocatalytic degradation with simulated solar UV irradiation and Degussa P-25 TiO2. These changes are compared with those reported for natural organic matter (NOM). The photodegradation of commercial HA and NOM proceeds in a similar and sequential manner, initially with the preferential adsorption of larger molecules, then the degradation of these larger molecular size fractions and proceeding towards smaller molecular size fractions, while decreasing THMs and AOX formation potential.

A new kinetic model for heterogeneous photocatalytic reactions has been developed as an alternative to the Langmuir–Hinshelwood (L–H) and the Direct–Indirect (D–I) models. The L–H model has been widely used to analyze the kinetics of the TiO2-photocatalytic degradation of water-dissolved organic compounds, assuming the adsorption/desorption equilibrium of the reactants (Langmuir isotherm). Nevertheless, it has been reported by some authors that the experimental data on photocatalytic oxidations are incompatible with the behavior predicted by L–H model. The proposed model, unlike the L–H model, considers all the basic steps involved in heterogeneous photocatalysis with TiO2, including the back reaction involved in the process, and it is applicable to organic species non-adsorbed on the TiO2 surface. In the case of phenol photodegradation, the proposed model better describes, mechanistically, the experimental data than L–H and D–I models.

Most promising catalysts for synthesising unsaturated fatty alcohols are based on group 8 metals with a promoter like tin, because the process can be carried out in moderate conditions, and these metals are less toxic than chromium. There have been no reports about the use of this catalyst to date using raw materials like methyl ester blends or evaluation reusing catalysts. This paper presents the hydrogenation of methyl esters from palm oil and commercial methyl oleate with Ru-Sn/Al2O3 catalysts prepared by impregnation, at moderate pressure and temperature (5 MPa and 270°C). Greater selectivity to unsaturated alcohol and the less selectivity to methyl stearate was found for an optimal Sn:Ru=2 ratio. Hydrogenation of palm oil methyl esters with this catalyst produced a mixture of oleyl alcohol, saturated alcohols having 16-18 carbon atoms and heavy esters. Raw material had no great effect on catalyst activity. However, the catalyst showed deactivation through several uses due to decreased catalytic area.

There are a few issues that still need to be covered regarding security in the Grid area. One of them is authorization where there exist good solutions to define, manage and enforce authorization policies in Grid scenarios. However, these solutions usually do not provide Grid administrators with semantic-aware components closer to the particular Grid domain and easing different administration tasks such as conflict detection or resolution. This paper defines a proposal based on Semantic Web to define, manage and enforce security policies in a Grid scenario. These policies are defined by means of semantic-aware rules which help the administrator to create higher-level definitions with more expressiveness. These rules also permit performing added-value tasks such as conflict detection and resolution, which can be of interest in medium and large scale scenarios where different administrators define the authorization rules that should be followed before accessing a resource in the Grid. The proposed solution has been also tested providing some reasonable response times in the authorization decision process.

Nowadays, managers of information systems use ontologies and rules as a powerful tool to express the desired behaviour for the system. However, the use of rules may lead to conflicting situations where the antecedent of two or more rules is fulfilled, but their consequent is indicating contradictory facts or actions. These conflicts can be categorised in two different groups, modality and semantic conflicts, depending on whether the inconsistency is owing to the rule language expressiveness or due to the nature of the actions. While there exist certain proposals to detect and solve modality conflicts, the problem becomes more complex with semantic ones. Additionally, current techniques to detect semantic conflicts are usually not considering the use of standard information models. This paper provides a taxonomy of semantic conflicts, analyses the main features of each of them and provides an OWL/SWRL modelling for certain realistic scenarios related with information systems. It also describes different conflict detection techniques that can be applied to semantic conflicts and their pros and cons. Finally, this paper provides a comparison of these techniques based on performance measurements taken in a realistic scenario and suggests a better approach. This approach is then used in other scenarios related with information systems and where different types of semantic conflicts may appear.

TiO2–SiO2 mixed oxides have been synthesised and modified by Ag and Pt deposition. Due to the effect of the silica on the mixed oxide, the prepared materials presented high surface areas and stabilised anatase as the only crystalline phase after calcination at 700 °C. Even using the same photodeposition experimental conditions, the yield for metal deposition depended highly on the metal considered, being much lower for Ag deposition. XPS studies permitted to estimate metal dispersion and oxidation state of the different samples, being both factors of high importance regarding photocatalytic improvement by metal deposition.

Hydrogenation of methyl oleate to oleyl alcohol was evaluated over Ru-Sn/Al 2 O 3 catalysts, prepared from different precursors, at 270 °C and 5.0 MPa. Two kinds of metal precursors were employed: chlorine-free precursors and inorganic chlorides. In addition, several methods for chlorine removal of metal-chloride-based catalysts were studied. Catalysts were characterized by EDX, XRF, DRX, BET and TPR analyses. Selectivity toward unsaturated alcohol was higher with the bimetallic catalyst based on chlorine-free precursors than with the catalyst based on metal chlorides, owing that chlorine avoids, at certain extent, an effective interaction between ruthenium and tin species. However, the most selective catalyst was the bimetallic one based on chloride precursors and reduced with NaBH 4 , due to elimination of residual chlorine and higher dispersion of Ru-Sn species.

RESUMEN: El comportamiento viscoso de pulpas de cuarzo provenientes de moliendas fue caracterizado midiendo su viscosidad a diferentes tiempos de molienda y para varias concentraciones de sólidos, utilizando un viscosímetro Brookfield. Se usó el modificador reológico hidroxietilcelulosa (HEC) para preparar las suspensiones, evitar el problema de la sedimentación y evaluar la influencia de la concentración de sólidos en la pulpa y la diferencia en la granulometría. Los resultados indican que la característica newtoniana de una solución de HEC al 0.3% se ve afectado con el incremento de sólidos en la suspensión, siendo este efecto más marcado para una concentración de sólidos de 60%. Se observó también que para una misma concentración de sólidos la disminución del parámetro de tamaño de la muestra no produce cambios significativos en el comportamiento reológico de la pulpa, para porcentajes bajos de sólidos (menor a 40%). ABSTRACT: The viscous behavior of quartz pulp from mills was characterized by measuring their viscosities at different times for several grinding times and solid concentrations, using a Brookfield viscometer. The rheology modifier hydroxyethylcellulose (HEC) was used for preparing the suspensions, for avoiding the problem of sedimentation and for evaluating the influence of the concentration of solids on the pulp as well as on the difference in particle size. The results indicate that the Newtonian characteristic of a solution of 0.3% HEC is affected by the increase of solids in the suspension. This effect is more notorious for a solid concentration of 60%. It was also observed that for the same concentration, the solid size reduction parameter of the sample does not produce significant changes in the rheological behavior of the pulp, for low percentages (lower than 40%). COL0014897

Resumen Sistemas Oxido de Titanio/Oxido de Silicio (TiO 2 /SiO 2 ) fueron obtenidos por anclaje de TiO 2 en SiO 2. El fotocatalizador TiO 2 se obtuvo por alcoholisis del TiCl 4 con 2-propanol y posterior cristalizacion a presion autogena a 200 °C, excluyendo etapas de calcinacion a altas temperaturas. Se emplearon diferentes relaciones SiO 2 /TiCl 4 para determinar su influencia en la estabilidad, propiedades y fotoactividad de los sistemas TiO 2 /SiO 2 . La actividad fotocatalitica fue evaluada por la fotodegradacion de metanol en fase gaseosa. El TiO 2 cristalizo como fase anatasa o como una mezcla rutilo/anatasa, dependiendo por la relacion SiO 2 /TiCl 4 inicial. Los resultados muestran que se producen materiales compuestos con alta cristalinidad del TiO 2 . Se encontro tambien que hay una fuerte relacion entre la actividad fotocatalitica con las propiedades fisicoquimicas y de estas con las composiciones iniciales de sintesis. Palabras clave: sistemas TiO 2 /SiO 2 , fotocatalisis, metodo solvotermico, materiales compuestos

RESUMEN: Se presentan los resultados del diseño y evaluación de dos sistemas de molienda en circuito cerrado, para un clasificador tipo ciclón neumático y uno tipo harnero vibratorio. Se comparan las eficiencias energéticas bajo similares condiciones de granulometrías a la entrada del molino, conservando el mismo tamaño de corte en el clasificador. El material se caracterizó mediante: fluorescencia de rayos X, area superficial por el método Brunauer-Emmet-Teller y análisis granulométrico por tamizado. Los resultados indican que la velocidad de giro del molino no tiene significancia estadística sobre la eficiencia mecánica de molienda. A partir de un análisis de superficies de respuestas se determinó que el ciclón favorece la eficiencia (valor óptimo 30%) comparado con el harnero (valor óptimo 18%). Los modelos encontrados para la determinación de la eficiencia mecánica del sistema molino-ciclón y molino-harnero, muestran correlaciones del 85 y 83 % respectivamente. ABSTRACT: The design and experimental evaluation of two grinding systems in closed circuit which use two types of classifiers, a pneumatic cyclone and a sieve vibratory, were carried out. The energetic efficiencies under similar conditions in material particle sizes at the mill entrance and keeping the same classifier were compared. The material was characterized by: X-ray fluorescence (XRF), surface area by the method Brunauer-Emmet-Teller and granulometry analysis by sieving. Results show that the mill speed does not have statistical significance over the grinding mechanical efficiency and using a response surface analysis was determined that the cyclone favors the milling (optimum value 30%) against the sieve vibratory type (optimum 18%). Models found for mechanical efficiency determination of the systems mill-cyclone and mill-sieve vibratory, show correlations of 85 % and 83%, respectively. COL0014897

RESUMEN: Se aplicaron las tecnologías avanzadas de oxidación, fotocatálisis heterogénea y foto-Fenton, para comprobar su viabilidad en el tratamiento de las aguas residuales provenientes del proceso de lavado de biodiesel. Las aguas presentaron altos niveles en demanda química de oxígeno, carbono orgánico total y metanol, sugiriendo la necesidad de implementar procesos posteriores de tratamiento. Los resultados muestran que la fotocatálisis heterogénea no es una tecnología adecuada debido a las altas cargas orgánicas, mientras que la foto-Fenton presenta altos valores de remoción. Se concluye que ésta es una tecnología viable que podría ser implementada a escala industrial. ABSTRACT: Advanced oxidation technologies, heterogeneous photocatalysis and photo-Fenton, were applied to verify its feasibility in the treatment of wastewater from the washing process of biodiesel production. These waters showed high levéis of chemical oxygen demand, total organic carbón and methanol, suggesting the need to implement subsequent treatment processes. The results show that heterogeneous photocatalysis is not an appropriate technology due to high organic loads, while the photo-Fenton has high valúes of removal. It is concluded that this is a viable technology that could be implemented at industrial scale. COL0014897

Resumen El presente trabajo describe el desarrollo de una novedosa sintesis de silices mesoporosas basada en un mecanismo en dos etapas en medio acido (pH = 2), empleando materias primas renovables. La primera etapa consistio en la formacion de micelas hibridas estables, producto de la interaccion entre silicatos y el agente porogeno, y la segunda en la policondensacion de silicatos para formar silice. Se evaluaron dos fuentes de silicio: tetraetilortosilicato (TEOS) y metasilicato de sodio (MSiNa). Como porogeno oleoquimico se uso monoestearato de glicerol y como iniciador de la reaccion de policondensacion se uso fluoruro de sodio (NaF). Las silices obtenidas con las mejores propiedades texturales, poseen caracteristicas superficiales interesantes para un potencial aplicacion en catalisis heterogenea, con area superficial BET de 727.4 m 2 /g, volumen total de poros de 0.50 cm 3 /g y distribucion de tamanos de poro alrededor de 46.2 A. Palabras clave: metasilicato de sodio, monoestearato de glicerol, porogeno oleoquimico, silices mesoporosas, tetraetilortosilicato.

Peliculas de TiO2 o TiO2/SiO2 fueron soportadas sobre granulos de poliester usando mecanismos de difusion y posterior tratamiento termico a 100oC. Se emplearon dos clases de geles. El primero fue preparado usando diferentes cantidades de TiO2, cloruro de metileno y silicona liquida. El segundo fue obtenido por medio del metodo sol-gel, empleado para producir una matriz de silice a partir de la hidrolisis el tetraetilo ortosilicato, en un medio organico de 2-propanol, en el cual se disperso el fotocatalizador. Los precursores de cada sistema fueron agregados en diferentes relaciones para determinar su influencia en la estabilidad, propiedades y fotoactividad de las peliculas. La actividad fotocatalitica fue evaluada en la fotodegradacion de metanol en fase gaseosa. Los resultados muestran la produccion de materiales con alta resistencia, funcionalidad y actividad asi como una fuerte relacion entre la actividad fotocatalitica con las propiedades fisicoquimicas.

RESUMEN: Se analizó el efecto de varias resinas ácidas como catalizadores para la adición de alcoholes a ésteres grasos epoxidados, usando alcoholes con diferentes configuraciones moleculares y haciendo énfasis en la adición de alcoholes ramificados en las posiciones a y b. Con respecto a los catalizadores, se determinaron los efectos de la fortaleza ácida y de las restricciones difusionales en la velocidad de reacción y la distribución de productos. Se encontró que la velocidad de reacción se incrementa con la fortaleza ácida pero la selectividad tiene una tendencia contraria cuando se adicionan alcoholes altamente ramificados. La velocidad de apertura del epóxido disminuye al incrementar el número de ramificaciones y el tamaño del alcohol; ramificaciones en posición a introducen un mayor impedimento estérico que las ramificaciones en posición b. Un bajo entrecruzamiento de la resina y/o una alta superficie externa son condiciones necesarias para activar el epóxido cuando se usan resinas basadas en poliestireno como catalizadores. Los productos que se obtuvieron fueron la cetona, proveniente del rearreglo del epóxido, y los trans-ésteres, cuando los tiempos de reacción fueron relativamente largos. ABSTRACT: The effects of different alcohol molecular configurations and resin structures were analyzed on the sulfonic acid-resin catalyzed addition of alcohols to epoxidized fatty esters. Emphasis was placed on the addition of a-and b-branched alcohols. Regarding the catalysts, the effect of the acid strength as well as that of the diffusion constraints on the reaction rate and products distributions, were determined. Reaction rate increases with the acid strength but the selectivity shows the opposite trend when highly branched alcohols are added. Epoxide ring-opening rate decreases by increasing the number of branches and size of the alcohol. Branches in a position introduce a higher steric hindrance than branches in b position. Low resin crosslinkage and/or high external surface area are necessary conditions to activate the epoxide when polystyrene-based resins are used as catalysts. The obtained byproducts were the ketone, from epoxide rearrangement, and trans-esterified products, when reaction times were relatively long COL0014897