Al/Fe-, Al/Cu- and Al/(Fe-Cu)-pillared clays: Structural features at low Atomic Active Metal Ratios (AMR)

A set of Al/Fe-, Al/Cu- and Al/(Fe-Cu)-pillared clays were prepared from a Colombian bentonite in sodium or natural (Ca/Mg) form as starting materials. The effect of the loading of the second metal(s) (Fe and/or Cu) related to Al (AMR) in the intercalating solutions at low range of values ≤ 10%, on the main physicochemical properties was investigated. The insertion of the active metals rose almost linearly with AMR for both binary, Al/Fe- and Al/Cu- mixed metal systems. For the three-metal Al/(Fe-Cu)- mixed system, the stabilization of copper behaved randomly as a function of AMR, while the stabilization of Fe was almost not affected by the presence of Cu. On the basis of the ionic radii of the metals involved, a possible competition of the two active metals for the octahedral sites available in the Al13 polycationic structure is proposed for the three-metal system (ionic radii values: Al3+ = 0.68 Å; Fe3+ = 0.67 Å; Cu2+ = 0.73 Å), but also as a good explanation for the efficiency of stabilization for iron around 15 times higher than copper in the binary metal systems. A clear dependence of the compensation of the cationic exchange capacity by polycations with the AMR value was found only for the system Al/Fe-, which was explained in terms of the opposite changes in the final pH obtained in the intercalating solutions, induced by the active metals in the Keggin-like polycations. The change in the basal spacings obtained in the XRD patterns from oriented glasses as a function of AMR was interpreted in terms of the opposite effect expected on the molecular size of the polycations as higher amounts of Fe or Cu would isomorphically substitute Al into the Al13 framework, allowing to propose that both, iron and copper are able to carry out such a substitution, although in different extent. The hydrogen consumption in the H2-TPR analysis of the materials was mainly distributed between two broad peaks: one from about 250ºC to 580ºC, and a second one from about 750ºC to 950ºC. Despite the several metal oxide species that are possible to form, the first signal in samples modified with the Al/Fe- system may correspond with the sequential overlapped reduction of Fe2O3 in up to three steps: (1) Fe2O3 → Fe3O4; (2) Fe3O4 → FeO; and (3) FeO → Fe, and to two sequential reduction effects in the range of 210-260 ºC for Cu2+→ Cu+ and Cu+→ Cu0 at higher temperatures of ca. 400 ºC to 700 ºC. In the Al/Fe- system two shoulders were observed at around 600ºC and 850ºC, whose intensity grow as the active metal loading increases, seem to be related to two kinds of metal sites repeatedly claimed in the literature as responsible for the high catalytic activity displayed by these materials in Fenton-like reactions; Fe “decorating” Al pillars and true mixed Al/Fe pillars, respectively. The textural analysis of the natural modified samples suggest that at AMR below 5.0 %, a discrete maximum exist for the systems Al/Fe- and Al/Cu- over which the sorption capacity starts to be significantly affected. Simultaneous thermal analysis (DSC/TGA) demonstrated that the addition of a second metal in the intercalating system enhanced more the fraction of physisorbed water and decreased the maximum temperature for such a thermal event than intercalation with simple Al- polycations. SEM micrographs showed significant changes in morphology of the particles as AMR increased from 2.0 to 5.0%; as the amount of iron and/or copper added to the system increased, a greater amount of tiny particles deposited on the clay surface was seen, may be corresponding with external oxide aggregates. Likewise, the ratio Fe/Al obtained from the semi-quantitative surface chemical EDX analysis of the samples modified with the system Al/Fe- indicated that the AMR increasing also leads to higher fraction of the iron inserted represented in intercalated, possibly less aggregated mixed species in the materials. Acknowledgements: Financial support from MEC and FEDER funds (Ref. MAT2007-66439-C02)

COMBUSTION MODEL FOR SPARK IGNITION ENGINES OPERATING ON GASOLINE-ETHANOL BLENDS

This article presents a phenomenological combustion model using turbulent flame propagation theory developed by Keck and coworkers, 1974. The model was adapted to work with gasoline-ethanol blends, following correlations presented by Bayraktar,2005. New sub-models were introduced for intake valve velocity and combustion efficiency. These allow simulating the effect of compression ratio, spark timing and fuel change. Results show good agreement with the ones in the original work as well as with experimental results in a Cooperative Fuels Research (CFR) engine

Comportamiento catalítico de una Bentonita modificada con Manganeso en la oxidación en fase húmeda de naranja de metilo con peróxido de hidrógeno

En este trabajo se presenta un estudio comparativo en el que se introduce manganeso en una bentonita colombiana proveniente del Valle del Cauca (BVC) utilizando tres métodos: i) pilarización con Al 2 O 3 y posterior impregnación húmeda con una disolución acuosa de manganeso, ii) co-intercalación con una disolución oligomérica mixta de Al-Mn seguida de una etapa de calcinación y iii) homoionización con Mn 2+ y posterior formación in-situ de agregados tipo MnS. Los sólidos resultantes son caracterizados por espectroscopía de absorción atómica (EAA), capacidad de intercambio catiónico (CIC) y difracción de rayos X en polvo (DRX), y evaluados como catalizadores en la oxidación de naranja de metilo con peróxido de hidrógeno

Impact of a rigid sphere onto an elastic membrane

We study the axisymmetric impact of a rigid sphere onto an elastic membrane theoretically and experimentally. We derive governing equations from first principles and impose natural kinematic and geometric constraints for the coupled motion of the sphere and the membrane during contact. The free-boundary problem of finding the contact surface, over which forces caused by the collision act, is solved by an iterative method. This results in a model that produces detailed predictions of the trajectory of the sphere, the deflection of the membrane, and the pressure distribution during contact. Our model predictions are validated against our direct experimental measurements. Moreover, we identify new phenomena regarding the behaviour of the coefficient of restitution for low impact velocities, the possibility of multiple contacts during a single rebound, and energy recovery on subsequent bounces. Insight obtained from this model problem in contact mechanics can inform ongoing efforts towards the development of predictive models for contact problems that arise naturally in multiple engineering applications

Computing the Global Irradiation over the Plane of Photovoltaic Arrays: A Step-by-Step Methodology

The quality of solar resource data is critical for the economic and technical assessment of solar photovoltaic (PV) installations. Understanding uncertainty and managing weather-related risk are essential for successful planning and operating of solar electricity assets. The input information available for PV designers is usually restricted to 12 monthly mean values of global horizontal irradiation (GHI) and average temperature, which characterize solar climate of locations. However, for calculating the energy production of a photovoltaic system, the global irradiation over the plane of the PV array is necessary. For this reason, this book chapter presents a methodology to appropriately determine the global irradiation over the plane of photovoltaic arrays. The methodology describes step by step the necessary equations for processing the data. Examples with numerical results are included to better show the data processing

Methodology for Sizing Hybrid Battery-Backed Power Generation Systems in Off-Grid Areas

In developing countries, rural electrification in areas with limited or no access to grid connection is one of the most challenging issues for governments. These areas are partially integrated with the electrical grid. This poor electricity distribution is mainly due to geographical inaccessibility, rugged terrains, lack of electrical infrastructure, and high required economic investment for installing large grid-connected power lines over long distances to provide electricity for regions with a low population. On the other hand, rapid depletion of fossil fuel resources on a global scale and progressive increase of energy demand and fuel price are other motives to reduce the reliance on fossil fuels. Hybrid renewable energy system (HRES) can be a suitable option for such remote areas. The objective of this chapter is to develop a methodology for sizing hybrid power generation systems (solar-diesel), battery-backed in non-interconnected zones, which minimizes the total cost and maximizes the reliability of supply using particle swarm optimization (PSO). The proposed methodology assists the sizing and designing process of an HRES for an off-grid area minimizing the cost of energy (COE) and maximizing the reliability of the system. Economic incentives offered by the Colombian government are considered in the model

Capillary-scale solid rebounds:Experiments, modelling and simulations

A millimetre-size superhydrophobic sphere impacting on the free surface of a quiescent bath can be propelled back into the air by capillary effects and dynamic fluid forces, whilst transferring part of its energy to the fluid. We report the findings of a thorough investigation of this phenomenon, involving different approaches. Over the range from minimum impact velocities required to produce rebounds to impact velocities that cause the sinking of the solid sphere, we focus on the dependence of the coefficient of restitution, contact time and maximum surface deflection on the different physical parameters of the problem. Experiments, simulations and asymptotic analysis reveal trends in the rebound metrics, uncover new phenomena at both ends of the Weber number spectrum, and collapse the data. Direct numerical simulations using a pseudo-solid sphere successfully reproduce experimental data whilst also providing insight into flow quantities that are challenging to determine from experiments. A model based on matching the motion of a perfectly hydrophobic impactor to a linearised fluid free surface is validated against direct numerical simulations and used in the low Weber number regime. The hierarchical and cross-validated models in this study allow us to explore the entirety of our target parameter space within a challenging multi-scale system

Evaluación de los contenidos de hierro y manganeso en sedimentos de la bahía de cartagena

En este estudio fueron evaluados los niveles de hierro y manganeso presentes en sedimentos de la Bahía de Cartagena, Colombia. La extracción de los metales se hizo empleando una mezcla de HNO3-HCI 90:10 y se determinaron por el método de absorción atómica por llama realizando un estudio previo de la interferencia de los elementos mayores sodio, potasio, magnesio y calcio sobre la señal de absorción atómica. Estos elementos mayores no afectaron la señal de absorción del hierro, mientras que para el manganeso, solamente el magnesio y el calcio disminuyeron la señal de absorción atómica. Para las estaciones localizadas dentro de la bahía, los contenidos de hierro y manganeso promedio estuvieron entre 27551 - 39598 y 306 - 715 mcg/g, respectivamente. Estos valores son menores que los dados para los sedimentos "Shale", considerados como patrón mundial de comparación; en igual forma las arenas de las estaciones fuera de la bahía muestran valores inferiores que los niveles naturales para las arenas. Se compararon estadísticamente los promedios de las estaciones, de acuerdo con el método de Mann-Whitney y se observó que la bahía no es un sistema homogéneo respecto a los contenidos de hierro y manganeso. Se encontró correlación positiva y significante a un nivel del 5% entre los contenidos de hierro y manganeso

Preparation of Al/Fe-PILC clay catalyst from concentrated precursors: process intensification towards scaling-up

Structural modification of bentonites by pillaring with Al/Fe mixed oxides provides them excellent catalytic response in catalytic wet peroxide oxidation (CWPO) of organic pollutants present in wastewaters but also potentially in surface waters for production of drinking water. However, in order to apply this process to real-scale, the scaling-up of the preparation of the catalyst from high-concentrated metal and clay precursors is mandatory. This work was then devoted to compare the preparation of highly-concentrated Al/Fe interlayering solution by three methodologies: (i) addition of elemental aluminum on the starting chlorides; (ii) microwave-assisted hydrolysis of the metals via urea decomposition; and (iii) basic hydrolysis by addition of sodium hydroxide under diluted conditions, used as reference method. Other series of solids (scale 50 g) were prepared for comparison of three methods of clay-interlayering: (a) addition of interlayering solution on ethanol clay-suspension (25 % w/v); (b) the same as (a) but using water instead of ethanol; and (c) clay powder directly added on interlayering solution (without previous clay-suspension). Al/Fe-PILC from methods (i) and (c) displayed the best physicochemical and catalytic properties based on XDR, XFR, textural properties from N2 isotherms, H2-TPR, DRIFTS and catalytic performance measured in CWPO phenol degradation (26