João M. Silva

Multigrid-based substrate coupling model extraction

Substrate noise is one of the most eminent problems in high-frequency mixed-signal designs, such as communication, biomedical and analog signal processing circuits and systems. Fast-switching digital blocks inject noise into common substrate hindering the performance of high precision sensible analog circuitry. Miniaturization effects on ICs complexity, inevitably make the accuracy requirements for substrate coupling simulation increase. However, model extraction and evaluation should not increase, leading to the need for fast and accurate substrate model extraction tools. We propose an extraction methodology based on a 3D finite difference formulation. The resulting 3D mesh is efficiently reduced to a circuit-level contact-based model by means of a fast multilevel algorithm. Extraction results show the proposed method to be very efficient, achieving linear complexity independently of accuracy and discretization and outperforming competing algorithms that show quadratic complexity.

Basic Cs-Pt/MCM-41 Catalysts: Synthesis, Characterization and Activity in n-Hexane Conversion

Cs-Pt/MCM-41 catalysts with basic character have been prepared by selective adsorption of Pt(NH3)4(OH)2 at pH = 8 on pure silica MCM-41 followed by incipient-wetness impregnation of CsNO3, then oxidation and reduction. The influence of the amount of Cs (0, 2 and 4 wt%) on the size of the reduced Pt particles and on their catalytic behavior in the conversion of n-hexane has been investigated. Whatever the Pt content (0.7 or 2.0 wt% Pt), the addition of Cs results in a higher Pt dispersion, a higher initial activity and a higher selectivity for aromatization. On the more basic Pt-richest MCM-41 sample (4 wt% Cs, 2 wt% Pt) the selectivity to benzene reaches values close to those obtained on Cs-enriched Pt/Cs-BEA zeolite. However, the catalytic stability is lower. The catalytic trends are discussed in view of the physicochemical properties of the solids determined by chemical analysis, N2 physisorption, XRD and TEM before and after catalytic test.

Influence of the exchanged cation in coke deposition during n-hexane reactions on Pt/Mβ zeolite catalysts

The performances of platinum β zeolite exchanged with alkali (Na, K, Cs) and alkali-earth (Mg, Ba) cations have been examined for n-hexane reactions. The nature of coke deposited on the catalysts is slightly influenced by alkali cations because coke is deposited on metallic sites. In Pt/alkali-earth catalysts the coke depends on the support acidity.

A systematic study on mixtures of Pt/zeolite as hydroisomerization catalysts

Mixtures of bifunctional catalysts were studied in the hydroisomerization of n-hexadecane. The study focused on the impact of the properties of individual catalysts on the hybrid catalysts’ performance. On the one hand, a Pt/HUSY catalyst was mixed with a series of Pt/zeolites with different topologies and acidities, all of the catalysts being individually well-balanced. Despite the diversity of Pt/zeolite catalysts in terms of both activity and isomerization selectivity, the performances of the hybrid catalysts corresponded to the average of individual components. Cooperative effects are proposed to be caused by a great difference in the relative activity of the Pt/zeolite catalysts rather than in selectivity. On the other hand, mixtures of large-pore Pt/HUSY and Pt/HBEA catalysts with different Pt loadings were tested. The performance of the resulting hybrid catalysts was observed to be a function of global metal–acid balance. Mixtures of poorly-balanced and well-balanced catalysts can be at the origin of cooperative effects, as demonstrated experimentally by an improved C16 isomer yield. The use of a dual-function kinetic model to simulate the performance of the hybrid catalysts corroborated these interpretations. This comprehensive work is expected to serve as a guideline for uncovering hybrid catalytic systems with industrial applications such as in the hydroisomerization of long chain n-paraffins.

Cordierite Foam Supports Washcoated with Zeolite-Based Catalysts for Volatile Organic Compounds (VOCs) Combustion

Reticulated cordierite foams produced by a direct foaming method were successfully washcoated with platinum-based zeolite catalysts. For comparison purposes, commercial cordierite monoliths were also washcoated. The effect of the structural properties on the fluid dynamics and catalytic behaviour for the toluene combustion were evaluated. Foam supports revealed highest performances, in terms of conversion into CO2, when compared to conventional honeycomb monoliths. The experimental results suggest that the catalytic behaviour is critically dependent on the fluid dynamics provided by structural characteristics of the supports, such as porosity, density and size of pores. The randomness and tortuosity of foams enhance reactant mixing, as it was evidenced by the higher axial and radial dispersions of the gas flow across the foam structure. This leads to better mass and heat transfers in the reaction system, thus improving the catalytic behaviour.

Isomerization of n-hexane on bifunctional catalysts Pt/HBEA and Pt/HMCM-22 with rare earth elements

The influence of rare earth (RE) elements La, Nd, and Yb was studied on the transformation of n-hexane using two catalysts with different porous structures, HBEA and HMCM-22. The zeolites were submitted to ion exchange with rare earth nitrate solutions of La, Nd and Yb, followed by platinum introduction. Platinum was characterized by Temperature Programmed Reduction (TPR-H 2 ) and by toluene hydrogenation. Pt/HBEA samples show higher hydrogenation activities than Pt/HMCM-22. In transformation of n-hexane both zeolites present high selectivity for the isomerization reaction. The presence of RE elements in Pt/HBEA increases the selectivity for di-branched isomers. Pt/HMCM-22 shows low selectivity in di-branched isomers due to shape selectivity effects provoked by the introduction of RE elements in the pores of this zeolite.

Creative thinking in chemical product and process design education

The purpose of this paper is to present some idea generation mapping methods in the context of product and process design teaching due to the important role that this methods can have in changing the usual thinking process and stimulating the creative thinking. Lifting the problem solving skills of the chemical engineering students by a small amount can have a huge effect on innovation and competitiveness. The role of idea mapping in chemical product and process design teaching is explored along with the discussion of the main characteristics of two different mapping methods, concept maps and mind maps. The distinctive characteristics are described along with an illustration and sample maps performed by a group of chemical engineering students showing the interest of ideas mapping in structuring the group thinking about a subject and allowing the group to gain new insights into the problem.

Methodologies for input-output data exchange between LabVIEW® and MATLAB®/Simulink®software for Real Time Control of a Pilot Scale Distillation Process

Abstract The use of different control applications in automated processes, poses the problem of how to exchange data in Real-Time (RT) between different software platforms. This paper presents a new methodology developed for input and output data exchange between LabVIEW® and MATLAB®/Simulink®, and provides an overview on available methodologies for data exchange comparing their advantages/disadvantages. Finally, a case study is presented in detail where a method based on TCP/IP plus Simulation Interface Toolkit (SIT) is implemented for experimental data exchange between a pilot-scale continuous distillation plant acquisition/control and supervision system carried out using a FieldPoint system from National Instruments (NI) that integrates with LabVIEW® software and a high level Model Based Predictive Control (MPC) algorithm developed in MATLAB®/Simulink® platform.

Strength Improvement of Cordierite Foams by a Dip Coating Method

The structure and morphological aspects of highly porous (higher than 90%) cordierite (Mg2Al4Si5O18) foams, prepared by a direct foaming method, have been evaluated by Scanning Electron Microscopy analysis. The resulting ceramic foams consisted of a three-dimensional array of struts forming a well-defined open-cell structure. This type of structure seems very attractive for catalyst support purposes. Attempts have been made in order to control the pore structure since it directly affects the physical properties, namely the mechanical strength. In this respect, the use of a dip coating method to improve the strength of the resulting foams was found to be effective in reducing defects (e.g. pores, flaws) in the struts. Based on image analysis, estimated mean cell sizes were about 550 µm whereas strut thicknesses varied in the range of 60-70 µm. The compressive strength of the developed foams increased by one order of magnitude (0.1 to 1 MPa) by increasing the relative density from 0.06 to 0.18.

Optimization studies through simulation of a methanol/water/glycerol distillation column

Abstract This paper presents an optimization study of a distillation column for methanol and aqueous glycerol separation in a biodiesel production plant. Considering the available physical data of the column configuration, a steady state model was built for the column using Aspen-HYSYS as process simulator. Several sensitivity analysis were performed in order to better understand the relation between the variables of the distillation process. With the information obtained by the simulator, it is possible to define the best range for some operational variables that maintain composition of the desired product under specifications and choose operational conditions to minimize energy consumptions.