Márcio L.L. Paredes

Removal of aromatics from multicomponent organic mixtures by pervaporation using polyurethane membranes: experimental and modeling

Polyurethane (PU) dense membranes were used in the separation of binary and multicomponent aromatic/aliphatic mixtures by pervaporation. The PU membranes found to be selective towards aromatics in all systems studied. Both, swelling of polymer matrix and the permeate flux increase with aromatic weight fraction in the feed. The highest selectivity was achieved with benzene/n-hexane mixture in the whole feed composition range. The permeation of the organics through the PU membrane was modeled based on the sorption–diffusion mechanism. The sorption equilibrium was calculated using Flory–Huggins (FH) or UNIQUAC equations and Stefan–Maxwell (SM) equations were used to describe the transport inside the membrane matrix. A correction was introduced in the diffusion coefficients of the permeating species to take into account the polymer matrix plasticization. The experimental and predict data showed a good agreement, indicating that the PU membrane are useful to reduce the aromatic content of industrial solvent by pervaporation process.

Square-well chain mixture: analytic equation of state and Monte Carlo simulation data

An analytic perturbation theory equation of state developed for mixtures of freely-jointed square-well chain fluids of variable well width is tested against Monte Carlo simulation data. The equation of state is based on second-order Barker and Henderson perturbation theory to calculate the thermodynamic properties of the reference sphere fluid, and on first-order Wertheim thermodynamic perturbation theory to account for the connectivity of spheres to form chains. A real function expression for the radial distribution function of hard spheres and one-fluid type mixing rule are used to obtain an analytic, closed form expression, for the Helmholtz free energy of mixtures of square-well spheres. In order to test the theories, Monte Carlo simulations for binary mixtures of square-well chains were performed to obtain the radial distribution function at the contact point, the compressibility factor, and the configurational internal energy of these mixtures. The proposed equation of state leads to good predictions of compressibility factor of square-well chains and their mixtures when compared with the simulation data.

An analytic equation-of-state for mixture of square-well chain fluids of variable well width

Abstract An analytic perturbation theory equation of state for a mixture of freely-jointed square-well fluids of variable well width (1≤ λ ≤2) is developed. The equation of state is based on second-order Barker and Henderson perturbation theory to calculate the thermodynamic properties of the reference sphere fluid, and on first-order Wertheim thermodynamic perturbation theory to account for the connectivity of spheres to form chains. A real function expression for the radial distribution function of hard spheres and a one-fluid type mixing rule are used to obtain an analytic, closed-form expression, for the Helmohltz free energy of mixtures of square-well spheres. Good results were obtained when this equation of state was used with temperature-independent parameters to correlate vapor–liquid equilibrium data of pure substances and mixtures.

Development and evaluation of a new DGA diagnostic method based on thermodynamics fundamentals

The dissolved gas analysis (DGA) is a well-accepted power transformer predictive maintenance technique. However, despite the importance of the technique, classical diagnostic methods were developed from observations of simplified thermodynamic and compositional models. This paper presents the development of a DGA diagnostic method based on a thermodynamic model that includes a contribution inspired on the kinetics of the process. The performances of the new phenomenological proposition and of classical DGA diagnostic methods are compared and discussed. Also, a general procedure for the application of the new diagnostic method is described.

Influence of Metal Oxides Impregnated on Silica-Alumina in the Removal of Sulphur and Nitrogen Compounds from a Hydrotreated Diesel Fuel Stream

The environmental legislation of many countries imposes severe restrictions on the emissions of gaseous pollutants, including NOx and SOx. Efficient alternatives for the removal of nitrogen and sulphur contaminants are required to obtain increasingly cleaner fuels. In this regard, adsorption is economically promising, because it requires less energy than the traditional hydrotreating processes due to mild conditions of temperature and pressure required. The objective of this study was to evaluate the influence of nickel, cerium, molybdenum and cobalt oxides impregnated on silica–alumina in removing nitrogen and sulphur compounds from a hydrotreated diesel. The incorporation of metal oxides increased the density of acid sites and promoted the removal of nitrogen and sulphur compounds, especially the one impregnated with molybdenum oxide. The influence of molybdenum oxide loading was also studied. It was observed that this synthesis parameter affected acid sites density and contaminant removal.

Synthesis and characterization of sulfonated poly(ether imide) with higher thermal stability and effect on CO2, N2, and O2 permeabilities

An experimental design in different reaction conditions was applied to modify poly(ether imide), PEI, by sulfonation using acetyl sulfate. Higher temperatures and reaction times led to higher ion exchange capacity. The thermal analysis showed that our sulfonation approach accomplished preparing sulfonated PEI maintaining the thermal stability of its parent material even for the film with highest degree of sulfonation, and assessed the effect of this change on CO