Abstract The mass transfer coefficient (K L ) determined using an electrochemical technique was used in this work as a parameter to evaluate the hydrodynamics of hollow fiber membrane modules. A new microfiltration module configuration was investigated, taking advantage of the hydrocyclone concept aimed at reducing the concentration of the polarization layer near the membrane surface promoted by the centrifugal field. The mass transfer coefficient for the new configuration was compared with that of a conventional longitudinal module. The experimental determination of K L was obtained by monitoring the electrochemical reactions that occur at the electrode surface under mass transfer-limiting conditions. The performance of the microfiltration modules, both hybrid and longitudinal, was evaluated based on parameters such as packing density and fluid flow regimes. The results achieved for the mass transfer coefficient with the electrochemical technique allowed for performance evaluations of the proposed new module configuration and a comparison with the longitudinal module.

Resumo A hidroxiapatita sintética (Ca10(PO4)6(OH)2; HA) devido à propriedade de biocompatibilidade com o tecido ósseo tornou-se um material cerâmico amplamente utilizado na reconstrução óssea. A biocompatibilidade assim como outras propriedades físico-químicas da hidroxiapatita podem ser modificadas por meio da adição de diferentes íons na sua estrutura. O íon nióbio (V) não tem sido empregado comumente na síntese de hidroxiapatitas. O objetivo deste trabalho foi verificar o emprego da rota hidrotérmica na síntese de hidroxiapatita dopada com íon nióbio (V). A rota empregada utiliza o complexo di-hidrogeno tris(oxalato) oxiniobato (V) de amônio trihidratado (NH4H2[NbO(C2O4)3].3H2O), como precursor de íon nióbio (V). A adição de ácido cítrico e ureia na rota hidrotérmica é usada para o controle do pH da síntese e da taxa de precipitação. Amostras pura e aditivada com 5,3 ppm de íon nióbio (V) foram obtidas. A coexistência de outras fases além da hidroxiapatita não foi observada em ambas amostras por meio dos empregos das técnicas de difração de raios X e espectroscopia no infravermelho. Por meio da técnica de FTIR observou-se a presença de grupos funcionais característicos da hidroxiapatita. Na análise por microscopia eletrônica de varredura, verificou-se a formação de aglomerados compostos por partículas arredondadas confirmadas pela técnica de microscopia eletrônica de transmissão. A análise espectroscópica de fluorescência de raios X detectou a presença de nióbio na amostra aditivada obtida. Os resultados apontam que podem ser sintetizadas hidroxiapatitas aditivadas com íon nióbio (V) por meio da rota hidrotérmica, podendo ser considerado como enorme o potencial para a aplicação em biocerâmicas.

Abstract Synthetic hydroxyapatite (Ca10(PO4)6(OH)2; HA) has become a widely used ceramic material for bone reconstruction due to its biocompatibility with the bone tissue. This biocompatibility as well as other physical and chemical properties of the hydroxyapatite can be modified by the addition of different ions to its structure. Niobium (V) ion has not been commonly used in the hydroxyapatite synthesis. The objective of this study was to evaluate the use of hydrothermal route in the niobium (V) doped hydroxyapatite synthesis. The route used the niobium ammonium oxalate (NH4H2[NbO(C2O4)3].3H2O) complex as a niobium (V) ion precursor. The addition of citric acid and urea in the hydrothermal route is used for the control of synthesis pH and precipitation rate. Pure sample and sample added with 5.3 ppm of niobium (V) ion were prepared. The coexistence of other phases besides the hydroxyapatite was not observed in any of the samples through the use of X-ray diffraction and infrared spectroscopy (FTIR) techniques. The FTIR technique revealed the presence of hydroxyapatite characteristic functional groups. The scanning electron microscopy analysis showed the formation of agglomerates composed of round particles, confirmed by the transmission electron microscopy technique. The X-ray fluorescence spectroscopic analysis detected the presence of niobium in the doped sample. The results showed that niobium (V) doped hydroxyapatite can be synthesized by means of hydrothermal route, which may be considered as huge potential for future application in bioceramics.

Our goal in this study was the immobilization of myoglobin in poly(vinyl alcohol) dense membranes. Glutaraldehyde was investigated both as the crosslinking agent, aiming to increase the membrane stability in aqueous medium, and as the vehicle to bind myoglobin and PVA. Reaction and membrane synthesis were carried simultaneously in mild operating conditions in order to maintain the native protein folding. Membrane characterization comprised the water swelling degree, DSC, TGA, UV-visible spectroscopy, FTIR analysis and oxygen transport in a dialysis cell. The incorporation of myoglobin in the film decreased the water swelling degree and improved the membrane thermal properties compared to unmodified PVA membrane. The reduction of ferric iron in the prosthetic group of the protein to the ferrous form was observed. The increased affinity between oxygen and the immobilized myoglobin did not favor the release of this solute from the biocarrier.

The separation of olefin/paraffin mixtures is one of the most important processes of the chemical industry. This separation is typically carried out by distillation, which is an energy and capital intensive process. One promising alternative is the use of facilitated transport membranes, which contain specific carrier agents in the polymer matrix that interact reversibly with the double bond in the olefin molecule, promoting the simultaneous increase of its permeability and selectivity. In this study, polyurethane (PU) membranes were prepared using two different silver salts (triflate and hexafluorantimonate). The membranes were structurally characterized and their performance for the separation of propylene/propane mixtures was evaluated. The results of the characterization analyses indicated that the triflate salt was the most efficient carrier agent. The membranes containing this salt showed the best performance, reaching an ideal selectivity of 10 and propylene permeability of 188 Barrer.

Pervaporation-assisted esterification of oleic acid and ethanol was investigated by means of heterogeneous acid catalysis with the aim of increasing the ethyl oleate yield. The experimental strategy comprised kinetic tests with Amberlyst 15 Wet (Rohm & Haas), the characterization of hydrophilic Pervap 1000 membrane (Sulzer) and the evaluation of the membrane-assisted reactor. Kinetic tests were carried out to study the effect of temperature, catalyst loading and ethanol/organic acid molar ratio for the esterification of oleic acid and ethanol. The ester yield and initial reaction rate were used as response. The hydrophilic poly(vinyl alcohol) membrane was able to remove water from the reaction medium and, hence, the ester yield was increased. The potential of coupling esterification and pervaporation was demonstrated, with a two-fold increase in the reaction yield of ethyl oleate.

Membrane separation processes have been extensively used for some important industrial separations, substituting traditional methods. However, some applications require the development of new membranes. In this work, we discuss recent progress achieved in this field, focusing on gas and liquid separation using facilitated transport membranes. The advantages of using a carrier species either in a liquid membrane or fixed in a polymer matrix to enhance both the flux and the selectivity of the transport are summarized. The most probable transport mechanisms in these membranes are presented and the improvements needed to spread this technology are also discussed. As examples, we discuss our very successful experiences in air fractioning, olefin/paraffin separation and sugar recovery using liquid and fixed carrier membranes.

Taking into account the close similarity between pervaporation and vapour permeation techniques, a method for employing pervaporation flux data in the modelling of vapour permeation modules is proposed. It is based on the use of fugacity gradients across the membrane, instead of concentration ones, as the driving force for mass transfer. This procedure is interesting, for instance, in the case of aroma recovery systems, for which there is much more experimental data on pervaporation available in the literature than on vapour permeation. In order to illustrate the application of this method, pervaporation experiments for an isotropic PDMS membrane were conducted with aqueous solutions of ethyl acetate (113-2474 mg/L), and the results obtained were used to enable simulation of different vapour permeation hollow-fibre modules for recovering ethyl acetate from diluted air streams.