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Now showing items 17 - 28 of 28

  • Alternative pore hindrance factors: What one should be used for nanofiltration modelization?

    Silva, V.   Pradanos, P.   Palacio, L.   Hernandez, A.  

    In nanofiltration it is important for predictive purposes to obtain retentions and/or reflection coefficients from known sizes of the pores and the molecules of uncharged solutes. This correlation is also needed in order to model the mass transport of salts or other charged species. To complete these model and predictive needs, the hindrance factors have to be correlated with the ratio between the pore and the molecule sizes, lambda. There are several correlations proposed in the literature. Moreover, the effect of the applied pressure was not accounted for in these correlations until recent revisions of the transport model. In some cases the action of the pore-wall friction has been also neglected. Here we make a revision of these different assumptions on the hindrance factors, we discuss their effect on the transport and we show some conditions that a correct correlation should accomplish. It is shown that it is important to consider both the pressure and the pore-wall friction because the corresponding terms have important contributions to both retention and reflection. It is, nevertheless, less relevant an accurate choice of a relationship for the pore hindrance factors in terms of lambda, as far as, both retention and reflection are mainly controlled by partitioning in the ranges where the different proposed correlations differ, what leads to the same transport predictions. In any case a theoretically correct correlation can be chosen attending to the conditions that the pore reflection must accomplish.
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  • Effect of phosphoric and hydrofluoric acid on the structure and permeation of a nanofiltration membrane RID B-7628-2011 RID B-4622-2012

    Gonzalez, M. P.   Saucedo, I.   Navarro, R.   Pradanos, P.   Palacio, L.   Martinez, F.   Martin, A.   Hernandez, A.  

    The changes have been analyzed by studying the permeability of industrial phosphoric acid aqueous solutions through a nanofiltration membrane caused by treatment with phosphoric and hydrofluoric acid solutions. The retention of phosphoric acid together with its cationic impurities were also analyzed and attributed to a complex process of active layer modification. This process was studied in terms of both pore size and surface modification, as confirmed by retention tests with known size neutral molecules and scanning probe microscopy. The very relevant changes in hydrophilic character of the membrane material were studied by using contact angle measurements. When the membrane was treated with HF solutions, the pore size remained relatively constant, while the hydrophilic character increased. Because of these changes, increases in industrial phosphoric acid permeability and in the rejection of impurities were observed. In the case of the treatment with H3PO4, the membrane also presented a significant increase in industrial phosphoric acid permeability. However, the rejections of the cationic impurities decreased. These facts are due to an increase in the pore size and in the hydrophobic character of the membrane. (c) 2006 Elsevier B.V. All rights reserved.
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  • Evaluation of several ultra- and nanofiltration membranes for sugar control in winemaking

    Garcia-Martin, N.   Palacio, L.   Pradanos, P.   Hernandez, A.   Ortega-Heras, M.   Perez-Magarino, S.   Gonzalez-Huerta, D. C.  

    Several membranes are here considered and studied in order to be applied to control of the sugar content of grape musts. This should allow decreasing somewhat the alcohol degree of wines that due to a warmer weather are being made from too mature grapes sometimes. This gives wines with a too high alcohol degree. Our objective is to reverse this degree to the original one without loosing the main appreciated characteristics of these wines. A non-aggressive technology that can be used in such a procedure consists in membrane processes. Total sugar retention and specifically glucose and fructose rejection have been studied both in must and synthetic water solutions through nanofiltration and tight ultrafiltration membranes. Also the most relevant high molecular weight (HMW) compounds of must along with their low molecular weight ones (LMW) have also been analyzed. From a detailed consideration of these retentions as a function of sugars that allow to design an adequate two steps nanofiltration process.
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  • Analysis of the Grafting Process of PVP on a Silicon Surface by AFM and Contact Angle RID F-3633-2010 RID B-4622-2012 RID B-7628-2011

    Fernandez, L.   Sanchez, M.   Carmona, F. J.   Palacio, L.   Calvo, J. I.   Hernandez, A.   Pradanos, P.  

    Silicon wafers have been silylated with VTMS (vinyltrimethoxysilane) and hydrolyzed. Subsequently, PVP (polyvinyl pyrrolidone) was grafted onto the silylated surface by two different techniques: the grafting-through (GT) and the grafting-onto techniques (GO). The measurement of contact angles along with the topography analysis by atomic force microscopy (AFM) has allowed monitoring the different stages of the process and the temporal evolution of polymer grafting. The results have demonstrated the feasibility of both methods of grafting but have shown that the GT method gives a higher density of polymer-grafted chains. The AFM technique in adequate liquid environments has been proven to permit the surface density of chains to be distinguished by both methods and to estimate the length of the resulting PVP chains.
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  • Morphological,chemical and electrical characterization of a family of commercial nanofiltration polyvinyl alcohol coated polypiperazineamide membranes

    Otero-Fernandez, A.   Diaz, P.   Otero, J. A.   Ibanez, R.   Maroto-Valiente, A.   Palacio, L.   Pradanos, P.   Carmona, F. J.   Hernandez, A.  

    Three AFC membranes from PCI, of the thin film composite (TFC) nanofiltration type, have been characterized by using XPS, AFM, Contact angles, Zeta potential and permeation experiments. This plethora of complimentary methods portrays a deep and exhaustive description of these membranes that could be used to tune fabrication and modification of nanofiltration membranes to get better properties. Morphological properties, including porosity, water permeability, fractal dimension, Wenzel parameter and roughness, correlate well with pore sizes. While functional characteristics as, for example wettability correlate well with the O/N ratio. Increasing O/N ratios should be interpreted as caused by increasing PVA coverages. The charge on the membrane's surface is ordered in a different way for different pH but are quite similar anyway. The effect of charges on retention of 1:1, 1:2 and 2:1 salts (as tested with NaCl, Na2SO4 and CaCl2) increases with increasing O/N and wettability. Consequently, the trend of salt retentions can be explained in terms of the PVA coverage and the details of the amphoteric behavior of the three AFC membranes studied.
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  • Fouling study of nanofiltration membranes for sugar control in grape must:Analysis of resistances and the role of osmotic pressure

    Salgado, C.   Carmona, F. J.   Palacio, L.   Hernandez, A.   Pradanos, P.  

    Three membranes are analyzed attending to their retention, flux, and fouling when used to nanofiltrate sugars in red grape musts. In the presence of high molecular weight compounds, that is, when filtering must, fouling develops from initial pore blocking to final cake deposition. A decrease of resistance appears due to a decrease of the effective transmembrane pressure and cake compaction. The final effective pore size corresponds to that of the compacted cake. Attending to flux decay and sugar retention, two membranes, HL and SR3, are appropriate to reduce the content of sugar of red must. Specifically SR3 shows the best passage of sugar and less fouling.
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  • Medicinal plants from the "Sierra de Comechingones", Argentina

    Goleniowski, Marta Ester   Bongiovanni, G. A.   Palacio, L.   Nunez, C. O.   Cantero, J. J.  

    Argentina is a country with both rich floral biodiversity and cultural diversity. Traditional herbal medicines are important in the health care of most people, and rely heavily on the use of indigenous plants. An ethnobotanical survey of the "Sierra de Comechingones" made over a 26-year period (1979-2005), indicated that 65 families and 149 different genuses were used in traditional medicines. The use of these medicines was observed to be widespread and prevalent over orthodox medicine. Medicinal native plants from this mountain range make up 31% of the total Argentina medicinal native flora. In addition, there are 15 endemic species that grow only in the region. The botanical name, popular uses, parts utilized, as well as the distribution of these medicinal plants from the "Sierra de Comechingones", Argentina, were summarized. Previous reports on phytochemical and biological activities in relation to cancer, antimicrobials and pesticides were also included. (c) 2006 Elsevier Ireland Ltd. All rights reserved.
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  • Influence of the PEO length in gas separation properties of segregating aromatic-aliphatic copoly(ether-imide)s

    Tena, A.   Marcos-Fernandez, A.   Lozano, A. E.   de Abajo, J.   Palacio, L.   Pradanos, P.   Hernandez, A.  

    A complete series of aliphatic-aromatic copoly(ether-imide)s has been synthesized in this work. All these copoly(ether-imide)s had the same structure, BPDA-PEO-ODA, but different lengths of PEO in the final polymer. These copolymers have been thermally treated and characterized by several techniques. A direct relationship between the temperature of treatment, the improvement of phase segregation, and permeability has been demonstrated. The Maxwell model has been applied to predict permeability (for CO2, CH4 and N-2) and it has been found that when the segregated PEO can be considered to be amorphous - it is at high temperatures when crystallinity disappears - the model fits reasonably well. This confirms that the aliphatic and aromatic portions of the copolymer behave approximately as a bi-phase of disperse domains within a continuous matrix. Results show that permeability is higher when the PEO chains are longer - when there is no crystallinity, or any kind of internal bonds, distorting the results - while selectivity does not depend on the PEO length in the copolymer. Remarkable are the results for the CO2/N-2 gas pair, with selectivity-versus-permeability very near to the Robeson's upper bound at 30 degrees C and even in closer proximity to the corresponding trade off line for higher permeation temperatures. (C) 2013 Elsevier Ltd. All rights reserved.
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  • Maometto secondoby Gioacchino Rossini; Cesare Della Valle; John McCarthy; J. Anderson; M. Zimmermann; E. Palacio; S. Ramey; L. Dale

    Review by: Piero Mioli  

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  • Mixed matrix membranes of 6FDA-6FpDA with surface functionalized gamma-alumina particles. An analysis of the improvement of permselectivity for several gas pairs RID B-4622-2012 RID B-7628-2011

    Tena, A.   Fernandez, L.   Sanchez, M.   Palacio, L.   Lozano, A. E.   Hernandez, A.   Pradanos, P.  

    Herein, mixed matrix membranes including alumina particles whose surfaces have been differently modified have been made and characterized. The polymeric matrix is a fluorinated polyimide, 6FDA-6FpDA, whereas the inorganic constituent parts are neat, silanized or poly-vinyl-pirrolidone-coated nanometric gamma-Al(2)O(3) particles of 40 nm in diameter, which have been added in an approximated percentage of a 12% w/w. All the modified or unmodified added particles lead to similar improvements in the permselectivity of the gas pairs studied. Only in the case of the O(2)/N(2) pair the increase in selectivity for the silanized particles is not as effective as the observed permeability enhancement for the uncoated and PVP-coated particles. In case of CO(2)/CH(4), the 1991 Robeson's upper bond line is overpassed. The characteristics of the permselectivity improvement for the different inorganic particles have been analyzed in terms of the properties of the particle-polymer interfacial properties. (C) 2009 Elsevier Ltd. All rights reserved.
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  • AFM analysis of the surface of nanoporous membranes: application to the nanofiltration of potassium clavulanate RID B-4622-2012 RID B-7628-2011

    Carvalho, A. L.   Maugeri, F.   Silva, V.   Hernandez, A.   Palacio, L.   Pradanos, P.  

    This study presents the structural characterization of the surface of four commercial nanofiltration membranes: NF90 (polyamide) and NF (polypiperazine amide) from Filmtec(TM) and NP010 and NP030 (polysulfone) from Microdyn Nadir(A (R)), by Atomic Force Microscopy (AFM). These membranes have been studied before and after undergoing a filtration process with potassium clavulanate. The fast Fourier filtering of AFM images with very high magnification (40 x 40 nm) has allowed identifying the pore size distribution and geometry of the pores on the surface of the membrane before their use. Images between 0.5 x 0.5 and 10 x 10 mu m(2) have allowed the study of the surface roughness of the samples before and after being used to filtrate potassium clavulanate solutions. The results of roughness and power spectral fractal dimension along with the skewness and kurtosis of the height distribution have been analyzed in terms of pore size, hydraulic permeability, and the adsorption of clavulanate for the different samples.
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  • Mass transfer and transport during purification of fructooligosaccharides by nanofiltration RID B-4622-2012 RID B-7628-2011

    Kuhn, R. C.   Maugeri Filho, F.   Silva, V.   Palacio, L.   Hernandez, A.   Pradanos, P.  

    In this work, a process has been designed for the purification of fructooligosaccharides obtained by enzymatic transformation of sucrose from sugar cane molasses. The designed protocol includes two nanofiltration stages with the same membrane. The first one is a diafiltration process, at constant volume followed by concentration. The second stage consists in the nanofiltration of the permeate of the first stage to obtain a concentrate similar in its characteristics to the initial solution. The process allows getting purities over 90% in fructooligosaccharides with yields around 80%. These processes are studied and modeled, by taking into account the effects of the resulting osmotic pressure and the changes in resistance due to solute adsorption on the membrane. The transport is modeled by assuming that there are diffusion and convection but hindered by friction in the pore. The steric partitioning, along with an adequate mass balance for the differently sized molecules have also been considered leading to get the pore size distribution of the membrane. (C) 2010 Elsevier B.V. All rights reserved.
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