Mixed matrix-composite membranes (MMCM) for gas separation are prepared and characterized in this work. Acrylonitrile-butadiene-styrene (ABS) copolymer was used for the continuum phase of the membrane filled with two different activated carbons (AC). The so-obtained membranes have been characterized by gas permeability, optical microscopy, electronic microscopy and atomic force microscopy. The membranes have different roughness on both their surfaces but are always recovered by the polymeric material. Better ABS-AC adhesion has been always reached giving high selectivity and permeability for CO2/CH4. Such intimate contact can be attributed to the rubber proper-ties of the butadiene-styrene chains in ABS. The morphological characteristics and the increase in both permeability and selectivity with the volume fraction of the filler are explained in terms of the properties of pure activated carbons. (c) 2006 Elsevier Ltd. All rights reserved.

Dilute Pb(II) aqueous solutions were nanofiltered through a tubular membrane with good rejections. Retention was modeled using the Modified Spiegler-Kedem theory. The true retention, evaluated from concentration-polarization measurements, was similar to the observed value. The three characteristic parameters of the model: reflection coefficient , solute permeability , and mass transfer coefficient were evaluated simultaneously. The reflection coefficient decreased with an increase in concentration until a plateau was reached at a concentration of 30 ppm. At low concentrations, the solute permeability increased with an increase in concentration, reaching a maximum at a concentration of 30 ppm. Subsequently, the permeability decreased with further increase in concentration, until at concentrations ae 100 ppm, it reached values close to those observed for very dilute solutions (< 10 ppm). Industrial scale nanofiltration of dilute solutions of Pb(II) is viable with high retentions. High pressures and tangential speeds and low temperatures increase retention. Moreover, moderately high concentrations of aqueous Pb(II) solutions can be reduced to totally sure levels in less than four nanofiltration steps. This makes nanofiltration a suitable tool to decrease Pb(II) levels below those recommended by the world health organization.

Mixed matrix membranes, MMMs, consisting of variable loads of a porous polymer network, PPN, within an o-hydroxipolyamide, HPA (6FCl-APAF, made from the reaction between 2,2-bis [4-chlorocarbonylphenyl)hexafluoropropane, 6FCl, and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, APAF), have been thermally treated to induce the rearrangement of HPA to a polybenzoxazole (beta-TR-PBO). HPA is 6FCl-APAF was loaded with a PPN synthesized, by us, by combining triptycene (TRP) and trifluoroacetophenone (TFAP). Mechanical, thermal and morphological properties of the membranes have been determined. CO2/CH4 selectivity of MMMs decreased slightly both when the PPN load was augmented and when thermal rearrangement took place. The changes in selectivity can be attributed mostly to solubility effects for beta-TR-MMMs and to diffusive effects for the MMM from neat HPA. CO2 and CH4 permeabilities increased to the 2008 Robesoris upper bond for an optimal 30% PPN load both before and after thermal rearrangement. These relatively good permselectivities are explained in terms of compaction, rigidity, fractional free volumes and filling-matrix interactions.

This work presents experimental observations on the permeation of multi-ionic solutions through a commercial DESAL-HL nanofiltration membrane. Two types of mixed-salt solutions have been analysed with a common co-ion (NaCl + Na(2)SO(4)) and with a common counter-ion ((NaCl + MgCl(2))). The NaCl concentrations have been similar to those of seawater with divalent ions with lower concentrations up to a tenth of that of the monovalent salt. In this study. SEDE-VCh model that includes the variation of the charge inside the membrane pores has been used to model the system and structural, electrical and dielectrical membrane parameters for such systems have been obtained. We show that accurate enough predictions can be achieved for the retention of monovalent ions in the presence of counter or co-ion divalent ions from the single NaCl salt results. While correct predictions for the retention of the divalent ions require membrane charges and dielectric constants dependent of the ionic composition of the solutions filtered. (C) 2011 Elsevier B.V. All rights reserved.

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.

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.

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.

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.

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.

Flux and retention of 0.1% w/w aqueous solutions of several proteins (lysozyme, pepsin, bovine serum albumin (BSA), lipase, and gamma-globulin) with molecular weights of 14.6, 36, 67, 80, and 150 kDa are studied when they are tangentially filtered, with transmembrane pressure differences until 1 MPa and circulation velocities in the retentate loop from 0.04 to 1.98 m/s (laminar regime), through two asymmetric polysulfone commercial membranes (E-100 with a nominal pore size of 0.01 mu-m and E-500 with a nominal pore size of 0.04 mu-m). Results are analyzed with the film theory for the concentration-polarization phenomenon, obtaining the mass transfer coefficient along with the apparent and true retention coefficients for the cell used, as a function of the feed circulation velocity and the molecular weight of the solute. The standard retention curves lead to pore size distributions differing from the nominal ones. These differences can be attributed to the modifications of the membranes when they are in operational conditions, probably due to protein adsorption.

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.

Three independent methods are used to get the pore size distribution of nanofiltration membranes. Two membranes from PCI - AFC-40 and AFC-80 - have been studied. The surface pore size distribution has been studied by AFM images of the membrane surface. A steric pore flow model with friction has been used for different neutral solutes to obtain the effective pore size seen by several organic uncharged solutes. This model is improved by taking into account the modifications of viscosity for confined geometries in narrow pores and by using the Hagen-Poiseuille model to isolate the pore radius as the only parameter of the model. The retentive fractions of pores for the solutes used, which sizes are over the effective pore size seen by them, have been considered to obtain the pore size distribution. Finally a liquid-liquid displacement technique has been used to directly get the open pore size distribution. A fairly good agreement has been obtained by all the three methods used. (C) 2007 Elsevier B.V. All rights reserved.

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.