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When natural feed waters are used in the operation of a reverse electrodialysis (RED) stack, severe fouling on the ion exchange membranes and spacers occurs. Fouling of the RED stack has a strong influence on the gross power density output; which can decrease up to 50%. Moreover, an increase in the pressure loss occurs between the feed water inlet and outlet, increasing the pumping energy and thus decreasing the net power density that can be obtained. In this work, we extensively investigated the use of CO2 saturated water as two-phase flow cleaning for fouling mitigation in RED using natural feed waters. Experiments were performed in the REDstack research facility located at the Afsluitdijk (the Netherlands) using natural feed waters for a period of 60 days. Two different gas combinations were experimentally investigated, water/air sparging and water/CO2 (saturated) injection. Air is an inert gas mixture and induces air sparging in the stack. In the case of CO2, nucleation, i.e. the spontaneous formation of bubbles, occurs at the spacer filaments due to depressurization of CO2 saturated water, inducing cleaning. Results showed that stacks equipped with CO2 saturated water can produce an average net power density of 0.18 W/m2 under real fouling conditions with minimal pre-treatment and at a low outside temperature of only 8 °C, whereas the stacks equipped with air sparging could only produce an average net power density of 0.04 W/m2. Electrochemical impedance spectroscopy measurements showed that the stacks equipped with air sparging increased in stack resistance due to the presence of stagnant bubbles remaining in the stack after every air injection. Furthermore, the introduction of CO2 gas in the feed water introduces a pH decrease in the system (carbonated solution) adding an additional cleaning effect in the system, thus avoiding the use of environmentally unwanted cleaning chemicals.

To understand and mitigate the role of surface water composition and associated membrane fouling in the removal of nC60 nanoparticles by low-pressure membranes, experiments were carried out with microfiltration membranes using natural feed waters, mimicking separation in real industrial water treatment plants. The effects of water composition, the presence of nanoparticles, and membrane fouling were investigated with a dead-end bench-scale system operated under constant flux conditions including a hydraulic backwash cleaning procedure. nC60 nanoparticles can be efficiently removed by microfiltration and the removal efficiency is found to be independent of the water surface composition. However, the water composition controls the extent of fouling occurring during filtration. A synergistic effect on membrane fouling between nC60 and surface water constituents such as natural organic matter (NOM) and its fractions is observed: the synergistic effect resulted in a transmembrane pressure (TMP) increase always higher than the sum of the TMP increase due to the filtration of nC60 in ultrapure water and the TMP increase due to the surface water without nC60.

Spacer-less RED stacks using membranes with integrated spacer profiles have been investigated during the last years to eliminate the spacer shadow effect. The presence of spacers partially blocks the membrane surface and creates a tortuous and thus longer path for ions in the channel, meaning higher ohmic resistance. Consequently, power outputs are reduced. Profiled membranes may solve this problem as they provide flow channels for the feed streams, while the relief formed on their surfaces keeps the membranes separated. Although the geometry and arrangement of so far used profiles led to lower ohmic resistance, it did not grant an efficient fluid mixing. Recently, so-called chevron profiles, with enhanced mixing, were proposed based on computational fluid dynamics (CFD) simulations. In the present study, the performance of such chevron-profiled membranes, prepared by thermal pressing, was experimentally validated in a reverse electrodialysis (RED) stack. According to the obtained experimental values of non-ohmic resistance and total pressure drop across the RED stack, the chevron-profiled membranes assure efficient fluid mixing at comparatively low hydraulic losses. The net power density obtained with chevron-profiled membranes was the highest obtained for the present stack design. It outperformed the alternative RED stack configurations investigated in this study, such as channels with optimized spacers and channels formed by pillar-profiled membranes. To allow for an even more straightforward and efficient RED stack assembling with chevron-profiled membranes, recommendations for a further simplified design, consisting of diagonal ridges that are assembled perpendicularly, are provided.

International audience; This manuscript encompasses the investigation into the solvent resistant nanofiltration (SRNF) performance of multilayer membranes prepared from weak polyelectrolytes. These weak polyelectrolytes are unique in that the charge density is not fixed and depends on the coating pH, adding an extra variable as tuning parameter for SRNF performance. The weak polyelectrolyte based multilayers (PEMs) were prepared on a hydrolyzed PAN support membrane from poly(allylamine hydrochloride) (PAH) as polycation and poly(acrylic acid) (PAA) as polyanion. Detailed investigations on the role of the pH of the coating solution on the performance of the prepared SRNF-membranes were carried out with organic dyes of different size (~300–1000 Da) and charge. Variation in pH of the coating solutions was found to lead to a large degree of control over the separation performance of the prepared SRNF-membranes for the different dyes. The solvent permeabilities and the dye retentions were measured and correlated to variations in the PEM membrane structures, with more dye adsorption being found for membranes with more free acid and amine groups. The membranes were also found to be stable for long term-filtrations in solvents such as isopropyl alcohol (IPA), acetonitrile (ACN), tetrahydrofuran (THF) and in the challenging polar aprotic solvent, N,N-dimethylformamide (DMF). Results of this study clearly demonstrate the potential of using pH as tuning parameter for weak PEMs to prepare SRNF-membranes optimized for specific applications

Block copolymer (BCP) membranes are a very promising new type of membranes, but often have a difficult fabrication method that involves a long evaporation step prior to phase inversion. In this work, we study new novel BCP phase inversion recipes for the fabrication of asymmetric membranes with a thin, ordered isoporous selective layer on top of a highly interconnected porous support layer. A key aim is to shorten the evaporation time while simultaneously allowing the formation of even thinner selective top layers. Asymmetric membranes were fabricated via the combination of polystyrene-block-poly(4-vinyl pyridine) self-assembly, solvent evaporation and liquid induced phase separation. Using a solvent mixture of THF and NMP, a selective top layer of just 60 nm thick was formed with an ordered honeycomb-like pore structure. The formed structure depended on several parameters, such as THF/NMP ratio, polymer concentration of the polymer solution and the duration of solvent evaporation. When a high THF/NMP ratio was used (more THF than NMP) the solvent evaporation step could be reduced to only 1 s, a clear advantage when considering scale up of this approach. The THF/NMP ratio also influenced the morphology of the support layer, which translated into a variety of permeabilities (270–1320 L m−2 h−1 bar−1). Filtration experiments showed that the different top layer structures result in different filtration performance, with more ordered pores resulting in more selective filtration.

Blend membranes of sulfonated poly(ether ether ketone) (SPEEK) and poly(arylene ether ketone) (PAEK) derivatives containing crown ether units in the main chain (CPAEK) were prepared and characterized in terms of water swelling and ion exchange capacity (IEC). The miscibility of the polymers was verified by DSC and HR-SEM. Ion transport characteristics of the membranes were established for the monovalent ions Li+ and K+ and the separation of these ions by the cation exchange membranes was investigated. Diffusion experiments for aqueous KCl, LiCl and their mixtures were carried out with pure SPEEK membranes as well as with the CPAEK/SPEEK membranes. Blending significantly decreased the ion permeability due to cation-crown ether complexation and increased the hydrophobicity of the matrix. The K+ over Li+ selectivity of the SPEEK membrane was enhanced by blending SPEEK with CPAEK by a factor of nearly 4, indicating that the presence of a crown ether polymer changes the relative transport of the ions in the membrane.

This work presents a detailed investigation into the long term stability of polyelectrolyte multilayer (PEM) modified membranes, a key factor for the application of these membranes in water purification processes. Although PEM modified membranes have been frequently investigated, their long term stability, critical for application, has not been considered up till now. We focus on both the physical stability of the multilayer on different membranes as well as on the chemical degradation of two different multilayers in the presence of sodium hypochlorite. Two different polymeric ultrafiltration membranes are modified to become dense nanofiltration membranes by applying a thin (PEM) coating on the membrane via the Layer-by-Layer technique. During sequential backwash cycles, no performance loss is observed for PEM modified membranes based on sulfonated poly(ether sulfone) (SPES). On the other hand, PEM modified membranes based on the non-ionic poly(ether sulfone) (PES) show a gradual increase in permeability and loss in retention after each backwash cycle. We demonstrate that a PEM on an ultrafiltration membrane that bears ionic charges has superior adhesion to the substrate, ensuring long term stability. In addition, the chemical stability of two different multilayers is assessed by means of the resistance against sodium hypochlorite degradation. An important factor in the chemical stability is the type of polycation. Membranes coated with multilayers based on the primary polycation poly(allylamine) hydrochloride (PAH) show a loss in performance after 24,000. ppm hours NaOCl (pH 8). Membranes coated with multilayers based on the quaternary polycation poly(diallyldimethylammonium) chloride (PDADMAC) are stable for more than 100,000. ppm hours NaOCl (pH 8), which is an excellent stability, comparable to that of commercial PES ultra- and microfiltration membranes.

BACKGROUND Recently much research has been focused on the production and refinery of biobased fuels. The production of biofuels derived from lignocellulosic biomass is recognized as a promising route to produce biobased fuels responsibly. Often, product streams (e.g. glucose) still contain small amounts of undesired components (e.g. furans such as HMF). This study focuses on the removal of furans produced during the fermentation. In earlier work, styrene based resins have been identified as promising materials for this separation. In this work the kinetic properties of the most promising resin: DowexTM OptiporeTM L493 are studied. RESULTS The diffusion coefficient of 5 mg L−1 HMF was ∼8 × 10−12 m2 s−1 in water and 3.0 × 10−12 m2 s−1 in a glucose solution. The reduced diffusion coefficient in the particle when glucose is present is caused by the higher viscosity of the glucose solution and it indicates that diffusion is controlled by surface and pore diffusion. The breakthrough curves of HMF on Optipore showed that the column is very efficient under conditions of interest. CONCLUSION This study shows that Optipore is a much more efficient resin for HMF removal than currently used resins. Its fast kinetics and capacity make it possible to efficiently remove HMF from glucose solutions. © 2015 Society of Chemical Industry

Membrane technology proves to be effective in the removal of nano-sized contaminants from water. However, not much is known on the filtration and fouling behavior of manufactured nanoparticles.The high surface-area-to-volume ratio of nanoparticles, significantly increases the effect of surface interactions on the stability of nanoparticle suspensions. Also, the stability of nanoparticle suspensions and their tendency to aggregate strongly affects the fouling mechanism during membrane filtration of nanoparticles. In this experimental study, fouling development and rejection mechanisms of mono-disperse silica model nanoparticles were investigated in great detail.A microfiltration hollow fiber membrane was employed in dead-end filtration mode for the filtration of commercially available silica nanoparticles under constant pressure. By applying a low concentration of nanoparticles and a large difference between the membrane pore size (∼200 nm) and the nominal size of the nanoparticles (22 nm), a detailed investigation of the fouling mechanisms was allowed. Five subsequent fouling stages were postulated: adsorption, unrestricted transport through pores, pore blocking, cake filtration and cake maturation. Higher concentrations of nanoparticles did not change the behavior of these fouling stages, but were found to lead to their acceleration. Fouling severity and occurrence of dynamic transitions between these fouling stages were quantitatively evaluated. The presence of salts, pH and valency of the cation strongly influenced nanoparticle properties and interactions and thus occurrence and character of the fouling stages. Lower repulsive interactions between the nanoparticles accelerate fouling by faster pore blockage and aggregation on the membrane surface. Porosity and permeability of the formed filtration cake layer are strongly dependent on the repulsive interactions between nanoparticles, with a lower repulsion leading to denser cake layers. This paper clearly shows that fouling development and rejection of nanoparticles by microfiltration membranes easily can be adjusted by tuning the electrostatic interactions between the suspended nanoparticles

This study introduces the concept of ion selective actuation in polymer metal composite actuators, employing crown ether bearing aromatic polyether materials. For this purpose, sulfonated poly(arylene ether ketone) (SPAEK) and crown ether containing SPAEK with molar masses suitable for membrane preparation are synthesized. The synthesized polymers are characterized using Nuclear magnetic resonance (NMR) and fourier transform infrared spectroscopy (FTIR) spectroscopy, thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). Ionic polymer metal composite (IPMC) actuators are fabricated by electroless chemical deposition of a platinum (Pt) layer on both sides of SPAEK and crown-ether containing SPAEK membranes, resulting in electrode layers of around 120 nm thickness. Actuation experiments demonstrate cation specific responses and bending degrees of the IPMC actuators. Incorporation of crown ether units in the polymer backbone results in an improved and ion-selective bending displacement compared with SPAEK actuators. S(25)C(50)PAEK actuators show an increased bending displacement of 28% for Na+ and 20% for K+ ions.

This paper describes fouling in simulated Point-of-Use (PoU) systems based on low pressure hollow fiber ultrafiltration membranes. Various operational configurations such as recirculation of feed, discontinuous vs. continuous filtration, and inside/out vs. outside/in were compared to study their effects on fouling and permeate production. Flux values stabilized around 2L/m2h for gravity driven (100mbar) ultrafiltration. Intermittent operation resulted in lower overall hydraulic resistances compared to continuously operated systems. This was due to the low organic loading and relaxation of the fouling layer during periods of standstill. In most experiments the fouling layer mainly consisted of diatoms, inorganic particles and few microbial clusters. The PoU systems investigated can be operated for longer duration without the need for strong chemical cleaning. &nbsp

Renewable energy can be generated using natural streams of seawater and river water in reverse electrodialysis (RED). The potential for electricity production of this technology is huge, but fouling of the membranes and the membrane stack reduces the potential for large scale applications. This research shows that, without any specific antifouling strategies, the power density decreases in the first 4 h of operation to 40% of the originally obtained power density. It slowly decreases further in the remaining 67 days of operation. Using antifouling strategies, a significantly higher power density can be maintained. Periodically switching the feedwaters (i.e., changing seawater for river water and vice versa) generates the highest power density in the first hours of operation, probably due to a removal of multivalent ions and organic foulants from the membrane when the electrical current reverses. In the long term, colloidal fouling is observed in the stack without treatment and the stack with periodic feedwater switching, and preferential channeling is observed in the latter. This decreases the power density further. This decrease in power density is partly reversible. Only a stack with periodic air sparging has a minimum of colloidal fouling, resulting in a higher power density in the long term. A combination of the discussed antifouling strategies, together with the use of monovalent selective membranes, is recommended to maintain a high power density in RED in short-term and long-term operations.

BACKGROUND Many countries have set goals to replace conventional energy sources with renewable energy sources. This has led to investigations into the use of lignocellulosic biomass as a feedstock for renewable fuels and base chemicals. Unfortunately hydrolysation of this biomass introduces impurities that are toxic to the fermentation bacteria. This study aims to find the key adsorber properties for the separation of toxic 5-hydroxymethylfurfural (HMF) from glucose. RESULTS Batch adsorption experiments on styrene based (anion exchange) adsorbers showed that a high surface area is a key property for effective HMF adsorption. Introduction of polar groups in the form of anion exchange groups appears to increase the HMF-affinity of the resin material, unfortunately these groups also introduce affinity for glucose. Competitive adsorption studies of HMF and glucose showed that glucose does not affect HMF adsorption in any of the resins. CONCLUSION Furan derivatives can be removed from water and sugar solutions with styrene based (anion exchange) polymeric resins. For efficient removal, a high surface area of the resin is a key property. Dowex Optipore L-493 shows the best specific HMF adsorption and no specificity for glucose, which makes it an excellent adsorber for HMF removal from hydrolysate for the fermentation of glucose. © 2013 Society of Chemical Industry

This article provides an up-to-date perspective on the use of anion-exchange membranes in fuel cells, electrolysers, redox flow batteries, reverse electrodialysis cells, and bioelectrochemical systems (e.g. microbial fuel cells). The aim is to highlight key concepts, misconceptions, the current state-of-the-art, technological and scientific limitations, and the future challenges (research priorities) related to the use of anion-exchange membranes in these energy technologies. All the references that the authors deemed relevant, and were available on the web by the manuscript submission date (30th April 2014), are included.

As water shortages are increasing, the need for sustainable water treatment and the reuse of water is essential. Water reuse from wastewater can be accomplished in a membrane bioreactor (MBR) in the secondary activated sludge stage of a wastewater treatment plant. To remove viruses, dissolved organics and inorganics still present in the MBR permeate, nanofiltration (NF) can be applied. Nevertheless, the major drawback of nanofiltration membranes is the production of a concentrate stream that cannot be discharged to the environment. In this research we investigate the concept of a combined MBR and NF system with NF concentrate recirculation back to the MBR to produce reusable water in a sustainable way. Long-term continuous operation (1 year) shows that the NF permeate quality is riot impacted by the recirculation. Fouling on the NF membrane is mostly the result of inorganics, while organics (e.g. humic acids) do not have a major impact on NF fouling. In fact, the flux of the NF was enhanced by the presence of humic acids due to recirculation. However, the MBR showed increased fouling and consequently more frequent membrane cleaning. The results presented show that the continuous production of reusable water from wastewater in a combined MBR and NO process with NO concentrate recirculation can be successful. (C) 2013 Elsevier B.V. All rights reserved

Reverse electrodialysis (RED) is a process that can be used to generate energy from salinity gradients. Since its application in practice requires the use of natural seawater and river water, the presence of multivalent ions is inevitable, but this currently limits RED performance. Membranes with selectivity for monovalent ions may overcome this limitation. Standard ion exchange membranes have low monovalent-ion selectivity. We used a relatively fast method to coat a standard commercial anion exchange membrane to improve its monovalent-ion selectivity. The coating layer was formed by copolymerization of 2-acryloylamido-2-methylpropanesulfonic acid (AMPS) as the active polymer and N,N-methylenebis(acrylamide) (MBA) as the crosslinker, using UV irradiation. The monovalent ion selectivity of the resulting membranes was comparable to that of commercial monovalent-selective membranes. Furthermore, the modified membranes with their negatively charged coating showed increased hydrophilicity and exhibited sufficient antifouling potential against organic foulants. When they were tested in an RED stack, their performance was found to depend especially on the proportion of the divalent ions (sulfate) in the river water stream. However, the use of the currently available monovalent selective membranes was not found to be very effective for obtaining higher gross power densities in RED

Energy is released when feed waters with different salinity mix. This energy can be captured in reverse electrodialysis (RED). This paper examines experimentally the effect of varying feed water concentrations on a RED system in terms of permselectivity of the membrane, energy efficiency, power density and electrical resistance. Salt concentrations ranging from 0.01 M to 5 M were used simultaneously in two stacks with identical specifications, providing an overview of potential applications. Results show a decrease of both permselectivity and energy efficiency with higher salt concentrations and higher gradients. Conversely, power density increases when higher gradients are used. The resistance contribution of concentration change in the bulk solution, spacers and the boundary layer is more significant for lower concentrations and gradients, while membrane resistance is dominant for high concentrations. Increasing temperature has a negative effect on permselectivity and energy efficiency, but is beneficial for power density. A power density of 6.7 W/m(2) is achieved using 0.01 M against 5 Mat 60 degrees C. The results suggest that there is no single way to improve the performance of a RED system for all concentrations. Improvements are therefore subject to the specific priorities of the application and the salt concentration levels used. Regarding ion exchange membranes, higher salinity gradients would benefit most from a higher fixed charge density to reduce co-ion transport, while lower salinity gradients benefit from a thicker membrane to decrease the osmotic flux. (C) 2013 Elsevier Ltd. All rights reserved.

The high total phosphorus content of raw domestic wastewater with its significant eutrophication potential offers an excellent possibility for phosphate recovery. Continuous recirculation of NF concentrate to an MBR and simultaneous phosphate recovery from the NF concentrate can be applied to produce reusable water, recovering phosphates, while at the same time decreasing the scaling potential of the recirculated NF concentrate, prolonging the retention times of slowly biodegradable soluble compounds (e.g. micropollutants) and recirculating multivalent cations to promote the bio-flocculation. Here we introduce an electrochemical system to recover phosphates. An electrochemical cell was divided into an anode and a cathode compartment separated by a cation exchange membrane. Precipitation of phosphates from nanofiltration concentrate was induced by locally increasing the pH at the cathode surface by water electrolysis and thereby creating supersaturated conditions at the cathode. 70–95% recovery of total phosphate was achieved at a pH of 8–10 near the cathode. Ion analysis, XRD and ATR-FTIR spectra indicated that the precipitate consisted of amorphous calcium phosphate (ACP) and minor proportions of amorphous calcium carbonate (ACC). The amount of ACC was dependent on the pH. Calcium phosphate scaling at the cathode surface did not occur due to H2-gas formation preventing nucleation and growth at the cathode.

BACKGROUNDAmino acids are valuable intermediates in the biobased economy for the production of chemicals. Electro-membrane processes combined with enzymatic modification have been investigated as an alternative technology for the fractionation of a mixture of amino acids with almost identical charge behavior. Up to now, the modification and subsequent separation were performed in two separate reactors. An interesting approach is the integration of both unit operations into one single device using mixed matrix membranes (MMMs) as platform for enzymatic conversion. RESULTSMMMs containing the enzyme glutamic acid decarboxylase (GAD, EC 4.1.1.15) Relizyme EP403/S as carrier were prepared showing satisfactory mechanical stability and enzymatic activity for L-glutamic acid conversion into -aminobutyric acid (GABA). ED with integrated MMM for simultaneous enzymatic decarboxylation of L-glutamic acid to GABA (33% conversion) and further separation of L-aspartic acid and unconverted L-glutamic acid from GABA was successful leading to current efficiency of 40% and low energy consumption of 3 kWh kg(-1). CONCLUSIONSTogether with the high mechanical stability obtained for the MMMs, this opens the route towards process intensification, combining enzymatic conversion and separation with electrodialysis in one integrated process for the successful isolation of amino acids for biorefinery applications. (c) 2013 Society of Chemical Industry

A novel way for anion exchange membrane (AEM) preparation has been investigated, avoiding the use of expensive and toxic chemicals. This new synthetic approach to prepare AEMs was based on the use of a porous polybenzylimidazole membrane as support in which functionalized ILs were introduced and subsequently grafted on the polymer backbone. These new AEMs were prepared and their chemical structures and properties including morphology, thermal stability, and ionic conductivity were characterized. The hydroxyl ionic conductivity of the synthesized membranes can reach values upto 6.62 × 10−3 S cm−1 at 20°C. Although the ionic conductivity is not very high yet, the work shows the strength of the concept. Membrane properties can be easily tailored toward specific applications by choosing the proper chemistry, i.e., porous polymer support, ionic liquid, and method of initiation and polymerization

In this work we propose the use of the ionic liquid 1-H-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([h-mim] Ntf2) as conductive filler in a tailor-made porous, polymeric polybenzimidazole (PBI) support as proton conductive membrane for high temperature (>100 °C) fuel cell applications. PBI is chosen because of its excellent thermal and mechanical stability, while the choice for the ionic liquid is based on its high proton conductivity, low water sorption, thermal stability and low viscosity. The morphology of the porous PBI support is especially tailored for this application using a delayed immersion precipitation process. The macrovoid free porous structure has a volume porosity of 65% and a pore size of approximately 0.5 μm. Pores filling with ionic liquid by direct immersion of the PBI support into molten ionic liquid at 50 °C introduced the membrane proton conductivity. After impregnation the proton conductivity of this PBI/IL membrane reached a value of 1.86 mS cm−1 at 190 °C. Fuel cell performance of these membranes clearly exceeds that of Nafion 117 at temperatures above 90 °C. A power density of 0.039 W cm−2 is obtained at the intended operation temperature of 150 °C, which proofs that the developed PBI/IL membrane can be considered as a serious candidate for high temperature fuel cell applications.

The recent exponential growth of nanotechnology and numerous applications of nanotechnology-based products resulted in water pollution by engineered nanoparticles. Over the last few decades, membrane technology has emerged as one of the most promising and reliable techniques in water purification. Therefore, it is an obvious candidate to remove manufactured nano-sized contaminants and to purify the water. Nanoparticle properties play a crucial role in the performance and effectiveness of membrane filtration. This experimental study investigates the role of nanoparticle size and polydispersity on fouling and rejection development during dead-end microfiltration of electrostatically stabilized silica nanoparticles. Our work on filtration of monodisperse silica nanoparticles (11 nm, 25 nm and 92 nm) smaller than the membrane pore size (~200 nm) demonstrates that an increasing nanoparticle diameter accelerates pore blockage and development of cake. The specific cake resistance of the filtration cake formed decreases with increasing nanoparticle diameter. Filtration of polydisperse nanoparticles (obtained by mixing monodisperse suspensions in various ratios) shows that increasing the fraction of smaller nanoparticles results in delayed pore blockage, and cake filtration occurring at a later stage. The specific cake resistance of the polydisperse nanoparticles is always found to be in between that obtained for the monodisperse nanoparticle suspensions. An increasing weight fraction of larger nanoparticles results in faster development of nanoparticle rejection due to accelerated pore blockage. However, because of the highly porous structure of the filtration cake originating from strong surface charges, the moderate transmembrane pressure applied and cake imperfections, the smallest (11 nm) nanoparticles were rejected only to a low extent, even during the cake filtration stage. An increase in applied transmembrane pressure during filtration of the polydisperse suspension resulted in faster pore blockage and higher specific cake resistance. Nevertheless, rejection of the nanoparticles in the cake filtration stage improved only slightly with increasing transmembrane pressure.

Thin sulfonated poly(ether ether ketone) films swell excessively in water. The extent of water-induced swelling is shown to be correlated with the optical anisotropy of the films, due to two distinct phenomena. Firstly, the optical anisotropy is directly related to the amount of water taken up from the surrounding ambient atmosphere, and thus to amount of water present in the material just prior to swelling. Secondly, the optical anisotropy corresponds to internal stresses in the film that affect the free energy of the film, and thus the potential of the film to swell. The anisotropy vanishes upon sorption of liquid water and returns when the water is desorbed. When the water is completely removed, the film changes from more or less colorless to an intense yellow color that can be attributed to molecular assembly of the aromatic rings in the polymer backbone. The color change is reversible and occurs immediately upon exposure to low humidity. For films prepared in the absence of water, the lack of hydration of the sulfonic acid groups affects the microphase separation behavior of the polymer. This is manifested by an apparent lower propensity to water-induced swelling. The possibility to affect the properties of sulfonated polymer films by varying the hydration state of the polymer during preparation can have important implications for applications of such films.

In this study, we prepared electrospun polyacrylonitrile (PAN) nanofibers functionalized with dibenzo-18-crown-6 (DB18C6) crown ether and showed the potential of these fibers for the selective recovery of K+ from other both mono- and divalent ions in aqueous solutions. Nanofibers were characterized by SEM, FTIR and TGA. SEM results showed that the crown ether addition resulted in thicker nanofibers and higher mean fiber diameters, in a range of 138 to 270 nm. Batch adsorption experiments were conducted in order to evaluate the potential of the crown ether modified nanofibers as an adsorbent for ion removal. The maximum adsorption capacity of the crown ether modified nanofibers for K+ was 0.37 mmol g-1 and the nanofibers followed the selectivity sequence of K+ > Ba2+ > Na+ ∼ Li+ for single ion experiments. Adsorption of Ba2+ ions onto crown ether-modified nanofiber was examined by XPS and the results confirmed the adsorption of the ion. Mixed ion adsorption experiments revealed competitive adsorption between K+ and Ba2+ ions for the available binding sites. This effect was not observed for the other monovalent ions present in the solution and exceptionally high selectivities for K+ over Li+ and Na+ were obtained. Also the crown ether modified nanofibers exhibited good regeneration properties and a good reusability over multiple consecutive adsorption-desorption cycles. Electrospinning is thus shown to be a very versatile tool to prepare crown ether functional polymer adsorbents for the selective recovery of ions.

Electrodialysis using commercially available ion exchange membranes was applied for the isolation of l -glutamic acid (Glu) and l -aspartic acid (Asp) from a mixture of amino acids. Based on the differences in their isoelectric points, Glu and Asp, being negatively charged at neutral pH, can be separated from neutral and basic amino acids. Outstanding recoveries for Glu and Asp of around 90% and 83%, respectively, were obtained. The further separation of Glu from Asp with electrodialysis is enabled with an enzymatic modification step where Glu is converted into γ-aminobutyric acid (GABA) with the enzyme glutamic acid α-decarboxylase (GAD) as the catalyst. Negatively charged Asp is separated from uncharged GABA at neutral pH conditions with a current efficiency of 70% and a recovery of 90%. Higher current efficiencies and lower energy consumption can be obtained when adjusting the current in time. This opens the route to successful isolation of amino acids for biorefinery applications using an integrated process of enzymatic conversion and separation with electrodialysis.

The current work describes the synthesis and mass transport properties of a series of blend membranes based on a highly permeable polyether based segmented block copolymer and a poly(ethylene glycol) based additive. This series of polymers integrates the knowledge of molecular design and molecular blending and presents CO2 permeabilities currently unknown to any polyether based block copolymer (system) known in literature. The concept presented is not limited to this specific case and hence opens a window of opportunity for further development of highly permeable block copolymer systems for CO2 separation and in particular for use in post-combustion CO2 capture.

This paper reports pure and mixed gas CO 2 /H 2 and CO 2 /CH 4 membrane separation performance of a highly permeable poly(ethylene oxide) based multi-block copolymer. Permeation and sorption properties have been studied over a wide temperature (−10 °C to +35 °C) and pressure range (up to 25 bar partial pressure of CO 2 ). In particular, we address the effect of plasticization by CO 2 . A strong dependency of CO 2 permeability on CO 2 concentration in the polymer matrix was observed in pure and mixed gas experiments. Plasticization effects increased the permeability of H 2 and CH 4 in mixed gas experiments compared to their pure gas values. The H 2 permeability was less influenced by plasticization than the CH 4 permeability due to H 2 's smaller kinetic diameter. As a result, mixed gas selectivities were systematically lower than pure gas selectivities. This difference between mixed and pure gas selectivity is exclusively dependent on the CO 2 concentration in the polymer matrix, which can change with temperature or CO 2 fugacity. Remarkably, the difference between ideal selectivity and mixed gas selectivity scales linearly with the CO 2 concentration in the polymer for all pressures and temperatures considered.

Amino acid salt solutions are a promising alternative to alkanolamines (e.g., MEA) as absorption liquid for CO2 removal due to their ionic nature, their low evaporative losses, and their assumed higher oxidative and thermal stability. Sarcosine is a promising candidate because of its relatively high CO2 loading capacity and reactivity. In this work, CO 2 absorption experiments in the so-called pseudo-first-order regime were carried out to determine the reaction rate expression and reaction rate constant of CO2 absorption in aqueous sarcosine salt solutions. Next to the influence of the sarcosine concentration (0.5-3.8 M) and the temperature (298-308 K) on the rate of reaction, the reaction rate constants for partially loaded sarcosinate solutions were investigated. Compared to MEA, very high reaction rate constants for the carbamate formation were obtained for aqueous sarcosine salt solutions. The reaction order in CO2 was found to be equal to 1, which is in accordance with the literature, and for potassium sarcosinate an (apparent) reaction order of 1.66 was found. The activation energy was found to be approximately 26 kJ/mol. The apparent rate of the reaction strongly decreases with increasing partial loading of the solution with CO2 and was found to be directly related to the decrease in free amine concentration in the solution. This observation is especially relevant for cyclic absorption processes such as gas-liquid membrane contactors, where incomplete solvent regeneration occurs.

The present article discusses the synthesis and various properties of segmented block copolymers with random copolymer segments of poly(ethylene oxide) and poly(propylene oxide) (PEO-r-PPO) together with monodisperse amide segments. The PEO-r-PPO contained 25 wt % PPO units and the segment presented a molecular weight of 2500 g/mol. The synthesized copolymers were analyzed by differential scanning calorimetry, Fourier transform infra-red spectroscopy, atomic force microscopy and dynamic mechanical thermal analysis. In addition, the hydrophilicity and the contact angles (CAs) were studied. The PEO-r-PPO segments displayed a single low glass transition temperature, as well as a low PEO crystallinity and melting temperature, which gave enhanced low-temperature properties of the copolymer. The water absorption values remained high. In comparison to mixtures of PEO/PPO segments, the random dispersion of PPO units in the PEO segments was more effective in reducing the PEO crystallinity and melting temperature, without affecting the hydrophilicity. Increasing the polyether segment length with terephthalic groups from 2500 to 10,000 g/mol increased the hydrophilicity and the room temperature elasticity. Furthermore, the CAs were found to be low 22–39° and changed with the crosslink density. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117:1394–1404, 2010

Polymer blending is a versatile tool to combine the beneficial properties of two or more components in one single material. Here, we present the preparation, thermal- and mass transport properties of a series of blend membranes made from the commercially available PEBAX® MH 1657 and a poly(ethylene glycol) (PEG) based additive. The additive (PDMS-PEG) consists for 80 wt.% of PEG and the remaining 20 wt.% is poly(dimethyl siloxane) (PDMS), which is highly flexible and permeable. As such, we combine the high selectivity of PEG for CO2 with the high permeability of PDMS. We extensively study the gas transport properties, and in particular the CO2/light gas separation performance, using pure and mixed gases. The pure gas CO2 permeability in the PEBAX®1657/PDMS-PEG blend membranes increased by a factor 5 to approximately 530 Barrer at 50 wt.% PDMS-PEG loading. CO2 sorption measurements revealed only a 50% increase in CO2 solubility and the increase in permeability could be mainly attributed to an increase in diffusivity. Remarkably, the CO2/H2 selectivity is enhanced (∼10%) at 50 wt.% loading, while the CO2/N2 and CO2/CH4 selectivity only slightly decreases. Mixed gas CO2/H2 and CO2/CH4 permeation measurements up to CO2 partial pressures of 25 bar reveal that the CO2 permeability is slightly reduced when gas mixtures are used. The CO2/H2 selectivity was found to be independent of the PDMS-PEG loading and feed pressure at a value of approximately 9-10. CO2/CH4 mixed gas selectivity decreased slightly with PDMS-PEG loading and pressure, but always remained above 10.

The cutting and functionalization of carbon nanotubes is described, applying a single-step ball-mill based process. Very short carbon nanotubes bearing primary amine functions were produced, characterized and incorporated in polymeric membranes. The gas separation performance of the composite membranes was tested.

In the present work we use a membrane contactor for the separation of CO2 from CH4 and we systematically investigate the influence of both the type of membrane and the different process parameters on the overall process performance (permeability and selectivity). This work is important because it reports real process performance data (permeances and selectivities) for the total process consisting of absorption and desorption under practical conditions using feed mixtures. Commercially available porous PP hollow fiber membranes and asymmetric PPO hollow fiber membranes have been applied and MEA was used as absorption liquid in the membrane contactor. The proposed approach allows us to identify the operating window and potential of the process. Although the performance of the PP membranes outperforms the performance of the PPO membranes in terms of productivity and selectivity, the PP fibers are extremely sensitive to only small variations in the feed pressure, resulting in severe performance loss. In addition to that, extremely high liquid losses are observed for the PP fibers especially at elevated temperatures. Factors that are significantly reduced when asymmetric PPO membranes with a dense, ultrathin top layer are used, which thus improves the performance and significantly increases the operating window and potential of the membrane contactor process.

We report on how the morphology of the polymer matrix, i.e. amorphous vs. semi-crystalline, affects the gas transport properties in a series of mixed matrix membranes (MMMs) using Cu3(BTC)2 as the metal organic framework (MOF) filler. The aim of our work is to demonstrate how incorporation of Cu3(BTC)2 affects the polyetherimide matrix morphology and thereby highlighting the importance of selecting the appropriate polyetherimide matrix for mixed matrix membranes.We used three amorphous poly(etherimide)s with very similar backbone structures. Polyetherimide ODPA-P1 was used as a linear flexible matrix, aBPDA-P1 is a non-linear rigid matrix and 6FDA-P1 was selected because the backbone structure is similar to ODPA-P1 but replacing the oxygen linker with two bulky –CF3 groups results in a linear polymer with a low chain packing efficiency. Using an in-situ polymerization technique, up to 20 wt.% Cu3(BTC)2 could be homogenously dispersed in all three PEIs. The ODPA-P1 matrix crystallized when Cu3(BTC)2 was introduced as a filler. Gas permeation studies were performed by analyzing membrane performance using a 50:50 CO2:CH4 mixed gas feed. The presence of crystalline domains in ODPA-P1 resulted in a decrease in permeability for both CO2 and CH4 but the selectivity increased from 41 to 52 at 20 wt.% Cu3(BTC)2. The non-linear, rigid, aBPDA-P1 matrix remains amorphous when Cu3(BTC)2 is introduced. SEM images of the MMM cross-section revealed a sieve-in-a-cage morphology and at 20 wt.% Cu3(BTC)2, the permeation of both CO2 and CH4 increased by 68% thereby negating any change in selectivity. For 6FDA-P1 with 20 wt.% Cu3(BTC)2, only the permeability of CO2 increased by 68% resulting in an increase in selectivity of 33%

Two-phase flow cleaning has been successfully applied to control fouling in spiral wound membrane elements. This study focuses on its experimental optimization using a Taguchi Design of Experiment method (L-25 orthogonal arrays) to elucidate the influence of different factors and to reveal the important one(s) affecting the cleaning efficiency of two-phase flow cleaning. All possible combinations of the factors, i.e. feed type, spacer geometry, gas/liquid ratio, and liquid velocity, each at five levels were evaluated. The main effect of each factor on the efficiency of two-phase flow cleaning was measured by determining the performance response (mean of cleaning efficiency) and by calculating the mean signal-to-noise ratio. An analysis of variance was applied to calculate the relative contribution of each factor on the efficiency of two-phase flow cleaning. The results showed that the feed type is by far the most essential factor contributing to the cleaning efficiency. The spacer geometry is ranked second, followed by the gas/liquid ratio and the liquid velocity, which both have an only very minor effect on the cleaning performance. In terms of practical application, the operator should consider first the type of foulant prior to taking a decision on whether or not two-phase flow cleaning will be effective. Once the foulant type is defined, the use of the highest gas/liquid ratio, the highest liquid velocity, and the thickest feed spacer (diamond type) are recommended to achieve maximum two-phase flow cleaning efficiency.

The potential environmental and health risks of engineered nanoparticles such as buckminsterfullerene C60 in water require their removal during the production of drinking water. We present a study focusing on (i) the removal mechanism and (ii) the elucidation of the role of the membrane pore size during removal of nC60 fullerene nanoparticle suspensions in dead-end microfiltration and ultrafiltration mimicking separation in real industrial water treatment plants. Membranes were selected with pore sizes ranging from 18 nm to 500 nm to determine the significance of the nC60 to membrane pore size ratio and the adsorption affinity between nC60 and membrane material during filtration. Experiments were carried out with a dead-end bench-scale system operated at constant flux conditions including a hydraulic backwash cleaning procedure. nC60 nanoparticles can be efficiently removed by low pressure membrane technology with smaller and, unexpectedly, also by mostly similar or larger pores than the particle size, although the nC60 filtration behaviour appeared to be different. The nC60 size to membrane pore size ratio and the ratio of the cake-layer deposition resistance to the clean membrane resistance, both play an important role on the nC60 filtration behaviour and on the efficiency of the backwash procedure recovering the initial membrane filtration conditions. These results become specifically significant in the context of drinking water production, for which they provide relevant information for an accurate selection between membrane processes and operational parameters for the removal of nC60 in the drinking water treatment.

Biofouling has detrimental effects on the feed channel pressure drop and the permeate flux in high-pressure membrane processes such as NF and RO. Two-phase flow cleaning is a chemical-free technique that is able to remove such biofilms. This paper presents a study into the effects of the gas/liquid ratio, feed spacer geometry, applied pressure and liquid velocity on the efficiency of two-phase flow cleaning in spiral-wound nanofiltration elements. A high-speed camera, optical coherence tomography and scanning electron microscopy were used to study biofouling and its removal. Our results show that two conditions must be met to ensure that a sufficiently high shear force is applied to biofilms on membrane and spacer surfaces. A good bubble distribution in the channel is the first requirement. While it is mainly the structure of the feed spacer that controls bubble flow and bubble size, a minimum gas/liquid ratio of 0.5 is necessary to achieve a good bubble distribution. The second condition is the use of a sufficiently high liquid velocity during cleaning. The bubble velocity was found to be 3.5–5.5 times as high as the used liquid velocity, and responsible for a marked improvement in the flux recovery.

The thickness, the refractive index, and the optical anisotropy of thin sulfonated poly(ether ether ketone) films, prepared by spin-coating or solvent deposition, have been investigated with spectroscopic ellipsometry. For not too high polymer concentrations (≤5 wt%) and not too low spin speeds (≥2000 rpm), the thicknesses of the films agree well with the scaling predicted by the model of Meyerhofer, when methanol or ethanol are used as solvent. The films exhibit uniaxial optical anisotropy with a higher in-plane refractive index, indicating a preferred orientation of the polymer chains in this in-plane direction. The radial shear forces that occur during the spin-coating process do not affect the refractive index and the extent of anisotropy. The anisotropy is due to internal stresses within the thin confined polymer film that are associated with the preferred orientations of the polymer chains. The internal stresses are reduced in the presence of a plasticizer, such as water or an organic solvent, and increase to their original value upon removal of such a plasticizer.

The modification of membranes by polyelectrolytes via the Layer-by-Layer technique is an attractive method to obtain nanofiltration membranes. We prepare such membranes by alternatively coating a polycation (poly(diallyldimethylammonium chloride) (PDADAMAC)) and a polyanion (poly(styrene sulfonate) (PSS)) on a porous support. Depending on the coating conditions, hollow fiber membranes with rejections of up to 71% NaCl and 96% Na2SO4 are obtained. Moreover, we demonstrate that the final membrane properties can be easily controlled by variation of the ionic strength of the coating solution, the number of layers and the choice of terminating polyelectrolyte layer. Coating at higher salt concentrations results in thicker multilayers that are more open to permeation. Furthermore, we show that by taking the effect of the terminating layer (the so called "odd-even" effect) into account, information on the structure of the multilayers on the membrane is obtained. Depending on the coating conditions and number of layers, two different regimes can be distinguished. Thinner layers show a pore-dominated regime, where the multilayer is coated on the inside of the pores. Thicker layers show a layer-dominated regime, in which case the multilayer is predominately coated on top of the pores. This conclusion is supported by our ion rejection measurements: for thin layers the rejections are primarily based on size exclusion, whereas for thick layers the ion rejections are based on Donnan exclusion.

Poly(arylene ether ketone)s (PAEKs) are the most commonly known high-performance materials used for ion exchange and fuel cell membranes. Described here is the design of novel sulfonated PAEKs (SPAEKs) and nonsulfonated PAEKs containing crown ether units in the main chain, which can be used in sensing applications and ion-selective membranes. To this end, 4,4′(5′)-di(hydroxybenzo)-18-crown-6 was synthesized and used as monomer in a step growth polymerization to form crown ether-containing PAEKs and SPAEKs. The successful synthesis of PAEKs containing 18-crown-6 and sulfonate groups was confirmed by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Membranes are fabricated from the sulfonated polymers. Potassium ion transport properties of the SPAEK and crown ether-containing SPAEK membranes are assessed by diffusion dialysis. Potassium ion diffusion in the crown ether-containing SPAEK membranes is almost four times lower than K+ diffusion in the native polymer membranes, without crown ether

Composite ultrafiltration membranes were fabricated by coating a thin film of self-assembling polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymers and poly(acrylic acid) homopolymers on top of a support membrane. Block copolymers self-assembled into a nanostructure where the minority component forms cylinders, whereas homopolymers reside in the core of the cylinders. Selective removal of the homopolymers led to the formation of pores. The morphology of the polymer layer was controlled by varying the content of homopolymers or polymer concentration of the coating solution, which led to membranes with different molecular weight cutoffs (MWCOs) and permeabilities. Uniform pores were obtained using low homopolymer contents, whereas high homopolymer contents caused macrophase separation and resulted in large polydisperse pores or craters at the surface. The thickness of the block copolymer film also influenced the structure and performance of the membranes, where a thicker film results in a strong decrease in permeability but a lower MWCO.

International audience; Mixed matrix membranes (MMMs) incorporating conventional fillers frequently suffer from insufficient adhesion between the polymer matrix and the fillers. This often results in the formation of non-selective voids at the filler/polymer interface, which decreases the performance of the membrane. A novel approach is presented here to develop metal organic framework (MOF) based MMMs by using the self-assembly of MOF and polymer particles followed by their controlled fusion. MOF-polymer interaction is optimized through this strategy and it overcomes MOF-polymer incompatibility, MOF agglomeration and MOF. distribution problems, happening especially at high loadings of MOFs when applying conventional methods. Matrimid (R) polymer particles were first prepared by precipitating a Matrimid (R) polymer solution in wafer. The surface of these particles was then modified by the introduction of imidazole groups, enhancing the chemical compatibility with the selected ZIF-8 MOF. ZIF-8 nanoparticles were then grown in situ to this modified polymer particle suspension by addition of the precursor for ZIF-8 synthesis. The resulted suspension was cast to dryness and annealed in a solvent vapor environment to induce particle fusion, leading to a dense NIMM structure. Scanning electron microscopy (SEM) images showed an excellent dispersion of the ZIF-8 nanoparticles forming a percolating pathway without any agglomeration, even at 40 wt% loading of the ZIF-8. Excellent dispersion of ZIF-8 and an excellent ZIF-8-polymer interfacial adhesion resulted in a significant improvement in both CO2 permeability and CO2/CH4 selectivity. The CO2 permeability of the MMMs increased by 200% and the CO2/CH4 selectivity increased by 65% as compared to unfilled Matrimid (R). More detailed analysis of the gas transport performance of the MNIMs showed that the CO2 permeability and the CO2/CH4 selectivity are mainly governed by the increase in CO2 diffusivity. The presented approach is a very versatile MMM preparation route, not only for this specific ZIF and polymer but for a wide range of material combinations.

The application of laccase and peroxidase from horseradish (HRP) to facilitate the removal of bisphenol A (BPA) from aqueous solutions was investigated. Effect of pH and the enzyme dose was evaluated in order to determine the optimum conditions for the enzyme performance. The results indicate that BPA was quickly removed from aqueous solution since a BPA conversion over 95% was obtained in 180. min for both enzymes in optimal conditions; the higher the enzyme dose, the higher the removal percentage of BPA. It was also found that the optimum pH for the removal efficiency of BPA was around 7 for both enzymes. The use of a membrane-reactor integrated system with recycling of enzyme for BPA degradation is also presented. These results demonstrate the potential and limitations of using enzymatic BPA degradation, operated in a recycling mode coupled to a nanofiltration membrane. BPA removal efficiencies for several NF membranes were related to the BPA molecular weight, membrane pore sizes and membrane hydrophobicity. NF270 showed the best performance in membrane-assisted enzyme treatment: 89% removal of BPA for the two enzyme treatments and less than 35% flux decay were observed. NF in combination with enzyme showed to be an attractive approach for water treatment. The results reveal the efficiency of the enzyme treatment for BPA degradation. Coupling of the enzyme with NF allows BPA removal and the recycling of the enzyme. The presence of enzymes and the polymeric products reduced the membrane permeability.

Reverse electrodialysis (RED) can harness the Gibbs free energy of mixing when fresh river water flows into the sea for sustainable power generation. In this study, we carry out a thermodynamic and energy efficiency analysis of RED power generation, and assess the membrane power density. First, we present a reversible thermodynamic model for RED and verify that the theoretical maximum extractable work in a reversible RED process is identical to the Gibbs free energy of mixing. Work extraction in an irreversible process with maximized power density using a constant-resistance load is then examined to assess the energy conversion efficiency and power density. With equal volumes of seawater and river water, energy conversion efficiency of ∼33-44% can be obtained in RED, while the rest is lost through dissipation in the internal resistance of the ion-exchange membrane stack. We show that imperfections in the selectivity of typical ion exchange membranes (namely, co-ion transport, osmosis, and electro-osmosis) can detrimentally lower efficiency by up to 26%, with co-ion leakage being the dominant effect. Further inspection of the power density profile during RED revealed inherent ineffectiveness toward the end of the process. By judicious early discontinuation of the controlled mixing process, the overall power density performance can be considerably enhanced by up to 7-fold, without significant compromise to the energy efficiency. Additionally, membrane resistance was found to be an important factor in determining the power densities attainable. Lastly, the performance of an RED stack was examined for different membrane conductivities and intermembrane distances simulating high performance membranes and stack design. By thoughtful selection of the operating parameters, an efficiency of ∼37% and an overall gross power density of 3.5 W/m2 represent the maximum performance that can potentially be achieved in a seawater-river water RED system with low-resistance ion exchange membranes (0.5 cm2) at very small spacing intervals (50 μm).

Mixed-matrix membranes (MMMs), filled with inorganic particles, provide a means to improve the gas separation performance of polymeric membranes. In this work, MMMs containing the mesoporous metal organic framework (MOF) Fe(BTC) in a Matrimid®-PI matrix were characterized in terms of their carbon dioxide (CO2) and methane (CH4) separation performance at low and high pressures. Physical properties (density, thermal degradation, and glass transition) of Fe(BTC) and prepared MMMs were analyzed. An optimized priming and suspension mixing protocol resulted in a homogeneous distribution of MOF particles in the Matrimid®-PI matrix, as observed by scanning electron microscopy (SEM). Experimental results showed decreased thermal degradation but increased membrane density and glass transition with increased Fe(BTC) loading, as well as improvement in CO2 permeability and CO2/CH4 selectivity. At high pressures, the native Matrimid®-PI membrane showed typical plasticization behavior, but as the MOF loading increased gas transport properties seem to be controlled by MOF particles leading to reduced plasticization tendencies. The favorable performance of MOF containing membranes can be attributed to the strong increase in the sorption capacity and chain rigidity by the Fe(BTC) particles which suppressed plasticization. At a mixed gas feed pressure of 40 bar, MMMs with 30 wt% MOF showed a CO2/CH4 selectivity increase of 62% compared to the native Matrimid®-PI membrane, while the permeability was about 30% higher than that of native polymer.

Ion exchange membranes (IEMs) are used for selective transport of ions between two solutions. These solutions are often different in concentration or composition. The membrane resistance (R-M) is an important parameter affecting power consumption or power production in electrodialytic processes. In contrast to real applications, often R-M is determined while using a standard 0.5 M NaCI external solution. It is known that R-M increases with decreasing concentration. However, the detailed effect of a salinity gradient present over an IEM on R-M was not known, and is studied here using alternating and direct current. NaCl solution concentrations varied from 0.01 to 1.1 M. The results show that R-M is mainly determined by the lowest external concentration. R-M can be considered as two resistors in series i.e. a gel phase (concentration independent) and an ionic solution phase (concentration dependent). The membrane conductivity is limited by the conductivity of the ionic solution when the external concentration, c(ext) 0.3 M, then differences of R-M are small. A good approximation of experimentally determined R-M can be obtained. The internal ion concentration profile is a key factor in modeling Rm. (C) 2014 Elsevier B.V. All rights reserved.

Mixed matrix membranes (MMMs) based on three distinctively different MOFs (MIL-53(Al) (breathing MOF), ZIF-8 (flexible MOF) and Cu3BTC2 (rigid MOF)) dispersed in Matrimid®-PI have been investigated. MOF loading was varied between 0 wt% and 30 wt%. The fabricated MOF-MMMs were characterized for pure and binary gas mixture separations at low and high pressures and their performance in terms of CO2 permeability and CO2/CH4 selectivity was evaluated. The use of a less volatile co-solvent, optimized priming protocol to prepare the MMMs and thermal annealing resulted in a good dispersion of MOF particles in the Matrimid®-PI matrix. Incorporation of MOFs resulted in increased density, Tg and improved degradation behavior of the membranes confirming a good compatibility between the polymer and the MOFs. Low pressure gas separation showed moderate enhancement in CO2 permeability and CO2/CH4 selectivity of MOF-MMMs compared to native polymer membranes, but the improvement becomes pronounced at high pressures. At high pressures, the native Matrimid®-PI membrane showed typical plasticization behavior, while in MMMs, MOF particles limit the mobility of polymer chains thus suppressing CO2 induced plasticization and maintain large separation factors over a wide pressure range investigated. The respective increase in performance of MMMs is very much dependent on MOF crystal structure and its interactions with CO2 gas molecules. Among the three MOF-MMMs, membranes based on Cu3BTC2 showed highest selectivity while ZIF-8 based membranes showed highest permeability. In general it can be concluded that the high CO2 permeability and CO2/CH4 selectivity of MMMs is the combined effect of an increased sorption and diffusion selectivity and reduced plasticization. Overall, this work reveals that MOF-MMMs delay CO2 induced plasticization and show good separation performance even at high pressures, showing their potential to a wide range of newly emerging high pressure energy applications

Renewable energy can be obtained from mixing waters with different salinity using reverse electrodialysis (RED). To obtain a high power per membrane area, combined with a low power consumption for pumping the feed water, RED is preferably operated using small intermembrane distances and low flow rates. However, the diffusive boundary layer near the membranes induces a significant (non-ohmic) resistance at lower flow rates. This is even more pronounced when a spacerless design, with profiled membranes, is used. This research presents how the non-ohmic resistance in RED can be reduced, and consequently the obtained power can be increased, without compromising the power consumed for pumping. Experiments were conducted using several designs, with and without mixing promoters such as twisted spacers and additional sub-corrugations on the membrane, to investigate the effect of additional mixing in the diffusive boundary layer on the obtainable power in RED. The results show that these mixing promoters are not effective at the low Reynolds numbers typically used in RED. The distribution of the feed water inflow, however, has a major impact on the non-ohmic resistance. The design with profiled membranes without sub-corrugations has the best performance, which is almost twice the net power density obtained with a design with normal spacers.

In-situ spectroscopic ellipsometry was used to investigate the swelling behavior of thin supported zwitterionic polymers based on sulfobetaine methacrylate and n-butylacrylate. This material represents an interesting class of zwitterionic polymers, with large potential in reduction of biofouling of ultrafiltration membranes. It was found that the swelling rate and magnitude depend strongly on the content of zwitterionic groups incorporated in the polymer structure. Overshoot anomalous swelling dynamics were observed, explained by an interplay between enthalpic and entropic effects in various stages of the process. To elucidate the changes in the film properties a detailed ellipsometric analysis was conducted during polymer dilation and relaxation. For the polymer with 11.6 mol% zwitterionic groups, the thickness relaxation process after the swelling maximum is shown to be best described by a thin filmwith a time dependent uniaxial anisotropy. The behavior is rationalized via the orientations of polymer backbone and zwitterionic side chains, as a result of swelling and relaxation in the presence of the screening electrolyte.

The mixing of sea and river water can be used as a renewable energy source. The Gibbs free energy that is released when salt and fresh water mix can be captured in a process called reverse electrodialysis (RED). This research investigates the effect of the intermembrane distance and the feedwater flow rate in RED as a route to double the power density output. Intermembrane distances of 60, 100, 200, and 485 μm were experimentally investigated, using spacers to impose the intermembrane distance. The generated (gross) power densities (i.e., generated power per membrane area) are larger for smaller intermembrane distances. A maximum value of 2.2 W/m(2) is achieved, which is almost double the maximum power density reported in previous work. In addition, the energy efficiency is significantly higher for smaller intermembrane distances. New improvements need to focus on reducing the pressure drop required to pump the feedwater through the RED-device using a spacerless design. In that case power outputs of more than 4 W per m(2) of membrane area at small intermembrane distances are envisaged.

This paper reports the potential of highly hydrophilic, poly(ethylene oxide) based block copolymers for the simultaneous removal of CO 2 and water vapor from a ternary gas simulating a flue gas in a post-combustion capture configuration. Water vapor sorption measurements show strong sorption of water vapor in these block copolymers especially above a water vapor activity of 0.6. Mixed water vapor/gas permeability measurements as a function of water vapor activity were performed using binary (H 2 O/CO 2 and H 2 O/N 2 ) and ternary (H 2 O/CO 2 /N 2 ) feed mixtures. The water vapor permeability increased exponentially with the water vapor activity whereas the gas permeability in all cases slightly decreased. As the effect of the presence of water vapor was relatively stronger on the N 2 permeability, the CO 2 /N 2 selectivity increased slightly with increasing water vapor activity. No noticeable differences between the pure gas (from binary mixtures) and the mixed gas (from ternary mixtures) membrane performance have been observed. This indicates that plasticization effects, due to the sorption of CO 2 , are not significant at the low feed pressure (2.5 bar) used. Also, increasing water content did not cause plasticization. Overall, the block copolymers studied in this work combine a high CO 2 permeability with a reasonable CO 2 /N 2 gas selectivity. Due to their highly hydrophilic character, they also have the ability to simultaneously remove CO 2 and water vapor from flue gases, which makes these PEO- ran -PPO based block copolymers an attractive membrane material for post-combustion CO 2 capture applications.