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Salt transport properties of cellulose acetate membranes are reported for a series of chloride salts with monovalent and divalent cations (LiCl , NaCl , MgCl 2 , CaCl 2). Measurements include salt permeability and sorption, with diffusivity values calculated from the permeability and sorption results. We report an exceptionally high LiCl/MgCl 2 selectivity of 750:1. Salts with similar valence (LiCl and NaCl ; MgCl 2 and CaCl 2) have similar transport properties. The high monovalent/divalent selectivity arises from differences in both sorption and diffusion, with a LiCl/MgCl 2 solubility selectivity of about 11 and a diffusivity selectivity of about 70. Atomistic molecular dynamics simulations show that ions tend to reside in isolated clusters of water. Increasing ion charge strengthens ion–water interactions relative to ion–polymer interactions, explaining the reduced sorption of divalent ions. Diffusion of ions through the membrane occurs via hop-like motion between water clusters. Lithium diffuses faster than magnesium due to weaker ion–water coordination for lithium, which allows for greater mobility within water clusters and more frequent hopping. Overall, our atomistic simulations suggest that the high LiCl/MgCl 2 selectivity is linked to cellulose acetate's high water/salt selectivity and is a consequence of low water content and relatively uniform water distribution. [Display omitted] • Cellulose acetate membranes display high monovalent to divalent cation selectivities. • Selectivity arises due to differences in both salt diffusion and sorption. • Molecular dynamics simulations probe the experimental trends' origins. [ABSTRACT FROM AUTHOR]

In this research, a novel aromatic poly(sulfide sulfone) (PPY) containing pyridine and sulfide groups is synthesized by polycondensation reactions of a new diol(diol‐PY) with bis(4‐fluorophenyl) sulfone. Also a poly(ether sulfone) (PBM) is prepared through reaction of 4,4′‐(1,3‐phenylenediisopropylidene) bisphenol(bisphenol M) with bis(4‐fluorophenyl) sulfone similarly. The chemical structure of diol‐PY and polymers is identified by spectroscopic techniques. PBM/PPY blending dense membranes with composition of 100/0, 75/25, and 50/50 wt% are developed via phase inversion induced method by solvent evaporation. The prepared dense membranes are specified by water contact angle, water absorption, scanning electron microscope (SEM), atomic force microscope (AFM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tensile strength. Pure water flux, hydraulic water permeability, and salt permeability are applied to evaluate the process performance of the membrane. According to SEM and DSC results, good miscibility of two polymers is concluded. Thermal stability of PBM/PPY blend membranes enhance compared with PBM membrane. Water contact angle and water absorption evaluation indicate that the hydrophilicity of PBM membrane improve by incorporating of PPY in the casting polymer solution. The similar result is observed for pure water flux and hydraulic water permeability of the synthesized dense membranes. [ABSTRACT FROM AUTHOR]

Perimeter artefacts, such as test cell induced membrane damage and unrepresentative hydrodynamics, can significantly affect bench scale performance evaluation using membrane coupons. By comparing separately collected center and perimeter permeate, the effect of perimeter artefacts can be identified. The additional salt passage in the perimeter area (i.e., along the edges of the membrane coupon) depends non-linearly on pressure, and is implicitly affected by flux, temperature and salinity (osmotic pressure), leading to a potential increase of the measured salt passage by a factor two. We observed a very slow dynamic response (τ ≈ 12 h) to changes in operational conditions, suggesting that in our case the perimeter artefact was diffusive in nature. Due to this slow response, the perimeter salt passage trails previously evaluated operational conditions, possibly resulting in a false trend, hysteresis or high variance, depending on the sequential ordering and duration of test condition intervals. The effect of perimeter artefacts can be largely mitigated by measuring salt rejection from only the central area of the coupon. [Display omitted] • Perimeter artefacts can increase measured salt passage by a factor of two. • Artefact warning signs: high salt passage, high variance, slow dynamics, hysteresis. • Separate collection of center and perimeter permeate allows more representative sampling. • Perimeter artefacts correlate with flux, temperature, salinity and permeability via TMP. • Slow dynamic response can add false trend to ordered sequence of test conditions. [ABSTRACT FROM AUTHOR]

Ion rejection by composite membranes for RO/NF is performed by an ultrathin polyamide active layer (AL) with non-uniform thickness. Current models explain the solute and water fluxes by concentration and potential in AL of uniform properties, there are studies showing the effects of its topology on permeability. We developed a two-dimensional extension of the solution-friction model, coupling ion and water transport in irregularly-shaped charged AL, with geometry extracted from TEM images. Simulations indicated that AL with pronounced roughness lead to highly non-uniform distribution of ionic fluxes and lead to NaCl permeability greater than obtained by uniform layers. The transmembrane pressure and membrane charge can shift the relative dominance of ion transport mechanisms. In weakly charged membranes diffusion dominates, even at high water fluxes. Electromigration can counteract the convective flux in highly charged membranes. The model revealed the possibility of circular ionic currents within/around the AL. The response of the 2D model to variations in flux and salinity can be identical to the response of a 1D model, providing that the 1D model uses an appropriate equivalent membrane thickness. We provided a method to convert the detailed 2D geometry into a single number that can be computed from images' active layers. [Display omitted] • A 2D solution-friction model reveals new effects of active layer on ion permeability. • Ionic current loops may develop inside and around the active layer. • Different transport mechanisms are dominant in different conditions. • An equivalent 1D active layer thickness leads to the same permeability as in 2D. • The equivalent thickness can be computed from images of the active layer. [ABSTRACT FROM AUTHOR]

Two low water content copolymers, rubbery 2-hydroxyethyl acrylate- co -ethyl acrylate (HEA- co -EA) and glassy 2-hydroxyethyl methacrylate- co -methyl methacrylate (HEMA- co -MMA), were crosslinked with poly(ethylene glycol) diacrylate and studied to investigate the influence of polymer backbone segmental dynamics on salt transport size selectivity. These copolymers were chosen for chemical similarity and because HEA- co -EA is rubbery while HEMA- co -MMA is glassy at room temperature. Thermal analysis indicated that the copolymers are relatively homogeneous as a single glass transition temperature was observed for each material. The copolymers were prepared to have low water content (approximately 8% by mass) similar to the reported water content of many commercially available desalination membrane polymers. At low water content, most of the water in the polymer is expected to interact either with the polymer backbone or sorbed ions, suggesting that the influence of backbone segmental dynamics on the transport properties of these low water content materials may be different from the situation in more highly hydrated polymers. Salt sorption similarly increased with water content for the two copolymers due to their chemical similarity. Size selectivity was quantified as ratios of the salt permeability and diffusion coefficients to the corresponding values for a reference salt, and salt size was quantified using the salt diffusivity in bulk aqueous solution at infinite dilution to take into account both ion size and hydration properties. At comparable water content, the salt permeability and diffusion coefficients of the rigid HEMA- co -MMA copolymer decreased to a greater extent as a function of salt size compared to the more flexible HEA- co -EA copolymer. These results suggest that more rigid polymer backbones may drive increases in size-based permeation and diffusion selectivity when polymer water content is sufficiently low. [ABSTRACT FROM AUTHOR]

The solution-diffusion-electromigration approximation model (SDE-A) was formulated to describe the salt permeability of effectively uncharged, weakly charged and strongly charged reverse osmosis (RO) membranes. The model uses three of fewer parameters, depending on the type of charge behavior that a particular membrane exhibits under the allowable experimental conditions regarding feedwater salinity and acidity. The resulting algebraic equation is an approximation of an analytical solution of the Nernst-Planck equations for a 1:1 salt where the membrane charge depends on the feedwater conditions. The SDE-A model was compared to the more complex solution-friction (SF) model, by converting SF parameters to SDE-A parameters, resulting in a typical difference in computed salt permeability of less than 20%. Furthermore, the SDE-A model was applied to datasets from literature, corresponding to strongly charged, weakly charged and uncharged membranes. The SDE-A model can describe the effect of salinity and pH in these datasets comparably to the SF model. Because the model parameters can be easily determined experimentally and the algebraic model equation does not require elaborate solvers, the model is suitable for process design and optimization. [Display omitted] • SDE-A model parameterizes charged, uncharged and weakly charged membranes. • Different membrane types require different number of SDE-A parameters (3 or fewer). • Solution friction (SF) and SDE-A model parameters can be converted to each other. • SDE-A model approximates salt permeability by more complex SF model within 20%. [ABSTRACT FROM AUTHOR]

Controlled molecular weight poly(arylene ether sulfone) oligomers with aromatic amine end groups and systematically varied degrees of disulfonation were synthesized by direct polymerization of disulfonated and non-sulfonated 4,4′-dichlorodiphenylsulfone. The oligomers were crosslinked with a tetrafunctional epoxy curing agent in the membrane casting process. Water uptake and IEC were investigated to understand how the structure and ion content affected the fixed charge concentrations (moles of ions/L of sorbed water). The hydrated mechanical properties of these copolymer networks were also studied in light of their ion contents and water uptake. At similar IECs, membranes with shorter ∼5000 Da oligomers absorbed less water than those with ∼10,000 Da blocks. The salt permeabilities correlated with water uptake and fixed charge density. Among the crosslinked membranes, the one with the 10,000 Da oligomer and with 50% disulfonation ( m B5-10) had an excellent combination of water uptake, hydrated mechanical properties, fixed charge density, and low salt permeability. [ABSTRACT FROM AUTHOR]

Osmotic power extracted from the mixing of freshwater with seawater is a renewable energy resource that has gained increasing attention during recent years. The estimated energy can significantly contribute to the production of power worldwide. However, this power production will be subject to variation due to both local conditions and seasonal variation. The present paper explores the effect of concentration and temperature on water and salt fluxes in osmosis at zero transmembrane pressure for five different membranes. Further, the measured fluxes have been utilized to model water and salt permeabilities (A and B), and the structure parameter (S). The observed flux variations at different combinations of concentration and temperature have been ascribed to skin properties, i.e., changes in A and B of each membrane, whereas S was assumed constant within the range of concentrations and temperatures that were tested. Simplified equations for the variation in A and B with temperature and concentration have been developed, which enable A and B to be calculated at any concentration and temperature based on permeabilities determined from osmotic experiments at standard test conditions. The equations can be used to predict fluxes and specific power production with respect to geographical and seasonal variations in concentration and temperature for river water/seawater pressure-retarded osmosis. The obtained results are also useful for forward osmosis processes using seawater as draw solution.

Magnetic fields have been used as a mitigation process for controlling mineral scaling in diverse applications, including membrane systems. Changes in scale formation have been attributed, in part, to changes in ion hydration. The objective of this study was to evaluate how passage through a multi-directional magnetic field affected the permeability of relevant cations and anions through a seawater reverse osmosis membrane (SW30HR). Changes in ion permeability were evaluated as a function of flow velocity through the magnetic system and described in terms of changes in the ion hydration and in turn changes in the energy penalty that a given ion must incur to permeate across the RO membrane. Ion permeability across the SW30HR membrane increased after having passed through the magnetic system. Increases in ion permeability became most pronounced once a flow velocity through the magnetic system was ≥35 cm/s and were a function of the ion charge density for ions of the same valence. Increases in ion permeability were attributed to dehydration of the ions by the magnetic system resulting in a reduction in the energy penalty required for the relevant ions to transport across the membrane barrier. [Display omitted] • Salt permeability across RO membranes is increased upon exposure to magnetic fields. • Ion dehydration is not permeant and has a lifetime. • Energy from passage through magnetic fields was quantified using quantum mechanics. • Ion response to magnetic fields is a partial function of ion charge density. [ABSTRACT FROM AUTHOR]

ABSTRACT Despite great interests in using zwitterionic polymers for membrane surface modification to enhance antifouling properties, there lacks fundamental understanding of the relationship between polymer structure and water/salt separation properties. In this study, two series of zwitterionic polymers were prepared from sulfobetaine methacrylate and 2-methacryloyloxyethyl phosphorylcholine. Both are crosslinked by poly(ethylene glycol) diacrylate (PEGDA). These copolymers were thoroughly characterized in terms of sol-gel fraction, density, glass transition temperature, contact angle, water and salt transport properties, and pure-gas permeability. Interestingly, the zwitterionic polymers exhibit water sorption and permeability similar to noncharged poly(ethylene glycol)-based materials. These zwitterionic polymers exhibit lower NaCl diffusivity and permeability and thus higher water/NaCl selectivity than the non-charged PEG-based materials at similar water volume fractions, demonstrating their promise for membrane surface modification for desalination and wastewater treatment. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1924-1934 [ABSTRACT FROM AUTHOR]

The possibility of NaCl permeation through a polymeric matrix of polypropylene membranes was studied. A non-porous polypropylene film, which was assembled in a flat sheet module, separates a saturated solution of NaCl from pure water. The changes of water composition were determined by the application of ion chromatography and measurements of the electric conductivity. The studies were carried out for 4 years, and the permeation of salt through the polypropylene film from the feed to pure water was not observed over this period. In the first month the results of studies were affected by the impurities, which were introduced to pure water from the installation walls. Moreover, the electrical conductivity of water was also enhanced by adsorption of components from the ambient air. The used polypropylene film demonstrated a high resistance to polymer degradation. SEM observations revealed that the film was free from micropores and cracks after 4 years of studies. The DSC examinations demonstrated only slight changes in the polymer crystallinity. FTIR spectra recorded for a new film and film assembled in the module were similar. The XPS studies did not demonstrated the presence of NaCl in the surface layer of polymer on the side of brine flow. Moreover, a significant change of material hydrophobocity did not take place over the period studied. A dynamic wetting angle measured for a new film amounted to 103–106° and was decreased to 95° on the water side and to 84° on the brine side after 4 years of contact of the polymer with water and a saturated NaCl solution, respectively. [ABSTRACT FROM AUTHOR]

Two series of crosslinked zwitterionic polymer films were synthesized via UV-photopolymerization of aqueous solution, and the films were prepared using sulfobetaine methacrylate (SBMA) or carboxybetaine methacrylate (CBMA) as the zwitterionic co-monomer and poly(ethylene glycol) diacrylate (PEGDA) as the crosslinker. The water and salt transport properties of the obtained polysulfobetaine methacrylate (PSBMA) and polycarboxybetaine methacrylate (PCBMA) films were studied using permeation and kinetic desorption methods with crosslinked poly(ethylene glycol) acrylate (PEGA) films as a control. Zwitterionic films absorb more water and are more permeable to both water and salt than PEGA films as a result of interactions between the zwitterions, water molecules, and salt ions. The transport properties of PSBMA and PCSMA depend similarly on crosslinking density, and high water and salt permeability correlates with high water uptake. However, the relationship between salt permeability and salt concentration differed between PSBMA and PCBMA. PSBMA behaves like a charged film, and its salt permeability increases with salt concentration while PCBMA shows the opposite trend. Transport properties for both materials are consistent with a trade-off between water permeability and water/salt selectivity. Zwitterionic films exhibit high permeability/low selectivity among polymers reported in the literature. This result suggests that they could be useful as coating materials for membrane fouling control where the anti-fouling properties of the zwitterionic material is more important than water/salt selectivity. [ABSTRACT FROM AUTHOR]

Salt permeability and ionic conductivity are critical properties for membranes in water purification and energy applications. Both properties depend on individual ion sorption and diffusion coefficients, which are significantly influenced by polymer chemical and physical parameters such as fixed charge concentration and membrane water content. However, systematic studies connecting polymer structure to ion transport properties are still lacking. In this study, a series of uncharged and charged membranes were synthesized using poly(ethylene glycol) diacrylate (PEGDA) as a cross-linker and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as a charged monomer. Membrane fixed charge concentration and water uptake were systematically varied by adjusting AMPS content in the pre-polymerization mixture. Salt sorption and permeability coefficients and ionic conductivity of these membranes were measured as a function of NaCl solution concentration (0.01–1 M). Combining the solution-diffusion model and Nernst-Planck equation, individual ion diffusion coefficients were calculated. Experimental Na+ diffusion coefficients for all materials were well described by the Mackie and Meares tortuosity model, highlighting the strong influence of water content on ion diffusivity in both uncharged and charged polymers. Model predictions for Cl− diffusion coefficients agree reasonably well with experimental values, with some deviations occurring in more highly charged membranes. This discrepancy might result from interactions not captured by the Mackie and Meares model (e.g., fixed charge-ion interactions). [Display omitted] • Salt diffusion coefficients are well described by the Mackie and Meares model. • Experimental ionic conductivities agree well with model predictions in charged membranes. • Donnan/Manning model fails to describe ion sorption in weakly charged membranes. [ABSTRACT FROM AUTHOR]

Water/Ion NMR Detected – Phospholipid Vesicle Permeability Assay (WIND-PVPA), is presented as a novel, straightforward and automatable method to assess lipid barrier integrity in vitro. The apparent permeability constants of water- and ions across the PVPA barriers are determined in a one-pot experiment under the influence of membrane-active guest molecules. NMR spectroscopy is used to quantify the water directly (D 2 O) and the ions indirectly (complexed with EDTA) as a function of time. WIND-PVPA is demonstrated using four anti-microbial peptides, to show that membrane active molecules can be differentiated by their disruptive influence on the PVPA system. The results obtained are compared with explicit molecular dynamics simulations of lipid bilayers, AMPs, water and salt, where the motions of all individual water molecules relative to the lipid bilayer are monitored over the course of the simulations, allowing the calculation of theoretical apparent permeability constants of the corresponding single bilayer systems. Proof-of-principle is presented that WIND-PVPA can be used to evaluate the lipid barrier destabilizing effect of active guest molecules by measuring changes in passive water- and ion permeabilities upon exposure. The method is highly flexible in terms of barrier composition, choice of probes and membrane active compounds. [Display omitted] • In vitro permeability assay for water and salt • Lipid barrier integrity reduced by antimicrobial peptides • Automatable permeability assay • PVPA application • Water permeability simulation [ABSTRACT FROM AUTHOR]

Abstract: Fundamental water and salt transport properties of polymers are critical for applications such as reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), and membrane capacitive deionization (MCDI) that require controlled water and salt transport. Key developments in the field of water and salt transport in polymer membranes are reviewed, and a survey of polymers considered for such applications is provided. Many polymers considered for such applications contain charged functional groups, such as sulfonate groups, that can dissociate in the presence of water. Water and ion transport data from the literature are reviewed to highlight the similarities and differences between charged and uncharged polymers. Additionally, the influence of other polymer structure characteristics, such as cross-linking and morphology in phase separated systems, on water and salt transport properties is discussed. The role of free volume on water and salt transport properties is discussed. The solution–diffusion model, which describes the transport of water and ions in nonporous polymers, is used as a framework for discussing structure/property relations in polymers related to water and salt transport properties. Areas where current knowledge is limited and opportunities for further research are also noted. [Copyright &y& Elsevier]

Abstract: Sodium chloride permeability and sorption measurements were used to calculate average salt diffusion coefficients for charged, sulfonated polymers of interest for membrane applications. A sulfonated polysulfone random copolymer and two phase-separated, sulfonated styrenic pentablock copolymers were considered, and data for these materials were compared with those for an uncharged cross-linked poly(ethylene glycol diacrylate) hydrogel. The average salt diffusion coefficients reported for the block copolymers are apparent salt diffusion coefficients because the values have not been adjusted for the polymer’s phase separated morphology. The sodium chloride permeability of the uncharged hydrogel decreases by about 16% as upstream salt concentration increases from 0.01 to 1molL−1. This salt permeability change results from a decrease in the salt diffusion coefficient with increasing salt concentration because the polymer’s water content decreases as salt concentration increases (i.e., osmotic de-swelling). This decrease in salt diffusion coefficient is consistent with free volume theory, wherein a decrease in water content leads to a decrease in free volume, thereby decreasing the salt diffusion coefficient and, in turn, salt permeability. In contrast, the sodium chloride permeability of the charged polymers increases by more than an order of magnitude as upstream salt concentration increases from 0.01 to 1molL−1. This salt permeability increase is due to increases in both mobile salt sorption and diffusion coefficients with increasing salt concentration, despite the fact that water content (and, therefore, free volume) in the polymer decreases as salt concentration increases. Thus, the increase in salt diffusion coefficient with increasing salt concentration in the charged polymers results from factors (which are currently poorly understood) other than simply water uptake or free volume. [Copyright &y& Elsevier]

Abstract: Modification caused in cellophane matrix (a highly hydrophilic natural polymer) by γ-irradiation was studied by determining changes in different electrochemical parameters obtained from measurements carried out with the membranes in contact with NaCl and MgCl2 solutions. Three different irradiation doses (10Gy, 30Gy and 80Gy) were used in order to consider its possible effect in membrane modification. Changes in salt permeability, electrical resistance and permselectivity show modifications in the membrane matrix, which seem to produce: (i) a reduction in the inter-chains free space (around 40%), which slightly decreases when the irradiation dose increases (20% at the highest dose); (ii) an increase of the cation-exchange character of cellulose membranes, which is directly dependent on the irradiation doses (between 10% and 20%). Salt permeability and electrical resistance hardly depend on the kind of electrolyte, but higher values were obtained for cationic membrane permselectivity with NaCl solutions for both pristine and irradiated samples. [Copyright &y& Elsevier]

Asymmetric charged porous membranes were prepared by imbedding 10% (W/W) ion-exchange resin in cellulose acetate binder. Membrane potential and conductance measurements have been carried out in sodium chloride solutions at different concentrations to investigate the relationship between concentration of fixed charges and electrochemical properties of developed nonselective cation- and anion-exchange membranes. Counterion transport number and permselectivity of these membranes were found to vary due to the presence of ion-exchange resin. The hydrodynamic and electroosmotic permeability of sodium chloride solutions has been studied in order to compute equivalent pore radius. For cation- and anion-exchange membranes good agreement was observed between pore radius values estimated from hydrodynamic and electroosmotic permeability coefficient separately, while for nonselective membranes no correlation was found. Membrane conductance data, along with values of concentration of fixed charges, were used for the estimation of the tortuosity factor, salt permeability coefficient, and frictional coefficient between solute and membrane matrix employing an interpretation by nonequilibrium thermodynamic principles based on frictional forces. Moreover, surface morphological studies of these membranes also have been carried out and the membranes were found to be reasonably homogeneous. [Copyright &y& Elsevier]

Understanding the salt-water separation mechanisms of reverse osmosis (RO) membranes is critical for the further development and optimization of RO technology. The solution-diffusion (SD) model is widely used to describe water and salt transport in RO, but it does not describe the intricate transport mechanisms of water molecules and ions through the membrane. In this study, we develop an ion transport model for RO, referred to as the solution-friction model, by rigorously considering the mechanisms of partitioning and the interactions among water, salt ions, and the membrane. Ion transport through the membrane is described by the extended Nernst-Planck equation, with the consideration of frictions between the species (i.e., ion, water, and membrane matrix). Water flow through the membrane is governed by the hydraulic pressure gradient and the friction between the water and membrane matrix as well as the friction between water and ions. The model is validated using experimental measurements of salt rejection and permeate water flux in a lab-scale, cross-flow RO setup. We then investigate the effects of feed salt concentration and hydraulic pressure on salt permeability, demonstrating strong dependence of salt permeability on feed salt concentration and applied pressure, starkly disparate from the SD model. Lastly, we develop a framework to analyze the pressure drop distribution across the membrane, demonstrating that cross-membrane transport dominates the overall pressure drop in RO, in marked contrast to the SD model that assumes no pressure drop across the membrane.

Regenerated cellulose forms a very important class of basic material with diverse applications because of its hydrophilicity and insolubility in water. Thus, one of the applications of regenerated cellulose is used to fabricate membranes. However, short operational lifetime is one of the disadvantages of the regenerated cellulose. In this research, surface modification of the cellophane membrane was carried out by silver nanoclusters. Silver colloids were formed in situ by chemical and photochemical reduction, and then, silver particles were deposited uniformly onto the surface of the cellophane membrane. The maximum amount of silver deposition was found to be 2.55% by weight in this modification. The modified and unmodified membranes were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy‐dispersive X‐ray analysis to indicate silver nanocrystalline cluster particles on the modified membrane. SEM images indicate well‐dispersed silver particles with an average size of 0.65 μm on the membrane. XRD patterns showed that the size of the silver crystals was 3.9 nm. The surface properties of modified and unmodified membranes were studied by the contact angle. Water absorption, oxidative resistance, salt permeability, and thermal stability were investigated. This study revealed that the modified membrane is more resistant against the oxidative cleavage than the unmodified one moreover, the salt permeability increased after the treatment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48292. [ABSTRACT FROM AUTHOR]

Osmotic power extracted from the mixing of freshwater with seawater is a renewable energy resource that has gained increasing attention during recent years. The estimated energy can significantly contribute to the production of power worldwide. However, this power production will be subject to variation due to both local conditions and seasonal variation. The present paper explores the effect of concentration and temperature on water and salt fluxes in osmosis at zero transmembrane pressure for five different membranes. Further, the measured fluxes have been utilized to model water and salt permeabilities (A and B), and the structure parameter (S). The observed flux variations at different combinations of concentration and temperature have been ascribed to skin properties, i.e., changes in A and B of each membrane, whereas S was assumed constant within the range of concentrations and temperatures that were tested. Simplified equations for the variation in A and B with temperature and concentration have been developed, which enable A and B to be calculated at any concentration and temperature based on permeabilities determined from osmotic experiments at standard test conditions. The equations can be used to predict fluxes and specific power production with respect to geographical and seasonal variations in concentration and temperature for river water/seawater pressure-retarded osmosis. The obtained results are also useful for forward osmosis processes using seawater as draw solution. [ABSTRACT FROM AUTHOR]

Abstract: It is proposed that simple electrical resistance measurements of a polymer film immersed in alternate salt and acid solutions could provide an estimate of the inherent reverse osmosis performance of membranes made from said polymer. [Copyright &y& Elsevier]

This study presents a framework for predicting salt permeability coefficients in ion exchange membranes in contact with an aqueous salt solution. The model, based on the solution-diffusion mechanism, was tested using experimental salt permeability data for a series of commercial ion exchange membranes. Equilibrium salt partition coefficients were calculated using a thermodynamic framework (i.e., Donnan theory), incorporating Manning's counterion condensation theory to calculate ion activity coefficients in the membrane phase and the Pitzer model to calculate ion activity coefficients in the solution phase. The model predicted NaCl partition coefficients in a cation exchange membrane and two anion exchange membranes, as well as MgCl 2 partition coefficients in a cation exchange membrane, remarkably well at higher external salt concentrations (>0.1 M) and reasonably well at lower external salt concentrations (<0.1 M) with no adjustable parameters. Membrane ion diffusion coefficients were calculated using a combination of the Mackie and Meares model, which assumes ion diffusion in water-swollen polymers is affected by a tortuosity factor, and a model developed by Manning to account for electrostatic effects. Agreement between experimental and predicted salt diffusion coefficients was good with no adjustable parameters. Calculated salt partition and diffusion coefficients were combined within the framework of the solution-diffusion model to predict salt permeability coefficients. Agreement between model and experimental data was remarkably good. Additionally, a simplified version of the model was used to elucidate connections between membrane structure (e.g., fixed charge group concentration) and salt transport properties.