Extended adsorption transport models for permeation of copper ions through nanocomposite chitosan/polyvinyl alcohol thin affinity membranes

Transport of copper ions through nanocomposite chitosan/polyvinyl alcohol thin adsorptive membranes has been mathematical y investigated in the current study. Unsteady-state diffusive transport model was coupled with the Freundlich isotherm to predict the concentration of the ions in dialysis permeation operation. Pristine model was not successful in predicting the experimental data based upon its low coefficients of determination (0.1﹤R2﹤0.65). Well-behaved polynomial and exponential functions were used to describe time-dependency of the inlet-concentration in the first extension of the model with a little improvement in the model adjustment (0.4﹤R2﹤0.69). Similar time-dependent functions were employed for tracking the ion diffusivity and then applied in combination with the optimized functions of inlet-concentration in the second extension of the model. A sensible enhancement was obtained in the adjustment of the second extended models as a result of this combination (0.73﹤R2﹤0.93). APRE, AAPRE, RSME, RMSE, STD and R-square statistical analyses were per-formed to verify the agreement of the models with the experimental results. Concentration distribution versus time and location (inside the membrane) was obtained as 3D plots with the help of the optimized models. Modeling results emphasized on the transiency of diffusivity and feed-side concentration in dialysis permeation through chitosan membranes.     

Optimization of the elastic modulus for polymeric nanocomposite membranes

The mechanical properties of polymeric membranes are critical factors for a successful and durable application in water treatment technologies. Fabricating membranes with optimal mechanical properties require delicate balancing between material, additives, processing conditions, porosity, and many other variables. Several variables to be optimized demands detailed experimental and computational investigations. The design of experiments (DOEs) technique using a validated framework with a computational model for the prediction of the elastic behavior can lower the number of conducted experiments for optimal membrane fabrication conditions. In this study, optimization of the elastic modulus of polymeric membranes is performed using DOE with computational modeling and validated with experiments. The optimum storage modulus of polymeric nano-filled membranes is determined at an operating temperature of 35°C. DOE is employed with a three-factor–three-level problem. The Taguchi DOE is utilized to obtain the experiments scheme, followed by the prediction of the storage modulus and fabrication of the polymeric nano-filled membrane with the optimum modulus. Predicted results demonstrate that the modulus of polyether sulfone (PES) reinforced with 0.3 wt.% halloysite nanotubes (HNTs) is the optimum combination. The fabricated PES/0.3 wt.% HNT membrane is in good agreement with the predicted modulus with a percentage error of 3%.     

Stable zirconium hydrogen phosphate-silica nanocomposite membranes with high degree of bound water for fuel cells

Zirconium hydrogen phosphate (ZrP)-silica nanocomposite polymer electrolyte membranes (PEMs) were prepared by sol-gel method in aqueous media. Hydrophilic and hydrophobic regions of PEMs were tailored by molecular level of architecture to introduce proton conducting pathways and methanol impervious nature. ZrP-silica nanocomposite PEMs showed improved thermal, mechanical, oxidative and hydrolytic stabilities along with high conductivity, methanol retention capacity, which are essential requirements. Furthermore, high degree of bound water content in membrane matrix indicates suitability of reported PEMs under anhydrous or low-humidity conditions. These PEMs were well processed as self-supporting film, and exhibited high selectivity parameter in comparison to Nafion117 membrane for direct methanol fuel cell (DMFC) applications.     

Surface modification of nanocomposite ceramic membranes by PDMS for condensable hydrocarbons separation

PDMS/ceramic nanocomposite membranes were fabricated via dip-coating method. Tubular porous nanocomposite ceramic supports were used as membrane substrates and polydimethylsiloxane was applied as a top active layer. The hybrid membranes were characterized morphologically by scanning electron microscopy (SEM) and their gas transport properties were measured using single gas permeation (butane and hydrogen) at ambient temperature and different pressures. SEM micrographs confirmed the penetration of polymeric layer into ceramic support pores at low concentrations of PDMS solution. Experimental results clearly indicated that the undesirable penetration during the dip-coating stage could be avoided by increasing the concentration of PDMS coating solution. This led to the formation of a uniform and dense coating layer without penetration into pores of the support. These hybrid membranes showed higher permeability combined to a suitable selectivity in comparison with dense homogeneous PDMS membrane. In addition, at low pressures, the high selectivity of PDMS/ceramic nanocomposite membranes for condensable hydrocarbons separation revealed that the dominant mechanism is solution-diffusion.     

Chitosan membranes filled by GPTMS-modified zeolite beta particles with low methanol permeability for DMFC

Uniform zeolite beta particles about 800 nm in diameter were synthesized by a hydrothermal method, and functionalized by γ-glycidoxypropyltrimethoxysilane (GPTMS). Subsequently, chitosan (CS) membranes filled by GPTMS-modified zeolite beta particles were prepared, and characterized by SEM, FT-IR, XRD and TGA. Compared with the pure CS and Nafion^®117 membrane, these CS/zeolite beta hybrid membranes show apparently the lower methanol permeability, which could be assigned to the better interfacial morphology and compatibility between the GPTMS-modified zeolite beta particles and chitosan matrix. In all the prepared CS/zeolite beta hybrid membranes, the CS membrane filled by 10 wt.% GPTMS-modified zeolite beta particles exhibits the lowest methanol permeability, which is 4.4 × 10⁻⁷ and 2.2 × 10⁻⁷ cm² s⁻¹ at 2 and 12 M methanol concentration, respectively. The proton conductivity of this hybrid membrane is 1.31 × 10⁻² S cm⁻¹, which is slightly lower than that of the pure CS membrane. The selectivity of CS/GPTMS-zeolite beta membranes is comparable with Nafion^® 117 at 2 M methanol concentration, and much higher at 12 M methanol concentration.     

Size of polymeric particles forming hemodialysis membranes determined from water and solute permeabilities

Regarding hemodialysis membranes as layers packed with uniform polymeric particles, the size of the particles is determined using the Kozeny–Carman equation. Diameter of the spheres forming cellulosic membranes is the same order as the size of primary polymeric particles determined by electron microscopy in a previous article. Pore radii of the membranes calculated by the Kozeny–Carman equation are in agreement with those determined by the tortuous capillary pore model. The result suggests that an estimate of a pore radius of a membrane is feasible by the Kozeny–Carman equation only with water permeability of the membrane. Intramembrane diffusion coefficients of vitamin B₁₂ calculated from an equation derived from the analogy of heat conduction in heterogeneous media consisting of a continuous phase and particles are larger than the experimental values. The result suggests the failure of the analogy between heat conduction and diffusion of vitamin B₁₂ in a heterogeneous medium. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:833–840, 1998     

Modeling a dense polymeric catalytic membrane reactor with plug flow pattern

A theoretical study on a tubular membrane reactor assuming isothermal operation, plug flow pattern and using a dense polymeric catalytic membrane is performed. The reactor conversion for an equilibrium gas-phase reaction generically represented by AB is analyzed, considering the influence of the product’s sorption and diffusion coefficients. It is concluded that the conversion of such a reaction can be significantly improved when the overall diffusion coefficient of the reaction product is higher than the reactant’s one and/or the overall sorption coefficient is lower, and for Thiele modulus and contact time values over a threshold. Though a sorption coefficient of the reaction product lower than that of the reactant may leads to a conversion enhancement higher than that one obtained when the reaction product diffusion coefficient is higher than that of the reactant, the contact time value for the maximum conversion is much higher in the first case. In this way, a higher diffusion coefficient for the reaction product should be generally preferable, because it leads to a lower reactor size. The performance of a dense polymeric catalytic membrane reactor depends in a different way on both sorption and diffusion coefficients of reactants and products and then a study of such a system cannot be based only on their own permeabilities. Favorable combinations of diffusion and sorption coefficients can affect positively the reactor’s conversion.     

Preparation of monodispersed polymeric microspheres for toner particles by the shirasu porous glass membrane emulsification technique

This investigation describes the experiment directed toward the production of monodispersed toner particles by suspension polymerization. That is, relatively monodispersed poly(styrene-co-divinylbenzene) microspheres containing electrifying additives were successfully prepared by suspension polymerization employing the Shirasu Porous Glass (SPG) membrane emulsification technique. The diameter distribution of the dispersed droplets prepared with an SPG membrane module was fairly narrow, compared with that prepared with a conventional mechanical homogenizer. The effect of Sumiplast Blue S as coloring matter and E-81 as charge control agent on the triboelectric discharging properties of prepared polymeric microspheres was studied. The addition of electrifying additives strongly affected the triboelectric discharging property. It was consequently clarified that a small amount of electrifying additives added raised the electrostatic capacity of polymeric microspheres. However, a further addition reduced the triboelectric discharge of polymeric microspheres. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1107–1113, 1997     

Novel Nafion–zirconium phosphate nanocomposite membranes with enhanced stability of proton conductivity at medium temperature and high relative humidity

In order to increase the stability of Nafion conductivity at temperatures higher than 100 °C, composite membranes made of recast Nafion filled with different percentages of zirconium phosphate (ZrP) were investigated. The membrane preparation was carried out by a simple synthetic procedure based on the use of solutions of ZrP precursors in dimethylformamide. The formation of insoluble -type ZrP nanoparticles within the Nafion matrix was proved by ³¹P-MAS NMR and X-ray diffractometry. The membranes were characterized by TEM microscopy, ion-exchange capacity determinations, static stress–strain mechanical tests and conductivity measurements as a function of filler loading, at controlled relative humidity (r.h.) and temperature. An increasing filler loading results in enhanced membrane stiffness and in lower conductivity compared with pure recast Nafion. At 90% r.h. and 100 °C, the conductivity decreases from ≈0.07 S cm⁻¹ for pure Nafion to ≈0.03 S cm⁻¹ for the composite membrane containing 25 wt.% ZrP. Systematic conductivity measurements as a function of r.h. and temperature were carried out to draw a stability map for the conductivity of pure recast Nafion and of a composite membrane filled with 10 wt.% ZrP. These maps provide for each r.h. value the maximum temperature at which the conductivity remains stable for at least 150 h. The effect of zirconium phosphate is to increase the stability of conductivity at high temperature, with a gain up to 20 °C. This stability enhancement has been ascribed to the higher stiffness of the composite membrane.     

Crosslinking and stabilization of nanoparticle filled poly(1‐trimethylsilyl‐1‐propyne) nanocomposite membranes for gas separations

Poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) has been crosslinked using 4,4′‐diazidobenzophenone bisazide to improve its chemical and physical stability over time. Crosslinking PTMSP renders it insoluble in good solvents for the uncrosslinked polymer. Gas permeability and fractional free volume decreased as crosslinker content increased, while gas sorption was unaffected by crosslinking. Therefore, the reduction in permeability upon crosslinking PTMSP was due to decrease in diffusion coefficient. Compared with the pure PTMSP membrane, the permeability of the crosslinked membrane is initially reduced for all gases tested due to the crosslinking. By adding nanoparticles (fumed silica, titanium dioxide), the permeability is again increased; permeability reductions due to crosslinking could be offset by adding nanoparticles to the membranes. Increased selectivity is documented for the gas pairs O₂/N₂, H₂/N₂, CO₂/N₂, CO₂/CH and H₂/CH₄ using crosslinking and addition of nanoparticles. Crosslinking is successful in maintaining the permeability and selectivity of PTMSP membranes and PTMSP/filler nanocomposites over time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thin film composite nanofiltration membranes fabricated from polymeric amine polyethylenimine imbedded with monomeric amine piperazine for enhanced salt separations

Thin film composite (TFC) nanofiltration membranes were fabricated by interfacial polymerization using polymeric amine polyethylenimine (PEI) and monomeric amine piperazine (PIP) as the amine reactant. Membranes with a single-ply polyamide layer were produced by reacting trimesoyl chloride (TMC) with mixed amines of PEI and PIP, and incorporation of a small amount of PIP in PEI was found to increase the permeation flux effectively while still maintaining a good solute rejection. For instance, adding 10 wt% PIP in the amine reactant solution resulted in a 6-fold increase in permeation flux, while a 91.6% MgCl₂ rejection was maintained. In addition, 2-ply polyamide membranes were also prepared by two cycles of PEI–TMC and PIP–TMC interfacial reactions separately, and they showed a higher rejection than the single-ply polyamide membrane. At a low PIP/PEI concentration ratio, the single-ply polyamide membranes formed with mixed amines of PIP and PEI tended to be more permeable than the 2-ply polyamide membranes. However, it was demonstrated that by properly controlling the PIP/PEI concentration ratio, the 2-ply polyamide membranes with both a higher permeation flux and salt rejection than conventional single-ply polyamide membranes could be produced. The resulting membranes were characterized for chemical composition, surface hydrophilicity, surface charge and morphology of the polyamide skin layer.     

Modelling and process development for gaseous separation with silicone‐coated polymeric membranes

This paper proposes a permeance equation for vapour–permanent gas mixtures in a silicone‐coated polymeric membrane. The equation was derived from the Arrhenius relationship by combining an apparent activation energy and interaction parameter. Accurate values of transmembrane flux were obtained by incorporating this proposed equation, which was dependent on temperature and feed composition. The equation parameters were correlated with the experimental data of eight mixtures consisting of hydrocarbons such as ethylene, ethane, propylene and propane with nitrogen covering a broad range of temperature and concentration. A numerical integration scheme was used for developing a crossflow model utilizing the above equation, which allowed the estimation of product properties including the membrane plasticization cases. The study also reports examples of implementation of this approach in potential industrial applications for the recovery of ethylene and propylene from nitrogen.     

Gas permeation properties for organosilica membranes with different Si/C ratios and evaluation of microporous structures

Organosilica membranes were fabricated using bridged organoalkoxysilanes (bis(triethoxysilyl)methane (BTESM), bis(triethoxysilyl)ethane (BTESE), bis(triethoxysilyl)propane (BTESP), bis(trimethoxysilyl)hexane (BTMSH), bis(triethoxysilyl)benzene (BTESB), and bis(triethoxysilyl)octane (BTESO)) to produce highly permeable molecular sieving membranes. The effect of the organoalkoxysilanes on network pore size and microporous structure was evaluated by examining the molecular size and temperature dependence of gas permeance across a wide range of temperatures. Organosilica membranes showed H₂/N₂ and H₂/CH₄ permeance ratios that ranged from 10 to 150, corresponding to network pore size, and both H₂ selectivity decreased with an increase in the carbon number between 2 Si atoms. Organosilica membranes showed activated diffusion for He and H₂, and a slope of temperature dependence that increased approximate to the increase in the carbon number between 2 Si atoms. The relationship between activation energy and He/H₂ permeance ratio for SiO₂ and organosilica membranes suggested that the molecular sieving can dominate He and H₂ permeation properties via the rigid microporous structure, which was constructed by BTESM and BTESE. With increased in the carbon concentration in silica, polymer chain vibration in organic bridges, which is a kind of solution/diffusion mechanism, can dominate the permeation properties. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4491–4498, 2017     

Preparation of thin film nanocomposite membranes with surface modified MOF for high flux organic solvent nanofiltration

Preparation of defect‐free and optimized thin film nanocomposite (TFN) membranes is an effective way to enhance the process of organic solvent nanofiltration. However, it still remains a great challenge due to poor filler particle dispersibility in organic phase and compatible issue between fillers and polymers. Aiming at these difficulties, UiO‐66‐NH₂ nanoparticles were surface modified with long alkyl chains and used in the preparation of TFN membranes. As a result, defect‐free TFN membranes with ultrathin MOF@polyamide layer were successfully prepared benefited from the improved particle dispersibility in n‐hexane. Significant enhancement was found in methanol permeance after nanoparticle incorporation, without comprising the tetracycline rejection evidently. Especially, the novel TFN membrane prepared with organic phase solution containing 0.15% (w/v) modified UiO‐66‐NH₂ nanoparticles showed a superior methanol permeance of 20 L·m^?2·h^?1·bar^?1 and a tetracycline rejection of about 99%, which is appealing to the application in pharmaceutical industry for example. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1303–1312, 2017     

A novel model equation for the permeation of hydrogen in mixture with carbon monoxide through Pd–Ag membranes

Hydrogen permeance decrease, owing to the covalent interaction of carbon monoxide with the Pd–Ag membrane surface, represents a considerable drawback, since this decreases the efficiency of the alloy membranes. This work proposes a novel Sieverts–Langmuir's model taking into account the mentioned adsorption. The proposed model equation, in order to take into account the fraction of the membrane surface not active for hydrogen permeation, introduces Langmuir's isotherm, which is the surface loading in the classical Sieverts’ permeation equation. The evaluation of the parameter and the Langmuir affinity constant involved in the proposed model was carried out using experimental data measured using a 60 μm thick Pd–Ag commercial membrane at 647 K (374 °C), up to a total pressure of 700 kPa. The presented model yields, in a parametric form, a quantitative assessment of hydrogen permeance decrease caused by the adsorption of gases on Pd–Ag membrane surfaces. Therefore, this novel Sieverts–Langmuir's equation models hydrogen permeation through Pd–Ag-based membranes in the presence of inhibitor gases such as CO. In addition, by ab initio evaluation of the and the Langmuir affinity constant, the proposed Sieverts–Langmuir's equation can identify a new membrane with better efficiency.     

Organic-inorganic nanocomposite polymer electrolyte membranes for fuel cell applications

Organic-inorganic nanocomposite polymer electrolyte membrane (PEM) contains nano-sized inorganic building blocks in organic polymer by molecular level of hybridization. This architecture has opened the possibility to combine in a single solid both the attractive properties of a mechanically and thermally stable inorganic backbone and the specific chemical reactivity, dielectric, ductility, flexibility, and processability of the organic polymer. The state-of-the-art of polymer electrolyte membrane fuel cell technology is based on perfluoro sulfonic acid membranes, which have some key issues and shortcomings such as: water management, CO poisoning, hydrogen reformate and fuel crossover. Organic-inorganic nanocomposite PEM show excellent potential for solving these problems and have attracted a lot of attention during the last ten years. Disparate characteristics (e.g., solubility and thermal stability) of the two components, provide potential barriers towards convenient membrane preparation strategies, but recent research demonstrates relatively simple processes for developing highly efficient nanocomposite PEMs. Objectives for the development of organic-inorganic nanocomposite PEM reported in the literature include several modifications: (1) improving the self-humidification of the membrane; (2) reducing the electro-osmotic drag and fuel crossover; (3) improving the mechanical and thermal strengths without deteriorating proton conductivity; (4) enhancing the proton conductivity by introducing solid inorganic proton conductors; and (5) achieving slow drying PEMs with high water retention capability. Research carried out during the last decade on this topic can be divided into four categories: (i) doping inorganic proton conductors in PEMs; (ii) nanocomposites by sol-gel method; (iii) covalently bonded inorganic segments with organic polymer chains; and (iv) acid-base PEM nanocomposites. The purpose here is to summarize the state-of-the-art in the development of organic-inorganic nanocomposite PEMs for fuel cell applications.     

Surface modification of macroporous Al2O3 tubes with carbon-doped TiO2 intermediate layer and preparation of highly permeable palladium composite membranes for hydrogen separation

ABSTRACT

To prepare H₂-permeable palladium composite membranes, a novel carbon-doped microporous TiO₂ intermediate layer was introduced to modify the surface of macroporous Al₂O₃ substrates. The Pd/TiO₂–C/Al₂O₃ membrane was prepared via electroless plating, and thereafter, carbon residue in the intermediate layer was removed by calcination in air, yielding a Pd/TiO₂/Al₂O₃ membrane. Experimental results indicate that the carbon residue shrinks the pore size of the intermediate layer and facilitates a decrease of membrane defects. Additionally, carbon removal induces a higher effective membrane area at the permeate side, which enhances hydrogen permeability. Furthermore, the apparent activation energy (E_A) and stability of the as-prepared Pd/TiO₂/Al₂O₃ membrane were investigated.