Stanisław Koter

Comparative investigations of ion-exchange membranes

Abstract The equilibrium and transport properties (conductivity, transport number, diffusion) of crosslinked ionomer membranes based on sulfinated and sulfonated PSU in aqueous solutions of HCl, NaCl and KCl have been investigated and compared with a Nafion 117 membrane. It has been found that these membranes are more compact and their conducting paths are of smaller dimension than that of the Nafion 117. The influence of length of crosslinking chain, changing from –(CH 2 ) 4 – to –(CH 2 ) 12 –, is particularly indicated by the diffusion coefficients; the conductivity and transport numbers of counterions are influenced only slightly. Practically no dependence of this effect on the transport number of H + has been found.

Ions and water transport across charged nafion membranes. Irreversible thermodynamics approach

Abstract The isothermal transport of ions and water across the perfluorinated Nafion 120 membrane in contact with sodium chloride solutions of concentration 0.05 up to 4 mol/l has been studied basing on irreversible thermodynamics of transport. The interactions of ions with water and polymer matrix on passing across the membrane have been discussed on the ground of the resistance coefficients rik, friction coefficients fik, coupling coefficients qik and mobility indexes uNa+ and uH2O. The variations of the coefficients with concentration of an external electrolyte made it possible to comment on the structure-selectivity problems and reflect sensitivity of a cluster-like morphology of the membrane to sorption and swelling.

Transport of simple electrolyte solutions through ion-exchange membranes-the capillary model

Abstract The transport of aqueous binary electrolyte solutions (NaCl, HCl) through the cation- and anion-exchange membranes (Nafion, Neosepta) has been described in terms of the capillary model based on the thermodynamics of irreversible processes. The equivalent radius of pores has been calculated from the electroosmotic number of water. The L ik coefficients have been calculated for each membrane/electrolyte system basing on the experimental equilibrium properties of the membrane (IEC, water content) and on the transport coefficients of ions in a free solution. Having L ik the electrical conductivity, the permeability coefficient of electrolyte, the osmotic and hydrodynamic permeability coefficients of solvent have been calculated and compared with the experimental values. The best agreement has been found for the classical Boltzmann equation and those transport coefficients, which are dependent on counterions, the poorest—for the permeability coefficient of electrolyte, which depends on coions. Other tested distributions of ions inside the pores (the modified Boltzmann equation and the homogeneous distribution) have yielded poor results. The negative osmosis for the anion-exchange membrane AM1/HCl and the relatively small transport number of Cl − counterions can be explained by assuming a high mobility of the H + coions in that membrane. The change of pore geometry from the cylinder to infinite slit does not change the results substantially.

Highly Efficient Hydrophobic Titania Ceramic Membranes for Water Desalination

Hydrophobic titania ceramic membranes (300 kD) were prepared by grafting of C6F13C2H4Si(OC2H5)3 and C12F25C2H4Si(OC2H5)3 molecules and thus applied in membrane distillation (MD) process of NaCl solutions. Grafting efficiency and hydrophobicity were evaluated by contact angle measurement, atomic force microscopy, scanning electron microscopy, nitrogen adsorption/desorption, and liquid entry pressure measurement of water. Desalination of NaCl solutions was performed using the modified hydrophobic membranes in air gap MD (AGMD) and direct contact MD (DCMD) processes in various operating conditions. High values of NaCl retention coefficient (>99%) were reached. The permeate fluxes were in the range 231-3692 g·h(-1)·m(-2), depending on applied experimental conditions. AGMD mode appeared to be more efficient showing higher fluxes and selectivity in desalination. Overall mass transfer coefficients (K) for membranes tested in AGMD were constant over the investigated temperature range. However, K values in DCMD increased at elevated temperature. The hydrophobic layer was also stable after 4 years of exposure to open air.

Membrane distillation properties of TiO2 ceramic membranes modified by perfluoroalkylsilanes

Abstract The tubular and planar TiO2 ceramic membranes were modified by grafting with perfluoroalkylsilanes (PFAS) molecules. Two types of PFAS were used for grafting process: 1H,1H,2H,2H-perfluorooctyltriethoxysilane (C6) and 1H,1H,2H,2H-perfluorotetradecyltriethoxysilane (C12). Studies showed that hydrophilic surface of titania ceramic membranes can be efficiently modified as a results of the proposed grafting method. Grafting efficiency of the tubular membranes was determined by measurement of liquid water entry pressure (LEPw), whereas grafting efficiency of planar membranes was verified by contact angle measurement. The contact angle values of the planar membranes are 130 and 140° for grafting with C6 and C12, respectively. The LEPw of the tubular membranes increased from 2 bar to 10 bar after modification by C12, whereas the LEPw values were constant at 2 bar when TiO2 membrane was modified by C6 molecules. It was found that water contact angle, LEPw, and water flux in the membrane distillation (MD)...

Application of membrane techniques in a water softening process

Abstract The paper presents the results of tests carried out on selected membranes, SEPA (Osmonics Inc., USA). The efficiency of membrane water softening was evaluated on the basis of permeate flux and the physicochemical analysis of raw water and permeate. The transport-separation properties of the membranes were determined using (a) the model solutions of NaCl and MgSO4 and (b) the natural waters of high degree of hardness. The performed tests indicate that the DS-5-DK and DS-3-SE membranes may be applied to the softening of water for drinking and household purposes. The model based on the extended Nernst—Planck and the Donnan equations has been quantitatively fitted to the experimental data. The obtained values of model parameters indicate that in the case of RO membranes a mechanism other than the Donnan exclusion is responsible for the high retention of ions. The membrane filtration modelling will be performed in the next stage of project.

Modelling of nanofiltration in softening water

In this work, the results of membrane filtration of natural water together with theoretical description (modelling) are presented. The obtained results were described in terms of the semi-empirical mass transport models and the extended Nernst-Planck equation. The model of NF based on that equation, taking into account membrane structural parameters and ionic composition of waters, effective for ternary systems, in the case of real multi-ionic solutions (no. of ions 8) needs further improvement.

Transport number of counterions in ion-exchange membranes

Abstract The transport number of counterions in ion-exchange membranes (Nafion, Neosepta) has been predicted using the homogeneous and capillary models of transport. In the case of capillary model, two distributions of ions — described by the traditional and modified by Gur Boltzmann equations — have been applied. It has been found that the homogeneous model based on the experimental sorption and the capillary model, with the traditional Boltzmann equation, predict the transport number relatively well. The only exception is the anion-exchange membrane Neosepta AM1 in HCl solutions, because of facilitated transport of protons through that membrane. It has been proved that the sorption given by the Boltzmann equation is always higher than that given by the modified Boltzmann equation and than the Donnan sorption. The modified Boltzmann equation, successful in predicting partition coefficient in Nafion 117 membrane equilibrated with H 2 SO 4 solutions and salt mixture solutions, as reported by other authors, failed here.

Irreversible thermodynamics of transport across charged membranes. Part V. Isothermal transport through anion-exchange membranes and macroscopic resistance coefficients

Abstract Membrane properties: swelling, Donnan sorption, conductivity, transport numbers; and isothermal transports: diffusional, pressure driven, osmotic and electro-osmotic of the acid (HCl) and salt (NaCl) across two anion-exchange membranes Neosepta AM-1 and AFN-7 (Tokuyama Corp. Japan) are presented and discussed. Experiments have been performed aimed at the detailed analysis of transport phenomena applying irreversible thermodynamics. In this paper the ion-ion, ion-water and ion-polymer network interactions are discussed in terms of the molar straight, r ii , and cross, r ik , resistance coefficients. The effect of strong cation-anion and co-ion-membrane interactions have been discussed from the point of view of the composition and state of internal liquid phase. The results point out again that the permselectivity of operating membranes depends not only on the properties of the networks but not less on the mutual interactions of the species moving within. These interactions may oppose or accelerate permeations of individual ions.

Irreversible thermodynamics of transport across charged membranes. Part VI. Frictional interactions and coupling effects in transport of acid through anion exchange membranes

Abstract Having performed experiments described in [1–3] the friction coefficients,fik, coupling coefficients, qik, and diffusion indexes for ions and water, D i , have been computed in order to discuss the interactions on transport of acid (HCl) through anion exchange membranes. Two membranes were examined — diffusion dialysis Neosepta AFN-7 and standard grade Neosepta AM-1 (Tokuyama Corp.). The frictional interactions and coupling effects in AFN-7 membrane, the dual mode sorption, high diffusion coefficient, D HCl , and negative reflection coefficient, σ, can be explained postulating the dual mechanism of transport: a simple diffusion of acid dissolved in internal water combined with a kind of facilitated transport of the “absorbed” acid.