Comparison of the Volume Charge Density of Nanofiltration Membranes Obtained from Retention and Conductivity Experiments

Abstract

A version of the Donnan steric-partitioning pore model with dielectrical exclusion (DSPM-DE) has been used to get information on the pore size and charge density of a commercial membrane, NF45 from FilmTec, from its retention of KCl solutions. The conductivity inside the pores has been measured by impedance spectroscopy, and the electric potential drop during retention experiments has also been measured. These experimental data on conductivity and electric potential are analyzed, by using the thermodynamics of irreversible processes and the space charge model, to obtain the pore charge density of the membrane. These two methods give results in fair accordance which probes that the sometimes controversial method of DSPM-DE can give accurate results for the charge as well as for the mean pore size of a nanofiltration membrane. Some clues to improve the way this model can be used are given as well.

Assessment of the hindered transport model in predicting the rejection of trace organic compounds by nanofiltration

“…The absolute value was too large to be meaningful. A few previous studies pointed out that the membrane charge parameter might have lost its physical meaning and was used to compensate for physical phenomena not included in the DSPM model [39,40].) NF270 was determined to have a slightly smaller average pore size and a higher effective thickness, which may explain its lower MWCO than HL.…”

Electrochemical Characterization of a Polymer Inclusion Membrane Made of Cellulose Triacetate and Aliquat 336 and Its Application to Sulfonamides Separation

“…Two separated contributions associated to the membrane (frequency ranging between 10 kHz and 1000 kHz) and the electrolyte solution placed between the membrane and the electrodes (frequency > 1000 kHz) can be observed in Figure 3, which correspond to a depressed semicircle (membrane) and a semicircle (electrolyte solution). This kind of impedance curve is typical of composite systems, in particular it is similar to that exhibited by low permeability systems such as dense non-swollen membranes [31] or nanofiltration/reverse osmosis membranes [32][33][34], and it is related with the significant difference in the electrical characteristics of the two parts forming the composite system: the membrane and the electrolyte solution, respectively. The equivalent circuit for the whole electrolyte(e)/membrane(m) system consists in the addition (series association) of two sub-circuits: a parallel association of a resistance (R) and a capacitor (C) for the electrolyte solution placed between the electrodes and the membrane (R e C e ), plus a parallel association of a resistance and a generalized capacitor (R m Q m ) for the membrane contribution due to a distribution of relaxation times [35] (see Materials and Methods section).…”

“…Two separated contributions associated to the membrane (frequency ranging between 10 kHz and 1000 kHz) and the electrolyte solution placed between the membrane and the electrodes (frequency > 1000 kHz) can be observed in Figure 3, which correspond to a depressed semicircle (membrane) and a semicircle (electrolyte solution). This kind of impedance curve is typical of composite systems, in particular it is similar to that exhibited by low permeability systems such as dense non-swollen membranes [31] or nanofiltration/reverse osmosis membranes [32][33][34], and it is related with the significant difference in the electrical characteristics of the two parts As it can be observed in Figure 2, ∆Φ mbr values for 26% AlqCl/74% CTA and AR204-SZRA-412 membranes are rather similar, being those corresponding to the ion-exchange sample slightly more negative. Moreover, in both cases, ∆Φ mbr values differ significantly from those corresponding to the NaCl solution, which is an indication of the control of both membranes on ions transport.…”

“…This description is only valid for homogeneous systems, which present a unique relaxation time τ (with τ max = 2πRC), but in the case of non-homogeneous systems the Nyquist plot is a depressed semi-circle due to a distribution of relaxation times, then a non-generalized capacitor (usually represented as Q) is considered [35]. Moreover, for composite systems consisting of layers with different electrical characteristics, a series association of semi-circles/depressed semi-circles (one for each layer) is commonly obtained [31][32][33][34]. For NaCl diffusion, the membrane separated a donor solution (c d = 0.01 M) from a receiving diluted solution (c r ), which initially was distilled water (that means, c r o = 0) [39].…”

Decontamination of polluted discharge waters from surface treatment industries by pressure-driven membranes: Removal performances and environmental impact

“…In this model, the mass transfer is described by a coupling between the hindered transport inside the pore and the equilibrium partitioning at the membrane/solution interfaces [41,42]. The transport inside the membrane pores is classically modeled by the so-called extended Nernst-Planck equation, for which the flux of a species results from the combination of various contributions, namely diffusion, convection and electromigration:…”