Effect of temperature on ion transport in nanofiltration membranes: Diffusion, convection and electromigration

Abstract

Nanofiltration performance as a function of feed temperature is relevant to several industrial settings including pretreatment for scale control in thermal desalination. Understanding of solute transport as a function of temperature is critical for effective membrane and system design. In this study, nanofiltration is modeled at 22, 40 and 50 o C using the Donnan Steric Pore Model with dielectric exclusion (DSPM-DE).This modeling includes the temperature dependence of the three modes of solute transport, namely the convective, electromigrative, and diffusive modes, and the three mechanisms of solute exclusion, namely Donnan, steric, and dielectric exclusion. The effect of temperature is captured through the variation of membrane parameters and solvent and ionic mobilities with temperature. We compare the most abundant ionic compound in natural water, sodium-chloride with magnesium-chloride to portray how the salt passage and rejection change for a 1:1 salt compared to a 2:1 salt, and we analyze Arabian Gulf seawater to understand how rejection of scale-forming ions, such as Mg 2+ and Ca 2+ , is affected by feed temperature.In all cases, solute transport increases with temperature, attributed predominantly to the cumulative effect of membrane parameters and only to a small extent (up to 5%) to the solvent viscosity and ion diffusivity together.Keywords: Nanofiltration, Temperature, Ion transport, Desalination

A review of polymeric membranes and processes for potable water reuse

“…In NF, solute rejection occurs as a result of several exclusion and transport mechanisms. Solutes are excluded from the membrane through steric, dielectric, and Donnan exclusion [38] and, in some cases, by adsorption to the membrane surface [4]. Solute rejection is also a function of the relative transport resistances of solutes and water.…”

“…Solute rejection is also a function of the relative transport resistances of solutes and water. Solute transport occurs through three mechanisms, according to the extended Nernst-Planck equation (see Ref [38]): (1) convection of solute with the flowing water, (2) diffusion down the concentration gradient across the membrane, (3) electromigration down the potential gradient that develops across the membrane due to the unequal diffusion rates of different ions. Water transport is generally modeled using a modified Hagen-Poiseuille equation (see Refs.…”

Factors contributing to the change in permeate quality upon temperature variation in nanofiltration

“…Our previous work, reference [18], explained the effect of temperature on individual ion transport modes in NF, i.e. diffusion, convection and electromigration, as well as the effect of temperature on partitioning mechanisms.…”

Integrated Valorization of Desalination Brine through NaOH Recovery: Opportunities and Challenges

“…A common method of removing Ca 2+ and Mg 2+ through precipitation is the use of sodium carbonate (Na 2 CO 3 )a nd NaOH to produce calcium carbonate (CaCO 3 )a nd magnesium hydroxide (Mg(OH) 2 )salts,which can remove up to 96 and 99 %o fc alcium and magnesium ions,r espectively,f rom the NF permeate. [22][23][24] Additionally,N Fh as different configurations,such as flat sheet, spiral-wound, [25,26] or hollow fiber. Alternatively,insearch of effective methods to eliminate divalent ions,r ecent work on cross-linked layer-by-layer polyelectrolyte nanofiltration hollow fiber membranes by Liu et al [16] and Labban et al [17] has demonstrated the selective rejection of multivalent ions at exceedingly low pressures, showing that advanced NF membranes may be useful for removing scalants from the feed stream without the precipitation step.A dditionally,c arbon nanotube composite and graphene oxide-incorporated polymeric membranes have been shown to exhibit greater mechanical stability and ability to purify water.…”

“…Like most membrane-based processes,NFcan be operated at different pressures,t emperatures,f lowrates, and concentrations,which can all affect the energy efficiency and consumption of the process. [22][23][24] Additionally,N Fh as different configurations,such as flat sheet, spiral-wound, [25,26] or hollow fiber. [27] While all three configurations have been implemented at the lab-scale,the spiral-wound configuration is the most prevalent in industrial settings.Reig et al studied the reliability of al ab-scale flat sheet configuration to approximate the results of an industrial-scale spiral-wound configuration.…”