Modeling permeate pH in RO membranes by the extended Donnan steric partitioning pore model

Zhang, Li; Hamelers, H.V.M.; Biesheuvel, P.M.

doi:10.1016/j.memsci.2020.118511

Cited by 17 publications

(19 citation statements)

References 43 publications

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“…Inside the RO membrane, we consider the interactions among the various species (i.e., ion−water, water− membrane matrix, and ion−membrane matrix interactions) and include hindrance factors for ion transport. The ion flux is governed by diffusion, electromigration, and advection and can be described by the extended Nernst−Planck equation 23,25,28…”

Section: ■ Model Developmentmentioning

confidence: 99%

“…Several continuum modeling approaches assume that the three partitioning mechanisms are independent of each other. ,, However, it is likely that some of these partitioning mechanisms are interrelated. For instance, both steric and dielectric effects are related to the pore size and the ion Stokes radius; hence, the partial dehydration of ions during partitioning into the membrane may be considered in both mechanisms.…”

Section: Model Developmentmentioning

confidence: 99%

“…Inside the RO membrane, we consider the interactions among the various species (i.e., ion–water, water–membrane matrix, and ion–membrane matrix interactions) and include hindrance factors for ion transport. The ion flux is governed by diffusion, electromigration, and advection and can be described by the extended Nernst–Planck equation ,, where J i is the flux of ion i , K c , i and K d , i are the advective and diffusional hindrance factors, respectively, c i is the concentration of ion i , v f is the permeate water velocity, ε is the effective membrane porosity, D i is the bulk ion diffusivity, φ is the dimensionless electrical potential inside the membrane, and x is the dimensionless coordinate through the membrane.…”

Section: Model Developmentmentioning

confidence: 99%

“…Over the past decades, significant efforts have been made to develop mechanistic models describing salt exclusion mechanisms and transport of water and salt through RO membranes. A mean-field Donnan-steric pore (DSP) model was developed to account for partitioning by Donnan equilibrium, steric exclusion, and dielectric exclusion. − However, the model was mainly used to describe salt rejection or passage without a thorough investigation of the effects of operation conditions and membrane properties on desalination performance. Furthermore, previous studies on the DSP model described the hydraulic pressure drop inside the membrane using the Hagen–Poiseuille equation, , neglecting the influence of membrane charge and the resulting electrical potential gradient on the pressure drop across the membrane.…”

Section: Introductionmentioning

confidence: 99%

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Salt and Water Transport in Reverse Osmosis Membranes: Beyond the Solution-Diffusion Model

Wang

Cao

Dykstra

et al. 2021

Environ. Sci. Technol.

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119

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Understanding the salt−water separation mechanisms of reverse osmosis (RO) membranes is critical for the further development and optimization of RO technology. The solutiondiffusion (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.

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Section: ■ Model Developmentmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Salt and Water Transport in Reverse Osmosis Membranes: Beyond the Solution-Diffusion Model

Wang

Cao

Dykstra

et al. 2021

Environ. Sci. Technol.

Self Cite

119

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“…pH is a key factor that strongly influences the membrane and the electrolyte solution, specifically in weak acids [ 35 ], e.g., lactic acid. pH also affects the charge of the active and selective layers of membranes.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of Nanofiltration Membranes for Pure Lactic Acid Permeability

et al. 2022

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Lactic acid (LA) is an organic acid produced by fermentation or chemical synthesis. It plays a crucial role in the pharmaceutical, food and plastic industries. In the fermentation of, for example, grass silage, LA and different compounds are produced. To purify lactic acid, researchers have tried to investigate membrane technology to achieve a high yield of lactic acid permeance. This study tested four commercially available nanofiltration membranes (NF270, MPF-36, Toray NF, and Alfa Laval NF). Nanofiltration experiments were performed to investigate the rejection levels of lactic acid from a binary solution by using distinct molecular weight cut off membranes. All of the experiments were conducted with a lab-scale cross-flow membrane unit. Different operating conditions (pH, temperature) were studied for each membrane; the optimal process condition was found at 25 °C and pH 2.8. With higher temperatures and pH, an increase in LA rejection was observed. The MPF-36 membrane shows the lowest lactic acid rejection yield of 7%, while NF270 has the highest rejection yield of 71% at 25 °C and pH 2.8. These results will be helpful in the future to understand both the interaction of lactic acid permeance through nanofiltration membranes and process scale-up.

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