Mechanisms and models for water transport in reverse osmosis membranes: history, critical assessment, and recent developments

Heiranian, Mohammad; Fan, Hanqing; Wang, Li; Lu, Xinglin; Elimelech, Menachem

doi:10.1039/d3cs00395g

Cited by 38 publications

(6 citation statements)

References 109 publications

(304 reference statements)

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“…Solvent flow under pressure leads to a porosity gradient, with the membrane being more compacted at the downstream side. Notably, this porosity or solvent concentration gradient was erroneously interpreted in past studies as evidence for solvent transport by a solution-diffusion mechanism ( 35 ). In addition, we demonstrate that solvent permeance is influenced by solvent viscosity and the affinity of the solvent to the membrane.…”

Section: Discussionmentioning

confidence: 99%

The physical basis for solvent flow in organic solvent nanofiltration

Fan,

He,

Heiranian

et al. 2024

Sci. Adv.

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Organic solvent nanofiltration (OSN) is an emerging membrane technology that could revolutionize chemical separations in numerous vital industries. Despite its significance, there remains a lack of fundamental understanding of solvent transport mechanisms in OSN membranes. Here, we use an extended Flory-Rehner theory, nonequilibrium molecular dynamic simulations, and organic solvent transport experiments to demonstrate that solvent flow in OSN membranes is driven by a pressure gradient. We show that solvent molecules migrate as clusters through interconnected pathways within the membrane pore structure, challenging the widely accepted diffusion-based view of solvent transport in OSN. We further reveal that solvent permeance is dependent on solvent affinity to the OSN membrane, which, in turn, controls the membrane pore structure. Our fundamental insights lay the scientific groundwork for the development of next-generation OSN membranes.

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Section: Discussionmentioning

confidence: 99%

The physical basis for solvent flow in organic solvent nanofiltration

Fan,

He,

Heiranian

et al. 2024

Sci. Adv.

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“…Numerous studies have initially concentrated on developing continuum-based transport models [ 13 , 14 ] aimed at providing insights into the separation properties at the nanometer scale. However, continuum-based models possess limitations: (i) they do not take into account the discrete nature of matter and its impact on the properties of the confined liquid, and therefore they use either the properties of the bulk-phase liquid, or the properties under confinement are fitting parameters for these models, and (ii) they tend to be more descriptive than predictive due to their dependence on fitting parameters (some of which are likely to be dependent on the composition of the liquid, preventing “universal” calibration of the model from fits made on a series of experiments conducted with a “reference” liquid.).…”

Section: Introductionmentioning

confidence: 99%

Multiscale modelling of transport in polymer-based reverse-osmosis/nanofiltration membranes: present and future

Zhu,

Szymczyk,

Ghoufi

2024

Discover Nano

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Nanofiltration (NF) and reverse osmosis (RO) processes are physical separation technologies used to remove contaminants from liquid streams by employing dense polymer-based membranes with nanometric voids that confine fluids at the nanoscale. At this level, physical properties such as solvent and solute permeabilities are intricately linked to molecular interactions. Initially, numerous studies focused on developing macroscopic transport models to gain insights into separation properties at the nanometer scale. However, continuum-based models have limitations in nanoconfined situations that can be overcome by force field molecular simulations. Continuum-based models heavily rely on bulk properties, often neglecting critical factors like liquid structuring, pore geometry, and molecular/chemical specifics. Molecular/mesoscale simulations, while encompassing these details, often face limitations in time and spatial scales. Therefore, achieving a comprehensive understanding of transport requires a synergistic integration of both approaches through a multiscale approach that effectively combines and merges both scales. This review aims to provide a comprehensive overview of the state-of-the-art in multiscale modeling of transport through NF/RO membranes, spanning from the nanoscale to continuum media.

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“…Water can flow through a coarse porous membrane, like those used in early research [ 3 , 9 ], or even capillary walls with pores about 5 nm diameter [ 10 ], in more or less its bulk form. Current indications are that the membranes used in the purification of water by reverse osmosis, although densely structured, may be sufficiently porous to accommodate water in bulk form as well [ 7 ]. Carbon nanotubes of, say, about 1 nm diameter (two to three water molecules abreast) convey water in interesting structural modifications from bulk [ 11 ].…”

Section: Introductionmentioning

confidence: 99%

A hard sphere model for single-file water transport across biological membranes

Manning

2024

Eur. Phys. J. E

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We use Gürsey’s statistical mechanics of a one-dimensional fluid to find a formula for the $$P_\textrm{f}/P_\textrm{d}$$ P f / P d ratio in the transport of hard spheres across a membrane through a narrow channel that can accommodate molecular movement only in single file. $$P_\textrm{f}$$ P f is the membrane permeability for osmotic flow and $$P_\textrm{d}$$ P d the permeability for exchange across the membrane in the absence of osmotic flow. The deviation of the ratio from unity indicates the degree of cooperative transport relative to ordinary diffusion of independent molecules. In contrast to an early idea that $$P_\textrm{f}/P_\textrm{d}$$ P f / P d must be equal to the number of molecules in the channel, regardless of the physical nature of the interactions among the molecules, we find a functional dependence on the fractional occupancy of the length of the channel by the hard spheres. We also attempt a random walk calculation for $$P_\textrm{d}$$ P d individually, which gives a result for $$P_\textrm{f}$$ P f as well when combined with the ratio. Graphical Abstract The convection/diffusion ratio for hard spheres in single-file transport

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Mechanisms and models for water transport in reverse osmosis membranes: history, critical assessment, and recent developments

Abstract: Water scarcity is one of the greatest societal challenges facing humanity.

Cited by 38 publications

References 109 publications

The physical basis for solvent flow in organic solvent nanofiltration

The physical basis for solvent flow in organic solvent nanofiltration

Multiscale modelling of transport in polymer-based reverse-osmosis/nanofiltration membranes: present and future

A hard sphere model for single-file water transport across biological membranes

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