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

Wang, Li; Cao, Tianchi; Dykstra, J.E.; Porada, S.; Biesheuvel, P.M.; Elimelech, Menachem

doi:10.1021/acs.est.1c05649

Cited by 121 publications

(106 citation statements)

References 60 publications

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“…We note that such a performance evaluation framework was developed on the basis of the solution-diffusion model and the assumption that B is a constant for a given salt and a given membrane ( 50 ). However, recent literature rightfully questioned the validity of the solution-diffusion model and assumption of B being a constant and an intrinsic membrane property parameter ( 51 , 52 ). Therefore, the comparison between performance of the MARIP membrane and that of the existing membranes, especially those measured with different solution and operating conditions, should be interpreted with caution.…”

Section: Discussionmentioning

confidence: 99%

Metal-organic framework enables ultraselective polyamide membrane for desalination and water reuse

et al. 2022

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While reverse osmosis (RO) is the leading technology to address the global challenge of water scarcity through desalination and potable reuse of wastewater, current RO membranes fall short in rejecting certain harmful constituents from seawater (e.g., boron) and wastewater [e.g., N -nitrosodimethylamine (NDMA)]. In this study, we develop an ultraselective polyamide (PA) membrane by enhancing interfacial polymerization with amphiphilic metal-organic framework (MOF) nanoflakes. These MOF nanoflakes horizontally align at the water/hexane interface to accelerate the transport of diamine monomers across the interface and retain gas bubbles and heat of the reaction in the interfacial reaction zone. These mechanisms synergistically lead to the formation of a crumpled and ultrathin PA nanofilm with an intrinsic thickness of ~5 nm and a high cross-linking degree of ~98%. The resulting PA membrane delivers exceptional desalination performance that is beyond the existing upper bound of permselectivity and exhibited very high rejection (>90%) of boron and NDMA unmatched by state-of-the-art RO membranes.

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Section: Discussionmentioning

confidence: 99%

Metal-organic framework enables ultraselective polyamide membrane for desalination and water reuse

et al. 2022

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“…The solution–diffusion model is the most widely used model to describe transport in polymeric reverse osmosis membranes . However, recent studies ,− have challenged the key assumptions used in the solution–diffusion model for transport of water in reverse osmosis membranes. Molecular simulations can be used to assess the validity of these continuum-based models by rigorously studying the nature of driving forces within membranes (e.g., pressure-driven or concentration-driven transport).…”

Section: Discussionmentioning

confidence: 99%

Molecular Simulations to Elucidate Transport Phenomena in Polymeric Membranes

Heiranian

DuChanois

Ritt

et al. 2022

Environ. Sci. Technol.

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Despite decades of dominance in separation technology, progress in the design and development of high-performance polymer-based membranes has been incremental. Recent advances in materials science and chemical synthesis provide opportunities for molecular-level design of next-generation membrane materials. Such designs necessitate a fundamental understanding of transport and separation mechanisms at the molecular scale. Molecular simulations are important tools that could lead to the development of fundamental structure–property–performance relationships for advancing membrane design. In this Perspective, we assess the application and capability of molecular simulations to understand the mechanisms of ion and water transport across polymeric membranes. Additionally, we discuss the reliability of molecular models in mimicking the structure and chemistry of nanochannels and transport pathways in polymeric membranes. We conclude by providing research directions for resolving key knowledge gaps related to transport phenomena in polymeric membranes and for the construction of structure–property–performance relationships for the design of next-generation membranes.

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“…69 The interpretation of f as an electrostatic driving force leads to the Nernst−Plank equation for electromigration, the extension of which can model salt transport in reverse osmosis, including advection. 70 Our considerations also include the interpretation of f as a low-Reynolds-number drag force from a uniform flow velocity, relevant for processes such as reverse osmosis. 8,66 The potential field G(z) constitutes the membrane as a finite energy barrier (or attractive well) in the system and originates from the microscopic interactions between penetrants and the membrane.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The latter generally represents any uniform driving force other than the former two contributions, such as external electrostatic, gravitational, and centrifugal forces, or active forces as in biology . The interpretation of f as an electrostatic driving force leads to the Nernst–Plank equation for electromigration, the extension of which can model salt transport in reverse osmosis, including advection . Our considerations also include the interpretation of f as a low-Reynolds-number drag force from a uniform flow velocity, relevant for processes such as reverse osmosis. , …”

Section: Introductionmentioning

confidence: 99%

Permeability of Polymer Membranes beyond Linear Response

et al. 2022

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The permeability of a membrane to solute penetrants is well defined on the linear response level simply as the ratio of penetrants' flux and concentration gradient at the membrane boundary layers. However, nonlinearities emerge in the flux−force relation j(f) for large driving forces f, in which the definition of permeability becomes ambiguous. Here, we study nonequilibrium membrane permeation orchestrated by a generic driving force using penetrant-and monomer-resolved computer simulations of transport in a polymer network, supported by exact solutions of the Smoluchowski (drift−diffusion) equation in the stationary state. In the simulations, we consider the transport across a finite polymer membrane immersed in a reservoir of penetrants, addressing one-and two-component penetrant systems. We calculate the f-dependent inhomogeneous steady-state density profiles, boundary layer concentrations, and fluxes of the penetrants. The Smoluchowski approach, using solely coarse-grained equilibrium partitioning and diffusion profiles as input, exhibits remarkable qualitative agreement with our nonequilibrium simulations, which serves for rationalization of the observations. We discuss possible definitions of nonequilibrium, f-dependent permeability, distinguishing between "system" and "membrane" permeabilities. In particular, we introduce the concept of dif ferential permeability as a response to f. The latter turns out to be a highly nonmonotonic function of f for low-permeable systems, demonstrating how a differential permselectivity is substantially tunable by the driving force beyond linear response.

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

Cited by 121 publications

References 60 publications

Metal-organic framework enables ultraselective polyamide membrane for desalination and water reuse

Metal-organic framework enables ultraselective polyamide membrane for desalination and water reuse

Molecular Simulations to Elucidate Transport Phenomena in Polymeric Membranes

Permeability of Polymer Membranes beyond Linear Response

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