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Membranes 2018, 8(4), 127; https://doi.org/10.3390/membranes8040127

Molecular Dynamics Simulation Study of Polyamide Membrane Structures and RO/FO Water Permeation Properties

1
Center for Membrane and Film Technology, Graduate School of Science, Technology, and Innovation, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
2
Center for Membrane and Film Technology, Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
3
Research and Development Division, Kurita Water Industries Ltd., 1-1 Kawada, Nogi, Shimotsuga, Tochigi 329-0105, Japan
*
Author to whom correspondence should be addressed.
Received: 31 October 2018 / Revised: 17 November 2018 / Accepted: 26 November 2018 / Published: 6 December 2018
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Abstract

Polyamide (PA) membranes possess properties that allow for selective water permeation and salt rejection, and these are widely used for reverse osmotic (RO) desalination of sea water to produce drinking water. In order to design high-performance RO membranes with high levels of water permeability and salt rejection, an understanding of microscopic PA membrane structures is indispensable, and this includes water transport and ion rejection mechanisms on a molecular scale. In this study, two types of virtual PA membranes with different structures and densities were constructed on a computer, and water molecular transport properties through PA membranes were examined on a molecular level via direct reverse/forward osmosis (RO/FO) filtration molecular dynamics (MD) simulations. A quasi-non-equilibrium MD simulation technique that uses applied (RO mode) or osmotic (FO mode) pressure differences of several MPa was conducted to estimate water permeability through PA membranes. A simple NVT (Number, Volume, and Temperature constant ensemble)-RO MD simulation method was presented and verified. The simulations of RO and FO water permeability for a dense PA membrane model without a support layer agreed with the experimental value in the RO mode. This PA membrane completely rejected Na+ and Cl ions during a simulation time of several nano-seconds. The naturally dense PA structure showed excellent ion rejection. The effect that the void size of PA structure exerted on water permeability was also examined. View Full-Text
Keywords: molecular dynamics; polyamide; water permeability; reverse osmosis; forward osmosis molecular dynamics; polyamide; water permeability; reverse osmosis; forward osmosis
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Yoshioka, T.; Kotaka, K.; Nakagawa, K.; Shintani, T.; Wu, H.-C.; Matsuyama, H.; Fujimura, Y.; Kawakatsu, T. Molecular Dynamics Simulation Study of Polyamide Membrane Structures and RO/FO Water Permeation Properties. Membranes 2018, 8, 127.

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