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Computer simulations of water flux and salt permeability of the reverse osmosis FT-30 aromatic polyamide membrane

 

Yun Luo^a, Edward Harder^a,1, Ron S. Faibish^b, Benoit Roux^a,b,*

 

^a Department of Biochemistry and Molecular Biology, The University of Chicago, Gordon Center for Integrative Science, 929 East 57th Street, Chicago, IL 60637, USA

^b Argonne National Laboratory, Argonne, IL 60439, USA

 

Summary

 

Polyamide membranes are synthesized by interfacial polymerization and their performance is checked by their volume flux of water and percentage of salt rejection. Experimentally, it is difficult to study the water and ion dynamics inside membrane structure, but, molecular dynamics (MD) simulation can show these dynamics. Because of cross linkings in the polymer, the structure is complex and can't be drawn for MD simulations. A heuristic approach was used to solve this problem. In this paper, this heuristic approach is used to study the dynamics of water and ions inside FT-30 membrane and compare results with experimental studies.

According to linear response theory, water flux across an FT-30 membrane is computed by Fick's law. From MD calculations, the partition coefficient was determined to be 0.3 while the experimental value is 0.29. The density of model membrane was found to be 1.34 g/cm³ which is close to experimental vlue 1.38 g/cm³. Diffusion equation was used to calculate the diffusive properties of the membrane. The water flux from MD simulation was found to be 2.1 x 10^-6 m/s compared to experimental value of 7.7 x 10^-6 m/s.

The position, pulling force, free energy, and number of water molecules in the first solvation shell are shown in the following figure. The top panel shows these results for sodium ion while the bottom panel shows these values for chloride ions.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reviewer: Aamir Alaud Din