Rejection mechanisms for contaminants in polyamide reverse osmosis membranes

Abstract Despite the success of reverse osmosis (RO) for water purification, the molecular-level physico-chemical processes of contaminant rejection are not well understood. Here we carry out non-equilibrium molecular dynamics (NEMD) simulations on a model polyamide RO membrane to understand the mechanisms of transport and rejection of both ionic and inorganic contaminants in water. While it is commonly presumed that the contaminant rejection rate is correlated with the dehydrated solute size, this approximation does not hold for the organic solutes and ions studied. In particular, the rejection of urea (2.4 A radius) is higher than ethanol (2.6 A radius), and the rejections for organic solutes (2.2–2.8 A radius) are lower than Na+ (1.4 A radius) or Cl− (2.3 A radius). We show that this can be explained in terms of the solute accessible intermolecular volume in the membrane and the solute-water pair interaction energy. If the smallest open spaces in the membrane's molecular structure are all larger than the solute size including its hydration shell, then the solute-water pair interaction energy does not matter. However, when the open spaces in the polymeric structure are such that solutes have to shed at least one water molecule to pass through a portion of the membrane molecular structure, as occurs in RO membranes, the pair interaction energy governs solute rejection. The high pair interaction energy for water molecules in the solvation shell for ions makes the water molecules difficult to shed, thus enhancing the rejection of ions. On the other hand, the organic solute-water interaction energies are governed by the water molecules that are hydrogen bonded to the solute. While these hydrogen bonds have pair interaction energies that are much larger than that of the non-hydrogen bonded water molecules in the solute solvation shell, they are significantly less than the ion-water pair interaction energy. Thus, organic solutes more easily shed water molecules than ions to pass through the RO membrane. Since urea molecules have more hydrogen-bonding sites than alcohol molecules, urea forms more hydrogen bonds with the membrane polymer chains leading to a higher rejection of urea than occurs for ethanol, a molecule of similar size but with fewer hydrogen bonding sites. These findings underline the importance of the solute's solvation shell and solute-water-membrane chemistry in the context of reverse osmosis, thus providing new insights into solute transport and rejection in RO membranes.

[1]  P. Keblinski,et al.  Effect of interfacial interactions and nanoscale confinement on octane melting , 2012 .

[2]  B. Mallik,et al.  A first-principles theoretical study of hydrogen-bond dynamics and vibrational spectral diffusion in aqueous ionic solution: Water in the hydration shell of a fluoride ion , 2012 .

[3]  V. Freger,et al.  Does hindered transport theory apply to desalination membranes? , 2014, Environmental Science and Technology.

[4]  A. Mohammad,et al.  Analysis of the Salt Retention of Nanofiltration Membranes Using the Donnan–Steric Partitioning Pore Model , 1999 .

[5]  Junmei Wang,et al.  Development and testing of a general amber force field , 2004, J. Comput. Chem..

[6]  J. G. Wijmans,et al.  The solution-diffusion model: a review , 1995 .

[7]  W. Peukert,et al.  An improved generalized AMBER force field (GAFF) for urea , 2010, Journal of molecular modeling.

[8]  W. L. Jorgensen,et al.  Comparison of simple potential functions for simulating liquid water , 1983 .

[9]  Christopher I. Bayly,et al.  Fast, efficient generation of high‐quality atomic charges. AM1‐BCC model: II. Parameterization and validation , 2002, J. Comput. Chem..

[10]  B. Mallik,et al.  Hydrogen bond and residence dynamics of ion-water and water-water pairs in supercritical aqueous ionic solutions: dependence on ion size and density. , 2006, The Journal of chemical physics.

[11]  Armand Soldera,et al.  Structure and dynamics of water confined in a polyamide reverse-osmosis membrane: A molecular-simulation study , 2014 .

[12]  T. Darden,et al.  Particle mesh Ewald: An N⋅log(N) method for Ewald sums in large systems , 1993 .

[13]  A. Savitzky,et al.  Smoothing and Differentiation of Data by Simplified Least Squares Procedures. , 1964 .

[14]  Weimin Gao,et al.  Understanding water and ion transport behaviour and permeability through poly(amide) thin film composite membrane , 2015 .

[15]  Julian D. Gale,et al.  A computational investigation of the properties of a reverse osmosis membrane , 2010 .

[16]  Anthony Szymczyk,et al.  Molecular simulations of polyamide reverse osmosis membranes , 2014 .

[17]  D. Cahill,et al.  Modeling the effect of charge density in the active layers of reverse osmosis and nanofiltration membranes on the rejection of arsenic(III) and potassium iodide. , 2013, Environmental science & technology.

[18]  Michael Kotelyanskii,et al.  Molecular dynamics simulation study of the mechanisms of water diffusion in a hydrated, amorphous polyamide , 1999 .

[19]  K Schulten,et al.  VMD: visual molecular dynamics. , 1996, Journal of molecular graphics.

[20]  Vesselin Kolev,et al.  Hydration, porosity and water dynamics in the polyamide layer of reverse osmosis membranes: A molecular dynamics study , 2014 .

[21]  Laxmikant V. Kalé,et al.  Scalable molecular dynamics with NAMD , 2005, J. Comput. Chem..

[22]  T. Arnot,et al.  A review of reverse osmosis membrane materials for desalinationDevelopment to date and future poten , 2011 .

[23]  S. Keten,et al.  Regulating Ion Transport in Peptide Nanotubes by Tailoring the Nanotube Lumen Chemistry. , 2015, The journal of physical chemistry letters.

[24]  Nancy Wilkins-Diehr,et al.  XSEDE: Accelerating Scientific Discovery , 2014, Computing in Science & Engineering.

[25]  Anthony Szymczyk,et al.  On the structure and rejection of ions by a polyamide membrane in pressure-driven molecular dynamics simulations , 2015 .

[26]  Benoît Roux,et al.  Computer simulations of water flux and salt permeability of the reverse osmosis FT-30 aromatic polyamide membrane , 2011 .

[27]  A. Fakhru’l-Razi,et al.  Review of technologies for oil and gas produced water treatment. , 2009, Journal of hazardous materials.

[28]  D. Chandler,et al.  Hydrogen-bond kinetics in liquid water , 1996, Nature.

[29]  S. Harvey,et al.  The flying ice cube: Velocity rescaling in molecular dynamics leads to violation of energy equipartition , 1998, J. Comput. Chem..

[30]  S. H. Kim,et al.  Positron annihilation spectroscopic evidence to demonstrate the flux-enhancement mechanism in morphology-controlled thin-film-composite (TFC) membrane. , 2005, Environmental science & technology.

[31]  Ben Corry,et al.  The importance of dehydration in determining ion transport in narrow pores. , 2012, Small.

[32]  Michael Kotelyanskii,et al.  Atomistic simulation of water and salt transport in the reverse osmosis membrane FT-30 , 1998 .

[33]  Jianwen Jiang,et al.  Zeolitic imidazolate framework-8 as a reverse osmosis membrane for water desalination: insight from molecular simulation. , 2011, The Journal of chemical physics.

[34]  Benoît Roux,et al.  Molecular dynamics study of a polymeric reverse osmosis membrane. , 2009, The journal of physical chemistry. B.

[35]  R. S. Dumont,et al.  Nonequilibrium molecular dynamics simulation of water transport through carbon nanotube membranes at low pressure. , 2012, The Journal of chemical physics.

[36]  Benito Jose Marinas,et al.  Absorption of water in the active layer of reverse osmosis membranes , 2009 .

[37]  Menachem Elimelech,et al.  Relating Nanofiltration Membrane Performance to Membrane Charge (Electrokinetic) Characteristics , 2000 .

[38]  R. Baker.  Membrane Technology and Applications , 1999 .

[39]  O. Talu,et al.  Gibbs Dividing Surface and Helium Adsorption , 2003 .

[40]  F. Frimmel,et al.  Parameters influencing the rejection properties of FT30 membranes , 1994 .

[41]  S. Keten,et al.  Tailoring the water structure and transport in nanotubes with tunable interiors. , 2015, Nanoscale.

[42]  Richard M. Lueptow,et al.  Removal of organic contaminants by RO and NF membranes. , 2005, Journal of membrane science.

[43]  D. Cahill,et al.  Physico-chemical integrity of nanofiltration/reverse osmosis membranes during characterization by Rutherford backscattering spectrometry , 2007 .

[44]  Benito Jose Marinas,et al.  Mechanistic interpretation of solute permeation through a fully aromatic polyamide reverse osmosis membrane , 1997 .

[45]  S. Hwang.  Fundamentals of membrane transport , 2011 .

[46]  Richard M. Lueptow,et al.  Membrane rejection of nitrogen compounds. , 2001, Environmental science & technology.

[47]  Miquel Rovira,et al.  Solution-diffusion-film model for the description of pressure-driven trans-membrane transfer of elec , 2011 .

[48]  Abdul Wahab Mohammad,et al.  Characterization and Prediction of Nanofiltration Membrane Performance—A General Assessment , 1998 .

[49]  Julian D. Gale,et al.  Molecular dynamics simulations of the interactions of potential foulant molecules and a reverse osmosis membrane , 2012 .

[50]  J. E. Cadotte,et al.  Interfacial Synthesis in the Preparation of Reverse Osmosis Membranes , 1981 .

[51]  P. Kollman,et al.  Automatic atom type and bond type perception in molecular mechanical calculations. , 2006, Journal of molecular graphics & modelling.

[52]  D. Beglov,et al.  Finite representation of an infinite bulk system: Solvent boundary potential for computer simulations , 1994 .

[53]  Richard M. Lueptow,et al.  Dynamics of water and solute transport in polymeric reverse osmosis membranes via molecular dynamics simulations , 2016, 1607.04627.

[54]  Ken A. Dill,et al.  Molecular driving forces : statistical thermodynamics in biology, chemistry, physics, and nanoscience , 2012 .

[55]  Viatcheslav Freger,et al.  Swelling and morphology of the skin layer of polyamide composite membranes: an atomic force microscopy study. , 2004, Environmental science & technology.

[56]  Car-Parrinello molecular dynamics simulations of Na + -Cl ion pair in liquid water , 2004 .

[57]  M. Reinhard,et al.  Characterization of isolated polyamide thin films of RO and NF membranes using novel TEM techniques , 2010 .

[58]  Gerhard Hummer,et al.  Osmotic water transport through carbon nanotube membranes , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[59]  V. Freger,et al.  Permeability and selectivity of reverse osmosis membranes: correlation to swelling revisited. , 2014, Water research.