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Communication Dans Un Congrès Année : 2010

Atomistic model of two commercial reverse osmosis membranes

Résumé

Although the main application of reverse osmosis (RO) filtration remains the separation or concentration of electrolytes from aqueous solvents (e.g. desalination), new promising applications including the recycling or purification of organic-rich effluents used in fermentation processes (bio-ethanol and other biofuel productions). Currently, no model exists to predict a priori the selectivity of given RO (mostly in aromatic polyamide) membrane to non-electrolyte organic compounds, such as non-dissociated acids, aldehydes, esters or aromatic compounds. The complication arises due to the mutual diffusion of water and small solutes within membrane, whose swelling is controlled by the stiffness of polymer segments and their cross-linking rates. The general objective of this study is to build atomistic-scale models of typical commercial aromatic polyamide (APA) membranes in order to analyze the contribution of their polymer chemical structure on swelling rate to water and on mutual diffusion mechanisms in the bulk. As APA membranes are polymerized in-situ as approximately 200 nm thick layer, our computational effort was combined with experimental isolation and deformulation of two commercial APA membranes (references: ESPA2 and CPA2, Hydranautics Membranes, USA) to provide both i) initial assumptions to build the atomistic model (monomers composition, average cross-linking rate, approximate swelling rate) and ii) independent reference data to validate the generated model at different relative humidity (X-ray structure factors). The active APA layer was separated from support by removing iteratively each support layer with N,N-dimethylformamide (DMF). Macroscopic properties such as swelling rates, sorption isotherms were assessed by ellipsometry and Intelligent Gravimetric Analyser respectively. A maximum swelling rate of 38% was determined. A cross-linking rate of 65 % was inferred from chemical composition analyses in X-ray photoelectron spectroscopy (XPS) and attenuated-total reflection mode Fourier transform IR (ATR-FTIR). A first atomistic model including the number of desired monomers and water content was built by a conventional compression box technique and classical molecular dynamics code (Discover, Accelrys, San-Diego). Cross-linking was subsequently performed by applying a specific reactive force-field within our own software. The degree of freedoms were i) the initial ratios in monomers (benzene-1,3,5-tricarbonyle chloride with a connectivity of 3, benzene-1,3-diamine with a connectivity of 2), ii) the initial length of block-oligomers (ranging from 5 to 62). Each system was finally equilibrated during long-term isobaric and isothermal molecular dynamics simulations at 600 K and 298 K. Final structure factors were in good agreement with RX scattering spectra.
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Dates et versions

hal-01594404 , version 1 (26-09-2017)

Identifiants

  • HAL Id : hal-01594404 , version 1
  • PRODINRA : 350259

Citer

Roland Kieffer, Olivier Vitrac, Bernard Rousseau, Claire Fargues, Marie-Laure Lameloise. Atomistic model of two commercial reverse osmosis membranes. International Workshop "Molecular Modeling and Simulation for Industrial Applications", Mar 2010, Würzburg, Germany. ⟨hal-01594404⟩
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