title: Does hindered transport theory apply to desalination membranes?
abstract: As reverse osmosis (RO) and nanofiltration polyamide membranes become increasingly used for water purification, prediction of pollutant transport is required for membrane development and process engineering. Many popular models use hindered transport theory (HTT), which considers a spherical solute moving through an array of fluid-filled rigid cylindrical pores. Experiments and molecular dynamic simulations, however, reveal that polyamide membranes have a distinctly different structure of a "molecular sponge", a network of randomly connected voids widely distributed in size. In view of this disagreement, this study critically examined the validity of HTT by directly measuring diffusivities of several alcohols within a polyamide film of commercial RO membrane using attenuated total reflection-FTIR. It is found that measured diffusivities deviate from HTT predictions by as much as 2-3 orders of magnitude. This result indicates that HTT does not adequately describe solute transport in desalination membranes. As a more adequate alternative, the concept of random resistor networks is suggested, with resistances described by models of activated transport in "soft" polymers without a sharp size cutoff and with a proper address of solute partitioning.
authors.affiliation: Faculty of Chemical Engineering and Technology, University of Zagreb , Marulićev trg 19, 10000 Zagreb, Croatia.
authors.forename: Emil
authors.initials: E
authors.lastname: Dražević
authors.forename: Krešimir
authors.initials: K
authors.lastname: Košutić
authors.forename: Vesselin
authors.initials: V
authors.lastname: Kolev
authors.forename: Viatcheslav
authors.initials: V
authors.lastname: Freger
mesh_terms: D004058:Diffusion; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force; D008962:Models, Theoretical; D009757:Nylons / Q000737:chemistry; D009995:Osmosis; D016062:Porosity; D054712:Salinity; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D008567:Membranes, Artificial; D009757:Nylons