Polyelectrolyte multilayer membranes for desalination of aqueous salt solutions and seawater under reverse osmosis conditions

Ultrathin, multilayered membranes of polyvinylamine (PVA) and polyvinyl sulfate (PVS) were electrostatically adsorbed on a porous polymer (polyacrylonitrile/polyethylene terephthalate) support. Their use for desalination of aqueous salt solutions, diluted and non-diluted artificial seawater was investigated under reverse osmosis conditions. Using 60 layer pairs of PVA/PVS as separating membrane, it was possible to completely reject MgCl2 and MgSO4 from feed solutions of 1 and 10 mM concentration independently from the operative pressure applied. The rejection of NaCl and Na2SO4 increased from 84 and 96 % at 5 bar to 93.5 and 98.5 % at 40 bar, respectively. From diluted seawater (1:10; 1:100; 1:1000), 99 +/- 1 % of Mg2+, 97.0 +/- 1 % of Ca2+ and 92.5 +/- 1 % of Na+ were rejected at 40 bar, and from non-diluted seawater, 98 +/- 1% of Mg2+, 96.4 +/- 1 % of Ca2+, and 74.5 +/- 0.8 % of Na+ were rejected at 40 bar. The permeation flux J increased linearly with the pressure applied. For a membrane of 60 PVA/PVS layer pairs, a flux value of 4 +/- 0.2 L m(-2) h(-1) was found at 40 bar. The influence of the number of deposited layer pairs on R and J was also investigated. (c) 2004 Elsevier B.V. All rights reserved.