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

Ultrathin, multilayered membranes of polyvinylamine (PVA) and polyvinylsulfate (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 MgCl ₂ and MgSO ₄ from feed solutions of 1 and 10 mM concentration independently from the operative pressure applied. The rejection of NaCl and Na ₂ SO ₄ 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 Mg ²⁺ , 97.0 ± 1% of Ca ²⁺ , and 92.5 ± 1% of Na ⁺ were rejected at 40 bar, and from non-diluted seawater, 98 ± 1% of Mg ²⁺ , 96.4 ± 1% of Ca ²⁺ , 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.