Ultra-low pressure water softening: a new approach to membrane construction

The ultra-low pressure water softening properties of a series of novel memb ranes containing cross-linked poly(4-vinylpyridinium) salts incorporated in to the pores of polyethylene or polypropylene microfiltration membranes hav e been examined. It has been shown that these membranes exhibit excellent s eparation properties with high permeabilities at low trans-membrane pressur es. The separation mechanism in these pore-filled membranes is primarily du e to Donnan exclusion, and as such bivalent cations are more strongly rejec ted than monovalent ions. Moreover, it has been shown that relatively large molecules such as sucrose are only rejected to a limited extent. The membr anes have been shown to withstand free chlorine at ambient temperatures. Th e performance of the pore-filled membranes has been shown to compare favora bly with existing state of the art thin-film composite (TFC) nanofiltration membranes (Osmonics Desal-51 and BQO1 and Hydranautics TFV-7450). In contr ast to the TFC membranes, the separating layer in these pore-filled membran es has been shown to be thick, ranging from 80 to 160 mu m. These polyelect rolyte pore-filled membranes offer a new paradigm in the construction of hi gh performance water softening membranes.