Preparation and properties of poly(acrylic acid) composite membranes

Abstract

Abstract A new type of membrane has been prepared for hyperfiltration (reverse osmosis) desalination that is essentially a very thin polyelectrolyte membrane. It is prepared by casting an aqueous solution of a polyelectrolyte, specifically poly(acrylic acid) (PAA), directly on one surface of a finely porous support membrane. In hyperfiltration tests, these composite membranes exhibit desalination performance comparable in dilute solutions to that observed with cellulose acetate membranes of the Loeb‐Sourirajan type. The water flux through these membranes is linear in the pressure up to 100 atm. Salt rejection is a function of pressure; it is also a function of the concentration of the feed solution and the charge of the counterion, in qualitative agreement with the Donnan ion‐exclusion mechanism. Typical long‐term results range from water fluxes of 2 × 10 −3 g/cm 2 ‐sec (50 gal/ft 2 ‐day) and 80% salt rejection to 0.2 × 10 −3 g/cm 2 ‐sec (5 gal/ft 2 ‐day) and >99.5% salt rejection at 1500 psi with 0.3 wt‐% NaCl. These membranes appear to be useful for brackish water desalination.