ULTRATHIN MEMBRANES FOR GAS SEPARATION AND PERVAPORATION PREPARED UPON ELECTROSTATIC SELF-ASSEMBLY OF POLYELECTROLYTES

Composite membranes with ultrathin separation layer were prepared by a lternating electrostatic adsorption of cationic and anionic compounds (polyelectrolytes and bolaamphiphiles) at porous supporting membranes such as Celgard 2400, PAN/PET (a polyethyleneterephthalate fleece coat ed with a thin layer of polyacrylonitrile) and Isopore (an etched ion- track polycarbonate membrane). As the ionic compounds poly(allylamine hydrochloride) (PAH), poly(styrenesulfonate sodium salt) (PSS), 3,6-di phenylpyrrolo-[3,4-c]-pyrole-4,4'-disulfonic acid and 10,12-docosadiyn e-1,22-disulfate disodium salt were used. The composite membranes were studied on their gas permeation and pervaporation properties. The ads orption of 20 layer pairs of PAH/PSS at PAN/PET membranes was sufficie nt to reduce the argon flow to 7% of the initial value, while 60 bilay ers reduced the flow to 0.1%. Gas flow rates of oxygen, nitrogen and a rgon were nearly identical, while the flow rate of carbon dioxide was higher by a factor of up to 2.4. Toluene/heptane pervaporation through composite membranes of 60 bilayers of PAH/PSS on PAN/PET gave a tolue ne enrichment from 20% in the feed to 24% in the permeate, while for e thanol/water permeation a water enrichment from 3% in the feed up to 5 0% in the permeate was found. (C) 1998 Elsevier Science S.A. All right s reserved.