Development of Novel Porous Substrates for Ultrafiltration, Desalination and Water Reclamation - Part II

摘要

Porous, synthetic polymer substrates were developed as support components for composite desalination membranes. The selected material was methyl-brominated poly(bromophenylene oxide), or M-PPO, a hydrophobic polymer readily formulated and cast into large, flat-sheet membranes. Morphological characterization of M-PPO substrates by scanning electron microscope revealed the spongelike matrix structure. Dried substrates could be rewetted by using a wetting agent, e.g., 20 percent acetone in water. Similar M-PPO membranes were previously evaluated in ultrafiltration applications after surface modification with 4-amino-1-naphthalene sulfonic acid sodium salt. Preparation of composite membranes involved deposition of a dense, ultrathin, permselective layer on the porous substrate. Two successful approaches were the in situ polycondensation of two reactive prepolymers to the substrate surface, and the direct application of a dilute polymer solution. Necessary properties of the perm-selective layer included reactive moieties which would crosslink the substrate surface under mild conditions, and the ability to form a continuous, nonporous film upon drying or curing. Commercially available polysulfone substrates were identically modified for comparison. Membranes were evaluated on a recirculating reverse osmosis rig with NaCl, and in some experiments, chlorine, over periods up to 49 days.