Development of polybenzimidazole ultrafiltration hollow-fiber membranes

ABSTRACT Polybenzimidazole (PBI) ultrafiltration (UF) hollow-fiber membranes (HFMs) were fabricated using a continuous fiber-spinning line developed at SRI International. Based on the previously developed fabricating conditions for reverse osmosis (RO) and nanofiltration (NF) HFMs, UF HFMs with a large open pore size (50–100 nm) at the shell barrier layer were obtained by switching the dry-jet wet-spinning process to a complete wet-spinning process. To maximize the membrane permeability, bore solution compositions were formulated based on the previous composition, and 100% isopropanol was noticed leading to the largest open pore size on the lumen side. The flow rate ratio of solutions was adjusted during fiber spinning to reduce the fiber wall thickness and the optimized wall thickness, 95 μm was obtained to sustain a running at 20 psi when the flow rates of bore solution and dope solution were 0.35 and 0.9 mL/min, respectively. With the above optimal fabricating protocol, a PBI UF HFM with a pure water flux of 58 LMH at 20 psi was fabricated and its pore size was measured to be 21–25 nm by capillary flow porometry. The resulting UF HFMs showed a good anti-fouling performance in a series of filtration tests with humic acid, bentonite clay, and bovine serum albumin as foulants.