Preparation of Polybenzimidazole Hollow-Fiber Membranes for Reverse Osmosis and Nanofiltration by Changing the Spinning Air Gap

Abstract

High-performance polybenzimidazole (PBI) hollow-fiber membranes (HFMs) were fabricated through a continuous dry-jet wet spinning process at SRI International. By adjusting the spinning air gap from 4″ (10.2 cm) to 0.5″ (1.3 cm), the HFM pore sizes were enlarged dramatically without any significant change of the fiber dimensional size and barrier layer thickness. When fabricated with an air gap of 2.5″ (6.4 cm) and a surface modified by NaClO solution, the PBI HFM performance was comparable to that of a commercial reverse osmosis (RO) HFM product from Toyobo in terms of salt (NaCl) rejection and water permeability. The PBI RO HFM was positively surface charged in acidic conditions (pH < 7), which enhanced salt rejection via the Donnan effect. With an air gap of 1.5″ (3.8 cm), the PBI HFM rejected MgSO4 and Na2SO4 above 95%, a result that compares favorably with that achieved by nanofiltration. In addition, the PBI HFM has a defect-free structure with an ultra-thin barrier layer and porous sublayer. We believe PBI HFMs are ideal for water purification and can be readily commercialized.

Polybenzimidazoles (PBIs) and state-of-the-art PBI hollow fiber membranes for water, organic solvent and gas separations: a review

“…Therefore, the early developed PBI RO HFMs were used in two specic applications; namely, seawater desalination in harsh environments and the recovery of washing water from space vehicles at pasteurization temperatures. 177 Recently, both Wang et al 178 and Wales et al 179 fabricated PBI RO HFMs without nger-like macrovoids from PBI/DMAc/ PVP/IPA dopes using MeOH/IPA mixtures as the internal and external coagulants. Fig.…”

“…Recently, both Wang et al 178 and Wales et al 179 fabricated PBI RO HFMs without finger-like macrovoids from PBI/DMAc/PVP/IPA dopes using MeOH/IPA mixtures as the internal and external coagulants. Fig.…”

“…16 shows one of their morphologies. 178 The PBI hollow fiber membranes exhibited good separation performance with a pure water permeability of 0.07 L m −2 h −1 bar −1 and a NaCl rejection of 99.0% after being treated with a 1000 ppm NaClO solution for 1 h. These performances were comparable to the commercial CTA RO HFMs produced by Toyobo Co. Ltd. 178 The PBI HFM demonstrated the stable operation of a single-stage RO system for treating concentrated flue gas desulfurization (FGD) wastewater with a salt rejection of 97%. 179 However, since polyamide-based thin-film composite (TFC) membranes invented in the 1980s 180,181 via in situ interfacial polymerization have impressively high RO performance and currently dominate the market of seawater desalination, the importance of PBI RO membranes has been significantly reduced.…”

Flue Gas Desulfurization (FGD) Wastewater Treatment Using Polybenzimidazole (PBI) Hollow Fiber (HF) Membranes

“…The bore solution and coagulation bath are non-solvent mixtures of IPA and methanol. The membrane formed has an integrally skinned asymmetric structure, with the dense skin layer on the shell (outer) side and the porous support on the lumen side (inside); the full fabrication method is published elsewhere [32]. The produced membranes have a 275-µm inner diameter (ID) and 550-µm outer diameter (OD).…”

“…Because of this, PBI membranes have been used in a wide range of applications, including those for fuel cells [25], high-temperature gas separations [26][27][28], nano filtration [29], and forward osmosis [30]. Our group has previously developed PBI hollow fiber membranes for use in gas separation and desalination applications [31][32][33][34][35]. However, to the best of our knowledge, this is the first time that PBI has been used for treating FGD WW.…”