Effect of primary structure on permselectivity of ultrathin semipermeable polybenzimidazole membrane

Abstract

A series of polybenzimidazoles (PBIs) with different main chains and sulfonated PBI were successfully synthesized from the corresponding dicarboxylic acids and 3,3'-diaminobenzidine for the formation of ultrathin, single-component, and semipermeable membranes. Furthermore, the covalently crosslinked PBI membrane was prepared by the reaction of sulfonated PBI with divinyl sulfone. Their water transport properties were evaluated under a reverse osmosis mode and compared with the primary structure based on the water permeability (A) and salt permeability (B) values normalized by the membrane thickness. It was found that the A and B values of the PBIs were improved with increasing the weight ratio of the imidazole rings per repeating unit, the introduction of sulfonate group as the hydrophilic group to the PBI was an effective way to enhance the A value, and the crosslinked structure enhanced the salt rejection rate (R) value while maintaining the water flux.

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

“…The desalination performance of PBI HF was sensitive to pH of the feed solution because the N-H functional groups in the imidazole ring have a lone pair on the nitrogen that acts as a proton acceptor. In an aqueous solution, the PBI membrane surface tends to be positively charged [5,31], and its rejection of salt is enhanced because it repels cations in the solution due to the Donnan exclusion effect. As is shown in Figure 9, the PBI HF rejects NaCl above 95% when the pH value is lower than 7.…”

“…After the post treatment, the salt rejection rate at 300 psi (20.7 bar) was boosted to 99.0% and the corresponding water flux decreased to 1.47 LMH. The PBI is known to possess a good anti-chlorine capability because of its molecular structure [31] and a technical report prepared by Celanese Research Company claims that PBI fibers retain their physical properties and do not suffer chemical degradation even when they are soaked in a 10-ppm free chlorine solution at pH 5.5 over 28 d [35]. However, the salt rejection achieved using NaClO solution in this experiment leads us to believe that PBI HF desalination performance may be influenced by chlorine.…”

Enhancing water flux through semipermeable polybenzimidazole membranes by adding surfactant‐treated CNTs

“…PBI was synthesized by polycondensation of 3,3’‐diaminobenzidine and isophthalic acid in PPA (Scheme ). The procedure is as follows: 3,3’‐diaminobenzidine (6.43 g, 30.0 mmol), isophthalic acid (4.98 g, 30 mmol), and polyphosphoric acid (216 g) were added into a two‐necked flask under argon atmosphere.…”

“…Polybenzimidazole (PBI) is reported as an excellent CNT dispersant . Moreover, it is an aromatic polymer that is expected to be used for highly chlorine‐tolerant semipermeable membranes due to its excellent properties of good thermal and chemical stabilities . However, the intrinsic water permeability through PBI membranes is not so high .…”

“…Moreover, it is an aromatic polymer that is expected to be used for highly chlorine‐tolerant semipermeable membranes due to its excellent properties of good thermal and chemical stabilities . However, the intrinsic water permeability through PBI membranes is not so high . To address this issue, we fabricated PBI‐based nanocomposite membranes by incorporating CNTs into PBI matrix.…”