Double cross-linked PBI/sPPSU blend dual-layer hollow fiber membranes by DBX and EDA vapor for stable H₂/CO₂ separation at 150°C

Pre-combustion carbon capture from hydrogen production streams has attracted global attention for net-zero carbon emission and producing H 2 as a clean energy. Due to the industrial demands for effective separation, process simplicity and cost savings, this work has investigated the blend membranes made of polybenzimidazole (PBI) and sulfonated polyphenylsulfone (sPPSU) with different degrees of sulfonation for H 2 /CO 2 separation at high temperatures. Dual-layer hollow fiber membranes consisting of PBI/sPPSU blends as an outer layer and polysulfone (PSU) as an inner support layer were co-extruded with aims to reduce material costs and maximize separation performance. The optimized as-spun membrane had an H 2 permeance of 139 GPU and an ideal H 2 /CO 2 selectivity of 14.1. To further improve its separation performance, an ethylenediamine (EDA) vapor-phase cross-linking modification was applied. The EDA modified membrane had an H 2 permeance of 147 GPU and an ideal H 2 /CO 2 selectivity of 17.3. It also exhibited stable performance under long-term mixed gas tests. However, its separation performance dropped under long-term humid mixed-gas tests. With the aid of α,α′-dibromo-p-xylene (DBX) introduction into PBI/sPPSU dopes and then EDA vapor-crosslinking modification, the resultant membrane not only displayed an ideal H 2 /CO 2 selectivity of 20 but also showed stable long-term performance under humid environments. The newly developed membrane had separation performance exceeding the modified Roberson upper bound under pure-gas, mixed-gas, and humid conditions at 150°C. Molecular dynamics simulation was employed to elucidate how DBX stabilized the membrane structure under humid environments.