In situ fabrication of cross-linked PEO/silica reverse-selective membranes for hydrogen purification

Targeting at hydrogen purification, cross-linked organic–inorganic reverse-selective membranes containing poly(ethylene oxide) (PEO) are fabricated in situ by using functional oligomers (O,O′-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol: Jeffamine® ED-2003) with a high content of PEO and epoxy-functional silanes (3-glycidyloxypropyltrimethoxysilane: GOTMS). Changes in physicochemical properties due to varying silica content have been characterized; including a great decline in melting temperature; an improvement in glassy and degradation temperature, and the suppression of PEO crystallinity. The strong affinity between quadrupolar CO2 and polar ethylene oxide (EO) groups enhances the CO2/H2 separation performance of hybrid membranes, which can be further tuned by controlling the organic/inorganic ratio. The organic–inorganic hybrid membrane with 90 wt% of ED-2003 demonstrates an appealing CO2 permeability of 367 Barrer with an attractive CO2/H2 selectivity of 8.95 at 3.5 atm and 35 °C. The transport performance trend with composition variations is explained by analyzing the calculated solubility and diffusivity based on the solution-diffusion mechanism. Moreover, CO2 permeability increases with applied pressure in pure gas tests because of CO2 plasticization phenomena, which is beneficial for CO2/H2 separation. Attributing to CO2 plasticization and CO2 dominant sorption, the mixed gas test results of the membrane containing only 25 wt% ED-2003 show greatly improved CO2/H2 selectivity of 13.2 with CO2 permeability of 148 Barrer at 35 °C compared to pure gas results. Interestingly, at a stipulated CO2 pressure, the inherent tension in cross-linked networks maintains the CO2 permeability stable with the time. The cross-linked organic–inorganic membranes with enhancements in mechanical and thermal properties are promising for industrial-scale hydrogen purification.