CO2-selective membranes for hydrogen purification and the effect of carbon monoxide (CO) on its gas separation performance

Industrial hydrogen production may prefer CO2-selective membranes because high-pressure H2 can therefore be produced without additional recompression. In this study, high performance CO2-selective membranes are fabricated by modifying a polymer–silica hybrid matrix (PSHM) with a low molecular weight poly(ethylene glycol) dimethyl ether (PEGDME). The liquid state of PEGDME and its unique end groups eliminate the crystallization tendency of poly(ethylene glycol) (PEG). The methyl end groups in PEGDME hinder hydrogen bonding between the polymer chains and significantly enhance the gas diffusivity. In pure gas tests, the membrane containing 50 wt% additive shows CO2 gas permeability and CO2/H2 selectivity of 1637 Barrers and 13 at 35 °C, respectively. In order to explore the effect of real industrial conditions, the gas separation performance of the newly developed membranes has been studied extensively using binary (CO2/H2) and ternary gas mixtures (CO2/H2/carbon monoxide (CO)). Compared to pure gas performance, the second component (H2) in the binary mixed gas test reduces the CO2 permeability. The presence of CO in the feed gas stream decreases both CO2 and H2 permeability as well as CO2/H2 selectivity as it reduces the concentration of CO2 molecules in the polymer matrix. The mixed gas results affirm the promising applications of the newly developed membranes for H2 purification.

► Liquid state PEGDME increases the gas diffusivity coefficient drastically.
► Methyl end groups in PEGDME hinder hydrogen bonding between polymer chains.
► The morphology of the siloxane network affects the gas separation performance.
► The presence of CO in the feed causes reduction in both CO2 and H2 permeability.
► The membranes are proved to be promising for hydrogen purification.