(386c) Carbon-Dioxide Selective Membranes for High-Pressure Synthesis Gas Purification

Hydrogen is a very important raw material in many industrial processes, such as chemical and refining hydrogenation as well as fuel cell applications.  Most hydrogen is produced by steam reforming of hydrocarbon fuels, such as CH₄, followed by the water gas shift (WGS) reaction.  Thus, the resulting synthesis gas mainly contains H₂ and CO₂, and the removal of CO₂ from H₂ to produce high purity H₂ has become an important industrial process.

In our previous work, we have presented the CO₂-selective facilitated transport membranes for low feed pressure (2 atm) CO₂/H₂ separation for fuel cell applications by incorporating amino groups into either crosslinked poly(vinyl alcohol) (PVA) or sulfonated polybenzimidazole (SPBI) copolymer networks [1].  However, the requirements by the refining and petrochemical industries for the applications of CO₂-selective membranes for CO₂/H₂ separation are more challenging since feed pressures of 220 psia or higher are preferred.  At high pressures, the facilitated transport membranes generally suffer from the carrier saturation problem, which results in lower CO₂ permeability and CO₂/H₂ selectivity.    

In this paper, The CO₂-selective facilitated transport membranes based on both the crosslinked PVA matrix and the SPBI copolymer matrix were synthesized and characterized for high-pressure (220 psia or higher) synthesis gas purification.  The newly synthesized crosslinked PVA-based facilitated transport membranes showed CO₂/H₂ selectivity higher than 30 and CO₂ permeability as high as close to 1000 Barrers (1 Barrer = 10^-10 cm³ (STP) • cm / (cm² • s • cmHg)) for a membranes thickness of 15 – 30 μm at a feed pressure of 220 psia.  The SPBI copolymer-based facilitated transport membranes generally showed lower separation performance because of their lower hydrophilicity.  However, they have the potential to be used for thin membrane preparation by the phase inversion technique because of the high copolymer Tg.  All these facilitated transport membranes have great potential to be used for high-pressure synthesis gas purification.

[1]        H. Bai, W.S.W. Ho, Recent developments in fuel-processing and proton-exchange membranes for fuel cells, Polym. Int. 60 (2011) 26-41 (Review Article).