Preliminary studies of CO₂ removal from precombustion syngas through pressure swing membrane absorption process with ionic liquid as absorbent

Using 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]) as the absorbent and either hydrophobized porous ceramic tubule or hydrophobized polyether ether ketone (PEEK)-based porous hollow fiber membranes, we have carried out preliminary studies for CO₂ removal from simulated precombustion syngas by a pressure swing membrane absorption process. We have used He as a surrogate for H₂ (40% CO₂ rest He) up to a temperature of 100 C and a pressure of 250 psig. A novel 5-valve system was designed to improve product quality. The optimal duration for the key absorption step was determined, and the influence of helium-rich product withdrawal time was investigated. Temperature increase will degrade product quality, so adding polyamidoamine dendrimer of generation 0 to [bmim][DCA] will mitigate the temperature effect, and 15 wt % dendrimer in [bmim][DCA] showed the best performance. Feed pressure increase will degrade helium product quality, while it is beneficial for CO₂ product quality, since more CO₂ will be absorbed with a higher feed pressure. When feed gas pressure was 250 psig at CO₂ side ∼88.2% CO₂-enriched gas product was produced. Using a simulated two-stage large PEEK module system, with a 14.0% CO₂ balance helium gas mixture, helium product with CO₂ concentration as low as 4.2-5.8% could be achieved at different temperatures. A brief analysis has been provided to explain why a PEEK membrane module shows much better performance than the ceramic tubule.