Facilitated-transport supported ionic liquid membranes for the simultaneous recovery of hydrogen and carbon monoxide from nitrogen-enriched gas mixtures

Abstract

Off-gases with high content of carbon monoxide and hydrogen are often generated after a partial combustion of hydrocarbons in some industrial processes performed in reductive conditions. In these mixtures, both gases are usually accompanied by nitrogen. The selective recovery of these valuable compounds, H2 and CO, employing an efficient membrane technology is sought as a means to reduce the environmental footprint of the industrial activity. In this respect, this work provides fundamental knowledge on the transport properties of H2 through supported ionic liquid membranes (SILMs) prepared with an imidazolium-based room-temperature ionic liquid (RTIL) combined with either a chloride or a chlorocuprate(I) anion; this latter anion has already proved to enhance CO permeability across these SILMs due to a facilitated transport mechanism. Results showed that H2 is more permeable than CO and N2 through these RTILs due to its higher diffusivity. The H2/N2 and H2/CO selectivities through the chloride-based RTIL are 11 and 6, respectively. However, when the RTIL with the chlorocuprate(I) anion is employed instead of the chloride anion, the H2/N2 selectivity does not change whereas the H2/CO selectivity decreases, hence allowing obtaining a gas permeate stream with high content of both H2 and CO, and very low content of N2.