Composite ionic liquid–polymer–catalyst membranes for reactive separation of hydrogen from carbon monoxide

Abstract

Novel composite ionic liquid and polyimide membranes with dissolved RuCl3 catalyst for H2/CO reactive separation were fabricated to combine gas diffusive separation and water-gas shift reaction. The CO concentration in the membranes is reduced via its reaction with H2O to form CO2 and H2, catalysed by the Ru carbonyl complex which forms in the reaction between dissolved RuCl3 and CO. In order to optimize the membrane configurations and operating conditions, water-gas shift reaction turnover frequencies (TOFs) of the membranes with various concentrations of ionic liquid and RuCl3 were determined at different pressures, temperatures and times-on-stream on a purpose-built test rig. The results show that the ionic liquid, [C4mim][OTf], improves TOFs by increasing the solubilities of H2O and the gases solubilities within the membrane. TOFs were found to increase initially, but reduce as time-on-stream increased, due to the formation and subsequent evaporation of a Ru carbonyl complex. Lower temperature and lower concentration of [C4mim][OTf] were found to minimize the loss of the catalyst. It is suggested that the 2wt% RuCl3·xH2O+20wt% [C4mim][OTf]+PI membrane operated at 140°C and 2bar has the best combination of reactivity and durability.