AgBF4/[emim][BF4] supported ionic liquid membrane for carbon monoxide/nitrogen separation

Abstract

In this paper, AgBF4/[emim][BF4] supported ionic liquid membranes (SILMs) were prepared successfully for CO/N2 separation using nitrogen pressure immobilization procedures. The incorporation of AgBF4 could decrease membrane weight loss, improve the pressure-resistant ability, and keep the critical pressure (0.45 MPa) of the SILMs. The high viscosity and undissolved AgBF4 solids in membrane liquid would disturb gas molecular transport through membrane and give rise to the gas transport resistance. Therefore, the gas permeability decreased remarkably with increasing AgBF4 carrier content in the membrane. When the molar ratio of AgBF4 to [emim][BF4] increased from 0:1 to 0.3:1, the CO/N2 selectivity of the SILMs showed a great increase from ∼1 to ∼9 at 20 °C and 0.4 MPa, suggesting that AgBF4 was an effective carrier for CO facilitated transport. The permeabilities of N2 and CO increased at higher transmembrane pressure, indicating that molecular transport would dominate the transport process at high pressure. The temperature-dependent gas permeability followed the Arrhenius equation. Moreover, the differences between the activation energies of CO and N2 became larger after introducing AgBF4, resulting in more obvious decrease in the CO/N2 selectivity at higher operating temperature.