Ionic Liquid Confined in Mesoporous Polymer Membrane with Improved Stability for CO₂/N₂ Separation.

Ming Tan,Jingting Lu,Heqing Jiang,Yang Zhang

doi:10.3390/nano7100299

Abstract

Supported ionic liquid membranes (SILMs) have a promising prospect of application in flue gas separation, owing to its high permeability and selectivity of CO2. However, existing SILMs have the disadvantage of poor stability due to the loss of ionic liquid from the large pores of the macroporous support. In this study, a novel SILM with high stability was developed by confining ionic liquid in a mesoporous polymer membrane. First, a mesoporous polymer membrane derived from a soluble, low-molecular-weight phenolic resin precursor was deposited on a porous Al2O3 support, and then 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) was immobilized inside mesopores of phenolic resin, forming the SILM under vacuum. Effects of trans-membrane pressure difference on the SILM separation performance were investigated by measuring the permeances of CO2 and N2. The SILM exhibits a high ideal CO2/N2 selectivity of 40, and an actual selectivity of approximately 25 in a mixed gas (50% CO2 and 50% N2) at a trans-membrane pressure difference of 2.5 bar. Compared to [emim][BF4] supported by polyethersulfone membrane with a pore size of around 0.45 μm, the [emim][BF4] confined in a mesoporous polymer membrane exhibits an improved stability, and its separation performance remained stable for 40 h under a trans-membrane pressure difference of 1.5 bar in a mixed gas before the measurement was intentionally stopped.

Highlights

Membrane-related processes including gas separation membranes and supported ionic liquid membranes (SILMs) are considered to be very promising technologies
The application of SILMs in industry is still limited because ionic liquid in this kind of membrane is mainly immobilized in the support by capillary forces, and can leak out from the larger pores of the support [6,7,17], whose pore size distribution is wide under a high trans-membrane pressure difference
The Fourier-transform infrared (FTIR) spectrum of [emim][BF4] confined in the mesoporous polymer membrane on the Al2O3 support shows a strong band at 1055 cm−1 arising from B–F stretching in BF4− and another band at 1173 cm−1 arising from the in-plane C–H deformation vibration of the imidazole ring [27], suggesting that ionic liquid [emim][BF4] was immobilized in the mesopores of the polymer phenolic resin

Summary

Introduction

Membrane-related processes including gas separation membranes and supported ionic liquid membranes (SILMs) are considered to be very promising technologies. The application of SILMs in industry is still limited because ionic liquid in this kind of membrane is mainly immobilized in the support by capillary forces, and can leak out from the larger pores of the support [6,7,17], whose pore size distribution is wide under a high trans-membrane pressure difference. Neves et al observed that the membrane weight of an SILM in a hydrophilic support decreased continuously at a trans-membrane pressure difference of 1 bar [18]. Ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate [emim][BF4] confined in a mesoporous polymer membrane with high stability was developed. A mesoporous polymer membrane was deposited on a porous Al2O3 support by self-assembly of triblock copolymers with soluble, low-molecular-weight phenolic resin precursors, followed by high-temperature treatment under Ar flow. By confining ionic liquid into the mesopores of the polymer, an improved stability was achieved

Results and Discussion

Gas Permeation Measurements

Characterization

Conclusions