Preparation And CO₂ Performance Of Ionic Liquids Based Composite Membranes

Effective separation and capture of CO2 play a significant role in environment,chemical industry and energy.Thus a CO2 separation technology with high performance and low energy is imminent.Membrane separation technology has good application prospects due to its advantages on lower energy consumption,high efficiency,and environmental friendly.In view of the trade-off between permeability and selectivity for polymeric membranes,combination of ionic liquid(IL)and membrane separation technology can improve the gas separation performance of the membrane materials meanwhile overcome the high viscosity and consumption of the IL.In this paper,a series of IL-based composite membranes have been designed and prepared,and ZIF-8 porous materials have been introduced to improve the separation performance and physical stability of the composite membranes.The relationships between different materials have been also studied.The main research contents and achievements were summarized as follows:(1)A serious poly(ether-b-amide-6)(Pebax 1657)+ IL composite membranes have been successfully synthesized and characterized.The IL are[Bmim][BF4]?[Bmim][DCA]?[Bmim][NTf2].The results showed that the imidazolium IL were physically blended with Pebax and have good thermal stability.It reveals that IL acted as a plasticizer in the composite membranes.With an increasing IL content,the crystallinity of the membranes decreased and the polymer chain became more relaxed,resulting in a more amorphous structure and a higher FFV(fractional free volume)of membranes.(2)The CO2 separation performance of Pebax/IL composite membranes with different ionic liquids has been investigated.The results showed that CO2 diffusivity coefficients increased significantly with the addition of IL.The CO2 permeability of different composite membranes were in the order of[Bmim][NTf2]>Pebax/[Bmim][DCA]>Pebax/[Bmim][BF4],which were consistent with the solubility of CO2 in pure IL.While CO2/N2,CO2/CH4 selectivity decreased due to the intrinsically lower selectivity of IL itself(3)The influence of ZIF-8 addition on the structure and separation performance of Pebax/ZIF-8 membranes has been studied.The results showed that the crystallinity of membranes decreased with an increasing ZIF-8 content,and agglomeration occurred resulting in forming non-selective "voids".The addition of ZIF-8 increased the CO2 solubility coefficients and diffusion coefficientsof membranes,but it blocked the diffusion of N2 and CH4.(4)A series of Pebax/ZIF-8/[Bmim][NTf2]three-component composite membranes have been prepared and the relationships between different materials have been also investigated.It was found that the addition of IL had two effects on the gas diffusion:a small amount of IL could fill the non-selective "voids" between ZIF-8 and Pebax,hindering gas diffusion while CO2/N2 selectivity increased.And with the IL increased,IL could decrease crystallinity and increase the fractional free volume of membrane,facilitating gas diffusion while CO2/N2 selectivity decreased.