(196d) Ionic Liquids Based Membranes for Gas Separation

A large number of undesired gases (e.g. CO₂, NH₃) inevitably emitted from the industries, causing serious environmental problems, like greenhouse effect, fog and haze. Meanwhile, CO₂ and NH₃ are basic raw materials to produce important chemicals, such as dimethyl carbonate, ethylene glycol and urea. Therefore, developing novel technologies for efficient gas separation is crucial. Among available methods, membrane gas separation is promising alternative due to high energy efficiency, small footprint and easy operation. However, the trade-off between permeability and selectivity of the membrane materials is still challenged. Ionic liquids (ILs) as a novel medium possess negligible vapor pressure, designable property and high gas affinity, making them widely applied in CO₂ capture and NH₃ separation. The unique properties of ILs incorporated into membranes will significantly influence membrane microstructures and separation performances, thus breaking through the trade-off limitation.

In this work, strategies including construction of nanochannels, regulation of interfacial properties and enhancement of gas affinity are used to design and fabricate novel functional ILs based membranes. The IL/polymer blended membranes were developed for efficient CO₂ capture. Due to the concurrent effect of the soft chain of Pebax copolymer and the inherent fluid nature and high CO₂ absorption ability of ILs, the CO₂ separation performance of IL/polymer blended membranes were improved. It was found that the continuous fluid phase was formed in the blended membranes with high IL content, enhancing the CO₂ solubility and diffusivity. Besides, ILs with ammonia interaction sites were introduced into sulfonated copolymer to fabricate hybrid membranes for NH₃ separation. The NH₃ permeability and selectivity of the hybrid membrane was simultaneously improved. The NH₃ permeability is up to 3248 Barrer and the NH₃/N₂ ideal selectivity reaches 1662. The various characterizations and simulations revealed that continuous ionic domains with well-distributed ILs were formed in the ILs/Nexar hybrid membranes, contributing to forming interconnected channels for enhanced NH₃ transport. In this case, addition of the ILs into the Nexar matrix significantly improves NH₃ separation performance.