(401aq) Composite Ionic Liquid and Dense Polymeric Membranes for CO2/N2 and CO2/CH4 Gas Separation at Elevated Pressures

Different types of ionic liquids (ILs) were blended with polysulfone (PSF) to produce functional dense polymer-supported IL membranes (DPSILMs). The main aim was to investigate the applicability of the DPSILMs in high-pressure CO₂ separation from N₂ and CH₄ streams with less or no IL loss. The DPSILMs showed a clear chemical and physical change in the PSF structure and a good IL distribution in PSF. CO₂/N₂ and CO₂/CH₄ binary mixtures (5 mol% CO₂) were used.

CO₂/N₂ separation results obtained from both systems showed that the addition of [C₄mim][NTf₂], [DIP-C₄mim][NTf₂], and [N₄₄₄₁][formate] to PSF increased the separation efficiency of CO₂. However, CO₂/N₂ selectivity decreased with the addition of [P₄₄₄₁][formate]. The optimum IL concentrations for CO₂/N₂ separation are 0.5 wt% [C₄mim][NTf₂] and [DIP- C₄mim][NTf₂], 50 wt% for [P₄₄₄₁][formate], and 25 wt% for [N₄₄₄₁][formate].

On the other hand, all of the used ILs showed increased CO₂/CH₄ selectivity compared to that of pure PSF. The highest CO₂/CH₄ selectivities were obtained with DPSILMs having low IL concentrations hence the optimum IL concentrations are 2.5 wt% for [C₄mim][NTf₂] and [DIP- C₄mim][NTf₂], 5 wt% for [P₄₄₄₁][formate], and 0.5 wt% for [N₄₄₄₁][formate].

Stability measurements on DPSILMs were conducted with regards to IL loss. DPSILMs incorporated [N₄₄₄₁][formate] and [P₄₄₄₁][formate] exhibited small loss of IL compared to that reported in literature. Conversely, no loss of [C₄mim][NTf₂] and [DIP- C₄mim][NTf₂] was observed. Thus, the synthesized DPSILMs are stable at high pressures for long durations.