Study on gas separation by supported liquid membranes applying novel ionic liquids

In the present study, the permeability of H2, N2 and CO2 was investigated through supported liquid membranes prepared by using four types of novel ionic liquids (VACEM 42, VACEM 44, VACEM 47, VACEM 58) under various gas phase pressures (2.2 bar, 1.8 bar, 1.4 bar) and temperatures (30°C, 40°C, 50°C). VACEM type ionic liquids, which are built up of a common hexafluorophosphate anion and different cations, were tailored in order to dissolve CO2. Since CO2 can cause unfavorable changes in the mechanical and chemical properties of the PVDF membranes used as the supporting phase, the stability of the membranes was studied by measuring decrease in H2 permeability after the permeation of CO2. For determining selectivity the membranes were used to separate binary and ternary gas mixtures. It was found that the permeability of CO2 was much higher than the permeability of the other two gases through the membranes prepared with VACEM type ionic liquids. Gas permeability exhibited an increase with increasing temperature and a slight decrease with increasing gas phase pressure. Experiments concerning stability showed that after several CO2 permeations through membranes containing VACEM type ionic liquids the permeability of H2 slightly decreased while the CO2/H2 selectivity improved. It was found that supported ionic liquid membranes prepared with VACEM type ionic liquids could be successfully used in separating CO2 from other gases.

It can be concluded that SILMs prepared with VACEM type ILs have a much higher permeability to CO2 than to H2 and N2 and a high CO2/H2 selectivity therefore they can be successfully applied for the separation of CO2. The gas permeation is effected by the temperature and transmembrane pressure; the increase in temperature increases, while the increase in pressure decreases the membrane permeability. After several cycles of CO2 permeation the membrane permeability shows a slight decrease, less than SILMs prepared with other type of ILs, and the CO2/H2 selectivity increases. Therefore it can be stated that these membranes are more stable.