PVDF/ionic liquid polymer blends with superior separation performance for removing CO2 from hydrogen and flue gas

We have demonstrated, for the first time, a polymer blend comprising poly(vinylidene fluoride) (PVDF) and a room-temperature ionic liquid (RTIL) that shows a high CO2 permeability of 1778 Barrer with CO2/H2 and CO2/N2 selectivity of 12.9 and 41.1, respectively. The low viscosity RTIL, 1-ethyl-3-methylimidazolium tetracyanoborate ([emim][B(CN)4]) possesses a high CO2 solubility, and plays a significant role in CO2 separation, whereas PVDF provides the mechanical strength to the blend membranes. A series of PVDF/[emim][B(CN)4] polymer blends with different compositions were tested for their gas separation performance involving H2, N2 and CO2 in both pure gas and mixed gas conditions. Both optical observation and Maxwell predictions confirm the heterogeneous nature of the PVDF/[emim][B(CN)4] system. However, compared to miscible ionic liquid based blends, where molecular level interactions may restrain chain flexibility and reduce gas permeability, heterogeneous PVDF/RTIL blend systems show far superior gas transport properties. Most of these blend membranes outperform most reported materials and their gas transport and separation capabilities fall within the attractive region bound by the “2008 Robeson Upper Limit” for CO2/H2 and CO2/N2 gas pairs, and are also very stable at trans-membrane pressure up to 5 atm. Therefore, they are potential materials for H2 purification and CO2 capture from hydrogen production and flue gas.