Remarkably enhanced gas separation properties of PIM-1 at sub-ambient temperatures

Abstract

Sub-ambient temperature membrane-based separation is attracting more and more attention in solving the industrial energy intensive separation challenges. However, the research on low temperature gas separation properties of polymeric membranes is limited. Here, gas separation performance of an intrinsic microporous polymer (PIM-1) at temperatures of −30, −20, −10, 0, 10, and 30 °C were fully characterized for the first time. As the temperature decreases, there was a continuous drop in He, H2, N2, O2, CH4 and CO2 permeability coupled with a sharply increased ideal gas pair selectivity with the overall performance gradually outperformed the latest trade-off curves for H2/N2, O2/N2, CO2/CH4 and CO2/N2. In which, the O2 and CO2 permeability of PIM-1 at −30 °C reached as much as 159 and 1380 Barrer, combined with O2/N2 and CO2/N2 ideal selectivity of 9.35 and 81.2, respectively. The drop in permeability originated from the decresaed diffusion coefficients that overweigh the solubility increase, whereas the increased ideal selectivity was due to the enhanced ideal diffusion selectivity (aD), especially the energetic factor of the ideal diffusivity selectivity upon decreasing temperatures. The higher performance induced by low temperatures derived from the shrinkage of the micropore in PIM-1 to more size sieving ultra-micropore region. Additionally, an O2 permeability of 157 Barrer and O2/N2 selectivity of 8.0 for mixed-gas at −20 °C under upstream pressure of 16 bar was observed. The results indicate that PIM-1 operates at sub-ambient temperature has great perspective in gas separation applications.