Improving gas permeation performance of PDMS by incorporating hollow polyimide nanoparticles with microporous shells and preparing defect-free composite membranes for gas separation

Recently, various types of hollow materials have been added into polymer matrices to improve the gas permeation and separation performance of polymer materials. In this study, hollow polyimide (PI) nanoparticles with microporous shells were synthesized by interfacial polymerization between 4,4-(9-fluorenylidene)-dianiline and 1,2,4,5-benzenetetracarbonyl tetrachloride in the microemulsion. Free-standing polydimethylsiloxane (PDMS)/hollow PI nanoparticles mixed matrix membranes were prepared and the gas permeation-separation performance was investigated. The hollow and porous structure of the nanoparticles was well-preserved in membranes, which reduced the mass transport resistance. The permeability firstly increased and then decreased as the nanoparticle loading increased without sacrificing the permselectivity. Compared to the neat PMDS membranes with O2 and CO2 permeability of 786 and 3484 Barrer, respectively, the mixed matrix membranes with 3 wt% hollow PI nanoparticles achieved a O2 permeability up to 1664 Barrer accompanied with an O2/N2 permselectivity of 2.3 and a CO2 permeability up to 6639 Barrer accompanied with a CO2/N2 permselectivity of 9.1 at 35 °C and 0.2 MPa. Mixed-matrix composite membranes were fabricated by dip-coating the porous polyetherimide substrate into a PDMS solution with 3 wt% nanoparticles. The resultant defect-free mixed-matrix composite membrane showed excellent O2 and CO2 permeances of up to 1677 and 6502 GPU, respectively. The air separation measurement showed that the composite membranes could produce oxygen-enriched permeate stream enriched to ca. 30 vol%.