Towards enhanced CO2 selectivity of the PIM-1 membrane by blending with polyethylene glycol

Abstract

Polymers of intrinsic microporosity are attractive membrane materials for gas separation due to their high specific surface and microporous structure. PIM-1 being the most representative one shows extremely high permeability but moderate selectivity for CO2 separation. In this study, the CO2 selectivity of PIM-1 is remarkably enhanced via blending with polyethylene glycol (PEG). A series of PIM-1/PEG blended membranes are prepared for separation of CO2/N2, CO2/CH4 by varying the molecular weight (MW) and content of PEG. Their structure and physicochemical properties are explicitly characterized including density, morphology and thermostability. The blended membranes have less d-spacing of packed chains than pure PIM-1. The pure gas permeabilities of CO2, N2 and CH4 are measured with varying MW and content of PEG. The PEG blend depresses gas permeability of the PIM-1 membrane but greatly improves the CO2 selectivity, especially for CO2/CH4 separation. The membranes with 2.5wt% PEG at different MWs have excellent separation performance for CO2/CH4 separation, which surmounts the 2008 upper bound line. Specifically the membrane with 3.5wt% PEG of 20kDa has the CO2 permeability of 1952 barrer and CO2/CH4 selectivity of 39.0 that is more than three times that of the pure PIM-1 membrane. The as-prepared PIM-1/PEG membranes have a great potential for CO2 separation.