Highly Selective Adsorption for Ethylene, Propylene, and Carbon Dioxide in Silver-Ionized Microporous Polyimide

Abstract

This paper presents the sulfonation and silver-ionization modifications using aromatic microporous polyimide (MPI) as precursor to obtain a new Ag+-decorated porous polyimide material (MPI-Ag). FTIR, XPS, and EDX spectra demonstrate the chemical structure of the resultant MPI-Ag and the homogeneously distribution of silver ions within the porous network. The evolution of porosity parameters and elemental compositions of the postmodified polymers and their effects on adsorption/separations of C1–C3 hydrocarbons and CO2 gas are studied in detail. The results show that the modified MPI-Ag exhibits the enhanced affinity for CO2 and the unsaturated hydrocarbons like C2H4 and C3H6 as evidenced by the significantly increased enthalpies of adsorption, Henry’s constants and first virial coefficients. Consequently, at 273 K, the adsorption selectivities of C2H4/C2H6 (0.9) and C3H6/C3H8 (2.0) for MPI dramatically rise to 3.5 and 16.5 for MPI-Ag, respectively. Moreover, the selectivities of C3H6/CH4 (3785) and CO2/CH4 (65.3) are achieved for MPI-Ag, which are among the highest values reported to date for porous materials. The excellent selective adsorptions for unsaturated alkenes and CO2 gas endow MPI-Ag with potential applications in stripping CO2 from natural gas and landfill gas as well as the purification of C2H4 and C3H6 from their mixtures with CH4, C2H6, and C3H6 impurities.