Structural effects of microporous polymers on adsorption/separation of C1–C3 light hydrocarbons and CO2 in natural gas

Abstract

Microporous polymers (PAN-T1 and PAN-T2) with the similar polymer skeleton but considerably different BET surface areas from 1106 to 1563 m2 g−1, micropore surface areas from 250 to 868 m2 g−1 and total pore volumes from 0.84 to 1.09 cm3 g−1 were synthesized utilizing two planar triangular-shaped hexamines to polymerize with para-phthalaldehyde, respectively. The pores in PAN-T2 are quite uniform centering at 1.50 nm, whereas PAN-T1 exhibits the hierarchical pores consisting of ultramicropore (0.48 nm), micropore (1.05 nm) and mesopore (4.71 nm). Of interest is the finding that the high micropore surface areas are more advantageous for the adsorption of C2H6 and C3H8 than CH4 and CO2. The introduction of methyl substituents brings about the increased selectivities for C3H8/CH4, C2H6/CH4 and CO2/CH4, but the selectivities of C3H8/CO2 and C2H6/CO2 exhibit an opposite trend. The effects of porosity parameters and chemical structure on the adsorption of CH4, C2H6, C3H8, CO2, and the separations of binary mixtures for C3H8/CH4, C2H6/CH4, C3H8/CO2, C2H6/CO2 and CO2/CH4 are interpreted in terms of the variations in adsorption enthalpies, Henry constants, first virial coefficients as well as the polarizabilities, critical temperatures and sizes of the adsorbates. The results are helpful to deeply understand the pore-modulation mechanism in microporous polymers and the correlations of porous/chemical structures to the adsorption/separation of CO2 and C1–C3 light hydrocarbons in natural gas.