Fluorine-Functionalized Nanoporous Polymers for Selective Adsorption/Separation of Ethylene, C₁–C₃ Alkanes, and CO₂

Four nonfluorinated and fluorinated nanoporous polymers [PAN-5H, PAN-5F, PAN-2F, and PAN-2(CF3)] were synthesized from a triazine-based tetramine with benzaldehyde, pentafluorobenzaldehyde, 3,5-difluorobenzaldehyde, and 3,5-bis(trifluoromethyl)benzaldehyde, respectively. It is interestingly found that the porosity parameters and selective adsorptions of CO2 and light hydrocarbons strongly depend not only on the number and kind of fluorine atoms and fluorinated groups, but also on the substituted position on the phenyl rings in the fluorinated porous polymers. Relative to PAN-5H and PAN-5F, PAN-2F, and PAN-2(CF3) with phenyls meta-substituted by two fluorinated groups exhibit considerably increased BET surface areas from 502 to 1269 m2/g. At 298 K and 1 bar, the uptakes of C3H8, C2H6, and C2H4 in PAN-2F reach 4.62, 3.64, and 3.20 mmol/g, respectively, whereas PAN-5F exhibits the highest adsorption selectivities of C3H8/CH4 (372.3), C3H8/CO2 (33.2), C2H6/CH4 (21.8), C3H8/C2H6 (9.4), and CO2/CH4 (7.1) among the four polymers. The dynamic breakthrough experiments demonstrate that the mixed gases of C2H6/C2H4, C3H8/CH4, C2H6/CH4, and CO2/CH4 can be separated by the fluorinated polymers under ambient condition. The achieved results are significant for understanding the effects of fluorine-functionalization on the separation of ethylene and CO2 from light hydrocarbons in nanoporous polymers.