Highly efficient separation of C1-C3 alkanes and CO2 in carbazole-based nanoporous organic polymers

Abstract

The rational design and preparation of nanoporous organic polymers (NOPs) with high-efficiency separation of natural gas remains challenging. Two carbazole-based NOPs, CNOP-3 and CNOP-4, are prepared via a facile Friedel-Crafts (FC) hydroxyalkylation reaction using inexpensive carbazole and tetrakis(4-aldehydephenyl)methane (TFPM) and 1,3,5,7-tetrakis(4′-aldehydephenyl)adamantane (TFPAd), respectively. The surface areas and pore size of spherical particles CNOPs range from 769 m2/g and 0.52 nm to 1007 m2/g and 1.14 nm, respectively. Additionally, the porosity parameters of the polymers, interactions between the gases and the polymer skeleton, and the physicochemical parameters of gases (e.g., polarizabilities, critical temperatures, molecular sizes) strongly influence the adsorption behaviors of light hydrocarbons, including propane (C3H8), ethane (C2H6), and methane (CH4). In addition, the CNOPs with high nanoporosity and rich polar N–H group demonstrated a significant adsorption of CO2 (72.3–83.4 cm3·g−1) at 273 K/100 kPa. Notably, at 298 K/100 kPa, the adsorption selectivities of C3H8/CH4, C2H6/CH4, CO2/CH4, and C3H8/C2H6 also reach 370, 25.3, 8.1, and 10.3, respectively, outperforming the previously reported nanoporous materials. These results indicate that the as-synthesized CNOPs derived from tetrahedral geometry building blocks and carbazole can efficiently separate C3H8, C2H6, CO2, and CH4 from natural gas under ambient conditions.