Facile Preparation of Triphenylamine-Based Nanoporous Organic Polymers for Adsorption/Separation of C₁–C₃ Hydrocarbons and CO₂ in Natural Gas

The development of porous organic polymers with high gas adsorption and separation performances by a facile preparation process has progressively addressed the urgent demand for cost-effective adsorbents employed in energy-efficient purification and recovery processes. However, these polymeric materials are still poorly developed for the practical adsorption and separation of light C1–C3 hydrocarbon components, such as methane (CH4), ethane (C2H6), and propane (C3H8), from natural gas under ambient conditions. The present work addresses this issue by reporting the facile preparation of two triphenylamine-based nanoporous organic polymers (ANOPs), ANOP-M and ANOP-A, via acid-catalyzed Friedel–Crafts hydroxyalkylation polymerization using commercially available triphenylamine with tetrakis(4-formylphenyl)methane and 1,3,5,7-tetrakis(4′-formylphenyl)adamantane monomers, respectively. The specific surface areas of the ANOPs vary from 1052 to 1272 m2/g, with average pore sizes of 1.36 nm. Furthermore, the ANOP networks are demonstrated to be highly interconnected. Interestingly, the ANOPs have different adsorption capacities toward different C1–C3 hydrocarbons (CH4, C2H6, and C3H8) and CO2 molecules, and ANOP-M shows the highest uptake of C3H8 (97.9 cm3/g) and C2H6 (64.6 cm3/g) among these gas molecules at 298 K and 1 bar. Analyses reveal that these differences depend greatly upon the physical parameters of the gas molecules (e.g., polarizability, critical temperature, and molecular size) and the porosity parameters of the ANOPs, as well as the affinity between the gases and the polymer skeleton. The adsorption selectivities of the ANOPs in conjunction with C3H8/CH4, C2H6/CH4, C3H8/C2H6, C3H8/CO2, C2H6/CO2, and CO2/CH4 gas mixtures also differ significantly and exhibit values of 151–164, 17.5–17.8, 6.16–6.43, 14.2–15.1, 2.93–3.17, and 4.35–4.70, respectively. Accordingly, the facile preparation and excellent light hydrocarbon adsorption and separation properties of the ANOPs make these materials highly promising for applications involving the adsorption/separation of C1–C3 light hydrocarbons and CO2 from natural gas under ambient conditions.