Effect of nitrogen group on selective separation of CO₂/N₂ in porous polystyrene

Hyper-crosslinked porous polystyrene adsorbents were successfully synthesized from 4-nitrobenzyl chloride using the Friedel-Crafts alkylation reaction. These porous polymer samples were characterized by SEM, TEM, FT-IR and TGA for their morphology, surface functionality and thermal stability. Nitrogen adsorption and desorption at 77K were used for characterizing their pore textural properties. The adsorption properties of CO₂ and N₂ were determined volumetrically at 298K and gas pressures up to 10bar. The experimental results showed that the porous polymer adsorbents have a relatively high N-content (up to 1.05%), a large BET surface area (up to 1275m²/g) and a large pore volume (up to 1.338cm³/g). It was observed that both pore texture and N-content in the porous polymers are equally important for adsorbing CO₂. The equilibrium selectivity for CO₂/N₂ separation on the five samples is well correlated with the N-content and micropore volume percentage in the polymers, and the N-content strongly affects the adsorbent selection parameter. Adding N-functional group in porous polymer adsorbents is an effective way for improving their capability for CO₂/N₂ separation. Using the CO₂ adsorption capacity alone is not sufficient for evaluating adsorbents, and the adsorbent selection parameter is calculated to screen adsorbents for CO₂ capture from flue gas.