Improving hypercrosslinked polymer CO2/N2 selective separation through tuning polymer's porous properties: Optimization using RSM-BBD

This study investigates the effect of synthesis and operating parameters on the adsorption of CO₂ and N₂ and the CO₂/N₂ selectivity of a hypercrosslinked adsorbent based on waste-expanded polystyrene. Six factors were examined, including synthesis time, crosslinker and catalyst amounts, adsorption temperature and pressure, and CO₂ percentage in the mixture. The response surface methodology (RSM) and ideal adsorbed solution theory (IAST) were employed to design the experiment. After synthesizing 19 adsorbents under different conditions, characterization tests were conducted. Results indicate that the specific surface area and micropore volume initially increase and then decrease with increased synthesis time, crosslinker, and catalyst amounts. The highest specific surface area and micropore volume were 803.84 m²/g and 0.1355 cm³/g, respectively. CO₂/N₂ selectivity and the adsorption of CO₂ and N₂ also increase and decrease with increased synthesis parameters. Furthermore, it was observed that CO₂ adsorption and CO₂/N₂ selectivity increased with an increase in pressure and CO₂ percentage and a decrease in temperature, while N₂ adsorption decreased. The adsorbents were optimized using RSM to maximize CO₂ adsorption and CO₂/N₂ selectivity with a target of 15 % CO₂ in the gas mixture. The optimal synthesis parameters for the hypercrosslinked adsorbent, including synthesis time, crosslinker, and catalyst amounts, were determined to be approximately 13 hours, 30 mmol, and 30 mmol, respectively. Under optimal conditions for flue gas applications (CO₂:N₂/15:85), the adsorbent demonstrated a CO₂/N₂ selectivity of 11.05, making it suitable for flue gas capture.