Low-cost, regenerable composite zeolite X beads derived from kaolin via microwave-assisted synthesis and ion exchange for CO₂ capture

This study investigates the carbon-capture capabilities of zeolite X beads synthesized from kaolin using microwave heating, which reduces synthesis time and costs. Forming the material into beads allows for its use in fixed-bed column systems, thereby overcoming the high pressure drops and operational difficulties inherent to using fine powders. The use of microwave heating reduced the conventional hydrothermal crystallization to just 4 h. The synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer–Emmett–Teller (BET) method, and were evaluated for CO 2 adsorption. Potassium-exchanged beads (KX-B) outperformed the sodium-exchanged counterparts (NaX-B), exhibiting a 2.5-fold increase in breakthrough time under identical test conditions. Under humid conditions, KX-B showed a lower overall capacity drop (25.4% vs. 34.9% for NaX-B) and maintained a steady baseline over five consecutive adsorption-desorption cycles, whereas NaX-B suffered a 9% capacity reduction. Kinetic models for CO 2 adsorption showed excellent correlation (R 2 > 0.95), and successful validation on a pilot-scale column confirmed the material's potential for industrial scale-up. In conclusion, microwave-synthesized zeolite beads from alternative sources represent a promising, low-cost, and effective adsorbent suitable for practical flue gas treatment.