Comparative Studies on CO2 Adsorption Performance of Different Morphologies of Silicalite-1 Zeolites Synthesized from Fly Ash

Solid waste fly ash has a great impact on the environment and pollutes water, air and soil to different degrees. Therefore, it is of great significance to realize the high-value utilization of fly ash. In this paper, high purity SiO₂ was successfully extracted from fly ash by high temperature calcination, alkali fusion activation and pickling. Then silicalite-1 zeolite molecular sieves with different morphologies were synthesized using SiO₂ extracted from solid fly ash as silicon source. The influencing factors such as crystallization time, crystallization temperature, NaOH dosage, TPAOH dosage and different hydrosilica ratios were investigated separately. The results show that under the conditions of crystallization time of 12 h, crystallization temperature of 180 ℃ and molar ratio of water–silicon of 42, the prepared P-S (plate-like silicalite-1) has good morphology, high relative crystallinity and adsorption capacity of CO₂ of 1.89 mmol/g.When the molar ratio of TPA⁺/ SiO₂ was 0.28, the relative crystallinity of the prepared S–S (spherical-like silicalite-1) reached the highest and the adsorption capacity of CO₂ was 1.34 mmol/g.When the molar ratio of NaOH / SiO₂ was 0.11, C-S (cross-type Na-silicalite-1) can be prepared, and the adsorption capacity of CO₂ is only 1.06 mmol/g. The CO₂ adsorption capacities follow P-S > S–S > C-S. The research results can not only pave the way for high-value utilization of fly ash, but alao provide a valuable reference for zeolite-based adsorbents in the adsorption removal or recovery of CO₂.

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