A green and efficient strategy for utilizing of coal fly ash to synthesize K-MER zeolite as catalyst for cyanoethylation and adsorbent of CO2

Abstract K-MER zeolites of great crystallinity and purity have been synthesized from coal fly ash (CFA) with the method of microwave and ultrasound collaborative activation (MUCA) for the first time, which significantly improving the extraction efficiency of required components (Si and Al) from CFA in lower energy consumption. After activated in 4 mol/L potassium hydroxide solution for 1 h at 100 °C, the conversion rate of CFA reaches to 53.80 wt% as well as the molar conversion rate of silicon is 75.39%, greatly enhanced in comparison with the methods of only microwave or ultrasound. The MER samples of various morphologies have been prepared through comprehensively adjustments of crystallization time, pressures and dynamic pressure programs. The maximum adsorption volume of CO2 is 47.58 cm3/g at 25 °C as well as 36.55 cm3/g at 0 °C and 34.16 cm3/g at 50 °C. Furthermore, the as-obtained MER zeolites have been utilized as catalysts in cyanoethylatic reaction between methanol and acrylonitrile. The conversion rate of acrylonitrile finally reached up to as high as 99 wt% after reacting for 30 min with pre-pressure of 1.5 MPa. The method of MUCA will provide a new strategy for green utilization and high value-added conversion of CFA.