Preparation And CO₂ Adsorption Properties Of NaA And NaX Molecular Sieves Derived From Coal Fly Ash

Coal fly ash as a solid waste of coal-fired power generation was large amount produced recently accompanied by the acceleration of industrial processes,which leads to the waste of natural resources such as silica and alumina element.In addition,CO2 is the primary greenhouse gas harmful to environment.It is necessary to develop novel technology to capture CO2 from coal-fired flue gas.In this thesis,zeolite molecular sieves are synthesized by alkali melting-hydrothermal method using coal fly ash.The resulting materials are applied to CO2 adsorbents,which promotes the pollution control and carbon reduction developments.The main contents and conclusions are as follows:The optimal pickling process was discussed by combining orthogonal experimental method with control and variable method to remove Fe3+ and Ca2+under the premise of Al3+ remaining.The results show that the best condition is at a concentration of 3 mol/L,stirring for 80 min and a liquid-solid ratio of 4 ml/g.NaA and NaX zeolite molecular sieves were synthesized by alkali melting-hydrothermal method and characterized on structure and morphology.The influence of precursors and ash/alkali ratio on their synthesis was investigated by control variable method.The optimal process parameters for the synthetic NaA zeolite sieve are ash/alkali ratio of 1.2,roasting temperature of 650℃,solid-liquid ratio of 1:6,mixing time of 2 h,aging time of 1 h and crystallization time of 12 h;the optimal process parameters for NaX zeolite sieve are ash/alkali ratio of 1:1.2,roasting temperature of 650℃,solid-liquid ratio of 1:12,stirring time of 1 h,aging time of 2 h,and crystallization time of 12 h.CO2 adsorption and desorption performance of NaA and NaX zeolite molecular sieves synthesized under different process parameters were evaluated.The results show that the best adsorption temperature with the maximum capacity of 2.44 mmol/g for NaX and 1.64 mmol/g for NaA.It suggests that the zeolite molecular sieves provide a suitable temperature,which can stimulate the best adsorption performance.The adsorption-desorption recycling performance of NaA and NaX zeolite molecular sieve were tested four times and compared.The results show that the adsorption capacity of NaA molecular sieve decreased by 6.1%,and the adsorption capacity of NaX molecular sieve decreased by 4.5%,indicating that the NaX molecular sieve has better recycling renewable performance.