Synthesis Of Waste Fly Ash Based Heteroatomic Molecular Sieves And Its CO₂/H₂O Adsorption Properties

Since the industrial revolution,CO₂ concentration in atmosphere has increased greatly because of the combustion of fossil fuels.The increase of CO₂ concentration leads to serious greenhouse effect and global warming.Coal-fired power plants are one of the most CO₂emitting industries.Combustible components in coal are converted to CO₂ and released into the atmosphere causing greenhouse effect,and non-combustible components are converted to fly ash which takes up too much land.Due to the large amount of water vapor contained in the power plant flue gas,the adsorption capacity of commonly used adsorbents is reduced in this environment.Therefore,synthesizing heteroatom molecular sieve with coal fly ash as silicon source is of great significance.In this investigation,High purity heteroatomic molecular sieves SGU-29 and ETS-10 was synthesized by coal fly ash with two-step hydrothermal method.Then,CO₂ pure-component adsorption properties and CO₂/H2O binary-component adsorption properties of ETS-10 and SGU-29 was surveyed.In order to synthesize high-purity SGU-29,the optimal synthesis conditions were explored by experiment.The samples were characterized by XRD,FTIR and TGA to obtain the optimal conditions for the synthesis of SGU-29.The optimal conditions for the synthesis of SGU-29 are pH=10.6,Si/Cu=6 and crystallization time is 5 day.The sample synthesized under optimal condition was characterized with DTG,SEM,XRF and surface area analyzer.The results of DTG exhibits that the synthesized sample has a better thermal stability and its structure does not been damaged at 900℃.The results of SEM exhibits that the micro topography of synthesized sample is square bipyramid crystal.The results of XRF exhibits that the main chemical elements of synthesized sample is are Si,Cu,Ti,Na and K,and Al in the fly ash has disappeared.The results of surface area analyzer exhibits that the specific surface area is 741m2/g.The results all above exhibit high purity SGU-29 was synthesized using fly ash as silicon source.In order to explore the CO₂ adsorption property of SGU-29,adsorption kinetic model,adsorption thermodynamics analysis,adsorption equilibrium equation and CO₂/H2O binary adsorption experiment were carried out.The result of adsorption kinetic model analysis exhibits that waste ash based SGU-29 has a high CO₂ adsorption capacity and a high adsorption rate.The CO₂ uptake of SGU-29 is 1.63 mmol/g at 60℃,and the CO₂ uptake can reach 90%of equilibrium uptake.In order to explore CO₂ adsorption capacity of SGU-29 in the surrounding of the industrial practical application,binary-component adsorption equipment was built up.The result exhibits that SGU-29 can still maintain the adsorption capacity of 0.76mmol/g under RH=71%.In order to explore the CO₂ adsorption property of SGU-29,adsorption kinetic model,adsorption thermodynamics analysis,adsorption equilibrium equation and CO₂/H2O binary adsorption experiment were carried out。The results exhibit that CO₂ uptake of ETS-10 is 1.55mmol/g at 60℃ and it can still maintain the adsorption capacity of 0.81mmol/g under RH=25%.Both heteroatom molecular sieves are able to maintain high adsorption capacity in high humidity environments.However,SGU-29 adsorption performance is better.