Preparation On A Zeolite From Coal Fly Ash And Its Adsorption Of CO₂ And CH₄

Coal fly ash is a solid waste that comes from power plant.It occupy farmland,and also cause pollution to the surrounding environment.This paper used coal fly ash which come from Chongqing Luohuang power plant as raw material.The high crystallinity and purity 4A zeolite was synthesized successflilly by the method of alkali fusion followed by hydrothermal treatment.Then used the 4A zeolite which was synthesized on the optimal conditions as raw material,the 5A zeolite was successflilly synthesized by the secondary synthesis processing of ion exchange with CaCl₂ solution.And it was verified that the 5A zeolite synthesized has a good application prospect on CO₂/CH₄ separation.Firstly,this paper analyzed the basic characteristics of fly ash,the phase of fly ash used are mainly composed of mullite,quartz.And its main chemical composition is SiO₂ and Al₂O₃,which was similar with the composition of natural zeolite precursor.This paper used the industrial solid waste coal fly ahs as the raw material,and 4A zeolite was synthesized by the method of alkali fusion followed by hydrothermal treatment.The influence on synthetic samples have been studied by changing the calcination temperature,silica alumina ratio,and crystallization time,and the optimum condition for synthesis of 4A zeolite was determined by the XRD test of the samples.Through repeated experiments,the optimum condition for synthesis of 4A zeolite by the method of alkali fusion followed by hydrothermal treatment was as followed: solid/water was 1:5,calcination temperature was 800°C,alkali ash ratio was 1:1,and crystallization time was 4 hours.The crystallinity of 4A zeolite synthesized on the condition was over 89%.Secondly,used the 4A zeolite which was synthesized on the optimal conditions as raw material,the 5A zeolite was successflilly synthesized by the secondary synthesis processing of ion exchange with CaCl₂ solution,and the optimum condition for synthesis of 5A zeolite was determined by the XRD test,the pore structure and FTIR of the samples.Through repeated experiments,the best concentration of CaCl₂ solution was determined for 3 mol/L.Finally,the adsorption isotherms of single component CO₂ and CH₄ on the 4A zeolite synthesized,5A zeolite synthesized,and commercial 5A zeolite were studied at 298 K over the pressure range of 0–1 MPa.And the pore structure on the influence of the saturated adsorption amount was studied with the molecular sieve pore structure and chemical properties of the zeolite samples.The experimental results show that the adsorption isotherm type of single component CO₂ and CH₄ on the three types of zeolite samples were type I,and the Langmuir model was fit well with the experimental data.Under the same pressure,the adsorption capacity of CO₂ the same sample were greater than the adsorption capacity of CH₄.The adsorbed amounts of 4A zeolite synthesized,5A zeolite synthesized and commercial 5A zeolite for CO₂ were 2.12 mmol/g,2.62 mmol/g and 4.43 mmol/g.The adsorbed amounts of 4A zeolite synthesized,5A zeolite synthesized and commercial 5A zeolite for CH₄ were 1.20 mmol/g,1.56 mmol/g and 2.84 mmol/g.And the separation factor of 4A zeolite synthesized,5A zeolite synthesized and commercial 5A zeolite were 4.88,8.48,6.64.Though compared with the commercial 5A zeolite,the saturated adsorption amount of CO₂ and CH₄ of the 5A zeolite synthesized was lower,but its separation factor was higher,which higher than the commercial 5A zeolite.It had a good separation effect on CO₂ and CH₄,and the separation effect was better in the low pressure.The 5A zeolite synthesized has a good application prospect on the separation of CO₂ and CH₄.The adsorbed amounts of both CO₂ and CH₄ are found to be highly related with the BET specific surface area and the volume of micropores.