Preparation Of ZSM-5Zeolite From Fly Ash By Two-step Method

Fly ash, a kind of solid pollutant generated during the combustion of coal for energyconversion, not only occupies a lot of farmland, but also pollutes the environment and doesharm to human health.It is important that the fly ash was utilized, which will help reduce theenvironmental burden and enhance economic benefit. Due to the nature and chemicalcomposition of fly ash (containing more than70%Al2O3and SiO2), it can be used to producehigh added-value ZSM-5zeolite, which was widely used in the applications of industrycatalysis. The way can not only reduce production costs and improve the competitiveness ofZSM-5, but also lessen the environmental pollution, is very important to promote the rapidgrowth of the national economy.Fly ash, as raw material, was pretreated and activated in this paper. After removal ofimpurities, silicon and aluminum components were obtained, which can be usedhydrothermal synthesis ZSM-5zeolite. ZSM-5zeolite with Ce metal ion after impregnationwas used in FCC regeneration process, the performance of ZSM-5zeolite was evaluated byusing the removal rate of NOx. The main contents and results are as follows:(1) Grading pretreatment experiments of fly ash were shown that grinding can destroythe structure of fly ash. Unberned carbon in fly ash can be completely removed at800℃bycalcining for2.5h. However, the high temperature process may cause the the fly ash crystalform changed and its activation effect was limited. The soluble salts in fly ash can beremoved about97.96%at75℃by washing for3h. Hydrochloric acid was used to removemetal ironis, which was better than the sulfuric acid. The removal of iron ions is about70%at80℃by washing with5mol/L HCl for2h, and aluminum ion leaching rate of was higher than14.02%. The acid solution easily reacts with alkaline oxides, but amphoteric oxide (Al2O3)reaction is weaker. In the process of removing iron via acid leaching, iron ionis was difficultto be completely removed. It is considered that fly ash was activated by adding someadditives.(2) Sodium carbonate was used as the activator, the separation of silica and alumina wasrealized by high temperature activation of fly ash in acid leaching processing. The singlefactor experimental analysis and orthogonal experiments were discussed, which were aboutvarious factors levels of calcination experiment. The best conditions of calcinationexperiment were obtained: the calcination time was3h, and the calcination temperature was840℃, and the ratio of fly ash to alkali was1:1.5, the order of the influence factors:temperature>calcination time>ratio of raw materials. The optimum leachingconditions were3mol/L HCl, the solid-liquid ratio of1:10, the reaction was2h at80℃, therotation speed was600r/min. The leaching rate of aluminum and iron in fly ash treated bycalcination and acid leaching was up to80.89%and95.3%respectively. Acid leachingprocess of salt-activated fly ash was a unreacted shrinking core model, the rate controllingstep of the reaction process was by a surface controlled chemical reaction, the kineticequation is1-（1-）1／3＝kt, reaction order is1.05, the activation energy was44.74kJ/mol.Adjusting the pH by NaOH solution method can effectively remove Fe, Ca, Mg and otherimpurities of fly ash. When PH=3.5was the best iron removal pH. Aluminum hydroxide andsodium silicate was obtained by carbon separation.(3) ZSM-5zeolite was obtained by hydrothermal synthesis method with silicon andaluminum groups, which was gettedd in the fly ash as raw material. The optimum conditionswere as follows:1SiO2:0.02Al2O3:0.25TPAOH:80H2O, the crystallization temperature was210℃, crystallization time was12h.(4) Porous ZSM-5zeolite prepared was loaded with active component Ce, which was inzeolite surface or pores. The prepared catalyst can effectively reduce NOx emission duringFCC regeneration. In the absence of catalyst, the reaction temperature was700℃, theconversion rate of NOx can reach80%. With the1.0%Ce-catalyst, the reaction temperaturewas600℃, the conversion rate of NOx can reach90%. With the2.0%Ce-catalyst, thereaction temperature was500℃, the conversion rate of NOx can reach100%. It was shownthat thesupported Ce catalyst for the reduction of NOx has a better catalytic effect.