Hydrothermal Synthesis Of Clinoptilolite And Its Ion Exchange Properties For The Effect Of CH₄/N₂ Separation

Clinoptilolite is one of the most widely distributed mineral in nature,which has been widely used in many fields,such as gas separation and sewage treatment and so on.However,due to the presence of many impurities in natural clinoptilolite,it is difficult to achieve maximum performance.However,the synthesized clinoptilolite can exert more superior performance than natural clinoptilolite.In this dissertation,hydrothermal synthesis of clinoptilolite is mainly used to investigate the influence of different synthesis paramters on the structure of synthetic clinoptilolite,meanwhile,the effect of different ion exchange on the separation of methane and nitrogen is investigated.The following results are obtained:?1?Using aluminum hydroxide as the aluminum source and silica sol as the silicon source,the clinoptilolite was successfully synthesized by hydrothermal method.The influence factors of the synthesis were studied by XRD,TEM,BET,FT-IR,TG,²⁹Si MAS-NMR and other characterization methods,such as molar ratio of OH^-/Si,crystallization time and crystallization temperature,and got the optimum parameters for the synthesis of clinoptilolite.Finally,clinoptilolite can be successful synthesized under the conditions of crystallization temperature of 150 ^oC,crystallization time of6 d,OH^-/Si=0.55,Si/Al=5.5 and Na/K=1.Besides,in the process of synthesizing clinoptilolite,the crystallization kinetics profiles at different crystallization temperatures were studied.According to Arrhenius equation,we can calculate the apparent activation energy values of the induction period and the growth period,suggesting that their activation energy for induction period En=91.5 kJ/mol,but for the growth period Eg=7.2 kJ/mol,respectively.The En value is much higher than the Eg,indicating that the induction period belongs to the kinetic control behavior,but the growth process is attributed to thermal control process.?2?The selectivity for the separation of methane and nitrogen by different ion-exchanged clinoptilolites were investigated,such as Na⁺,K⁺,Ca²⁺,Mg²⁺,Li⁺,Fe³⁺,et al.The results showed that the K⁺-exchanged clinoptilolite has not only the highest adsorption amount of CH₄ and N₂,showing 1.09 mmol/g and 0.33 mmol/g at0 ^oC,respectively,but also the highest selectivity for CH₄/N₂ of 4.5 at 0 ^oC with a working adsorption pressure of about 0.35 atm.These results indicated that K-clinoptilolite is promising as an adsorbent for the separation of CH₄ and N₂ by adsorption.?3?Before and after ion-exchanged natural clinoptilolites such as K⁺,Ca²⁺,Mg²⁺,Li⁺were used as adsorbents to separate CH₄ and N₂.The results demonstratesd that both adsorption amount of N₂ and CH₄ and selectivity for CH₄/N₂ for natural clinoptilolites were lower than that for synthetic clinoptilolite.The main reason may be related to the presence of amorphous substances and other impurity in natural clinoptilolites.