Modification Of LiX Zeolite Molecular Sieve And Its Adsorption Properties Of Nitrogen And Oxygen

The non-framework cations in zeolite molecular sieves are distributed in a relatively fixed form around the framework structure,with a certain degree of fluidity,and can undergo ion exchange reactions.Zeolite molecular sieve is an excellent adsorbent with strong adsorption capacity for polar small molecules,it can selectively adsorb to different molecules such as critical diameter,polarity,shape,and degree of unsaturation.Therefore,zeolite molecular sieves are widely used in many fields,especially in the gas separation industry.LiX zeolite molecular sieve is one of the representative,LiX zeolite molecular sieve has better nitrogen and oxygen adsorption separation performance.The cation exchange modification of rare earth metal cerium ions was performed to analyze the change of nitrogen and oxygen adsorption performance,which is favorable for obtaining zeolite molecular sieve with better oxygen adsorption performance.The LiX zeolite molecular sieve was modified by cation exchange method under different conditions to prepare a CeLiX zeolite molecular sieve.The TG-DSC,FT-IR,XRD,SEM,XRF and other characterization methods were used to analyze the composition and structure changes of the modified molecular sieve before and after the modification.The specific surface area,pore diameter change,nitrogen and oxygen adsorption of CeLiX zeolite molecular sieves obtained under different reaction conditions were analyzed by BET and gas adsorption instruments.Adsorption model was used to fit the adsorption of nitrogen and oxygen on Ce LiX zeolite.The kinetics of ion exchange reaction of CeLiX zeolite was analyzed by the pseudo first-order and second-order kinetic equations.The exchange times and the exchanger concentration are the main factors affecting the structural characteristics of CeLiX zeolite molecular sieves.In a certain range,with the increase of the exchange concentration and the exchange times,the intensity of Ce LiX infrared absorption peak and XRD diffraction peak will be weakened,and the surface of the powder will become rough,but CeLiX can maintain a stable skeleton and crystal structure.As the exchange concentration continues to increase and the exchange times continues to increase,its skeleton and crystal structure are easily damaged and the powder surface becomes smooth.The reaction time and reaction temperature have little effect on the structure of CeLiX zeolite molecular sieve.With the increase of reaction time and reaction temperature,the intensity of infrared absorption peak of Ce LiX zeolite molecular sieve will be weakened,but it will not affect the structure of Ce LiX zeolite molecular sieve.The exchange times,exchanger concentration,reaction time and reaction temperature have certain effects on specific surface area,nitrogen adsorption capacity and oxygen adsorption capacity of CeLiX zeolite.The main influencing factors are the exchange times and the exchanger concentration.With the increase of the exchange times and the exchanger concentration,the specific surface area and nitrogen adsorption amount gradually decreased,and the oxygen adsorption amount increased first and then decreased.The optimal level conditions for preparing high-oxygen-adsorbing Ce LiX zeolite molecular sieves are:exchange times 3 times,exchanger concentration 0.1 mol/L,reaction time 1 h,reaction temperature 30°C.The O₂/N₂ separation coefficient of the CeLiX zeolite molecular sieve is closely related to the exchanger concentration and the exchange times.With the increase of exchanger concentration,the separation coefficient gradually increases.When the exchanger concentration is increased to 0.15 mol/L,the separation factor is 0.97,which is592.9%higher than that of LiX zeolite molecular sieve.With the increase of the exchange times,the separation coefficient gradually increased.When the exchange times was four,the separation factor reached 1.80,which was 718.2%higher than that of the LiX zeolite molecular sieve.Using the Langmuir equation and the Virial equation to fit the nitrogen and oxygen adsorption capacity of CeLiX zeolite molecular sieve with different exchange times,the fitting result is consistent with the experimentally measured variation of nitrogen and oxygen adsorption.Kinetic analysis revealed that the ion exchange reaction of Ce³⁺modified LiX zeolite molecular sieves met the pseudo-second-order kinetics model.