Effect Of Cation Exchange Of Zeolite/Activated Carbon Composite On CH₄/N₂ Adsorption Separation Performance

Compared with coal and petroleum,natural gas is such a clean energy that its combustion dilivers less carbon emission and hardly discharges NOx and SOx.Therfore promoting the use of natural gas worldwide could fundamentally improve environmental pollution issues nowadays.China has abundant reserves of unconventional natural gas,such as coalbed methane,tight gas and shale gas etc,which could offset insufficient conventional natural gas.During exploitation,unconventional natural gas will be mixed with massive air for the sake of safety.Under normal conditions methane and nitrogen share so extremely similar physical and chemical property that over a long period CH₄/N₂ separation is a tough issue in the separation field.For the purpose of preparing high efficient adsorbents for CH₄/N₂ separation,this thesis studied the preparation of shaped NaX/activated carbon starting from main material elutrilithe,and investigated the effect of different ion exchange on crystallinity of X zeolite in composites,pore structure and adsorption separation of methane and nitrogen after K+ and Cs+ exchange.In addition,we synthesized NaA/activated carbon starting from elutrilithe and pitch,and reviewed the effect of different crystallization time on formation of zeolite A,pore structure and adsorption separation of methane and nitrogen.The main research and experimental results of this paper are as follow:1.The composite crystallinity decreases with the increase of K+ content,and BET surface area,micropore surface area and pore volume is gradually declined.Compared with parent NaX/AC,methane and nitrogen adsorption amount decrease after K+ exchange,however nitrogen adsorption amount drops with a larger latitude compared with methane.The percentage of 0.45-0.55 nm micropore volume in the micropore volume below 1nm increase during K+ exchange degree between 28 and 55%,additionally the interaction between K+ and nitrogen molecule decreases,therefore CH₄/N₂ intial selectivity and equilibrium separation ratio get gradually improved at both 298 K and 273 K.At 298,K?51?NaX/AC shows CH₄ adsorption amount of 13.0mL/g,with CH₄/N₂ equilibrium separation ratio of 3.5.2.The composites crstallinity,specific surface area and pore structure parameters decrease with the increase of Cs+ content,thus compared with parent sample,methane and nitrogen adsorption amount decrease after Cs+ exchange.Absolute and relative content of 0.45-0.55 nm during Cs+ exchange degree between 7 and 21% get graduate increased,additionallycompared sodium ion,cesium exchange further weakens its interaction with nitrogen molecule,therefore CH₄/N₂ intial selectivity and equilibrium separation ratio get gradually improved at both 298 K and 273 K.At 298 K,Cs?07?NaX/AC shows CH₄ adsorption amount of 12.9mL/g,with CH₄/N₂ equilibrium separation ratio of 3.8.In addition,at 273 K,Cs?21?NaX/AC shows CH₄ adsorption amount of 19.3mL/g,with CH₄/N₂ equilibrium separation ratio of 3.7.3.A shaped activated carbon prepared after carbonization and physical activation,starting from pitch and elutrilithe,was further hydrothermal treated with alkaline solution.The effect of crystallization time on formation of zeolite 4A,pore structure and the adsorption ability towards CH₄ and N₂ of the composite was investigated.Characterized by X-ray diffraction?XRD?,Scanning electron?SEM?,N₂ adsorption-desorption at 77 K and CO₂ adsorption isotherm at 273 K,the result shows silicon and aluminum in this composite is converted to zeolite 4A during the hydrothermal treatment.Simultaneously,micropore between 0.45-0.6nm is appeared,micropore volume is increased,accompanied by the presence of little mesopore and macropore.Adsorption isotherms at 298 K indicate that CH₄ adsorption amount of AC-2 is elevated to 10.8mL/g with high CH₄/N₂ equilibrium selectivity 3.7.