Study On The Application Of ZIF-8 Slurry In The Separation Of Methane Mixture

This dissertation mainly focuses on the experimental study of CH₄ mixtures separation,like biogas,coalbed methane and cracked gas,and conducts a process simulation study of CH₄/N₂ separation,aiming to provide data support for the practical application of ZIF-8/water-glycol slurry in separation of CH₄ gas mixture by hybrid absorption-adsorption method,and solve the problems that may be encountered.The conclusions of this work are as follows:（1）When ZIF-8/water-glycol slurry is used to separate CH₄/CO₂ mixture,the pore structure of ZIF-8 will change irreversibly.It is found that the addition of a certain amount of m Im can not only keep the structure of ZIF-8 stable but also significantly improve the CO₂ capture capacity of ZIF-8 slurry.It is determined that the mole fraction of CO₂ in gas phase is reduced from 24.4 mol%to 7.5 mol%when the content of liquid phase m Im is 5wt%,it can still be reduced to 6.5 mol%after three cycles.The selectivity coefficient of CO₂ for CH₄ and the adsorption capacity of CO₂ are 76 and 0.42 mol/L,respectively.After that,the structure characterization of recovered ZIF-8 also shows that the structure of ZIF-8 can be protected by more than 5 wt%of m Im in the liquid phase.We also successfully introduced ZIF-8 slurry into the aqueous system.（2）The equilibrium separation experiment of CH₄/N₂ mixture was carried out with ZIF-8/water-glycol slurry,and the influence of ZIF-8 solid content,pressure,temperature,gas-liquid ratio and feed gas composition on the separation effect was systematically investigated.It was found that ZIF-8 solid content of 20-30 wt%,273.2-278.2 K,1.5-2.5MPa,the gas-liquid ratio of 40 and feed gas with high content of CH₄ are more favorable for the separation of the mixture.The adsorption isotherms of CH₄ and N₂ in ZIF-8/water-glycol slurry were measured.The Langmuir adsorption model was used to fit the adsorption model parameters of mixture gas at 273.2 K,the average relative error was only 3.23%.It is calculated that the adsorption heat of CH₄ in ZIF-8 slurry is only 9k J/mol,indicating that the adsorption process is mainly physical adsorption.（3）The multi-stage separation of cracked gas CH₄/C₂H₆/C₂H₄/C₃H₆/H₂ by ZIF-8/water-glycol slurry was carried out.We have investigated the influence of gas-liquid ratio,operating pressure and temperature on the multi-stage separation of cracked gas.It is found that low temperature and low gas-liquid ratio are conducive to the separation of cracked gas.Finally,the suitable conditions for the first stage separation are determined as follows:the gas-liquid ratio is around 40,the temperature is between 273.2-278.2 K;the suitable conditions for the secondary separation are:the gas-liquid ratio is around 50,the temperature is between 268.2-273.2 K.Finally,the continuous separation experiment of CH₄/H₂ mixture was carried out,it was found that with the increase of methane concentration in feed gas,the solubility（Sv₁）and separation selectivity（β）of methane increased significantly.When the concentration of methane in feed gas was 74.6 mol%,the separation selectivity（β）of methane to hydrogen reached 27.9.（4）The breakthrough experiments of CH₄/N₂ mixture in ZIF-8/water-glycol slurry were carried out in a bubble column under different operating conditions of slurry volume,operating pressure,gas flow and temperature.It was found that the lower the temperature and gas flow,the larger the operating pressure and slurry volume,the better the separation effect and the stronger the CH₄ capture capacity.（5）The binary interaction parameters between methane-slurry and nitrogen-slurry were fitted by ZIF-8/water-glycol slurry to separate CH₄/N₂ mixture.The multi-stage separation of CH₄/N₂ by ZIF-8 slurry was simulated by Aspen.The theoretical stage number,feeding position,operating pressure of flash tank,absorption-absorption tower and desorption tower,gas-liquid ratio were determined.