The Simulation Of CH₄/H₂ In ZIF-8/glycol-water Slurry Separation Using Absorption-adsorption-hybrid Method

High purity hydrogen is needed in many applications such as fuel cells,gas chromatography and LED production.The most economical way to produce hydrogen is the catalytic reforming of natural gas combined with water gas shift reaction.Unfortunately,this reaction produces several impurities like water vapor,carbon dioxide,methane,carbon monoxide and nitrogen.Recent research shows that a kind of slurry system formed by suspending zeolitic imidazolate framework-8(ZIF-8)in liquid water or ethylene glycol(EG)can recover hydrogen effectively.In this work,based on the extensive collection of experimental data for this separation system,a thermodynamic model was developed for providing theoretical guidance for the industrial design.The contents of the work are as follows:(1)Proposing the thermodynamic model:Use the Patel-Teja equation of state(PT EOS)coupled with the Kurihara mixing rule for calculating gas solubility in water or EG and determining the liquid phase composition.Then,use the Langmuir adsorption equation to calculate the adsorptive capacity of gas in ZIF-8.The difference between the adsorption and vapor-liquid equilibrium fugacity is defined as the osmotic pressure of absorption film surrounding ZIF-8.(2)Determination of the parameters in the model:The experimental mole fraction data of pure H2 in liquid EG and water,respectively,were used to correlate the H2-EG and H2-water binary interaction parameters in the EOS mixing rule.The parameters for H2 in the Langmuir equation were determined by correlating the the experimental data of adsorption capacity of H2 in ZIF-8.(3)Determination of the osmotic pressure of glycol and water liquid membrane on the surface of ZIF-8:The osmotic pressures of EG and water film surrounding ZIF-8 were determined from experimental solubility of pure H2 in slurry with ZIF-8 dispersed in EG and water,respectively.And then the osmotic pressure was correlated as a function of equilibrium fugacity.The proposed thermodynamic model was used to predict the recovery of H2 from gas mixture using ZIF-8,ZIF-8/glycol,and ZIF-8/water system,respectively.The results of comparison with experimental data show that the calculation results are satisfactory and the proposed model is of significance for designing the technological process.