Absorption-adsorption Coupled Phase Equilibrium Model For CO₂ Capture By ZIF-8 Slurry

At present,climate change is one of the focus issues of global concern.The impact of the greenhouse gas CO₂ on the climate should not be underestimated.Many countries around the world have committed to capturing and reducing CO₂.The traditional CO₂capture techniques are energy intensive,and the development of energy-saving and efficient CO₂ capture technique has been the research hotspot.During the development of the new capture process,a lot of experimental research and accurate process design are required,and the establishment of a thermodynamic model is the key step in analyzing and predicting experimental results and ensuring the accuracy of process simulation.My research group proposed a new absorption-adsorption coupling separation method to capture CO₂,using ZIF-8 as the adsorbent and selecting different absorbents,which effectively combines the advantages of absorption and adsorption methods.The ZIF-8slurry absorption-adsorption coupling separation method is still in the experimental stage.In order to develop an efficient slurry and further enlarge the technique,it is necessary to establish a thermodynamic model to predict the separation effect of the system.This paper mainly investigates the solubility calculation model of CO₂ in ZIF-8slurry and 2-methylimidazole aqueous solution,which is intended to provide a phase equilibrium model for the design of mass transfer unit equipment and process simulation for CO₂ capture by ZIF-8 slurry method and 2-methylimidazole aqueous solution.In this thesis,the process of CO₂ capture by slurry method is decomposed into three steps:gas-liquid absorption,liquid membrane permeation and gas-solid adsorption.Firstly,this thesis establishes an absorption-adsorption coupled model that uses the PR EOS combined with the UNIFAC model as the absorption phase equilibrium model,the Langmuir adsorption equation as the adsorption phase equilibrium model,and the selective osmotic pressure of the liquid membrane on ZIF-8 to link the absorption and adsorption processes.And the model was applied to predict the separation effect of ZIF-8/DMAC slurry from CO₂/H₂ mixture and 2-methylimidazole aqueous solution for CO₂absorption.For the process of ZIF-8/DMAC slurry separating CO₂/H₂ mixture,the experimental data of the solubility of pure gas absorbed by pure solvent were used to fit the group interaction parameters of the absorption model,the equilibrium experimental data of ZIF-8 dry material adsorbing pure gas were used to fit the parameters of the adsorption model,and then the relationship between the osmotic pressure of the solvent membrane and the equilibrium pressure of the components is determined by the phase equilibrium experimental data of the pure gas adsorbed by the slurry,and finally a complete absorption-adsorption coupled phase equilibrium prediction model is formed.The model with the known parameters was applied to calculate CO₂ solubility in CO₂/H₂ mixture in ZIF-8/DMAC slurry,and the prediction error was 8.20%.For the process of CO₂ absorption by 2-methylimidazole aqueous solution,the experimental data of the phase equilibrium of water-（2-methylimidazole）and CO₂-water binary system were used to fit the group interaction parameters of the UNIFAC model,and these parameters were applied to the parameter fitting and result prediction of CO₂-（2-Methylimidazole）-water ternary system.Finally,the model with known parameters was used to predict the effect of 2-methylimidazole aqueous solution to absorb CO₂,with an error of 15.11%.In this thesis,the absorption/absorption-adsorption coupling model with certain parameters is used to predict and calculate the CO₂ capture process using 2-methylimidazole aqueous solution and ZIF-8/DMAC slurry.The prediction error is acceptable for engineering design.