Preparation Of Pebax/porous Two-dimensional Material Mixed Matrix Membrane And Study Of CO₂/CH₄ Gas Separation Performance

Bio-natural gas（BNG）is mainly composed of CH₄.However,the CO₂ mixed in BNG will reduce the combustion calorific value of CH₄ and corrode the transportation pipeline.Therefore,the separation of CO₂is the key to the application of BNG.Compared with the traditional separation method,the gas membrane separation method has the advantages of simple separation device,high efficiency,environmental protection,and low energy consumption.Therefore,gas membrane separation technology has become a promising CO₂separation technology.The choice of membrane material is at the heart of gas separation membranes.In this thesis,polyether-polyamide block copolymer（Pebax 1657,Pebax）was used as the membrane matrix,and different two-dimensional（2D）porous materials were used as fillers to construct different types of gas transport channels in the membrane to prepare mixed matrix membranes（MMMs）to separate the CO₂/CH₄mixture.The main research contents are as follows:（1）2D Li_1.6Mn_1.6O₄（LMO）nanosheets were designed and prepared and used as filler to prepare Pebax/LMO MMMs for the study of CO₂/CH₄ separation performance.The pore size of the LMO is about10.79 nm,which can establish a fast CO₂ transport channel in the membrane and expose a large number of Li metal sites and oxygen defect sites(O^δ-).Li and O^δ-in LMO have an affinity for CO₂,which can increase the solubility of CO₂ in the membrane,thereby improving the permeability of MMMs and the selectivity of CO₂ separation.In addition,the ultrathin structure and large aspect ratio of LMOs are also beneficial for gas separation.The pure CO₂ permeability and CO₂/CH₄ ideal selectivity of Pebax/LMO-2.0 membrane are117.90 Barrer and 18.74,respectively,which are 119.70%and 35.80%higher than that of Pebax membrane,respectively.The CO₂/CH₄ wet mixed gas separation results of the Pebax/LMO-2.0 membrane show that the CO₂ permeability is 388.40 Barrer,and the CO₂/CH₄ selectivity is 37.10,which are 77.04%and 7.60%higher than that of the Pebax membrane,respectively.（2）Porous Cu（BF₄）₂（bpy）₂（Cu MOF）with interlayer channels was used as filler to prepare Pebax/Cu MOF MMMs for the study of CO₂/CH₄ separation performance.The interlayer channels of Cu MOF and its own micro-mesoporous structure facilitate the diffusion of CO₂,shorten the diffusion distance of CO₂,and increase the amount of CO₂ infiltration.The pyridyl group,unsaturated Cu²⁺and BF₄^-contained in Cu MOF have affinity with CO₂,which strengthens the dissolution mechanism of CO₂ and improves the selectivity of CO₂.In addition,the membrane characterization results demonstrate the excellent compatibility between Cu MOF and Pebax matrix,which is beneficial to enhance the gas separation performance of MMMs.The pure CO₂ gas permeability and CO₂/CH₄ ideal selectivity of Pebax/Cu MOF-10 membrane are 148.80 Barrer and 19.20,respectively,which are 121.53%and 106.90%higher than that of Pebax membrane,respectively.The CO₂/CH₄ wet mixed gas separation results of the Pebax/Cu MOF-10 membrane showed that the CO₂permeability was 430.30 Barrer,and the CO₂/CH₄ selectivity was 38.78,which were 107.87%and 21.11%higher than that of the Pebax membrane,respectively.（3）Cu BDC-MBA was designed and prepared,and it was used as a filler to prepare Pebax/Cu BDC-MBA MMMs for the study of CO₂/CH₄ separation performance.The microporous structure of Cu BDC is beneficial to the selective sieving of CO₂ and CH₄.MBA as a regulator can make Cu BDC-MBA have colloidal stability without changing the structural characteristics of Cu BDC itself.Cu BDC-MBA with colloidal stability has good dispersibility in the membrane,which is beneficial to its own pore structure to facilitate the diffusion of CO₂ and shorten the diffusion distance of CO₂.In addition,the CO₂ affinity sites（carboxyl group）functioned to improve the solubility of CO₂ in the membrane and increase the CO₂/CH₄ selectivity.The pure CO₂ gas permeability and CO₂/CH₄ ideal selectivity of Pebax/Cu BDC-MBA-8 membrane are 157.50 Barrer and 17.74,respectively,which are 178.27%and 83.83%higher than that of Pebax membrane,respectively.The wet mixed gas separation results of Pebax/Cu BDC-MBA-8 membrane show that the CO₂ permeability is 481.84 Barrer,and the CO₂/CH₄ selectivity is 43.80,which are 111%and 27.40%higher than that of Pebax membrane,respectively.