Preparation And Performance Characterization Of High-performance Oxygen And Nitrogen Separation Membran

Membrane separation technology is widely used in all walks of life due to its small footprint,fast start-up,low investment,no pollution,and low energy consumption.At present,more and more polymer membrane materials with high O₂ permeability and O₂/N₂selectivity have been developed.However,how to convert the above high-permeability polymer into membrane with practical application potential is the only way for the above polymer materials to be applied.Based on this,we have carried out the following series of work.The process of polymer materials to phase inversion membranes and hollow fiber membranes is explored and the membranes forming mechanism is analyzed.It is specifically manifested in the following three aspects:（1）:Using commercial Polysulfone as a raw material,the preparation mechanism of its anisotropic membrane was explored.The asymmetric membrane was prepared by using the non-solvent induced phase separation（NIPS）method,and its cloud point under different conditions was determined by the method of non-solvent titration.The influence of the thickness of the casting knife,the membrane casting temperature,the phase inversion time,the content of THF,the post-treatment conditions and other factors on the microstructure of the Polysulfone anisotropic membrane,as well as the O₂ permeance and O₂/N₂ selectivity were explored.A Polysulfone asymmetric membrane with a O₂permeance of 4.9 GPU and an O₂/N₂ selectivity of 7.4 was obtained.（2）:In order to further improve the separation efficiency,we have prepared a ternary Polyimide 6FDA/PMDA-FDA with a higher permeability by a high-temperature one-step method.The structure of the product was verified by NMR and IR,and the thermal stability of the polyimide was tested by thermogravimetry.The preparation of the polymer homogeneous membrane as well as the phase inversion membrane was explored by solvent exchange in deionized water,methanol,and hexane baths,and coating the membrane surface with polydimethylsiloxane（PDMS）coating.Defect repair to prepare defect-free composite asymmetric flat membranes.The O2/N2separation performance of the Polyimide dense membrane,anisotropic membrane and composite membrane were tested respectively.The results show that the higher the non-solvent content,the greater the permeance,but the non-solvent content above 7%may cause the casting solution to be in an unstable state.M3 obtained by controlling the volatilization time of 30 s has the best gas permeance,its O₂ permeance reaches 25 GPU,and its O₂/N₂ selectivity reaches 5.4,which is significantly higher than that of the original polyimide.The original polyimide has an intrinsic O₂ permeability of 52 Barrer and an O_2/N₂ selectivity of 4.7.The composite membrane obtained after coating with PDMS showed more excellent oxygen/nitrogen separation performance,in which the oxygen/nitrogen selectivity was increased to 7 and the O₂ permeance could still reach 17.8 GPU.In addition,we also found that in the case of uniform dissolution,the casting solution with high solid content has better film-forming properties,and it is easier to form defect-free asymmetric gas separation membranes.The higher the THF content,the lower the gas permeance,However,it is still necessary to maintain a sufficient amount of THF content above 10%to ensure the integrity of the skin.Water as a coagulation bath is more likely to form finger-like pores than ethanol.（3）:The hollow fiber gas separation membrane has a larger specific surface area and is the most widely used form of gas separation membrane module.In order to further improve the separation efficiency,we explored the use of commercial Ultem1000 polyetherimide as a raw material to prepare hollow fiber membranes by dry-jet wet spinning.We have studied the influence of various spinning and other process conditions on the hollow fiber gas separation membrane,including the relationship between the membrane structure and performance under the conditions of dope and bore fluid flow rate,air gap,spinning temperature,and coagulation bath temperature.When the flow rate of the spinning solution was 2.4 ml/min and the flow rate of the core solution was 1.2 ml/min,a hollow fiber membrane with an O₂ permeance of 0.74GPU and a selectivity of 2.76 was obtained.The higher the flow rate of the spinning solution,the faster the winding speed.The smaller the outer diameter of the membrane,the smaller the outer diameter of the membrane can increase the packing density of the hollow fiber membrane module and improve the separation efficiency It provides a possibility for the hollow fiber gas separation membrane to play an important role in large-scale H₂ recovery,CO₂ capture,and O₂/N₂separation.