Study On Preparation And Modification Of 6FDA Polyimide Membrane Based On Co₂ Separation

With the continuous improvement of the global industrialization level,the emission of CO₂and other greenhouse gases is increasing year by year,which has led to increasingly serious environmental problems.Therefore,seeking a method that can effectively control and reduce CO₂emissions has become one of the problems in the field of scientific research.Nowadays,gas separation membranes are widely used to separate CO₂,because they have the advantages of high separation efficiency,low energy loss,simple and convenient operation.Polyimide（PI）is a high-performance material containing imide ring,which has excellent performance in gas separation.In addition,graphene oxide（GO）is commonly used to prepare mixed matrix membranes（MMMs）to improve gas separation performance.The modified GO can increase the dispersion of GO and improve the gas separation performance more effectively by using the affinity of amino CO₂.In this paper,in order to select the type of PI suitable for gas separation,molecular simulation technology was used to study the separation performance and separation mechanism of four different types of PI in the separation of CO₂/N₂,firstly.Then PI was synthesized based on the result from aboved molecular simulation.Finally,mixed matrix membranes was prepared by using GO and amino siloxane-based GO to achieve the improvement of membranes gas separation performance.Through the regulation of the membrane channel.In this paper,molecular dynamics（MD）and grand canonical ensemble Monte Carlo（GCMC）simulation methods have been used to study the CO₂/N₂permeation mechanism and separation performance of four types of PI,and they are Matrimid^?5218,TBDA2-ODPA,6FDA-DABA,6FDA-durene,respectively.The results show that the greater the free volume of the material,and the easier it is for gas to pass through the material.And among the four polyimide membrane materials selected in this paper,the 6FDA-DABA type PI has the highest gas selectivity,but its gas permeability is relatively low due to the Trade-off effect.Therefore,this paper synthesized 6FDA type PI with two different imidization methods,and used molecular simulation technology to study the optimal solvent for the synthesis of PI and the mechanism of the PI imidization process.The results show that the interaction parameter between PI and DMAc is the smallest,the compatibility is the best.And the simulation calculation proved that the depletion of the catalytically active carboxyl group in the PI imidization process is the possible reason for the incomplete cyclization of PI.In this experiment,chemical imine and thermal imine were used to synthesize PI,FT-IR shows that PI have been successfully synthesized by both chemical PI and thermal PI method.The PI synthesized by the thermal imidization method has a larger molecular weight and better thermal stability than the PI synthesized by the chemical imidization method.Then,GO was modified with siloxanes containing different numbers of amino functional groups（APTES,en-APTAS,AEPTMS）,to prepare aminated siloxane GO.Finally,amino siloxane GO（NH-GO）and GO were introduced into PI to prepare MMMs by chemical modification method.The results show that the PI matrix reacts with GO and NH-GO to form new amide bonds,and then successfully crosslinked into a network polymer.The solubility and thermal stability of MMMs are higher than those of pure PI.And the CO₂permeability coefficients of MMMs increased from 8.93 Barrer of pure PI membrane to17.33 Barrer,20.10 Barrer,24.29 Barrer and 21.63 Barrer,respectively.And the addition of GO and modified GO can effectively improve the gas selectivity of the membrane.When the filler is GO,the increase in selectivity is the largest,from 21.34 for pure membrane to 30.58.The gas separation performance of 2NH-GO-PI membrane is close to the upper limit Robeson 1991.