Study On Chemical Grafting Modified Polyimide And Its Membrane For CO₂ Separation

As a new technology,membrane separation process is widely used in gas separation process,such as biogas and natural gas purification,nitrogen production in air,hydrogen recovery and flue gas treatment.Aromatic polyimides are commonly used in these applications because of their high selectivity,excellent thermal,chemical and mechanical properties,and excellent film-forming ability.However,it is difficult to obtain polyimide membrane materials with high throughput and high selectivity.Therefore,it will be an important research direction to design a kind of polymer membrane which can maintain high selectivity and achieve high permeability.In this paper,a new type of polyimide was synthesized by grafting histamine into polyimide structure from the perspective of molecular design;Then SBA-15 molecular sieves functionalized with amino and imidazole were used as fillers to prepare mixed matrix membranes,the main research contents are as follows:Firstly,6FDA-ODA-DABA polyimide polymer was prepared by two-step method,and then histamine was grafted onto 6FDA-ODA-DABA polyimide to synthesize H-PI polyimide.The effects of material ratio,copolymerization ratio,synthesis time,synthesis temperature,catalyst dosage and aging temperature on the properties of membrane gas were investigated.FT-IR,TG,SEM and XRD were used to characterize the synthesized polymer.Based on the polyimide polymer of 6FDA-ODA-DABA（10%）,CO₂,N₂and CH₄permeation fluxes of the synthesized matrix membrane were 29.184 Barrer,1.78 Barrer and 1.5 Barrer under the condition of 30℃ and 0.2 MPa pressure.The selectivity of CO₂/CH₄was 19.52 and the selectivity of CO₂/N₂was 16.44.Based on the polyimide polymer of H-PI（20%）,CO₂,N₂and CH₄permeation fluxes of the synthesized matrix membrane were 23.548 Barrer,0.87Barrer and 0.84 Barrer under the condition of 30℃ and 0.2 MPa pressure.The selectivity of CO₂/CH₄was 28 and the selectivity of CO₂/N₂was 27.The overall performance of the membrane is better than that of the common commercial polyimide membranes.Using NQ-62（Trimethoxysilyl Propyl Diethylenetriamine）to modified SBA-15molecular sieve,the aminated SBA-15 material（3N-SBA-15）was obtained,which was compared with commercial material Matrimid^?5218.The effect of different amount of dopant（3N/PI）on the separation performance of the membrane was investigated.The mixed matrix membranes were measured by EDS,FT-IR,SEM,TEM,XRD,etc.And experimental results show that the addition of 3N-SBA-15 increases the CO₂permeation flux and CO₂/CH₄selectivity of PI membrane.When the particle content was 0.5 wt.%,the CO₂permeation flux and CH₄permeation flux were 11.36 Barrer barrer and 0.35 Barrer respectively.Compared with the matrix membrane,the CO₂permeation flux and CO₂/CH₄selectivity were increased by 9.87%and 47.57%respectively.The synthesized 3N-SBA-15 molecular sieve was further modified by imidazole-2-carboxaldehyde to obtain a new type of SBA-15 molecular sieve with imidazole group（IM-SBA-15）.The mixed matrix membranes were measured by EDS,FT-IR,SEM,TEM,XRD,etc.The results showed that compared with 3M-SBA-15,IM-SBA-15 could significantly improve the gas permeability and selectivity of the membrane.When the particle content was 1 wt.%,the permeation flux of CO₂was 15.07 Barrer and that of CH₄ was 0.28Barrer.Compared with the matrix membrane,the permeation flux of CO₂ was increased by 34.04%and the selectivity of CO₂/CH₄was increased by 137.37%.