Preparation And CO₂ Separation Performance Of Thermal Rearrangement Membrane Materials Containing Pyridine Ring Structure

One of the greatest challenges facing mankind in the 21st century is energy consumption and climate warming.As non-renewable energy sources such as coal,oil and natural gas are burnt in large quantities,carbon dioxide（CO₂）emissions are increasing rapidly,causing serious environmental problems such as rising sea levels,melting glaciers and rising global temperatures.Membrane separation technology has a good application prospect in purification of air,regeneration and recovery of energy and treatment of environmental problems.Polyimide（PI）is an ideal membrane material for gas separation,but its low permeability limits its practical application in separation field.Polyimides containing o-hydroxyl groups（HPI）have become a new generation of gas separation membrane materials due to their high gas permeability and selectivity.TR membrane prepared by heat treatment will effectively improve the CO₂ separation performance of membrane materials by introducing pyridine ring and large volume side group into HPI.Therefore,the main contents of this dissertation are as follows:（1）A novel diamine monomer 4-（4-tert-butylphenyl）-2,6-bis[（4’-hydroxy-3’-amino）phenyl]pyridine（TUPPBA）was designed and synthesized,and a series of PI membranes were prepared by copolymerization with 2,2-bis（3-amino-4-hydroxyphenyl）hexafluoropropane（6FAP）and 4,4’-（hexafluoro isopropenyl）phthalic anhydride（6FDA）.Research showed that the copolymer membranes had good mechanical properties,with a glass transition temperature（T_g）of 309°C.Co TR（6FAP-TUPPBA-6FDA）membrane was obtained after thermal rearrangement at 450°C.The experimental results indicated that as the content of TUPPBA increased,the gas permeability of TR membrane gradually increased.Among them,the permeability coefficients of TR（6FAP-TUPPBA-6FDA）-5:5 for H₂,CO₂,O₂,and N₂ reached 345.9,321.8,67.84,and 9.31 Barrers,respectively.The selectivity for CO₂/N₂ was 37.15,close to the 1991 Robeson upper limit.（2）A new type of diamine monomer 4-（4-trifluoromethylphenyl）-2,6-bis[4-（3’-hydroxy-4’-aminophenoxy）phenyl]pyridine（TFPBBA）was designed and synthesized,which was synthesized with six types of dianhydride 3,3,4,4’-biphenyltetracarboxylic dianhydride（BPDA）,3,3’,4,4’-benzophenone tetracarboxylic dianhydride（BTDA）,6FDA,1,2,3,4-cyclobutane tetracarboxylic dianhydride（CBDA）,pyromellitic dianhydride（PMDA）,and 3,3’,4,4’-diphenyl ether tetracarboxylic dianhydride（ODPA）respectively to prepare six poly（ether imide）（PEI）membranes.Then,six types of TR membranes were obtained after thermal rearrangement at 450°C.The experimental results showed that the gas permeability of TR（TFPBBA-6FDA）was significantly higher than other thermal rearrangement membranes.Among them,TR（TFPBBA-6FDA）exhibited gas permeabilities of 270.9,282.1,56.23,and 7.10 Barrers for CO₂,H₂,O₂,and N₂,respectively.The selectivity for CO₂/N₂ was 34.34,approaching the1991 Robeson upper limit.（3）A novel diamine monomer 4-（4-trifluoromethylphenyl）-2,6-bis[（4’-hydroxy-3’-amino）phenyl]pyridine（TFPPA）was designed and synthesized,and a series of copolymer membranes and thermal rearrangement membranes were prepared by copolymerization with TFPBBA and 6FDA.Research results showed that the heat treated coTR membranes had excellent gas separation performance,and their permeability increased with the increase of the content of the rigid pyridine ring structures.Among them,the permeabilities of coTR（TFPBBA-TFPP A-6FDA）-6:4 to H₂,CO₂,O₂,and N₂ were 549.2,426.42,94.84,and 14.01 Barrer,respectively,and the selectivity for CO₂/N₂ was 30.86,exceeding the 1991 Robeson limit.