Study On Preparation Method Of Kapton Hollow Fiber And Carbon Molecular Sieve Gas Separation Membrane

Polyimide(PI)is an engineering plastic with superior properties.It has characteristics such as high chemical stability,resistant to heat and excellent mechanical performance.Some polyimides are soluble but others are insoluble.Insoluble polyimides are more suitable for the separation of highly soluble gases,such as carbon dioxide,alkanes and olefins,due to their good anti-plasticizing property.PMDA-ODA polyimide has the advantages such as high glass transition temperature,high gas separation performance,low cost and easy synthesis.It is selected as the membrane material in this study.The hollow fiber membrane(HFM)was prepared by the soluble precursor polyamic acid(PAA)of PMDA-ODA,and then the polyimide membrane was obtained by thermal imidization,and the carbon molecular sieve membrane was prepared by further heating up the PMDA-ODA hollow fiber.The main achievements of the thesis was as given below:1.Carbon molecular sieve membrane(CMSM)possess superior antiplasticizing properties,high gas permeability and selectivity.PMDA-ODA PAA was used to prepare hollow fiber membrane with regular morphology.Then,the PMDA-ODA hollow fiber was crosslinked using polyethylenimine(PEI)to inhibit the shrinkage and pore collapse of the membrane in the carbonization process.The defects on the membrane surface were repaired by a dip-coating method with PMDA-ODA PAA solutions.The carbon molecular sieve HF composite membrane with good GS performance was successfully made.After a single coating of 5wt%PAA,the CO2,O2,N2 and CH4 permeances of carbon molecular sieve hollow fiber composite membrane were 93.4GPU,19.6GPU,6.5GPU and 4.7GPU,respectively.The CO2/CH4,CO2/N2 and O2/N2 permeances were 19.8,14.4 and 3.0,respectively.2.By adding lithium chloride into the casting solution,the phase inversion rate of PDMA-ODA PAA solution was significantly improved.As a result,highspeed spinning of PMDA-ODA PAA hollow fiber was achieved.The effects of lithium chloride content on the viscosity,front movement of casting solution,porosity and mechanical properties of the flat-sheet membrane was studied.The optimal content of lithium chloride was determined to be 3 wt%.Under these conditions,the defect-free hollow fiber membrane was prepared.Using tetrahydrofuran(THF)as the low boiling point non-solvent and isopropanol(IPA)with high non-solvent strength as another additive in the casting solution,the hollow fiber membrane without surface defect was prepared using a take-up speed of 20m/min and an air gap of 5cm.The permeances of H2,CO2,O2 and N2 were 6.75 GPU,2.17 GPU,0.4 GPU and 0.07 GPU,respectively,and the selectivity of H2/CO2,CO2/N2 and O2/N2 were 3.11,31 and 5.71,respectively.