Preparation Of Polyimide Hollow Fiber Gas Separation Membrane

Hollow fiber gas separation membrane has attracted widespread attention at home and abroad as a new separation method with low energy consumption and low cost.The use of polyimide as a material for preparing a hollow fiber gas separation membrane allows the separation membrane to have good gas separation selectivity.In particular,the separation performance for the CO2/CH4 system is greatly improved.At present,polyimide hollow fiber gas separation membranes have been applied in some countries such as Germany.The research progress of polyimide hollow fiber gas separation membranes in China is relatively slow.How to solve the contradiction between gas permeability and selectivity of gas separation membrane is also an important issue.In view of these problems,this paper starts from the synthesis of polyimide and uses ?-ray irradiation to improve the separation performance of polyimide gas separation membrane,and uses dry-wet phase transformation method to prepare polyimide hollow fiber membrane.Investigating the effect of process parameters on the membrane structure during the preparation of polyimide hollow fiber membranes,and optimized the preparation process to prepare a dense polyimide hollow fiber membrane.In this paper,N,N-dimethylacetamide(DMAc)is used as solvent,and 3,3',4,4'-benzophenonetetracarboxylic dianhydride(BTDA),toluene diisocyanate(TDI),4,4-The ternary copolymerization of diphenylmethane diisocyanate(MDI)was carried out.The molecular structure of the polyimide was characterized by infrared spectroscopy.The heat resistance of the synthesized polyimide was analyzed by thermogravimetric analyzer.The reaction was studied.The influence of the reaction temperature and reaction time in the process on the structural properties of the ternary copolymerized polyimide polymer.When the reaction temperature was selected at 80?,the obtained polyimide product had the highest intrinsic viscosity.The intrinsie viseosity of the polyimide increases as the reaction time increases,which is consistent with the tendency of the tensile strength of the film to reach a maximum at 8 hours.The effect of radiation on the structural properties of the polyimide gas separation membrane,especially the gas separation performance,was investigated by 60Co-? source ray irradiation.Using infrared spectroscopy,thermogravimetric analyzer,and differential pressure gas permeation performance test,the following conclusions were obtained:When the irradiation amount is 100 kGy,the molecular backbone of the polyimide is destroyed to cause structural changes.Irradiation is less than 100 kGy,and ?-ray irradiation has little effect on the molecular structure.As the amount of irradiation increases,the thermal decomposition temperature of the material decreases.When the irradiation amount is 100 kGy,the temperature at which the sample loses 10%of the weight is reduced from 564? to 555? of the unirradiated sample,indicating that the irradiation of ? ray causes the PI thermal decomposition temperature to drop.When the irradiation dose is rising,the separation factor of the separation membrane for CO2/CH4 and CO2/O2 mixed gas systems shows an upward trend.At the same time,the gas permeability of the polyimide gas separation membrane for the single O2,N2,CO2,and CH4 increases first and then decreases.When the absorbed dose is 50 kGy,for the CO2/CH4 mixed gas system,the separation membrane exhibits a phenomenon that the permeability coefficient and the selection coefficient increase simultaneously.This indicates that the polyimide gas separation membrane has a certain degree of improvement in the gas separation performance of the CO2/CH4 mixed gas system by 60Co-? irradiation.This method provides a new idea for improving the gas separation performance of a polymer gas separation membrane.The polyimide hollow fiber membrane was prepared by dry-wet phase transformation method.The influence of main influencing factors on the hollow fiber structure during the spinning process was investigated.The experiment showed that the spinning solution could not be spun when the concentration was too low,As the concentration improves the spinning effect,the pore diameter of the hollow fiber membrane sublayer gradually decreases.However,if it is too high,there will be problems such as difficulty in spinning.In the comprehensive experiment,the concentration of spinning solution is 25%wt;the height of the air gap will affect the outer surface structure of the membrane.As the air gap increases,the outer surface cortex increases.However,excessive air gaps cause difficulty in spinning.In general,the selection of a 30 mm high air gap is beneficial to the preparation of hollow fiber membranes;the extrusion rate and winding speed will affect the outer diameter,wall thickness and shape of the hollow fiber membrane,and should be adjusted according to the wall thickness requirements of the hollow fiber membrane required;Different external coagulation baths have a greater impact on the internal structure of the hollow fiber membrane.The non-solvent solidification medium has a significant influence on the thickness and structure of the dense layer and the sublayer.With the change of the external coagulation bath,the intermal finger structure of the membrane is significantly reduced.Reduction from large to small is acetone>IPA>ethanol>water.When the temperature of the coagulation bath is 35?,the inside of the spun fiber has fewer finger-like voids.The core liquid can determine the fluency of the entire spinning process and the formation of the intermal structure of the hollow fiber membrane.The use of IPA or the like as an internal coagulation bath can form a denser inner surface structure with respect to water.