| Poly(phthalazinone ether sulfone ketone)(PPESK) was selected as the membrane material because of its high glass-transition temperature, good mechanical performance and solubility, well membrane-froming ability and good permselectivity. In this study, the PPESK hollow fiber membrane for gas srparation was prepared. The relationship between the stucture and performance of PPESK hollow fiber membrane was also researched in detail.The thermodynamic property of PPESK spinning solution was investigated. Based on the cloud point titration, the linearized cloud point(LCP) curve correlation were employed in the research of phase separation of PPESK/solvent/non-solvent(NS) ternary systems. The theta composition of NS/solvent mixture was determined in the PPESK/N, N-dimethylacetamide(DMAc)/gamma-butyrolactone(GBL), PPESK/ N-methyl-2-pyrrolidone(NMP)/GBL, PPESK/DMAc/ethanol(EtOH), PPESK/NMP/EtOH, PPESK/DMAc/EtOH/THF and PPESK/DMAc/propionic acid(PA) systems using the method of Elias. The solubility parameters of PPESK, solvent, NS were calculated by group-donation method. The results showed that the experimental cloud point curves and the calculated cloud point curves by LCP had a good agreement in most systems. The solubility difference of different solvents and the precipitation ability difference of different NS indicated by the solubility parameters of PPESK, solvent, NS agreed well with the results showed in the cloud point curves of PPESK/solvent/NS systems.Based on the the study of the thermodynamic property of PPESK spinning solution, the recipe of the PPESK spinning dope was investigated in detail. The effects of solvent, NS, PPESK content, PPESK molecular weight on membrane performance were researched. The results showed that good permselectivity of PPESK hollow fiber membrane could be obtained using DMAc as solvent. The NS had important influence on membrane performance, the volatile EtOH/THF mixture with relatively weak precipitation ability was suitable for preparing good hollow fiber membrane. Along with the increase of NS content, the gas permeation increased and the gas selectivity decreased, when the NS content was higher than that at theta composition, the performance of membrane dropped sharply. The high polymer concentration resulted in denser skin layer leading to the low gas permeation and high gas selectivity. Along with the increase of PPESK molecular weight, the gas permeation decreased and the gas selectivity increased slightly.PPESK hollow fiber membranes for gas separation were prepared by phase-inversion technique using water as coagulant. The effects of air gap, bore fluid rate and spinning temperature on membrane performance were also studied. The results showed that along with the increase in air gap, the gas permeation decreased and the gas selectivity increased, when the air gap was excessively long, the membrane performance dropped. For PPESK/DMAc/EtOH/THF system, when the air gap was controlled as 110mm, the O2/N2 selectivity of PPESK hollow fiber membrane reached the maximum value of 5.3 at 25℃. Along with the increase in bore fluid rate and spinning temperature, the gas permeation increased and the gas selectivity decreased.Polydimethylsilane(PDMS) was imployed to seal the defects on the outer surface skin layer of PPESK hollow fiber membrane so that a good gas selectivity could be obtained. The effects of degree of vacuum, period of vacuum applied and PDMS curing temperature in the coating process were investigated. The results showed that the degree of vacuum should be carefully controlled; improper degree of vacuum could not ensure the PDMS to seal the defects on the surface of PPESK hollow fiber membrane. Along with the increase in period of vacuum applied, the gas permeation decreased and the gas selectivity increased, when the period of vacuum applied was excessively long, the membrane performance dropped, such membrane performance drop had different degrees for different PPESK substrates having different skin layer structure. The cross linkage of PDMS was very sensitive to the curing temperature, low curing temperature would result in uncompleted cross linkage which led to the low gas selectivity and high curing temperature would lead to nonuniform cross linkage which led to the low gas selectivity and gas permeation.After the PPESK hollow fiber membranes for gas separation were prepared, the mechanical property and heat-resistant property of PPESK hollow fiber membranes were examined. The result showed that the mechanical property of PPESK hollow fiber was excellent. The fracture strengths of PPESK hollow fiber membranes were as high as 9.31 to 14.87MPa. The DSC thermograms and Dynamic TG curves showed both the uncoated PPESK hollow fiber membranes and PDMS coated PPESK hollow fiber membranes had good heat-resistance. The O2/N2 selectivity of PPESK hollow fiber membrane made from the PPESK/DMAc/EtOH/THF system with the ratio of near-to-cloud point,β, of 0.85 and PPESK content of 25wt% could remain 4.8 at 70℃with the oxygen permeation of 3.3 GPU; when the operation temperature was elevated to 90℃, the O2/N2 selectivity could remain higher than 3.0 with the oxygen permeation of 6.2 GPU indicating that the PPESK hollow fiber membrane could remain good performance under high temperature. Besides, the average O2/N2 selectivity could remain steady during a long period of test time of 50 days at 60 and 70℃respectively indicating that the PPESK hollow fiber membrane could work steady under high temperature during a long period of time.The structure parameters of PPESK hollow fiber membrane made from the PPESK/DMAc/EtOH/THF system with the ratio of near-to-cloud point,β, of 0.85 and PPESK content of 25wt% was calculated according to series arrangement resistance model. The results were as follow: the porosity of dense skin layer was 3.38×10-6, the effective thickness of dense skin layer was 47nm, the average coating thickness was 493nm, the degree of penetration was 3.87×10-3. The average coating thickness calculated based on the series arrangement resistance model agreed well with the coating thickness obtained by SEM image of hollow fiber membrane cross section, indicating that series arrangement resistance model could be used to calculate the structure parameters of PPESK hollow fiber membrane.The water vapor permeations of PPESK hollow fiber membranes were also tested. The result showed that the water vapor permeation was much higher than the permeations of oxygen and nitrogen in both uncoated and PDMS coated PPESK hollow fiber membranes. The water vapor permeations of PPESK hollow fiber membranes were much higher than that of polysulfone. The high water vapor permeations and the good heat-resistance of PPESK hollow fiber membranes indicated the PPESK hollow fiber membranes had a bright prospect in the field of heat-resistant gas dehydration.
|
PDF Full Text Request