Preparation And Intensification Of Gas Transport Mechanisms Of PIM-based Hybrid Membranes

The development of membrane materials with high performance is the core for membrane gas separation.A variety of hybrid membranes based on polymers of intrinsic microporosity(PIMs)were carefully designed and successfully prepared in order to meet the requirements of CO2 separation process.The interface morphology,affinity to gas molecules and free volume characteristics of the membranes were regulated by incorporating fillers with different geometric shape,functional groups,and pore structure.Single/synergistic intensification of diffusion-based mechanism,solution-based mechanism and reaction-based mechanism was achieved.PIM-1/PEG-POSS hybrid membranes were prepared by incorporating CO2-philic PEG-POSS in order to strengthen solution-based mechanism.Solubility coefficient and selectivity of CO2 were significantly improved as a result of dipole-quadrupole interaction between CO2 and PEG-POSS.PIM-1/PEG-POSS(10)showed a CO2 permeability higher than 1300 barrer,and CO2/CH4(N2)selectivity increased from 12(19)to 30(31)compared to pure PIM-1,surpassing the Robeson upper bound in 2008.PIM-1/g-C3N4 hybrid membranes were prepared by incorporating two dimensional graphitic carbon nitride nanosheets in order to strengthen diffusion-based mechanism.g-C3N4 nanosheets effectively interfere with PIM-1 polymer chains and gas permeability increased at relative low loadings.The highest CO2 permeability reached 10528 barrer and the highest H2 permeability was 6344 barrer.The intrinsic ultramicropores of g-C3N4 nanosheet rendered hybrid membranes with size sieving effect.H2 selectivity increased without compromise in permeability and the performance of the prepaed hybrid membranes surpassed the Robeson upper bound in 2008.The aging process of PIMs was also retarded with the incorporation of g-C3N4 nanosheets.PIM-1/SNW-1 hybrid membranes were prepared by incorporating covalent organic framework materials SNW-1 which could preferentially recognize CO2.The pore size of SNW-1 was suitable for CO2 diffusion and SNW-1 contains basic groups which can interact with CO2 by the acid-base interactions,facilitating the transport of CO2.Thus,diffusion mechanism and reaction mechanisms were synergestically strengthened.CO2/CH4 and CO2/N2 selectivity of PIM-1/SNW-1(10)were 13.5(increased by 27.4%)and 22.7(increased by 37.6%),respectively.The CO2 permeability of PIM-1/SNW-1(15)was 7954 barrer,increasing by 116% compared with PIM-1.The separation performance of the hybrid membranes was significantly enhanced compared with pure PIM-1,especially for CO2/N2,surpassing the Robeson upper bound in 2008.Mixed gas separation factors of PIM-1/SNW-1(20)were higher than their corresponding ideal ones owing to the advantage of CO2 in competitive adsorption in SNW-1 which possessed suitable pore size and basic groups.