Preparation And Properties Of PDMS/hollow Nanosphere Mixed Matrix Membranes

Gas separation can separate or purify gas mixtures.In various separation methods,gas separation membrane technology has become a very important part.It has been industrially applied in chemical industry,energy,environment and other fields,and has become a separation technology with low energy consumption,environmental protection and high utilization rate.Among many polymer materials,polydimethylsiloxane(PDMS)has attracted much attention in the field of mixed matrix membranes and composite membranes because of its high gas permeability,low price,good adhesion and good membrane-forming property ability.In this study,hollow polymer nanospheres were added to PDMS to modify PDMS.Due to the characteristic hollow structure in the hollow nanospheres,the mass transfer path of gas in the membrane is shortened and the mass transfer resistance is reduced,thus improving the gas permeability of PDMS/hollow nanospheres mixed matrix membranes.Firstly,4,4-(9-fluorenylidene)-diamine and 1,2,4,5-benzene tetracarbonyl chloride were used as aqueous phase and oil phase reaction monomers.Hollow polyimide nanospheres were prepared by interfacial polymerization in the microemulsion system.The diameter of the hollow nanospheres was 50 nm,and the pore diameter of the shell was 1.1 nm.The PDMS/hollow polyimide nanospheres mixed matrix membrane were prepared by adding hollow nanospheres as dispersed phase to PDMS,and the influence of the doping amount of the hollow nanospheres on the gas permeation and separation performance was investigated.The results showed that the permeability of O₂,N₂ and CO₂ in the mixed matrix membrane increased first and then decreased with the increasing of the content of hollow polyimide nanospheres.At 0.2 MPa and 35°C,when the doping amount of hollow polyimide nanospheres was 3 wt.%,the permeability of O₂ in the mixed matrix membrane increased from 786 to 1664 Barrer,the permeability of CO₂ increased from 3484 to6639 Barrer,the permselectivity of O₂/N₂ was 2.3,and the permselectivity of CO₂/N₂was 9.1.Compared with that of pure membrane,the gas permeability increased by more than 90%,and the permselectivity did not change much.Then,the mixed solution of PDMS/hollow polyimide nanospheres with 3 wt.%of nanospheres was used as the coating solution.With polyetherimide membrane as the supporting layer,the PDMS/hollow polyimide nanospheres/PEI composite membrane was prepared by dip-coating method.The effect of the supporting membrane state,curing temperature,pulling speed,polymer concentration,immersion time and pre-crosslinking time on the permeance and separation of composite membrane were investigated.The results showed that PEI membrane dried with filter paper had better permeance when the curing temperature was 80°C,the pulling speed was 0.5 m/min,the polymer concentration was 3 wt%,the immersion time was 2 min,and the pre-crosslinking time was 3 h.At 0.2 MPa and 25°C,the permeance of O₂and N₂ were 1676 and 765 GPU respectively,and the slectivity of O₂/N₂ was 2.2.In the mixed gas permeation tests carried out using pure air,the composite membrane showed the potential to produce the low concentrated oxygen(?30 vol.%).