Preparation Of Polypropylene Hollow Fiber Membrane Modified By Silane Coupling Agent And Application Of Membrane Distillation

Specifically,during vacuum membrane distillation(VMD),the hot solution passes through one side of the hydrophobic separation membrane,while the other side is evacuated to enhance the mass transfer driving force.The water molecules in the hot solution evaporate through the membrane pores and condense into a liquid on the other side of the membrane,which results in water separation/purification.The higher the hydrophobicity of the membrane material used in the vacuum membrane distillation technique,the better,thereby ensuring the retention of the liquid and maintaining the gas phase only through the pores of the membrane.The most commonly used polymer materials for membranes for membrane distillation are polytetrafluoroethylene(PTFE),polypropylene(PP)and polyvinylidene fluoride(PVDF).PP hollow fiber membranes are used herein because of their relative advantages in terms of materials and manufacturing costs.First,PP hollow fiber membranes were used as substrate to carry out superhydrophobic modification.SiO2 nanoparticles were prepared by modified sol-gel method.In order to improve the hydrophobicity of SiO2 nanoparticles,they were modified with low surface energy silane coupling agents,namely methyltriethoxysilane(MTES),vinyltriethoxysilane(VTES),isobutyltriethoxy Isosilane(ITES)and n-octyltriethoxysilane(OTES),respectively.Polypropylene(PP)particles and non-solvent cyclohexanone were added to prepare a homogeneous coating solution,which was applied to the surface of PP hollow fiber membrane by dip coating method using phase inversion principle.PP hollow fiber membranes coated with solutions containing MTES,VTES,ITES,and OTES were denoted as MTES-PP,VTES-PP,ITES-PP,and OTES-PP,respectively.The modified membranes were character:ized by transmission electron microscopy(TEM),fourier transform infrared spectroscopy(FTIR),cold field scanning electron microscopy(SEM),contact angle measuring instrument(DSA),atomic force microscopy(AFM),etc.The effects of different modification conditions on the modified membranes were investigated.When the molar ratio of the silane coupling agent to SiO2 was 0.57,the content of SiO2 was 4.0 wt%,the content of PP particles was 2.5 wt%by weight,and the content of non-solvent cyclohexanone was 15 wt%by weight,the outer surface of the modified membranes were covered with a layer of micro-nano roughness.The above modification significantly improved the dispersibility of SiO2 particles and reduced their surface energy,e.g.,the membrane based on n-octyltriethoxysilane(OTES)-modified SiO2 was superhydrophobic and exhibited water contact angles of up to 153°.The vacuum membrane distillation performance of the OTES-PP membrane was compared to that of the original PP membrane.As the temperature increased,the vacuum pressure increased,and the sodium chloride concentration decreased,the permeation flux of the two membranes gradually increased.During 30 h operation,the permeation flux of the original PP membrane and the OTES-PP membrane decreased slowly.In a short period of time,the permeate conductivity of both membranes stable at 2?7 ?S/cm,and the corresponding rejection efficiency was higher than 99.99%.When the operation time reached 30 h,the conductivity of the PP membrane increased to 50 ?S/cm,while the OTES-PP membrane substantially unchanged.Thus,the OTES-PP membrane exhibited a higher moisture resistance and was concluded to be well-suited for a wide range of potential applications such as seawater desalination.