Preparation And Properties Of Asymmetric SiO₂-PDMS-PVDF Blend Hollow Fiber Membranes

In this study,the mechanisms of mass transfer and heat transfer for vacuum membrane distillation?VMD?were determined;a VMD model has been developed.The influence of the temperature polarization and the concentration polarization for VMD has been studyed.The effect of operating conditions like feed flow rate,feed temperature,feed salt concentration and vacuum degree were investigated.The influence of membrane structural such as porosity,thickness,pore size and morphology were investigated.It provided guidance for the preparation of membrane and the operation of the vacuum membrane distillation?VMD?.PVDF and Polydimethylsiloxane?PDMS?were used as main membrane materials,hydrophobic nano-fumed silica was used as additive,polyvinylpyrrolidone K30?PVP?was used as additive,Ethylorthosilicate four?TEOS?was used as the crosslinking agent and Dibutyltin dilaurate?DBTDL?was used as the catalyst,N,Ndimethylacetamide?DMAC?,Triethyl phosphate?TEP?and tetrahydrofuran?THF?were employed as the solvent.Hydrophobic asymmetric SiO₂-PDMS-PVDF hollow fiber membranes were prepared by phase inversion immersion method for the vacuum membrane distillation?VMD?.First the viscosity of the casting solutions was measured with rotary viscometer,and the coagulation kinetics of SiO₂-PDMS-PVDF dope solutions were characterized by the curve of light transmittance verse immersion time.The characters of the prepared membranes were tested in terms of wide-angle X-ray diffraction?WXRD?,porosity,pore size,Liquid entry pressure?LEP?,attenuated total reflection Fourier transform infrared spectroscopy?ATR–FTIR?,burst pressure measurement,TGA,field emission scanning electron microscopy?FESEM?,water contact angle?WCA?and mechanical property.The effect of changing SiO₂ nanoparticles concentration on permeability of the composite membranes have been investigated.The best performance SiO₂-PDMS-PVDF blend hollow fiber membrane was investigated in VMD process.The experiments operational condition such as flow pattern,feed temperature,and vacuum have been optimized,and the stability of the membrane for VMD has been investigated.The asymmetric cross-linked SiO₂-PDMS-PVDF blend hollow fiber membranes maintained a stable high flux of 47.27 kg/m2·h and a high salt rejection of over 99.9% during continuous desalination experiment at the optimum conditions of feed temperature 75 °C,feed salt concentration 35 g/L,vacuum degree 87 kPa,and feed flow rate 50 L/h.It is believed that the asymmetric SiO₂-PDMS-PVDF blend hollow fiber membranes may be of great potential to be utilized in the MD process.