Research On Preparation Of Polyvinylidene Fluoride Membrane With High-flux For Membrane Distillation

Membrane distillation(MD)is a separation technology combining membrane separation and traditional distillation processes,which was developed in the early 1980s.Compared to other membrane separation techniques,MD has the advantages of higher rejection,higher concentrating factor,lower operating temperature and the potential to use low-grade waste heat and/or alternative energy sources such as solar and geothermal energy.Hence,it has been widely applied niche fields such as seawater desalination,high salt concentration waste water treatment and concentration of temperature sensitive materials.The research in MD is needed now more than ever since that water pollution and shortage of fresh water resource becomes more critical.Despite its great potential,wide commercialization application of this technology is yet to be realized widely applied due to its relatively low flux.Therefore,the development of new MD membranes,innovative modules and efficient process that can lead to higher flux has always been the core goal in MD research.For hollow membrane synthesis process that involves phase inversion method,operating parameters like spinning condition and membrane size can affect the final structure formation hence the work performance of the membrane.Whilst it is difficult to make an excellent membrane with high flux and high strength just by changing spinning conditions or membrane thickness,works can be done in changing the composition and raw ingredients in the hope of better performing membrane.Using combined organic/inorganic membrane is a promising measure as it can potentially retain excellent properties from both organic and inorganic components,providing a new method for the preparation of membrane with superior flux and strength.In this study,porous hydrophobic inorganic particles-AC were incorporated into the PVDF matrix hypothetically to improve the mechanical properties of membrane as well as to increase the membrane interconnected pore structure utilizing its mechanical enhancement and porous structure.The prepared PVDF/AC membrane showed better performance in terms of membrane permeability,hydrophobicity,mechanical properties,and long-term VMD operating performance than that of pristine PVDF hollow fiber membrane.In addition,dual-layer hydrophobic PVDF hollow fiber composite membrane was prepared by a simultaneous co-extrusion spinning process.Thin membranes with high permeability and high strength can be fabricated by refining the composition of internal and external dope solutions.Recently,the design of the hydrophilic/hydrophobic composite membrane provides an improved way for the preparation of superior membrane,A new simultaneous heat and mass transfer theoretical model has been deduced under direct contact membrane distillation(DCMD)mode.It is then utilized to calculate the flux ratio of dual-layer membrane to single-layer hydrophobic membrane with the same wall thickness.The experimental data resemble well with the theoretical values for the flux ratio in the experimental range,which accurately verifies the validity of the proposed model within standard deviation of 10%.AC enhanced PVDF hydrophilic/hydrophobic composite membrane was prepared by electrospinning.This dual-layer structure has resulted in superior membrane performance,attaining higher flux while maintaining high mechanical properties.The addition of AC nanoparticles was proven to have enhanced the DCMD flux and rejection performance of the composite membrane.