Fabrication Of Highly Hydrophobic Polypropyl-Ene Microporous Membrane And Performance Of Membrane Distillation

Membrane distillation is a newly rapidly developed technology, using hydrophobic membrane as the separation medium. The advantages of membrane distillation technology are of low operating temperature, low energy consumption and high separation efficiency, which can be applied to the preparation of ultrapure water, desalination of seawater and brackish water, wastewater treatment, concentration and separation of medicine and food. The main problem of membrane distillation when applied to concentrate Traditional Chi-nese Medicine is membrane fouling. How to improve the hydrophobicity of membrane used in membrane distillation process, improve the anti-fouling performance of membrane has become the main research branch of membrane material.This work explored, in the process of fabricating hydrophobic polypropylene mi-croporous membrane through TIPS method, the hydrophobicity which was improved by adding hydrophobic modified nano-SiO2particles into the casting solution; also the per-formance of pre-fabricated membrane in concentrating astragalus extract solution by VMD process was studied.Firstly, the hydrophobic polypropylene microporous membrane was fabricated via TIPS method and the effect of adding hydrophobic modified nano-SiO2particles on the hydrophobicity of polypropylene microporous membrane was studied. The incorporation of nano-SiO2to a casting solution mixture had a20.9%higher contact angle (CA) relative to SiO2free membranes (membrane Ma). The addition of nano-SiO2also induced morpho-logical changes in membrane structure. When the mass ratio of nano-SiO2particles and polypropylene was10:100(membrane Me), the fabricated membrane had loose membrane structure, macroporous reduced and pore size distribution narrowed compared with the pure iPP membrane; the porosity of membrnae Ma was35.45%while membrane Me was59.75%; mean pore size. of Ma and Me was0.36μm and0.13μm, respectively; the maxi-mum pore size of Ma and Me was0.77μm and0.29μm, respectively.Secondly, the optimum extraction condition of astragalus extract was determined by orthogonal experiment. The extraction condition was as follows:extraction temperature was70℃, the added amount of water was3times to the raw astragalus materials, extract-ed3times, every round last for120min. Explored the vacuum membrane distillation (VMD) performance of membrane Ma and membrane Me by concentrating astragalus ex-tract aqueous solution. The memMc had a lower flux decline, exhibited higher fouling re-sistance compared with membrane Ma. Also, pretreatment of feed solution can improve membrane anti-fouling performance.Finally, the contaminants on membrane surface, which was used to concentrate astragalus extract solution by VMD process, was determined. Results showed that the con- taminants were mainly oil, protein and carbohydrate. Took consideration of both contami-nants on membrane surface and the property of the membrane itself, selected oxi-dant--potassium permanganate as the cleaning agent. The optimized cleaning condition was as follows:the concentration of cleaning agent was2g/L, cleaning temperature was30℃, and cleaned for30min. Operated membrane distillation process continuously under the optimized cleaning condition, fully validated the fouling resistance of the above two kinds of membranes. The results showed that in the VMD process of concentrating astragalus ex-tract, membrane added with nano-SiO2particles exhibited slower flux decline than the pure polypropylene membrane and showed stronger fouling resistance.