Dissertation > Industrial Technology > Chemical Industry > General issues > Chemical processes ( physical processes and physical and chemical processes ) > Separation process > Single-phase system liquid mixture separation process > Distillation and rectification

Fabrication of Hydrophobic Microporous Membranes and Their Application in Membrane Distillation

Author XuLi
Tutor XuYouYi
School Zhejiang University
Course Polymer Chemistry and Physics
Keywords Membrane distillation Polyvinylidene fluoride Polyethersulfone Membrane structure control Hydrophobically modified Microporous membrane
CLC TQ028.31
Type Master's thesis
Year 2007
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Membrane distillation is a new type of membrane separation process, has a broad application prospects in the field of seawater and brackish water desalination, ultra pure water preparation, concentrated chemicals and recycling. In recent years, membrane distillation are increasingly high requirements for the membrane material used, not only has a strong stability, oxidation resistance, corrosion resistance and hydrophobicity, but also must have a high gas flux. To solve this problem, the paper PVDF and PES membrane material for the study of membrane distillation hydrophobic separation membrane and the modified method, the main contents are: Phase Inversion PVDF homogeneous microporous membrane structure control PVDF composite membrane preparation and vacuum membrane distillation process, the hydrophobic modification of the PES microporous membrane and its application in the membrane distillation. Light transmission dynamics Experimental study of the PVDF phase transformation kinetics of the film-forming process, and were characterized by scanning electron microscopy (SEM), mercury porosimeter, contact angle instrument on the membrane structure and performance, and examines the main film parameters (concentration of polymer solution , the use of additives and concentration of the coagulation bath composition and temperature) on the performance of the membrane structure and membrane distillation. The results showed that: As the concentration of the polymer, additives CaCl 2 DMAc solvent content increases the content and the coagulation bath, PVDF film forming system more inclined the delayed demixing occurs, the formed film surface of the others dense sub-layer sponge-like structure by the the finger pore structure transition; When the the casting solution the the nonsolvent H 2 O the content and coagulation bath temperature increases, the system of instantaneous liquid - liquid demixing rate is accelerated, the formation of the sub-layer is a porous film interdigital macroporous; PVDF membrane casting solution concentration of 10.0 wt.% the CaCl 2 for the 3.0 wt% H 2 O 2.0wt.%, pure water at room temperature under the conditions of the coagulation bath the pores of the membrane system was 85.14%, the gas source capacity the 0.50 cm 3 / cm < sup> 2 · s · cmHg. As support material, the use of non-woven polyester with non solvent H of 2 O were 0, 1.0 wt% and 2.0 wt% of casting solution prepare the plate composite film, and with vacuum membrane distillation process, study material flow rate, feed temperature, feed concentration and degree of vacuum membrane distillation flux and salt rejection. The results showed that: increase the feed temperature or the degree of vacuum distillation flux increase in the feed temperature is 65 ° C. The conditions under distillation flux can be achieved 5.39L / m 2 · h; with feed concentration increases, a slight decrease in membrane distillation flux; when the feed flow rate increases, the temperature polarization weakened, while the permeate flux increases, but increased significantly slows down gradually. Perfluoro-n-hexane as the plasma source of the PES microporous membrane surface of the hydrophobically-modified, X-ray photoelectron spectroscopy (XPS) analysis results confirmed the presence of perfluoro-n-hexane in the film surface, the fluorine content of the film surface is up to 49.3%. The modified membrane hydrophobicity significantly improve the water contact angle increased from 92.0 ° to 123.0 °. Using a scanning electron microscope to find that the modified membrane surface is covered by a thin layer, but no significant change in the body structure of the film. The film after the modified for simulated seawater vacuum membrane distillation desalination test results showed that in the case the feed temperature of 60 ° C, the modified membrane desalination 99.99% pass amounted to 4.53L / m 2 · h.

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