Date

2018

Author

Yücel, Hazal

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Membranes are used in many separation processes such as gas separation, microfiltration, ultrafiltration and hemodialysis. Hollow fiber membranes are advantageous since they have a high surface area per volume and are easily backwashed which is an advantage for fouling removal. The most important factors that affect the performance of filtration membranes are concentration polarization and fouling. They increase operational cost and reduce membrane lifetime and permeate flux. One approach that can reduce concentration polarization and fouling is modifying the hydrodynamics around the membrane surface by creating flow instabilities such as Dean vortices. Dean vortices are centrifugal instabilities formed in curved channels, such as spiraling tubes In this study, helical hollow fiber membranes are produced to investigate the effect of Dean vortices on the fouling behavior of the membranes. Four different solutions were used to produce membranes. PES is used as the membrane polymer for all of them, dimethylsulfoxide (DMSO) or N-methyl pyrrolidone (NMP) as solvents, polyethlylene glycol (PEG 400K), Triton 100x were hydrophilic pore forming agents and water as non-solvent. Helical and straight hollow fiber membranes were produced by liquid rope coiling at 25°C (room temperature) and 50°C coagulation bath. Pure water permeances (PWP) and Bovine Serum Albumin (BSA, 66 kDa) rejections and fouling resistances with Baker’s yeast (Saccharomyces cerevisiae) were measured. Membrane geometry was seen to be affected by the air gap, polymer dope flow rate, bore liquid flow rate, ratio of polymer flow rate and bore liquid flow rate, bore liquid composition, coagulation bath temperature. For all solutions; increasing air gap turned membrane geometry straight to helical or irregular geometry. Increasing both polymer dope and bore liquid flow rate increased inner and outer diameter of the membranes. To observe effect of Dean vortices on fabricated membrane performance PWP and BSA rejections were measured for helical (H76) and straight (H77) membranes. For inside out process and outside-in process; helical membrane permeability during filtration decreased to 53% and 63% of the PWP, respectively. For inside out process and outside-in process; straight membrane permeability during filtration decreased to 33% and 36% of the PWP, respectively. BSA rejections of helical and straight membranes were 98% and 95%, respectively. Inside out results showing helical membranes fouling performance higher than straight membrane because of the Dean vortex. Outside in results showing fouling resistance of the straight fibers were more than helical ones. Helical membranes have improved hydrodynamics and less fouling compared to straight ones

Subject Keywords

Membranes (Technology)., Surfaces (Technology)., Polymers., Fouling.

URI

http://etd.lib.metu.edu.tr/upload/12622288/index.pdf
https://hdl.handle.net/11511/27480

Collections

Graduate School of Natural and Applied Sciences, Thesis