טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRafi Halaui
SubjectDevelopment of New Polymeric Membranes
DepartmentDepartment of Chemical Engineering
Supervisors Professor Emeritus Semiat Raphael
Full Professor Cohen Yachin
Full Thesis textFull thesis text - English Version


Abstract

Membrane separation processes have become an emerging technology at low energy consumption. The two main membrane modules that are commonly used are spiral-wound planar membrane and hollow fiber (HF). Although spiral-wound is easy to produce, it has a low ratio of surface area to volume. HF module production is more complicated but offers a smaller size for a given performance capacity.

Current techniques used for the production of hollow polymeric fibers for HF membranes allow manufacturing fibers with internal diameter of a few hundreds µm. Decreasing the diameter of hollow fibers will result in increasing the specific area of active membrane in the module and hence increase its separation capacity.

The main goal of this research was to develop and implement the fabrication of thin hollow fibers by the co-electrospinnning (co-ES) technique. Special focus was given to development of HF with asymmetric structure. Another goal was to consolidate a HF membrane module from the developed hollow fibers.

The overall structure (core-shell dimensions, inner structure and continuity) of the developed hollow fibers was characterized by the following techniques: light microscopy, scanning electron microscopy, small angle x-ray scattering and wide angle x-ray scattering.

Influencing parameters (e.g. solvents composition, applied voltage) of the co-ES process were investigated in order to achieve the optimal conditions to which fibers should be produced.

Deformation of the cylindrical shape of the hollow fibers was inhibited by using core polymer solution with low volatile solvents. Thus, stable and continuous hollow fibers were achievable.

Co-ES technique has proved to be a reliable way of producing thin and small hollow fibers with asymmetric or symmetric structure that suits water treatment. All the hollow fibers produced had inner diameter of up to 4 µm and average wall thickness of 600 nm. All attempts of developing hollow fibers with larger inner diameter were unsuccessful.

Poly(vinylidene fluoride-co-hexa fluoro propylene) hollow fibers showed a dense structure while the addition of poly(ethylene glycol) changed its structure to asymmetric. The fibers showed lamellar structure.

 Poly(vinylidene fluoride) hollow fibers showed an asymmetric structure. Polysulfone and poly(ether imide) hollow fibers showed a symmetric porous structure.

Micro-scale HF ultra-filtration membrane module was consolidated from asymmetric poly(vinylidene fluoride-co-hexa fluoro propylene) and exhibited high rejection values of molecular weight of 60 kDa accompanied by small flux.