Membrane fabrication via non-solvent induced phase separation for ultrafiltration and forward osmosis

다국어 초록 (Multilingual Abstract)

Demand for fresh water has risen consistently over the years, leading to the development of the water treatment and membrane industry. In the membrane industry, reverse osmosis (RO) makes up the largest portion, while ultrafiltration (UF) and microfiltration (MF) membranes also make up a considerable portion for waste water treatment or pretreatment for RO.
In the first topic, we introduce polyacrylonitrile (PAN) based amphiphilic block copolymer. In the membrane industry, pressure-driven processes suffer from fouling and chemical resistance. Commercial membrane materials such as polysulfone (PSf) and polyethersulfone (PES) are hydrophobic, making them susceptible to fouling and thus in need of chemical cleaning. In this process, chemical cleaning agents like NaOCl shorten the life expectancy of the membrane. Thus, research for hydrophilic materials for membrane materials is in progress. PAN is a widely used membrane material known for its relative hydrophilicity. We used PAN and a hydrophilic block or etchable polymer, synthesized block copolymer and fabricated hydrophilic UF membrane. PAN is soluble in only a few solvents, so the synthesized block copolymer has broad polydispersity.
In the second topic, we introduce “self-assembly and non-solvent induced phase separation” (SNIPS) membrane for FO support to reduce internal concentration polarization (ICP) effect. RO consumes a large amount of energy, so FO has attracted much attention because it uses osmotic pressure as driving force. However, due to the ICP effect, FO process has not been commercialized yet. Therefore, much research is focused on reducing ICP. The ideal FO support is thin, hydrophilic, and has high porosity and tortuosity. We use PS-b-P4VP SNIPS support as the FO support. Block copolymer was used because of its ability to self-assemble. Block copolymers are widely used in fabricating membranes with regular pores for size-sieving processes. A combination of SNIPS and conventional NIPS is used to fabricate UF membranes which have regular structures on the membrane surface. We fabricated PS-b-P4VP support with controlled polymer solution concentration, good solvent composition, and relative humidity. These are important parameters to form regular structures on the surface. Finally, we tested the performance of FO membranes.

목차 (Table of Contents)

• 1. Introduction 1
• 2. Theoretical Background 2
• 2.1. Water Treatment 2
• 2.2. Membrane Process 2
• 2.2.1. Membrane using size-sieving mechanism 3
• 2.2.1.1. 1 Micro filtration (MF) and Ultra filtration (UF) 3
• 2.2.1.2. Nano filtration (NF) 4
• 2.2.2. Membrane using solution diffusion mechanism. 7
• 2.2.2.1. Osmosis 7
• 2.2.2.2. Forward Osmosis 7
• 2.2.2.3. Reverse Osmosis 11
• 2.3. 3. RAFT polymerization of block copolymer 13
• 2.4. NIPS 15
• 2.4.1. SNIPS 17
• Chap. 1 20
• 1. Introduction 21
• 2. Theoretical Background 22
• 2.1. Polyacrylonitrile 22
• 3. Experimental Section 23
• 3.1. Materials 23
• 3.2. Polymer synthesis 23
• 3.3. Membrane fabrication 24
• 3.4. Characterization of polymer and membrane 24
• 3.4.1. Gel Permeation Chromatography (GPC) 24
• 3.4.2. Field Emission-Scanning Electron Microscopy (FE-SEM) 24
• 3.5. UF performance test 25
• 4. Results 25
• 4.1. Synthesis and characterization of PAN based block copolymer 25
• 4.2. Structure and performance of membrane using PAN based polymer 28
• 5. Conclusion 35
• Chap. 2 36
• 1. Introduction 37
• 2. Theoretical Background 38
• 2.1. FO membrane 38
• 2.2. Interfacial Polymerization 39
• 3. Experimental Section 41
• 3.1. Materials 41
• 3.2. Membrane Characterization 45
• 3.2.1. Field Emission-Scanning Electron Microscopy (FE-SEM) 41
• 3.2.2. Contact Angle 41
• 3.2.3. Porosity 42
• 3.3. Fabrication of support 42
• 3.4. Fabrication of PA layer 42
• 4. Results 44
• 4.1. Surface and cross structures of PS-b-P4VP 44
• 4.2. Performance of FO membrane 53
• 5. Conclusion 56
• 6. References 57