Title: Development of Poly (Ether Ether Ketone) Based Solvent Resistant Nanofiltration Membranes via Phase Inversion
Other Titles: Ontwikkeling van poly (ether ether keton)-gebaseerde solvent resistente nanofiltratie membranen via fase inversie
Authors: Hendrix, Katrien
Issue Date: 6-Dec-2013
Abstract: Solvent resistant nanofiltration (SRNF) is a separation technique with large applicability in the (petro-)chemical, pharmaceutical and food industry. Development of better performing membranes will boost the implementation of SRNF membranes in the coming years. The key factors that still need optimization to achieve this growth, are membrane stability in extreme pH conditions, thermal, mechanical and solvent stability and membrane cost. The majority of SRNF membranes are polymeric, since they are cheaper and easier to process than ceramic membranes. Most polymers applied to produce membranes are soluble in harsh solvents and sometimes in extreme pH conditions, a limitation that needs to be addressed. Another factor limiting the performance of SRNF membranes is the trade-off which is typically found between selectivity and permeability through the membrane. Membranes with very tight pores are known to combine a high selectivity with low flow rate. Optimization of the membrane preparation process can however improve this trade-off.One type of material is proposed in this research to produce SRNF membranes. Poly(ether ether ketone) (PEEK) was chosen as hydrophobic, mechanically and thermally stable lab-synthesized polymer. Some modifications were added to the standard polymer, making it soluble in polar aprotic solvents and usable for the production of membranes via phase inversion. Some of the prepared PEEKs contained carboxylic acid groups in the polymer chain to allow crosslinking, thus producing a solvent-stable membrane.In a first part of this research, uncrosslinked membranes were prepared that are stable in mainly alcohols and alkanes. The lab-synthesized PEEKs were dissolved first in the polar aprotic solvents n-methylpyrrolidone (NMP) and tetrahydrofuran (THF), after which they were spread onto a non-woven backing and immersed in water to ensure phase transition to the solid phase – the membrane. A number of phase inversion parameters were altered to investigate the potential of these materials for membrane preparation. First of all, polymer specific properties were investigated, namely molar mass and polydispersity. The influence of some synthesis parameters, such as composition of the polymer solution and evaporation time before immersion in the water bath, were subsequently investigated. The importance of post-treatment on membrane performance was also studied.In a second part of this research, a novel series of PEEKs were synthesized that could produce crosslinked membranes with good chemical stability in polar, aprotic solvents. For this, amines were used as crosslinkers, producing amide bonds between the polymer chains. The crosslinking occurred simultaneously with the phase inversion process, namely during immersion of the polymer films, by adding the amines to the water bath. These membranes can be implemented for separations in harsh solvents such as THF and NMP.In a final part of this research, SRNF membranes were developed to separate edible oils from solvents. By adapting the type of crosslinker, membranes were synthesized that are more hydrophilic than the abovementioned ones, making them more suitable for the purification of edible oils from solvents. This is indeed a very interesting industrial application in which the membranes developed in this research can be implemented.
Table of Contents: 1. Introduction and scope 2
1.1. General introduction 2
1.1.1. Edible oil refining with SRNF membranes 4
1.1.2. Poly(ether ether ketone) as membrane material 5
1.2. Scope 7
1.2.1. Phase inversion study from lab-prepared membranes 8
1.2.2. Crosslinking of PEEK membranes 9
1.2.3. Edible oil refining 9
References 10
2. Solvent Resistant Nanofiltration membranes: state of the art 14
2.1. Introduction 14
2.2. Basic principles 16
2.2.1. Performance 16
2.2.2. Mass transfer limitations 17
2.2.3. Filtration operations 18
2.3. Separation mechanism 19
2.3.1. Membrane characterization 19
2.3.2. Transport mechanism 25
2.4. Membrane materials 27
2.4.1. Polymeric 28
2.4.2. Ceramics 39
2.4.3. Mixed matrix membranes 41
2.4.4. Commercial membranes 44
2.5. Challenges and prospectives 45
References 45
3. Synthesis of modified poly(ether ether ketone) polymer for the preparation of ultrafiltration and nanofiltration membranes via phase inversion. 58
3.1. Introduction 58
3.2. Experimental 61
3.3. Results and Discussion 65
3.3.1. Polymer synthesis 65
3.3.2. Performance and morphology of TBPEEK membranes 69
3.3.3. From UF to NF membranes: tuning of phase inversion parameters 76
3.4. Conclusions 79
References 79
4. Study of phase inversion parameters for PEEK-based nanofiltration membranes 84
4.1. Introduction 84
4.2. Experimental 86
4.3. Results and Discussion 89
4.3.1. Polymerization 89
4.3.2. Influence of polymer concentration in the casting solution 91
4.3.3. Tuning the membrane properties toward NF 93
4.3.4. Performance in other conditions 100
4.4. Conclusions 103
References 103
5. Influence of post-treatment and additives on PEEK membranes developed for SRNF 108
5.1. Introduction 108
5.2. Experimental 110
5.3. Results and Discussion 112
5.3.1. Influence of post-treatment 112
5.3.2. Influence of additives in the casting solution 115
5.4. Conclusions 118
References 119
6. Crosslinking of modified poly(ether ether ketone) membranes for use in solvent resistant nanofiltration. 122
6.1. Introduction 122
6.2. Experimental 124
6.3. Results and discussion 129
6.3.1. Polymerization 129
6.3.2. Crosslinking reaction 131
6.3.3. Crosslinked membranes 134
6.4. Conclusions 139
References 139
7. SRNF membranes for edible oil purification: introducing free amines in crosslinked PEEK to increase membrane hydrophilicity 144
7.1. Introduction 144
7.2. Experimental 146
7.3. Results and discussion 151
7.3.1. Polymers 151
7.3.2. Crosslinking efficiency 154
7.3.3. SRNF performance 158
7.4. Conclusions 163
References 164
8. General conclusions and perspectives 168
8.1. Conclusions 168
8.1.1. PEEK membrane materials 168
8.1.2. Phase inversion parameters 168
8.1.3. Crosslinking 169
8.1.4. Possible applications: fuel cell, edible oil refining and others 170
8.2. Future work 170
8.2.1. Expanding the set of PEEK membranes 170
8.2.2. Continued characterization of existing PEEK membranes 171
Appendix 1: Calculation of Hansen solubility parameters 173
Appendix 2: Experimental setup 176
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Centre for Surface Chemistry and Catalysis

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