A step towards the development of compaction resistant organic solvent nanofiltration membranes
Creators: name: Siddique, Humera
Publisher: name: Imperial College London
Year: 2013

description: This thesis describes the development of compaction-free polymeric organic solvent nanofiltration (OSN) membranes and modules. Chemical crosslinking of integrally skinned (IS) asymmetric polyimide (PI) membranes using amines is a well-known technique. This crosslinking enhances the stability of PI membranes in harsh solvents such as dimethylformamide (DMF), tetrahydrofuran (THF), and acetone. The main issues related to the stability and performance of PI OSN membranes addressed in this thesis are: (i) Impact of pore preserving crosslinker on the stability and performance of OSN membranes It can be concluded on the basis of functional performance and characterization that no post treatment with any preserving agent was required when PI OSN membranes were crosslinked with the glycol based crosslinker known as Jeffamine. Variation in flux and rejection was &lt; 5% without post treatment with PEG. Compaction was &lt;10% in membranes after crosslinking with this pore preserving crosslinker. (Chapter 3) (ii) Development of compaction resistant mixed matrix membranes (MMM) for OSN It was found that OSN membranes with &lt;2% compaction could be produced by using polyfunctional crosslinker APTS due to the generation of an inorganic network (-Si-O-Si-). It was also concluded that flux of crosslinked polyimide membranes can be increased from 22L.m-2.h-1 to 35 L.m-2.h-1 without compromising rejection (more then 99% rejection for 236g.mol-1) by adding 4% (wt/wt) of a pore forming additive (maleic acid).(Chapter 4) (iii) Development of organic-inorganic composite membranes for hydrophobic organic solvents Defect free and compaction resistant (&lt;5% compaction) PI OSN membranes can be prepared by introducing inorganic materials into asymmetric PI membranes. These inorganic materials were helpful in creating an inorganic network throughout the membrane. An increase in hydrophobicity of the membrane was observed with the introduction of tetraehoxysilane (TEOS). Flux was increased from 7 L.m-2.h-1 to 60 L.m-2.h-1 in hydrophobic solvents such as heptane and toluene. Contact angle was changed from 65 to 87° after the introduction of TEOS (Chapter 5). (iv) Membrane for OSN based on pre-assembled nanoparticles OSN membranes with regular nanoscale structure can be produced by coating an ultrafiltration support with nanoparticles of different diameter (120-300nm used in this study). Separation performance could be finely tuned simply by varying the size of the nanoparticles and thickness of the nanoparticle layer. By varying the thickness of the membrane coated with 120nm sized particles from 0.76μm to 15.3μm, molecular weight cut off (MWCO) was shifted from 550 g.mol-1 to 340 g.mol-1. Analysis of layers with different sizes of nanoparticles suggests that more tuned and ordered structures can be obtained with smaller nanoparticles. Finally, chapter 7 describes the feasibility of OSN for the separation and reuse of a catalyst from a metathesis post reaction mixture. Commercially available membranes and membranes developed in chapter 3 and 4 were successfully applied in the separation and reuse of metathesis catalyst from their post reaction mixture. Catalyst rejection was above 99% in three consecutive cycles. It can be concluded that OSN membranes have the potential to be used in continuous reaction separation process. Catalyst turn over number varied from 58 to 140 with different with different continuous process schemes (CSTR and plug flow schemes). Overall this thesis focuses on major issues related to PI OSN membranes such as compaction and lack of regular structure. Overcoming these problems will provide more opportunities for the application of these OSN membranes on industrial scale.