AbstractSulfonated polyaniline (S-PANI) is a self-doped conducting polymer of the polyaniline family with improved chemical stability over a wide range of pH, easy of synthesis and better processability. The sulfonic groups are covalently bond to the PANI backbone, resulting in a permanent chemical modification and doping. Despite the interesting chemical properties, its widespread use in membrane fabrication is still limited and the few available studies have only investigated the addition of S-PANI to hydrophobic membranes to modify the surface properties and obtain low fouling systems to be used for ultrafiltration. There is also a lack of studies on the development of self-doped S-PANI membrane systems and the effect of the bulky sulfonic groups on the rejection of small molecules, performance in organic solvents, electrical conductivity and fouling behaviour of the membrane. Therefore, the aim of this research was to investigate the development of a new family of self-doped sulfonated polyaniline (S-PANI) membranes addressing i) the current limitations of PANI membranes namely acid leaching, fouling and limited solvent stability and ii) the need for robust nanofiltration membranes that could be used in complex chemical environments for the recovery of small molecules. The thesis has two components and has focused on trialling commercial membranes in complex reaction environments and on the synthesis, fabrication and testing of novel self-doped S-PANI membranes.
The work initially focused on the benchmarking of relevant industrial reaction systems such as the Suzuki coupling of aryl pyridines catalysed by palladium (II) catalyst and the lipase mediated kinetic resolution in organic solvents using commercial DURAMEM 500 and PURAMEM S600 nanofiltration membranes. The object was to evaluate product yield, catalyst activity, fouling and operating pressure and flux. Both catalytic systems were successfully retained by the membranes; furthermore, the monitoring of the reactions in batch offered a better understanding of the species contributing to membrane fouling and catalyst deactivation.
The work then focused on using S-PANI to prepare membranes that could be applied in these chemical challenging environments. Ultrafiltration and tight ultrafiltration membranes were prepared using well-established methodologies such as phase inversion in water and cross-linking using both chemical and thermal method as well as testing a novel fabrication method which make use of hexane in the coagulation bath to densify the porous polymer structure and obtained a nanofiltration S-PANI membrane. Pure S-PANI and cross-linked S-PANI membranes showed excellent antifouling behaviour when tested in BSA filtration, with the latter being resistant and reusable in DMF filtration. Furthermore, the membrane prepared via phase inversion in hexane was reusable in toluene, acetone and 2-propanol at least three times with no loss in mechanical stability at a maximum pressure of 30 bar and showed 100% rejection of low molecular weight polypropylene glycols in water.
Overall, this work has reported for the first time the development of a new family of low fouling, solvent resistant self-doped sulfonated polyaniline membranes that could be applied in various chemical environments.
|Date of Award||14 Oct 2020|
|Supervisor||Emma Emanuelsson Patterson (Supervisor), Salman Shahid (Supervisor) & Michael Bird (Supervisor)|