Thin film composite nanofiltration membranes at extreme conditions
Promotion date: 11. November 2011
Promotor: Prof. dr. ir. Matthias Wessling
Assistant promotor: Dr. Nieck Benes
Typically, nanofiltration (NF) involves separation of monovalent and divalent salts or organic solutes with molecular weight in the range 200 to 1000 g mol-1. Although most commercial NF membranes are suitable for treating aqueous streams at pH levels between 2 and 10, many potential applications in the chemical industry involve much more aggressive conditions. Thus advances in development of stable membranes and their performance characterization in these harsh applications will therefore expand the application window of such membranes in commercial processes.
The technique of interfacial polymerization was exploited to prepare commercially attractive thin-film composite (TFC) nanofilters. Apart from extensive stability tests at relevant pH, a comprehensive evaluation of membrane performance as a function of pH is essential. Accordingly a new method that allows molecular weight cut off characterization of NF membranes as a function of pH was developed. A popular transport model known as the Donnan steric partitioning pore model, revealed that observed pH induced performance changes could be correlated to morphological changes in the membrane matrix.
Of all the membranes investigated in this work, sulfonated poly (ether ether ketone) based TFC’s demonstrated the highest pH stability. Long term stability and performance tests on these membranes further highlighted their commercial viability.
Further in this work, novel hybrid TFC membranes containing Polyhedral oligomeric silsesquioxanes (POSS) were prepared via the Interfacial polymerization technique. Both, free standing as well as substrate supported films, could be obtained using trimesoyl chloride as an organic cross-linker. The obtained thin films were robust as well as flexible, and exhibited molecular selectivity during liquid permeation. This discovery allows development of a new generation of quasi 2-D hybrid macromolecular networks with amendable chain conformation. The presented strategy can easily be extended to various other cross-linkers and silsesquioxanes decorated with a variety of functional groups.
Could you tell something about the results you obtained?
Some of the results obtained in this work were of commercial significance while others were of substantial academic research interest. The analytic method used to realize the effect of pH on the membrane performance, could be useful for commercial membrane manufacturers as well as for researchers. The tool could help manufacturers to characterize their membranes at relevant industrial conditions of their customers, while academicians could use this to analyse why and how pH changes affect membrane performances.
Sulfonated poly (ether ether ketone) (Chapter 4) was concluded to be a suitable membrane material for industrial applications involving extreme pH conditions. The membranes performed well on stability as well as on performance when benchmarked against the most popularly used commercial nanofiltration membranes.
Interfacial polymerization (IP) technology is well established and can easily be scaled up to produce membranes economically in a roll-to-roll process. Although polyamide membranes developed using IP were unstable under extreme pH (>13), the technique was used to develop novel hybrid materials which combine the properties of polymeric and in-organic materials. These findings on novel hybrid materials open several further research possibilities for us. Due to their unique properties hybrid materials find use in several applications including beyond membrane science.
Did you manage to have nice publications along the way?
I managed three publications in the Journal of Membrane Science. One more publication is still underway.
Can you recall some special moments during your thesis work?
The project was within the Dutch Separation Technology Institute (DSTI) framework. During the entire project duration, we collaborated with partners from the industry including membrane manufacturers to membrane users, which were very memorable. This helped me learn the real-world applications. Although the research was application driven and oriented towards applications, there was still enough room for fundamental research.
What are your future plans?
Right now, I work as a R&D engineer at FujiFilm Membranes in Tilburg. As an expert in fabricating coatings the company is now diversifying into many applications, membrane technology being one of them. Here, our expertize in patented multilayer techniques are used for developing new types of membranes.
What is your view on Mesa+ in the future?
Mesa+ is an excellent platform that boasts of a huge number of research facilities, useful for a variety of fields. I plan to continue my contact with the institute by looking for collaboration possibilities within FujiFilm. We could for example utilise Mesa+ analytical facilities and expertize to develop or improve our products.