Polyimide Organic Solvent Nanofiltration Membranes-Formation and Function
Author(s)
Soroko, Iwona
Type
Thesis
Abstract
This thesis offers a comprehensive study that analyses the relationship between polyimide
(PI) organic solvent nanofiltration (OSN) membrane formation parameters, membrane
structure, and membrane functional performance. The dissertation starts by addressing the
structure-related problem of macrovoid formation, which arises when more open membranes
are prepared. Incorporation of TiO2 nanofillers into the membrane matrix results in
macrovoid-free, organic/inorganic PI/TiO2 mixed matrix membranes without compromising
rejection. Subsequently, a detailed analysis of the membrane formation process, considering
the dope solution composition, evaporation step, and structural properties of polyimides, was
conducted. The effect of the choice of polymer/solvent/co-solvent/non-solvent was found to
be very profound and qualitatively predictable through introduction of a complex solubility
parameter. Increasing value of complex solubility parameter can predict higher rejections.
The study of the evaporation in PI OSN membrane formation has shown that this optional
step is undesirable, as its presence results in unaltered rejection and significantly lower flux.
Nevertheless, the presence of a co-solvent, regardless of whether it is volatile or not, was
found to be required as it promotes formation of a dense membrane top layer. We have also
studied sensitivity of PI OSN membranes to small perturbations in polymer characteristics,
such as: molecular weight, alternating diisocyanates to form the PI chain, and copolymerisation
method (block vs random). Finally, we proposed a less hazardous route for
the PI OSN membrane formation process, which would reduce environmental impact without
compromising the separation performance of the existing membranes.
(PI) organic solvent nanofiltration (OSN) membrane formation parameters, membrane
structure, and membrane functional performance. The dissertation starts by addressing the
structure-related problem of macrovoid formation, which arises when more open membranes
are prepared. Incorporation of TiO2 nanofillers into the membrane matrix results in
macrovoid-free, organic/inorganic PI/TiO2 mixed matrix membranes without compromising
rejection. Subsequently, a detailed analysis of the membrane formation process, considering
the dope solution composition, evaporation step, and structural properties of polyimides, was
conducted. The effect of the choice of polymer/solvent/co-solvent/non-solvent was found to
be very profound and qualitatively predictable through introduction of a complex solubility
parameter. Increasing value of complex solubility parameter can predict higher rejections.
The study of the evaporation in PI OSN membrane formation has shown that this optional
step is undesirable, as its presence results in unaltered rejection and significantly lower flux.
Nevertheless, the presence of a co-solvent, regardless of whether it is volatile or not, was
found to be required as it promotes formation of a dense membrane top layer. We have also
studied sensitivity of PI OSN membranes to small perturbations in polymer characteristics,
such as: molecular weight, alternating diisocyanates to form the PI chain, and copolymerisation
method (block vs random). Finally, we proposed a less hazardous route for
the PI OSN membrane formation process, which would reduce environmental impact without
compromising the separation performance of the existing membranes.
Date Issued
2011
Date Awarded
2011-05
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
License URL
Advisor
Livingston, Andrew
Sponsor
6th Framework Programme of the European Commission Marie Curie Initiative
Creator
Soroko, Iwona
Grant Number
MRTN-CT-2006-036053- Insolex
Publisher Department
Chemical Engineering and Chemical Technology
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)