Dokument: Nanocomposite materials for membrane separation processes
| Titel: | Nanocomposite materials for membrane separation processes | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=26268 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20130715-143339-1 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Sieffert, Daniel [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Staudt, Claudia [Gutachter] Prof. Dr. Coronas Ceresuela, Joaquin [Gutachter] Prof. Dr. Weinkauf, Rainer [Gutachter] | |||||||
| Stichwörter: | Membrantrennverfahren, Nanokomposite, Copolyimide, MWCNT, Titanosilikate, Pervaporation, Gastrennung | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 540 Chemie | |||||||
| Beschreibung: | Membrane based separation processes represent a growing technique with many industrial applications. In order to maintain a growth it is important to further improve membrane materials. The fabrication of nanocomposites represents a promising approach towards a new generation of polymer based membranes. By incorporating nanometer sized components into a polymer matrix it is possible to drastically improve material properties or even introduce new ones. This improvement is usually due to the extreme aspect ratios of the nanoparticles (“nano-effect”). The aim of this work was to prepare novel nanocomposite materials based on the copolyimide 6FDA 4MPD/6FDA DABA 4:1, an outstanding polymer for various separation tasks. It allows further chemical modification and is well processable, which facilitates the fabrication of nanocomposites. On the one hand functionalized multi walled carbon nanotubes (MWCNTs) were added with the aim of preparing swelling resistant pervaporation membranes with enhanced permeability for the separation of aromatic mixtures. On the other hand titanosilicate JDF-L1 nanosheets were incorporated in order to obtain gas separation membranes with increased selectivity based on size exclusion.
The potential of MWCNT/copolyimide nanocomposites was assessed in pervaporation experiments with toluene/cyclohexane mixtures, a challenging separation task from conventional point of view. Admittedly high aromatic concentrations can induce membrane swelling which increases permeabilities but drastically lowers selectivities. This requires stronger interaction of the membrane material on molecular level. Usually cross-linking is used here, which however often leads to compaction of the membrane material which then again decreases permeability but increases selectivity. MWCNT/copolyimide nanocomposites represent an approach to surpass this tradeoff. In this work MWCNTs were successfully functionalized with OH-groups and a method to prepare MWCNT-OH/copolyimide nanocomposites was developed. Pervaporation experiments showed that an incorporation of 1 wt% MWCNT-OH drastically enhances the flux from 8.8 and 10.5 kg*μm*m^-2*h^-1 for the copolyimide to 17.3 and 16.5 kg*μm*m^-2*h^-1 for the nanocomposites, while selectivity remained unaltered. The addition of the MWCNTs noticeably reduces the activation energies for the permeation of both feed components. The effect could not be increased by addition of 3.5 wt% MWCNT-OH. However it was found that the addition of MWCNT OH generally enhances the swelling resistance of the material at high aromatic concentrations. The capabilities of JDF-L1/copolyimide nanocomposites were evaluated via gas separation with H2/CH4 mixtures. This separation task is of growing industrial interest as the demand for hydrogen and with it hydrogen recovery technologies become more and more important due to increasing environmental regulations. Membrane processes still exhibit growth potential here, provided that membrane separation characteristics can be improved further. On this background the aim was to increase the selectivity of 6FDA 4MPD/6FDA DABA 4:1 by adding JDF L1 nanosheets and thus incorporating the size exclusion effect of the filler. By achieving a horizontal filler orientation it was intended to further enhance this effect. Additional experiments were conducted with ion exchanged JDF-L1 in which the interlamellar Na+ cations were exchanged with H+, Li+, K+, Mg2+ or Ca2+ so as to facilitate permeation of hydrogen through the filler. MMM analyses showed that by varying the polymer concentration of the casting solution it is possible to influence the filler orientation in the membrane. Multiple analysis methods consistently showed that membranes containing 5, 8 and 10 wt% JDF-L1 sheet particles cast from a 10 wt% polymer solution possess a preferential horizontal filler orientation while MMMs cast from 13% polymer exhibit a more random alignment. Gas permeation experiments were performed with these membranes using H2/CH4 mixtures. Both permeabilities decreased with increasing filler loads. The reduction was however much stronger for CH4 which drastically increased the selectivity. For a MMM containing 5 wt% JDF L1 cast from a 10 wt% polymer solution the H2 permeability dropped from 360 Barrer for the pure polymer to 189 Barrer while the selectivity increased notably from 21.3 to 30.2. In the case of MMMs with a more random filler orientation (cast from a 13 wt% polymer solution) the decrease of CH4 permeability was not as strong and thus the increase of selectivity not as strong. By exchanging the interlamellar cation it is not possible to further enhance the separation characteristics for H2/CH4. The results for ion exchanged JDF-L1 instead show that higher permeabilities are possible with bivalent cations or H+ than with other monovalent cations (Li+, K+, Na+). Taking into account the extremely small size of H+ and the fact that bivalent cations replace two interlamellar sodium cations, this indicates that the interlamellar cation in fact noticeably influences the permeation of gases through the filler. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Chemie » Organische Chemie und Makromolekulare Chemie | |||||||
| Dokument erstellt am: | 15.07.2013 | |||||||
| Dateien geändert am: | 15.07.2013 | |||||||
| Promotionsantrag am: | 28.05.2013 | |||||||
| Datum der Promotion: | 10.07.2013 |
