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A Model for the Enhanced Water Dissociation On Monopolar Membranes
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-2906-9306
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0002-9392-9059
2009 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 0019-4686, Vol. 54, no 11, 2983-2991 p.Article in journal (Refereed) Published
Abstract [en]

A model for the enhanced water dissociation that takes place at the solution/membrane interface in electromembrane processes is presented. The mechanisms behind the enhanced water dissociation are poorly understood and therefore a semi-empirical approach is suggested. The enhanced water dissociation is introduced as a heterogeneous surface reaction similar to the well established Butler–Volmer law for electrode reactions. In the model there are two parameters that need to be determined through experiments. A 1D diffusion boundary layer problem is presented and solved in order to show that a sufficient rate of water dissociation can be obtained with the model. The advantage of the presented model is that it can easily be incorporated into simulations of electromembrane processes such as electrodialysis, electrodeionization and electropermutation. The influence of the enhanced water dissociation on these processes can then be studied.

Place, publisher, year, edition, pages
2009. Vol. 54, no 11, 2983-2991 p.
Keyword [en]
Electromembrane processes, Water dissociation, Simulations, Ion-exchange membranes, Water treatment
National Category
Chemical Engineering
URN: urn:nbn:se:kth:diva-5792DOI: 10.1016/j.electacta.2008.12.025ISI: 000265342100006ScopusID: 2-s2.0-61849101879OAI: diva2:10289
Ändrad från submitted till published 20101118. QC 20101118Available from: 2006-05-23 Created: 2006-05-23 Last updated: 2012-01-18Bibliographically approved
In thesis
1. Electropermutation assisted by ion-exchange textile: removal of nitrate from drinking water
Open this publication in new window or tab >>Electropermutation assisted by ion-exchange textile: removal of nitrate from drinking water
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Increased levels of nitrate in ground water have made many wells unsuitable as sources for drinking water. In this thesis an ion-exchang eassisted electromembrane process, suitable for nitrate removal, is investigated both theoretically and experimentally. An ion-exchange textile material is introduced as a conducting spacer in the feed compartment of an electropermutation cell. The sheet shaped structure of the textile makes it easy to incorporate into the cell. High permeability and fast ion-exchange kinetics, compared to ion-exchange resins, are other attractive features of the ion-exchange textile.

A steady-state model based on the conservation of the ionic species is developed. The governing equations on the microscopic level are volume averaged to give macro-homogeneous equations. The model equations are analyzed and relevant simplifications are motivated and introduced. Dimensionless parameters governing the continuous electropermutation process are identified and their influence on the process are discussed. The mathematical model can be used as a tool when optimising the process parameters and designing equipment.

An experimental study that aimed to show the positive influence of using the ion-exchange textile in the feed compartment of an continuous electropermutation process is presented. The incorporation of the ion-exchange textile significantly improves the nitrate removal rate at the same time as the power consumption is decreased. A superficial solution of sodium nitrate with a initial nitrate concentration of 105 ppm was treated. A product stream with less than 20 ppm nitrate could be obtained, in a single pass mode of operation. Its concluded from these experiments that continuous electropermutation using ion-exchange textile provides an interesting alternative for nitrate removal, in drinking water production. The predictions of the mathematical model are compared with experimental results and a good agreement is obtained.

Enhanced water dissociation is known to take place at the surface of ion-exchange membranes in electromembrane processes operated above the limiting current density. A model for this enhanced water dissociation in presented in the thesis. The model makes it possible to incorporate the effect of water dissociation as a heterogeneous surface reaction. Results from simulations of electropermutation with and without ion-exchange textile incorporated are presented. The influence of the water dissociation is investigated with the developed model.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006
Trita-MEK, ISSN 0348-467X ; 2006:10
Ion-exchange textile, Ion-exchange membrane, Electropermutation, Electroextraction, Electrodialysis, Electrodeionisation, Modeling, Conducting spacer, Nitrate removal, Water treatment, Water dissociation
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-3992 (URN)
Public defence
2006-06-08, D3, Lindstedtsvägen 5, Stockholm, 10:00
QC 20101118Available from: 2006-05-23 Created: 2006-05-23 Last updated: 2010-11-18Bibliographically approved

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Danielsson, Carl-OlaDahlkild, AndersBehm, Mårten
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