Electrodilysis
Yang, Seung Yun
(Biomaterials Science, PNU)
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Positive ions (the cations) migrate to the negative electrode (the cathode) whereas the negative ions (the anions) migrate to the positive electrode (the anode).
Driving force: electrical potential difference
Mechanism of ions transport: Donnan exclusion (ions with the same charge as the fixed ions in the membrane are excluded and can’t pass through the membrane)
Main Applications
Electrodialysis
Membrane electrolysis
Bipolar membranes
Fuel cells (convert chemical E into electrical E)
Ion Exchange membrane
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Milestones in Ion Exchange Membranes
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Electrically charged membranes are used to remove ions from an aqueous solution.
Cell pair (100 pairs are assembled)
Electrodialysis
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Preparations of ion exchange membrane
• Heterogeneous membrane: combining ion-exchange resins with a film-
forming polymer and then converting them into a film electrical resistance is relatively high and mechanical properties is poor
• Homogeneous membrane: introducing of an ionic group into a polymer film prepared by phase inversion charge is distributed uniformly over the
membrane and highly crosslinked to reduce their extensive swelling
Basic parameters for a good membrane
• High selectivity
• High electrical conductivity
• Moderate degree of swelling
• High mechanical strength
• High chemical stability
Materials for Ion Exchange Membrane
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Anion-exchange membrane
Cation-exchange membrane
Treatment with a sulfuric acid introduction of SO3H gro Introduction of a tertiary ammonium group
Stylene-divinylbenzen(DVB) Copolymer
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Production of potable water from brackish water
Production of salts by concentration of sea water (limited in Japa
Demineralisation of whey
Separation of amino acids
Applications of Electrodialysis
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Anion Dipolar ion Cation
Amino acids can be positively or negatively charged depending on the pH of the solution
At high pH, negatively charged (a) and positively charged (c) at low pH.
(a) (b): isoelectric (c)
point
Separation of Amino Acids
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Electrolysis
“Chlor-alkali” process: only one type (cation-exchange membrane) membrane is required in the production of chlorine and NaOH.
cation-exchange membrane
Production of NaOH and Cl 2
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Galvanic cell in which chemical energy is directly converted into electric energy.
High efficient energy production without any waste (product is water) (cf. fossil fuel produce Nox, SO
2, and CO
2)
Electrons flow from anode to cathode
4H
++ O
2+ 4e
- 2H
2O 2H
2 4H
++ 4e
-Fuel cells
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Summary of Electrodialysis
