Cation-exchange membrane MK-40 characteristics in electrodialysis of mixed solutions of mineral salt and amino acid
Abstract
The electrochemical and transport characteristics of cation-exchange membranes MK-40 which are
used in amino acids (AA) solutions demineralization by electrodialysis are studied. The peculiarities of
current-voltage curves and solution components mass transfer in electrodialysis of mixed solutions
containing organic ampholyte and mineral salt are revealed.
The experiments have been carried out in a multisection electrodialyzer with heterogeneous anionexchange
membranes MA-41 and cation-exchange membranes МК-40 manufactured by “»Shchekinoazot»
Ltd, Russia. The electrodialysis device has AgCl electrodes placed on the both sides of the cation-exchange
membrane for current-voltage curves registration. The behavior of various amino acids such as alanine (Ala),
phenylalanine (Phе) and tryptophan (Trp) is compared in this study.
Сurrent-voltage curves and transport characteristics of cation-exchange membrane MK-40 are
measured in electrodialysis of mixed solutions of mineral salt - NaCl (0.01M) and amino acid (0.02M). The
influence of AA side group on sodium ions and amino acids transport through the cation-exchange
membrane MK-40 is studied.
The ionic composition of organic ampholyte solutions depends on рH. When the pH of solution is
close to an amino acid pI (isoelectric point), the fraction of AA cations and anions is very low in a dilute
solution and their influence on limiting current density value is slight so iпред does not change significantly in
mixed solution (NaCl+AA) in comparison with iпред in individual NaCl solution. However, the solution pH
changes during electrodialysis at the overlimiting conditions lead to the formation of monopolar ions of amino
acids. They are the additional current carriers. One can find a difference in sodium ions fluxes through MK-40 and current-voltage curves of these membranes in the overlimiting mode making the comparison of
individual (NaCl) and mixed (NaCl+AA) solutions.
The increase of membrane surface hydrophobicity due to amino acid’s side group properties leads to
the intensification of electroconvection contribution in overlimiting mass transfer. In accordance with
hydrophobicity growth in a row: Ala<Phе<Trp the plateau length of current-voltage curve of the membrane
MK-40 decreases.
The results of this work can be used as electrochemical bases for amino acid solutions
demineralization.
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References
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