Transport Processes in Anion Exchange Membranes

McCallum, Colin (1971) Transport Processes in Anion Exchange Membranes. PhD thesis, University of Glasgow.

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Abstract

This thesis constitutes a study of transport processes in A.M.F.A-104 anion exchange membranes. Measurements were made on five different systems: the membrane equilibrated with 0.1, 0.5, 1.0 and 2.0 molar sodium chloride and 0.1 molar sodium iodide. For each system the concentrations of the mobile species counterion, coion and water -and the membrane fixed charged groups were determined, and measurements were made of the self diffusion coefficients of all the mobile species, coion and counterion transport numbers and the water transference number. Osmotic flows were obtained with 0.15/0.05 and 1.5/0.5 molal sodium chloride and 0.15/0.05 molal sodium iodide concentration gradients while salt flows across the membrane were measured in the two sodium chloride concentration cells. Membrane conductivity measurements were made in the 0.1 and 1.0 molar sodium chloride and 0.1 molar sodium iodide systems. General trends and features in the results of the individual transport experiments have been discussed and, where appropriate, comparisons have been made with the results of other workers in other membrane systems. Combination of the results of the transport experiment results permits a complete analysis of the membrane processes in terras of non equilibrium thermodynamics. This approach, which yields a set of characteristic phenomenological coefficients for the membrane at a given concentration, requires the performance of six independent transport experiments at that concentration,whereas under isothermal, isobaric conditions the maximum possible is five (conductivity, transport numbers, water transference number, salt and osmotic flows). To solve the matrix of coefficients, therefore, requires a specific assumption about the behaviour of species in the membrane. A number of plausible assumptions have been subjected to critical examination both from a theoretical standpoint and from the intercomparison of the resulting sets of coefficients calculated for the 0.1 and 1.0 molar sodium chloride systems. The iodide form was treated as a binary system rather than a ternary as the coion was present in sufficiently low concentrations as to be negligible. The phenomenological coefficients were obtained both as mobility (l) coefficients, (when the flows are expressed as linear combinations of the forces) and as resistance or frictional (R) coefficients (when the forces are expressed as linear combinations of the flows). The magnitudes and signs of the coefficients have been discussed at some length in an attempt to clarify the behaviour of the separate species in the membrane. The properties of the iodide form appear to be dominated by a strong interaction between the quaternary ammonium fixed group and the iodide ion and this appears plainly in the phenomenological coefficients. The matrix-counterion interaction in the chloride form is much less important but nonetheless seems to be significantly larger than the matrix-counterion interaction in a polystyrene sulphonate cation exchanger in the sodium form. In common with recent work on cation exchange membranes, the isotope-isotope frictional coefficients of the counterions have been observed to be both large and have the opposite sign to that which would be expected on theoretical grounds. An attempt to explain the phenomenon has been made, The structure of the membrane has been investigated using coion uptake and permeability data to calculate the parameters of the Glueckauf theory and the results have been compared with electron micrographs of sections of the membrane taken in the chromate and chloride forms. A short study of membrane selectivity was carried out using sodium chloride/iodide solutions of overall ionic strength 0.1 molar. The results confirmed the strong preference of the membrane for the iodide ion inferred from the transport results and the rational thermodynamic equilibrium constant and free energy of ion exchange in the chloride/ iodide system were calculated.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Chemical engineering, Bioengineering, Thermodynamics
Date of Award: 1971
Depositing User: Enlighten Team
Unique ID: glathesis:1971-78569
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:10
Last Modified: 30 Jan 2020 15:10
URI: http://theses.gla.ac.uk/id/eprint/78569

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