Abstract
An analysis of the production of sodium hydroxide (caustic) in diaphragm-type electrolyzers is presented. The analysis uses experimental data to characterize diaphragms in terms of measurable properties. These diaphragm properties are used in the development of three differential equation models of the mass transport in the electrolyzer. The three models describe: (1) the steady state transport of the hydroxyl ion and the voltage drop through the diaphragm; (2) the effect of acidic feed on the hydroxyl transport through the diaphragm; (3) the time dependent transport of hydroxyl ion through the diaphragm and catholyte. Consideration of the dimensionless groups in these models reveals which measurable diaphragm properties affect the caustic yield, the voltage drop, and consequently the energy consumed during production of caustic. Nonlinear least squares regression is used to compare the model predictions with the experimental data and to estimate the hydrogen and hydroxyl ion diffusion coefficients and the average solution conductivity. These parameter estimates are used to determine the diaphragm properties and operating conditions which minimize the electrical energy required to produce caustic. Also, a control scheme is presented which maintains a constant effluent caustic concentration when the current is changed to take advantage of a variable electrical energy cost structure. The results of the analysis show that the number of properties required to characterize the diaphragm depends on the complexity of cell operation. For the steady state case in which the velocity through the diaphragm is specified, only two diaphragm properties are required: the MacMullin number and the diaphragm thickness. For the steady state case in which the differential head is specified instead of the velocity through the diaphragm, three diaphragm properties are required: the MacMullin number, the diaphragm thickness and the Darcy's law permeability. For the time dependent case in which the differential head is specified, four diaphragm properties are required: the MacMullin number, the diaphragm thickness, the permeability and the porosity. The results of the analysis also show that the specific energy required for steady state NaOH production depends on the product of MacMullin number and diaphragm thickness rather than either separately when the velocity is specified. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI
Van Zee, John Willia (1984). Sodium hydroxide production in diaphragm-type electolyzers. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -557231.