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Title:Electrosorption of Organic Compounds in a Flow-Through Porous Electrode
Author(s):Eisinger, Ronald Steven
Department / Program:Chemical Engineering
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Chemical
Abstract:Electrosorption, the phenomenon in which the amount of material adsorbed from solution depends on the electrical potential applied to the adsorbent, is a separation process of possible commercial importance. A particularly promising application of electrosorption is for the adsorption of organics from dilute solutions containing electrolyte. For either the concentration and recovery of valuable organic compounds or for the removal of toxic ones, a cyclic process of adsorption/desorption may be envisioned. Cycling of potential can be coupled with cycling of flow of the process of stream and of a recovery/waste stream through a packed bed of electrically conductive adsorbent. A moderately high-surface-area adsorbent (flow-through porous electrode) is required, as well as a short cycle time.
There are complex constraints on the cycle time and on other engineering parameters in such an application. In this study, the electrosorption of a neutral organic species on a flow-through porous electrode was mathematically modelled to understand these constraints. In addition, an experimental flow-through porous electrode, made of glassy carbon, was used to study the electrosorption of (beta)-naphthol.
The geometric configuration of parallel flow of solution and of current was chosen to permit a one-dimensional analysis. The mathematical model predicted the transient adsorption behavior of the bed following a change in potential. The model treated two different processes. First, the traditional chemical engineering process of adsorption in a packed bed was considered. Adsorption was assumed to be mass-transfer-limited. The second process was the capacitive charging of the electrical double layer, which caused a transient potential distribution along the length of the bed. The two coupled processes were solved by finite difference. Effects on effluent adsorbate concentration of solution velocity, bed length, electrolytic conductivity of solution, and other system parameters were determined. Transient potential distribution, charging current, and energy consumption were also calculated.
The glass carbon/(beta)-naphthol system was chosen to test the model. Differential capacitance, adsorption isotherms, and physical parameters were experimentally measured for input to the model. Adsorption isotherms for (beta)-naphthol on glassy carbon, studied over a range of 1.0 V, followed the same modified Langmuir adsorption isotherm as for the graphite/(beta)-naphthol system, but with a different potential dependence.
Flow studies were carried out in packed beds consisting of non-porous microspheres of glassy carbon. Solutions of 2 x 10('-5) M (beta)-naphthol in phosphate-buffered 0.5 M K(,2)SO(,4) were pumped through the bed at superficial velocities up to 0.3 cm/s. During the transient operation, the concentration of (beta)-naphthol in the effluent was continuously monitored by UV spectrophotometry. Potential distribution along the bed and total current were also measured continuously. Major features and trends predicted by the model for both adsorption and desorption were observed experimentally.
Issue Date:1981
Description:246 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
Other Identifier(s):(UMI)AAI8127584
Date Available in IDEALS:2014-12-13
Date Deposited:1981

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