Dynamic Response of oxygen electrodes.Signal Deconvolution by Regularization Methods.
Advancing the chemical engineering fundamentals
Electrochemical Engineering (T2-14P)
Keywords: Oxygen electrodes, mass-transfer coefficient, transfer function, deconvolution
Oxygen electrodes are commonly used in monitoring biological reactors or for the determination of the volumetric oxygen mass-transfer coefficient in a bubble-column reactor. The measuring principle is based on the electrochemical reduction of the oxygen of a gold electrode covered by a gas-permeable polymeric membrane. The measured reduction current is proportional to the oxygen gradient near the electrode. Then, when these electrodes are used in dynamic experiments this gradient changes with time leading to systematic errors in the interpretation of the data.
The deduction of a transfer function of this kind of electrodes must contain information about the gas transport across the membrane and the distortion of the diffusion field near the edges of the gold catode. An analytical transfer function based on discontinuous Bessel integrals is proposed derived on the solution of the diffusion field in an disk microelectrode inlaid in an insulating surface [1,2]. This theoretical transfer function is compared with the experimental two-zone transfer function proposed in the literature [3].
Oxygen electrodes (InoLab OxiLevel2 + CellOx 325 WTW) are experimentally characterized with oxygen steps at different temperatures. The transfer functions of the electrodes are used for data deconvolution in dynamic oxygen-transfer experiments. The data treatment for signal deconvolution is based on Tikhonov’s regularization method in order to avoid the numerical unstability of the numerical inversion [4]. The oxygen mass transfer coefficient are determined from raw experimental data and after its deconvolution in desorption-absorption N2 + O2 experiments. A systematic difference between both values is shown and discussed in base to the mathematical description of the experiment.
The authors wish to acknowledge the Conselleria d’Empresa, Universitat i Ciència de la Generalitat Valenciana for the financial support to this work under the project Ref GV05/190.
1.- M.Fleischmann, S.Pons; J. Electroanal. Chem. 250 (1988) 277-83
2.- J.Navarro-Laboulais, J.J.García-Jareño, F.Vicente; J. Electroanal. Chem. 536 (2002) 11-18
3.- V.Linek, V.Vacek, J.Sinkule, P.Benes; Measurement of Oxygen by Membrane Covered Probes; Ellis Horwood Lim, Chichester, 1988
4.- A.Abad, SC.Cardona, J.I.Torregrosa, F.López, J.Navarro-Laboulais; J. Math. Chem. 38 (2005) 271-92
Presented Wednesday 19, 13:30 to 15:00, in session Electrochemical Engineering (T2-14P).
