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Abstract:
The nonlinear frequency response of a chromatographic column is analyzed using the concept of higher order frequency response functions (FRFs) based on the Volterra series and generalized Fourier transform. The FRFs are obtained as a result of solving the equilibrium-dispersive model for Danckwerts boundary conditions, when the inlet concentration changes in the sine wave form around a steady-state and all concentrations expressed in the Volterra series form. The analysis of the FRFs for one adsorbing component shown that these functions can be used for estimation of the adsorption isotherm parameters ([1]). The nonlinear frequency response method for determination of the adsorption isotherms is at first illustrated on the simulations of the frequency response of the chromatographic column ([2]). Afterwards, it is successfully applied for estimation of two different types of the single solute adsorption isotherms, the simple Langmuir isotherm and more complex BET isotherm possessing an inflection point ([3]). Since this method has shown its potential for estimation of complex isotherm shapes, an extension to the competitive adsorption isotherms is made. The first, second and third order FRFs for the adsorption of two components on the chromatographic column are derived theoretically using the same procedure as for the adsorption of one component. At the inlet, it is possible to change periodically concentration of one component keeping concentration of the other component constant or to change periodically concentrations of both components. Both cases are considered, as well as the functions related to the inlet and outlet concentration changes of both components.
[1] Petkovska M. and Seidel-Morgenstern A. (2005), Nonlinear frequency response of a chromatographic column. Part I: Application to estimation of adsorption isotherm with inflection point, Chem. Eng. Comm. 192, 1300-1333
[2] Ilić M., Petkovska M. and Seidel-Morgenstern A., Frequency response method for the determination of adsorption isotherms. Part 1. Theoretical basis, submitted
[3] Ilić M., Petkovska M. and Seidel-Morgenstern A., Frequency response method for the determination of adsorption isotherms. Part 2. Experimental study, submitted
