EVALUATION IN TIME DOMAIN OF MASS-TRANSFER PARAMETERS FROM CHROMATOGRAPHIC PEAKS

Impulse response experiments have been carried out in packed beds in order to determine parameters as interstitial velocities, dispersion coefficients, internal diffusion coefficients and film transfer coefficients. The transfer function of the Kubín-Kucera model is solved in the Fourier domain. Two types of beds are considered, viz. long columns (about 6 m), packed with small particles and a short tube (1 m), packed with particles with a diameter in the order of the tube diameter. Moment analysis, Fourier analysis and fitting in the time domain are applied. It is shown that for Gaussian curves Fourier analysis has no advantage with respect to the method of moments. Moreover, for asymmetric curves a combination of Fourier analysis and time domain fitting is to be preferred. This is exemplified with a system where internal diffusion is the most important process. By applying Fourier analysis and fitting in the time domain, the interstitial velocity, axial dispersion coefficient and internal diffusion coefficient could be determined from a single experimental run with an accuracy better than 10 percent. For the experiments, performed in this work, the contribution of the film resistance compared with internal resistance proved to be negligible. The values obtained for the internal tortuosity factor and for the Péclet number agree with literature. © 1979.