PERTURBATIVE SOLUTIONS FOR NONLINEAR FIXED-BED ADSORPTION .1. APPROXIMATE ANALYTICAL SOLUTIONS FOR ASYMPTOTIC FRONTS

The authors present a new theoretical approach for a general model of non-linear chromatography in the presence of axial dispersion and mass transfer resistances, based on perturbation analysis. They first derive aproximate analytical expressions for steady (constant-pattern) fronts, which allow them to clarify the empirical idea that the HTUs (height of transfer units) for mass transfer and axial dispersion are additive. This result is in fact an approximation for which they derive an applicability criterion. They also show how the concentration of the stoichiometric point of the constant pattern front depends on the kinetic mechanism. Computation of higher-order terms allows them to derive an approximation to the transient front, which, by comparison with numerical and experimental results, has been found to be very accurate.