Effect of mass-transfer coefficients on the elution of a binary mixture in nonlinear liquid chromatography

Abstract

A procedure for calculating numerical solutions of the nonlinear, nonequilibrium model of chromatography for a two-component mixture is described. Solutions are presented and discussed for a series of numerical values corresponding to a wide range of mass-transfer kinetics for either component. When the mass-transfer kinetics is not very slow, the band profiles are controlled by the thermodynamic effects and the solutions are identical with those obtained by solution of the corresponding semiideal model. When the kinetics becomes slow, the nonlinear thermodynamic effects decrease and vanish. The retention time of the maximum of the band profile first increases, then decreases, and eventually a bimodal band appears, with the second maximum eluted with nonretained compounds. When the mass-transfer kinetics of the two components are very different, elution profiles are complex. The coupling effect between the two bands disappears rapidly if the component which has the larger concentration is the one with the very slow kinetics. As the opposite of the semiideal model, previously discussed, this model permits an accurate prediction of the elution profiles of the components of a mixture when their mass-transfer coefficients are different.