Investigation of the validity of the kinetic plot method to predict the performance of coupled column systems operated at very high pressures under different thermal conditions

Abstract

The present study investigates how strong the kinetic plot method is influenced by the changes in plate height, retention factor and apparent column permeability that arise under conditions of very high pressure. More precisely, the study investigates how well a set of performance measurements conducted on a single short column can be used to predict the performance of a long sequence of coupled columns. This has been investigated for the two practically most relevant thermal conditions, i.e., that of a forced-air oven and that of a still-air oven. Measuring column performance data for acetophenone and benzene on a series of coupled 3.5 μm columns that could be operated up to 1000 bar, it was found that the kinetic plot method provides accurate predictions of time versus efficiency for the still-air oven systems, over the entire range of investigated pressures and column lengths (up to 60 cm), provided k′ and K v0 are evaluated at the maximal pressure. For the forced-air oven which leads to worse performances than the still-air oven, the kinetic plot prediction is less accurate, partly because the thermal conditions (near-isothermal) tend to vary if the number of coupled columns increases. The fact that the thermal conditions of the column wall might vary with the column length is an additional complexity making very-high pressure separations less predictable and harder to interpret and model.