“Profile Method” for the Measurement of k_La and k_Va in Distillation Columns. Validation of Rate-Based Distillation Models Using Concentration Profiles Measured along the Column

Abstract

The "profile method" enables the determination of vapor-and liquid-side volumetric mass-transfer coefficients k V a and k L a by comparing the concentration profiles measured in both phases in a distillation column with the simulated profiles. The method is based on the fact that the shape of the concentration profiles along the column depend significantly on the distribution of the mass-transfer resistance between the liquid and vapor phases. This makes it possible to measure k L a and k V a directly in the distillation columns, in the same manner that is possible in absorption columns, and therefore to validate the distillation models more conclusively than by means of comparing the experimental and calculated height equivalent to a theoretical plate values. The coefficients were measured on structured packing Mellapak250Y. A small axial mixing of phases on this type of packing enables the use of a plug-flow model for both phases. Three distillation systems, methanol-ethanol, ethanol-propanol, and methanol-propanol, were used under total reflux and atmospheric pressure. Samples of the phases were withdrawn directly from the column packing by means of special sampling devices. The dependence of the individual transport coefficients on the phase flow rate was obtained by changing the reboiler duty. The dependencies were compared with those predicted by the following three mass-transfer correlations developed for packed columns: RBF (Rocha et al.

Absorption methods for the determination of mass transfer parameters of packing internals: A literature review

“…The rigorous model of Aroonwilas and Veawab 25 accounts for heat of absorption, solvent evaporation, and simultaneous heat and mass transfer. Rejl et al 69 proposed a "profile method," where not only inlet and outlet concentrations, but also the concentration profiles are compared to the model results, although it was applied only for distillation. These methods allow relaxing experimental operating constraints required for the simpler "ideal" systems and open up alternatives.…”

Energy-Efficient Diabatic Distillation Using a Horizontal Distillation Column

“…While the vertical distillation in the lab scale experiment processed a feed of 3000 mL/min, a feed flow rate of 36.5 mL/min was handled in this study as listed in Table S1 in the Supporting Information. If the column diameter is counted in the experiments, the throughput of this study is 17% of that of the vertical column.…”

“…Table S2 in the Supporting Information lists the parameters used in the computation. The mass transfer coefficients were obtained from the previous experimental study using the methanol/ n -propanol mixture …”

Liquid-phase mass-transfer coefficients of Mellapak structured packings under desorption of oxygen from primary alcohols

“…Evaluation of the volumetric mass-transfer coefficients, kLa, kGa, under distillation conditions by the novel "profile method" [1], [2], [3] provided very reasonable results in terms of gas-phase ones, but results in dependence of kLa values on liquid flow rate of kLa~uL 1 , which is steeper than that found during absorption experiments, where kLa~uL 0.62-0.9 . The significant difference in the properties of the distillation mixtures and mostly aqueous systems used for the absorption experiments was suspected as a possible cause of the difference.…”