Browsing by Author "Luo, SK"

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Correlation of countercurrent extraction with countercurrent chromatography in aqueous matrixes. An improved model
(1999-01-15)
Yu, TI
;
Liang, CS
;
Luo, SK
;
應用化學系
;
Department of Applied Chemistry
A mathematical model was employed to simulate supercritical fluid extraction (SFE) efficiency in aqueous matrixes with supercritical fluid chromatography (SFC) data in a previous study. The SFE extraction vessel, i.e., the column for the SFC, was mathematically divided into limited layers. The analyte mass was uniformly distributed in the vessel before extraction. However, it changed when the fluid flowed through the aqueous sample and reached the column outlet. The mass redistribution as a function of the layer was computed using a countercurrent distribution approach. Afterward, each layer was considered to undergo a chromatographic process simultaneously. Each layer's chromatographic capacity factor and peak width were calculated using the true SFC experimental data, and the sum of all these peak distributions as a function of time gave the extraction efficiency, In this work, the mass redistribution was calculated through a chromatographic approach, which predicted the extraction recovery better than the previous approach,,Both the previous SFE and the newly acquired liquid/liquid extraction data using a countercurrent chromatographic apparatus were examined to demonstrate the upgrading of the model using this new chromatographic approach. Significant improvements were observed, especially for analytes with small capacity factors. The simulation deviations came mainly from the fact that analyte molecules in the individual layers would shift away from Gaussian shapes that were assumed in the model.
Correlation of supercritical fluid extraction with supercritical fluid chromatography in aqueous matrixes
(1998-05-15)
Yu, T
;
Luo, SK
;
Chen, SJ
;
應用化學系
;
Department of Applied Chemistry
A mathematical model is presented for correlating supercritical fluid chromatography (SFC) in aqueous stationary phases with supercritical fluid extraction (SFE) in aqueous matrixes. A solar coaxial countercurrent chromatography apparatus was used for the SFC and SFE experiments. The SFE extraction vessel, i.e., the column for SFC, was mathematically divided into limited layers. During extraction, each layer was considered to undergo a chromatographic process. The plate heights of all the layers were regarded equal throughout the column because pressure drops in the system were negligible. Each layer's chromatographic capacity factor and peak width were calculated using true SFC experimental data, and the sum of all these peak distributions as a function of time gave the extraction efficiency. Accordingly, the SFE analyte recovery curve could be simulated using SFC data and this model. Since SFC operations are more straightforward than SFE operations, SFE optimization may be more easily achieved using this mathematical correlation. The simulated analyte data of large capacity factors matched the experimental results very well. Deviations gradually became greater as analyte capacity factors were decreased. A rationale is proposed that satisfactorily interprets this deviation trend.