Back-extraction kinetic modeling

It was evident, from the separations of PGM, that their experimental CETP values were much larger compared to that for an organic analyte at identical distribution ratios. These results indicated that factors other than mass transfer and diffusion were responsible for the additional bandwidths in the case of the metal ions. The most likely factor is the slow kinetics of back-extraction of the metal ions as the forward extraction reactions are usually rapid. To test this hypothesis, 3-picoline was used as the model compound for the determination of the CPC bandwidth due to mass transfer and diffusion (CETP if), and the CETP value due to slow chemical kinetics (CETP k) was derived by expressing the experimental CETP (CETPobs) as a sum of CETP if and CETP k ... 

Kinetic Modeling of Membrane Extraction and Back-Extraction... 

The use of thermogravimetric analysis (TGA) apparatus to obtain kinetic data involves a series of trade-offs. Since we chose to employ a unit which is significantly larger than commercially available instruments (in order to obtain accurate chromatographic data), it was difficult to achieve time invariant O2 concentrations for runs with relatively rapid combustion rates. The reactor closely approximated ideal back-mixing conditions and consequently a dynamic mathematical model was used to describe the time-varying O2 concentration, temperature excursions on the shale surface and the simultaneous reaction rate. Kinetic information was extracted from the model by matching the computational predictions to the measured experimental data. 

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