Simulations of SMB-SFC Chromatography

Chromatographic separations of phytol isomers, ibuprofen enantiomers, and tocopherol homologs by SMB-SFC have been performed experimentally and were further investigated by simulations [29, 55, 58, 65-67]. The apparatus for experimental separations by SMB-SFC as well as the methods and models for determination of the adsorption equilibrium as the basis for chromatography simulation have been described elsewhere [27, 68]. 

For the dynamic simulation of the SMB-SFC process a plug-flow model with axial dispersion and linear mass-transfer resistance was used. The solution of the resulting mass-balance equations was performed with a finite difference method first developed by Rouchon et al. [69] and adapted to the conditions of the SMB process by Kniep et al. [70]. The pressure drop in the columns is calculated with the Darcy equation. The equation of state from Span and Wagner [60] is used to calculate the mobile phase density. The density of the mobile phase is considered variable. 

Phytol is a fatty alcohol with 20 carbon atoms (3, 7, 11, 15-tetramethyl-2-hexadecene-l-ol, C20H40O) from the group ofterpenes. Phytol is used in the synthesis of vitamins E and K]. In addition, it is a lipophilic component of chlorophyll. Because of a double bond cis- and trans-isomers exist. The trans-isomer is used as a fixener in the perfume industry. 

Before analyzing the effect of operating variables on the process performance, the model for the dynamic simulation of the SMB-SFC process has to be verified. For validation of the SMB-SFC model the triangle theory illustrated in Section 

4 is applied for different adsorption coefficients in the functional SMB zones. Assuming infinite numbers of theoretical stages and columns as well as the system being in a steady state, the triangle theory provides a checkable case for a system with a linear adsorption isotherm. 

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