Enantioseparation via SMB chromatography. A study of Tröger's base unique adsorption behavior and the influence of heterogeneity of the column set on the performance of the SMB process

Although simulated moving bed (SMB) technology has been used successfully for over 40 years in the chemical, pharmaceutical, and food industries, a number of simplifications are made to describe and model this complicated preparative separation process. The main focus of this theoretical and experimental study is on the heterogeneous characteristics of the chromatographic column set, especially on the variation of the porosity values. A revised set of separation conditions is introduced that guarantees the successful separation under those conditions. The theoretical study reveals the existence of a superperiod.

The combination of an UV-detector and polarimeter allows the recording of the internal concentration profiles of the simple enantiomers during the SMB-separation. The racemic mixture used, Tröger's base, has a unique anti-Langmuirian adsorption behavior, which is described by a complex three-layer isotherm model. In the detailed experimental study the parameters of the different models are estimated by frontal analysis and the perturbation method. The models were tested by re-calculating overloaded concentration profiles. To determine the proper separation area, the entire area is scanned numerically because it cannot be determined algebraically. The scan was performed with different adsorption isotherm models for the average values of the column porosity and the exact porosity values, which resulted in differently shaped separation areas depending not only on the adsorption model but also on the porosity values used. The comparison of experimental and calculated internal concentration profiles shows an excellent agreement when using the average porosity as well as the exact porosity values. Although impurities present in the mixture influence the shape of the concentration profiles, the isotherm model describes the separation of the model system successfully. Additionally, the separation is described for an SMB process with a "defective" column.

Although simulated moving bed (SMB) technology has been used successfully for over 40 years in the chemical, pharmaceutical, and food industries, a number of simplifications are made to describe and model this complicated preparative separation process. The main focus of this theoretical and experimental study is on the heterogeneous characteristics of the chromatographic column set, especially on the variation of the porosity values. A revised set of separation conditions is introduced that guarantees the successful separation under those conditions. The theoretical study reveals the existence of a superperiod.

The combination of an UV-detector and polarimeter allows the recording of the internal concentration profiles of the simple enantiomers during the SMB-separation. The racemic mixture used, Tröger?s base, has a unique anti-Langmuirian adsorption behavior, which is described by a complex three-layer isotherm model. In the detailed experimental study the parameters of the different models are estimated by frontal analysis and the perturbation method. The models were tested by re-calculating overloaded concentration profiles. To determine the proper separation area, the entire area is scanned numerically because it cannot be determined algebraically. The scan was performed with different adsorption isotherm models for the average values of the column porosity and the exact porosity values, which resulted in differently shaped separation areas depending not only on the adsorption model but also on the porosity values used.

The comparison of experimental and calculated internal concentration profiles shows an excellent agreement when using the average porosity as well as the exact porosity values. Although impurities present in the mixture influence the shape of the concentration profiles, the isotherm model describes the separation of the model system successfully. Additionally, the separation is described for an SMB process with a "defective" column.