Extra-column dead volume in simulated moving bed separations: Theory and experiments

In small-scale SMB units typically set up by a number of HPLC columns connected in series, the volume of the connecting tubing parts and valves may become comparable to the column volume. Therefore, to guarantee proper and satisfying separation results, the introduced extra-column dead volume needs to be considered in the calculations of the operating parameters. In this work, the impact of extra-column dead volume on the separation performance is studied, with the objective to introduce guidelines and rather simple rules to account for it. It is shown, how these results can be used in the frame of the triangle theory to determine operating conditions that allow to achieve the desired separation performance. For the experiments the separation of a racemic mixture of ( ± )-3,5-bis[1-(4-methoxyphenyl)-1-methyl]hepta-3,4-diene-1,6-diyne was carried out. The numerical model used for the simulation describes explicitly the geometric configuration of the HPLC–SMB laboratory unit to take into account the effect of extra-column dead volume.