Single‐column simulated‐moving‐bed process with recycle lag

It is shown that the periodic state of the simulated‐moving‐bed (SMB) process is reproduced by a single‐column chromatographic process with a recycle lag of (N − 1)τ time units, where N is the number of columns of the equivalent SMB unit and τ is the switching time. The operation of this ideal single‐column process is formulated by selecting an arbitrary column of the SMB and following its operation over a complete cycle. To implement the recycle lag in practice, a special type of plug‐flow tube has been designed. It includes internal elements to make the flow as close as possible to plug flow, and a piston to compensate for the difference between the inlet and outlet flow rates. This is necessary because the recycle lag is not a multiple of the overall cycle duration. The proposed system is a more compact, less‐expensive, and simpler‐to‐operate alternative to the SMB. It avoids the problem of packing reproducibility and the total pressure drop is 1/Nth of that of the equivalent SMB. Depending on the efficiency of the recycle tube, our single‐column process can achieve the same purities as the analogous SMB unit while keeping the specific productivity constant.