Chiral API purification: continuous SMB chromatography

A racemic active pharmaceutical ingredient (R/S enantiomers, dilute in ethanol eluent) is resolved continuously by simulated moving bed chromatography — the workhorse of chiral-drug manufacture that legacy steady-state flowsheet simulators have no native model for (engineers script it in MATLAB). This uses the native SMB unit op, which solves the standard steady-state True Moving Bed equivalent: a 4-zone counter-current equilibrium-stage cascade whose zone flow-rate ratios sit inside the triangle-theory separation region, so the more-retained enantiomer reports to the extract and the other to the raffinate — the separation is driven by the chiral adsorption selectivity (the two enantiomers are otherwise thermodynamically identical). Honesty note: this is the TMB steady-state equivalent, not the transient multi-column process with discrete port switching; stages are ideal equilibrium stages (no mass-transfer resistance / axial dispersion); the isotherm affinities are illustrative screening values.