In batch chromatography, solvent-gradient operations (SG) produce significant improvement in terms of
the enrichment of products and the separation time and the solvent consumption as compared with isocratic operations.
This work studied solvent-gradient operation in reversed-phase simulated moving bed unit to separate ortho-xylene
and para-xylene. In a solvent-gradient mode, different mobile phase compositions lead to a different retention behavior
of solutes, i.e., different adsorption isotherms. Frontal analysis experiments for ortho-xylene and para-xylene were
carried out with a reversed-phase column to measure adsorption parameters at several different mobile phase compositions,
such as 45%, 50%, 60%, 75% and 90% acetonitrile. Therefore, the parameters in the retention model for
solvent-gradient operation in the case of reversed-phase chromatography were estimated and applied to the design of
an SMB system. A modified design method for solvent-gradient simulated moving bed chromatography (SG-SMB)
was proposed. The robust operating conditions were obtained within the separation region on ( ϕR, ϕE) plane ( ϕR and ϕE
are the volumetric content of organic modifier in the raffinate and the extract streams, respectively). The performance
results of isocratic and solvent-gradient SMB were compared. A partial-discard strategy and increasing of the solvent
gradient level were also applied to improve the performance of the SG-SMB.