ABSTRACT
It is widely accepted that industrial separation processes, such as distillation or liquid extraction, are most effective when operated continuously, with the contacting fluids moving countercurrently in order to maximize the driving force for mass transfer between the phases. Operation of a chromatographic system in this fashion, however, is difficult because motion of the solid sorbent is likely to lead to disturbances in the packing structure, resulting in channeling and loss of efficiency. To retain the benefits of continuous countercurrent contact in a chromatographic separation, engineers in the late 1950s conceived the idea of simulated moving bed chromatography (SMB) (Broughton and Carson, 1959; Broughton and Gerhold, 1961). In SMB, a fixed bed is divided into subsections, and the flow path is switched between the sections at regular intervals to simulate countercurrent motion of solid and fluid. SMB chromatography is now used extensively in the chemical process industry, e.g., for purifying xylenes from C8 isomers, as well as in the sugar industry for fructose/glucose separations. Worldwide installed capacity today in these industries exceeds 8 million metric tons per year (Gattuso, 1995).
