Preparative Chromatography: Batch and Continuous

Chromatography, although initially prevalent in the analytical field, is increasingly extended as a preparative process for the commercial scale production of several chemicals whose separation from feed streams is difficult to achieve by conventional methods. In this chapter, the most relevant and recent preparative chromatography approaches are presented and discussed, divided in terms of batch and continuous processes. The fundamental conservation equations, kinetic laws, and equilibrium relations governing chromatographic systems are presented in detail as they are common to all processes modeling. Several models and approaches are presented in an order of higher approximation to reality that necessarily results in an increasing degree of mathematical sophistication. This complexity trend is linked to the sequential introduction of the various phenomena that take place inside the adsorption bed. In particular, the influence of finite mass transfer resistances and axial dispersion upon the dynamic behavior of the chromatographic system is highlighted. With regard to batch chromatography, the most frequent techniques, such as preparative HPLC and supercritical fluid chromatography are covered, along with key chromatography concepts. Closed loop recycling chromatography and steady-state recycling chromatography are recycling techniques that may be situated between batch and continuous strategies, being able to enhance the performance of batch systems while avoiding the higher complexity inherent to continuous approaches. Regarding continuous chromatography, the development of the simulated moving bed (SMB) technology has allowed improved productivity, product's purities, and lower operating costs compared to batch processing. Since its inception, several different strategies and modifications to the conventional SMB have been proposed. The well-established and the most innovative SMB operation modes, such as intermittent-SMB, supercritical SMB, and variable external streams systems, are presented and discussed, along with the necessary equipment designs that allow their implementation. Other continuous chromatographic processes include the high-speed countercurrent chromatography and the centrifugal partition chromatography, both involving two immiscible liquid phases, and annular chromatography that permits continuous operation while using a stationary phase. Some brief remarks are made on equipment and system designs. Keywords: batch and continuous processes; simulated moving bed; preparative chromatography