Absorption multistage contacting

Many chemical and biological systems include multistage processes rather than only continuous contact ones. The most common multistage systems are absorption and distillation columns. Most of these systems involve more than one phase and they therefore fall under the category of heterogeneous multistage systems. Multistage systems can be cocurrent or countercurrent. 

In a countercurrent multistage section, the phases to be contacted enter a series of ideal or equilibrium stages from opposite ends. A contactor of this type is diagramatically represented by Fig. 8.1, which could be a series of stages in an absorption, a distillation, or an extraction column. Here L and V are the molal (or mass) flow rates of the heavier and lighter phases, and x,- and y,- the corresponding mole (or mass) fractions of component /, respectively. This chapter focuses on binary or pseudobinary systems so the subscript / is seldom required. Unless specifically stated, y and x will refer to mole (or mass) fractions of the lighter component in a binary mixture, or the species that is transferred between phases in three-component systems. 

These operations are all similar in that the mixture to be separated is brou t into contact with another insoluble phase, the adsorbent solid, and the unequal distribution of the ori al constituents between the adsorbed phase on the solid surface and the bulk of the fluid then permits a s aration to be made. All the techniques previously found valuable in the contact of insoluble fluids are useful in adsorption. Thus we have batchwise single-stage and continuous multistage separations and separations analogous to countercurrent absorption and stripping in the field of gas-liquid contact and to rectification and extraction with the use of reflux. In addition, the rigidity and immobility of a bed of solid... 

Atchariyawut, S., Jiraratananon, R., Wang, R., 2008. Mass transfer study and modeling of gas-liquid membrane contacting process by multistage cascade model for CO2 absorption. Separation and Purification Technology 63 (1), 15—22. 

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