Crosscurrent adsorption

Multistage Crosscurrent Adsorption The amount of adsorbent required for the separation of a given amount of solute can be decreased by employing multistage crosscurrent contact, which is usually operated in batch mode, although continuous operation is also possible. The required adsorbent is further decreased by increasing the number of stages. However, it is seldom economical to... 

If the equilibrium isotherm can be expressed by the Freundlich equation and fresh adsorbent is used in each stage (Y0 = 0), the total amount of adsorbent used for a two-stage crosscurrent adsorption unit (Figure 10.9) is... 

Washing and adsorption The belt filters are used for washing and dewatering of fine solids in the manufacture of catalysts, zeolites, alumina and other crystalline substances, and so on. The belt filter requires the associated equipment — several vacuum pumps and separation drums. Through-circulation tray driers and through-circulation rotary driers are used to dry solids. All these are continuous crosscurrent processes. These could be replaced with a moving-bed, Hildebrand (screw) conveyer or Kennedy extractor [18], each of which is a countercurrent process. Their potential for PI has not been explored. 

Two inodes of crosscurrent adsorption processes (a) use of fresh adsorbent in each stage (b) repeated use of the same adsorbent. 

Operating diagram for a two-stage crosscurrent adsorption process using fresh adsorbent. 

Consider a crosscurrent adsorption process in which the equilibrium is linear, a condition that holds at low solute level. We then have... 

It has been shown that this principle applies to any number of stages i.e., the optimum use of adsorbent requires an equal division of that adsorbent among the stages of a crosscurrent cascade. The same principle applies to crosscurrent extraction of systems with mutually insoluble solvents. The solute recovery or removal that results in such cascades is depicted graphically in Figure 7.9. In this plot, m represents the distribution coefficient for extraction or Henry s constant H for adsorption, E is the so-called extraction factor mB/A or HS/L, and Y or x is the effluent concentration from the nth stage of the solution being treated. 

Prove that for crosscurrent two-stage treatment of liquid solutions by contact filtration, when the adsorption isotherm is linear, the least total adsorbent results if the amounts used in each stage are equal. 

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