The Hypersorption Process

FIGURE 12.6, McCabe-Thiele diagram for simplified fractionation process. (From ref. 2, reprinted by permission of Martinus Nijhoff Publishers.) 

As with distillation, the McCabe-Thiele analysis is strictly valid only for a binary system. To analyze the behavior of a multicomponent system it is, in principle, necessary to make plate-to-plate calculations. However, it is commonly found that only two components are present at significant concentrations within each individual section of the column. A preliminary analysis in which each section is considered as a pseudo binary McCabe-Thiele system can therefore provide useful guidance in the design of a multicomponent adsorption system. 

FIGURE 12.7. Schematic diagram of hypersorption process showing test mass balance, temperatures, and other operating data. 

In the rectification section, below the feed point, the lighter components are stripped from the adsorbed phase while the heavier components are concentrated in the adsorbed phase. Desorption of the heavier components is accomplished by steam stripping in the bottom section of the column in which the temperature is raised to 510°F by a dowtherm heat exchanger and live 

FIGURE llJi. Simplified engineering diagram of a hypersorption column. (From ref. 8, reprinted with permission.) 

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The third and final step in both cases consisted of operating the column or tower continuously with a constant feed and constant draw-off of products. In distillation this step is represented by the large continuous fractionating columns now used in many petroleum and chemical plants. In adsorption it is represented by the Hypersorption process (8, 4, 28, 29). 

Perhaps the hypersorption process (7) of recent years may be thought new and it is new in applying the mechanical principle of continuous operation to charcoal adsorption, but such adsorption on a batch process was in use more than 25 years ago and became obsolete in competition with absorption. Now the continuous hypersorption method appears to be finding a real field of usefulness, especially in making very high recoveries of propane and in recovering substantial amounts of ethane. Recovery of ethane is beginning to be important, in connection with its use as a chemical raw material for the reactions mentioned previously in this paper. 

Studies have been made of continuous systems. In the hypersorption process, a vertical column contains a bed of carbon that continuously moves downward. Raw gas enters at a point midway in the column. As the smaller hydrocarbon molecules are less adsorbable they flow upward to be collected and recovered at the top of the column whereas the larger hydrocarbon molecules are adsorbed and are carried with the carbon to the discharge at the bottom. The adsorbed hydrocarbons are recovered at a heating station and the denuded carbon is returned to the top of the column to repeat the cycle.25... 

Many industrial countercurrent fractionation processes for the separation of components operate on the principle of either the three and four section cascade or the simulated moving bed. A summary of simulated moving bed and countercurrent fractionation processes is given in Table S.l. With the exception of the Hypersorption process all are presently operated commercially. 

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