Adsorption countercurrent flow adsorber

To achieve good stability in the distribution conditions of the different compounds on the adsorbent, the operation must be conducted at a perfectly controlled temperature (< 100 ) and under pressure (< 2.10 Pa absolute) in order to keep ail the hydrocarbons in the liquid state. A pump picks up the mixture leaving the bottom of the adsorption column, recycles it to the top, to ensure continuous countercurrent flow. 

The bulk separation of mixtures (in contrast to the removal of trace components) into high-purity products by adsorption requires a countercurrent flow of phases as in other equilibrium-based separations. The moving-bed adsorber, which offers the eountercurrent flow of the phases, was used for the separation of a gaseous mixture of hydrocarbons using activated carbon as adsorbent.lt is known as a hypersorber. Though it performed well, it... 

With a favorable equilibrium and a high adsorption rate, the adsorption may be carried out in a single stage adsorber with packing. If, in a single stage, the desired concentration is not reached, two or more adsorption stages are connected in series. This is realized by cross or countercurrent flow of the adsorbent and the fed carrier phase. 

With multistage countercurrent adsorption, the receiving adsorbent phase passes from top to bottom in an adsorption column, while the carrier phase flows in the reverse direction toward the adsorbent phase (Fig. 4-16), i. e., upward. If only one adsorbate component is removed from the carrier phase, the determination of the number of theoretical separation stages A, of the adsorber and the calculation of the active adsorber height for mass transfer Z are analogous to countercurrent absorption. 

As another example, the case of air drying was calculated and compared with the complex calculation result obtained by the method introduced in the previous section (Chihara and Suzuki, I9 3a). The case of isothermal operation (Fig. 11.6, solid and open circles) is compared with the results of the continuous countercurrent flow model (solid and broken lines) in Fig. 11.14. Rigorous calculation was done for a throughput ratio of 0.01 and the change in the profiles of the amount adsorbed after adsorption and desorption steps found to be reasonably small. Thus the simple model simulated quite well the cyclic steady state profile of PSA. 

The process shown on the following page removes benzene from air by adsorption onto the surfaces of porous solids called zeolites. The adsorption unit shown below has a countercurrent flow of zeolites, and 1.00 kg zeolite can adsorb 0.10 kg benzene. Stream 6 purges 2% of the zeolite in stream 5. 

Countercurrent operation of an adsorption column in which gaseous or liquid feed is passed continuously through a bed of adsorbent countercurrent to a flow of solid adsorbent is, in principle, more efficient than the previous descriptions of cyclic batch operations because countercurrent flow maximizes the average driving force for mass transfer between fluid and adsorbent. The saturated spent adsorbent emerging from the adsorber... 

Additional stripping of the adsorbates from the adsorbent and purging of them from the voids can be accomplished by the addition or a purge step. The purge can begin toward the end of the depressurization or immediately afterward. Purging is accomphshed with a flow of produc t countercurrent to adsorption to provide a lower residual at the product effluent end of the bed. 

The PSA operation was carried out at 30-1000 and atmospheric pressure by using a N2 carrier gas (60 ml/min). Adsorbates was butanone. Before PSA operation the adsorbents was pretreated at 400-90010 for 2 h in flowing N2. In the adsorption operation, N2 with butanone vapor (27.2 or 5.44 Torr) was passed through a column of the adsorbent (0.3 g for 27.2 Torr and 0.6 g for 5.44 Torr of butanone pressure) until there was almost no further adsorption (2 h). In the desorption operation, pure N2 was passed through the column in a countercurrent way for 2 h instead of evacuation. The concentration of the organic solvent vapor in the effluent gas was always monitored with a TCD detector to obtain breakthrough curves. Amounts of adsorption and desorption were calculated from the breakthrough curves. 

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