Adsorption displacement-purge

Steps. A purge-swing cycle usually has two steps, adsorption and purge. Sometimes, a cocurrent purge is added. After the adsorption step has been completed and the less selectively adsorbed components have been recovered, an appreciable amount of product is still stored in the bed. A purge cocurrent to feed can increase recovery by displacing the fluid held in the voids. 

Regenerative adsorption units can be operated by a thermal-swing cycle, pressure-swing cycle, displacement-purge cycle, or inert-purge cycle. Combinations of these are frequently employed. 

While inert and displacement purge regeneration is widely used in liquid phase separations, there are few industrially relevant inert purge systems employed in gas phase separations. It is sufficient to note that an inert purge regeneration can be done and it will generally be most effective at relatively high adsorption temperatures. 

Displacement-Purge Cycle This cycle, which is somewhat similar to the previous one, differs from it in that a gas or vapor which adsorbs about as strongly as the adsorbate is used to remove the adsorbate (see Figure 1) Removal is thus facilitated both by adsorbate partial-pressure reduction in the fluid around the particles and by competitive adsorption of the displacement medium. As with the inert-purge cycle, the maximum delta loading is the equilibrium loading ... 

Gas bulk-separation processes consist mostly of pressureswing adsorption (PSA) variations and displacement-purge and Inert-purge processes Recently, however, a chromatographic cycle has been commercialized Below, these cycles will be discussed ... 

As mentioned earlier, the use of a non-condensable, non-adsorbing carrier gas simplifies the task of recovery of products compared to that task in displacement-purge adsorption. At the same time, the scale-up of this process means that the effects of separation-inhibiting thermal gradients accompanying adsorption and desorption have been dealt with successfully. 

FIGURE 14.20 Two-column displacement-purge adsorption system. 

A major requirement for a successful displacement purge gas/vapor, the displacer, however, is that it should not be too strongly adsorbed compared to the feed species to be desorbed. If it is, then it would be difficult to desorb it during the adsorption part of the next cycle. In fact, ideally, it should have an almost identical affinity for adsorption on... 

In gas separation by adsorption, the gaseous feed is put into contact, at adsorption conditions, with an adsorbent that selectively adsorbs some of the components. The feed is then removed from the adsorbent, and the adsorbed components are recovered by desorption at desorption conditions. The adsorbent is usually packed into one or more fixed-bed columns. The preferentially adsorbed species are then removed and the beds are regenerated by either increasing the temperature, as in temperature swing adsorption (TSA), or by purging with a displacement agent, as in displacement purge adsorption... 

---