Adsorption regeneration inert-purge

Liquid Adsorption. Adsorption takes place selectively because of (1) polarity differences between adsorbate and unadsorbed liquid, or (2) differences in size and structural characteristics of molecules. In the first category we may mention activated carbon, in the second one the molecular sieves. Liquid adsorption is suitable for both recovery of small amounts from dilute solutions, and for bulk separations. Purification is feasible with very selective adsorbent. Recovery of adsorbate and regeneration of the adsorbent may be performed by (1) Thermal Swing Adsorption, (2) Pressure Swing Adsorption, (3) inert-purge swing, or (4) displacement desorption. 

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. 

Compared to adsorption s use in bulk-gas separations, its use in gas purifications is much more frequent (see Table I and references 13, 36 and 37), and the technology is, for the most part, more conventional Temperature-swing adsorption, often combined with inert-purge stripping, is by far the most common process used Two or more fixed beds operated in parallel, typically with one adsorbing and one or more regenerating, constitute the standard flowsheet ... 

As adsorption occurs, the adsorbent increases in temperature as the heat of adsorption is released. Conversely, cooling occurs during regeneration. Because adsorption capacity is reduced as adsorbent temperature rises, inert-purge processes are usually limited to from 1 to only a very few kg adsorbate per 100 kg adsorbent. Cycle times, in ctMitrast to temperature-swing processes, are only a few minutes and almost always less than 10 min. 

If regeneration of the adsorbent is achieved at a higher temperature than used for adsorption and without the introduction of an inert purge, the equilibrium line corresponding to desorption will lie below the equilibrium line for adsorption and the requirement that the flow of desorbent be greater... 

Purging of the adsorbate with an inert gas at much reduced pressure is feasible in high pressure adsorption plants. The adsorption of Example 15.2, for instance, is conducted at 55 atm, so that regeneration could be accomplished at a pressure of only a few atmospheres without heating. If the adsorbate is valuable, some provision must be made for recovering it from the desorbing gas. 

The effects of the process variables on overall system performance may be examined by computing the cyclic steady-slate profiles for a range of parameter values. We consider a simple system, such as a gas drier, with a single adsorbable component in an inert carrier. We assume that the feed composition, temperature, and flow rate are fixed and that the adsorption cycle should operate at the feed temperature. For a given adsorbent this fixes the capacity and the nonlinearity of the equilibrium relationship (X ). The designer then has the freedom to choose the regeneration temperature and purge flow rate, the cycle time, and the bed depth. 

---