Adsorption operating practices

Experiments aimed at the characterization of the conversion kinetics under continuous reactor operation are not affected by adsorption phenomena. At steady state, the uptake of dye due to adsorption is practically zero since the biophase and supports are both in equilibrium with the liquid phase [53]. 

It is good operating practice to regenerate a bed in the reverse direction to that followed during adsorption. This ensures that the adsorbent at the end of the bed, which controls the quality of the treated stream, is that which is most thoroughly regenerated. Carter(44) has quantified the effect and showed that regeneration is achieved in a shorter time in this way. 

Considering most environmental applications, for catalytic as well as for adsorption operations, the gas species to be removed are in such low concentrations (large excess of inerts) that the expansion factor is practically zero and the temperature is nearly constant throughout the reactor volume. 

MTZ (mass transfer zone). 500. 501 multicomponent data, 503 operating cycles, 502 operating parameters, 502 operating practices, 504 packed beds, 500-504 regeneration, 502, 504 regeneration steam, 502 Adsorption equilibria, 495,497... 

The adsorption operations exploit the ability of certain solids preferentially to concentrate specific substances from solution onto their surfaces. In this manner, the components of either gaseous or liquid solutions can be separated from each other. A few examples will illustrate the great variety of practical applications of adsorption. It is used to dehumidify air and other gases, to remove objectionable odors and impurities from industrial gases, to recover valuable solvent vapors from dilute mixtures with air and other gases, to remove objectionable taste and odor from drinking water, and many other applications. 

Figure 1 shows schematically the pressure swing, thermal swing and combined adsorption operations. In order to estimate the practical adsorption capacities necessary to know the equilibrium relations. The equilibrium relation depending on temperatures between the specific adsorbed amount a (g/g) and the pressure p (bar) is plotted with continous line. In industrial operation this capacity can be as maximum considered and naturally it cannot be fully utilized. All of... 

As described above. Chapters 2 through 4 deal with the fundamentals of adsorption phenomena which are necessary to understand the operation and design of basic adsorption operations introduced in Chapters S to 7. Chapters 8 and 9 are fundamental topics specific to adsorption operations and Chapters 10, 11 and 12 introduce basic ideas on the practical and rather new applications of adsorption phenomena. The reader can start from any chapter of interest and refer to the fundamentals if necessary. 

Desiccant Materials, 1034 Mechanism of Water Adsorption, 1044 Dehydration System Design Approach, 1048 Operating Practices, 1069... 

It was stated in Section XIII-6C that an adsorption maximum, as illustrated in Fig. Xin-15, implies a second law violation. Demonstrate this. Describe a specific set of operations or a machine that would put this violation into practice. 

The question of whether adsorption should be done ia the gas or Hquid phase is an interesting one. Often the choice is clear. Eor example, ia the separation of nitrogen from oxygen, Hquid-phase separation is not practical because of low temperature requirements. In C q—olefin separation, a gas-phase operation is not feasible because of reactivity of feed components at high temperatures. Also, ia the case of substituted aromatics separation, such as xylene from other Cg aromatics, the inherent selectivities of iadividual components are so close to one another that a simulated moving-bed operation ia hquid phase is the only practical choice. 

Adsorbent drying systems are typicaHy operated in a regenerative mode with an adsorption half-cycle to remove water from the process stream and a desorption half-cycle to remove water from the adsorbent and to prepare it for another adsorption half-cycle (8,30,31). UsuaHy, two beds are employed to aHow for continuous processing. In most cases, some residual water remains on the adsorbent after the desorption half-cycle because complete removal is not economically practical. The difference between the amount of water removed during the adsorption and desorption half-cycle is termed the differential loading, which is the working capacity available for dehydration. 

---