Cyclic batch processes

The three main modes of chromatographic operation are elution chromatography, selective adsorption/desorption, and simulated countercurrent chromatography. Of these, elution chromatography, used as a cyclic batch process, was the first to be developed for large-scale separations. 

Cyclicalbatch. Both the formula and the processing instructions are the same from batch to batch. Batch operations within processes that are primarily continuous often fall into this category. The catalyst regenerator within a reformer unit is a cyclical batch process. 

A fundamental understanding of sorption processes requires a detailed mechanistic knowledge of the equilibria, kinetics, and dynamics of the sorption process. The FSR is a cyclic batch process for which adsorption is carried out at a relatively higher pressure and desorption (regeneration) is accomplished at a lower pressure, generally using part of the product from the adsorption... 

Steady-state operation of a continuous countercurrent adsorption system may be conveniently discussed in terms of the simple McCabe-Thiele analysis. The simplest type of continuous countercurrent process is illustrated in Figure 12.2, and it is evident that any of the separation processes discussed in Chapter 11 could, in principle, be carried out in such a system, rather than in a cyclic batch process. 

In the Molex process the Sorbex system is used for the separation of linear and branched hydrocarbons, using as adsorbent 5A molecular sieve. This is the same adsorbent as is used in the cyclic batch processes such as Ensorb and Isosiv. In contrast to the situation with the Cg aromatics, the separation factor is very large and it seems unlikely that for such an easy separation the increased cost of a Sorbex unit is justified by the reduction in adsorbent inventory and/or desorbent circulation rate. Detailed cost comparisons do not appear to have been published, but it seems likely that any economic advantage which the Molex process may have arises more from the energy savings associated with liquid phase operation than from the intrinsic advantages of a countercurrent adsorption system. 

PSA and VSA use a column filled with a molecular sieve, typically activated carbon, silicagel, alumina, or zeolite, for differential adsorption of the gases CO2 and H2O, alloeing CH4 pass through [47, 49]. The molecules are adsorbed loosely in the cavities of the molecular sieve and not irreversible bound [46]. It is a cyclic batch process where adsorption is performed on a relatively higher pressure (around 800 kPa) and desorption (regeneration) at lower pressure [51]. H2S,... 

Cyclic nature of Implement mechanical integrity program batch process (e.g.,, Design equipment for easy replacement start/stop, thermal cycling). Possibil- Consider demand of cycling while designing ity of mechanical equipment and controls wear and tear. Possible loss of containment. ... 

Most methods of separating molecules in solution use direct contact of immiscible fluids or a sohd and a fluid. These methods are helped by dispersion of one phase in the other, fluid phase, but they are hindered by the necessity for separating the dispersed phase. Fixed-bed adsorption processes overcome the hindrance by immobilizing the solid adsorbent, but at the cost of cyclic batch operation. Membrane processes trade direct contact for permanent separation of the two phases and offer possibilities for high selectivity. 

Both batch and continuous adsorption processes are used. In a batch process, the adsorbent bed is allowed to become saturated with adsorbed material and is subsequently regenerated in a cyclic manner. In a continuous process, usually the counter-current mode is adopted for adsorption and desorption, either in time form or in simulated mode. Continuous operation offers many advantages with respect to the efficiency of adsorbent utilization. Thus, for... 

Cyclic aromatic disulfides, polymerization reactions of, 23 706 Cyclic (arylene) disulfides, 23 712 Cyclic batch adsorption processes, 1-613 Cyclic bis(arylene tetrasulfide)s, 23 712 Cyclic carbon, polymer materials with, 15 177... 

Conoco operated a stirred tank Pfaudler glass-lined reactor for the batch S03 sulfonation of detergent alkylate. The plant utilized over-the-fence S03 converter gas (8% S03 in dry air) having 6-8 h batch cycles (264). Allied Chemical Company provided details for batch S03 sulfonation (265,266) and Conoco also published their procedure for S03 batch sulfonation (267). Andrew Jergens Company patented a cyclic batch sulfonation and sulfation process introducing nondiluted S03 vapors into a venturi contacter that emitted reaction product into a stirred reservoir tank where it was recycled from the reservoir vessel through a heat exchanger and back to the venturi in the cyclic loop. The unit operated in a vacuum (268). Derived color quality was unspecified. 

Adsorption Separation and Purification Processes. Adsorption processes can be classified according to the flow system (cyclic batch or continuous countercurrent) and the method by which the adsorbent is regenerated. The Iwo basic flow schemes arc illustrated in Figure 3 The cyclic batch scheme is simpler but less efficient. It is generally used where selectivity is relatively high. Countercurrent or simulated countercurrent schemes arc more expensive in initial cost and arc generally used only for difficult separations in which selectivity is limited or mass-transfer resistance is high. 

Industrial-scale adsorption processes can be classified as batch or continuous. In a batch process, die adsorbent bed is saturated and regenerated in a cyclic, operation. In a continuous process, a countercurrent staged contact between lire adsorbent and die feed and desorbent is established by cidier a true or a simulated recirculation of die adsorbent. The efficiency of an adsorption process is significantly higher in a eoiuinuous mode of operation than in a cyclic batch mode. For difficult separations, batch operation may require 25 times more adsorbent inventory and twice die desorbent circulation rate than does a continuous operation. In addition, in a batch mode, the four functions of adsorption, purification, desorption, and displacement of the desorbent from the adsorbent are inflexibly linked, wtiereas a continuous mode allows mure degrees of freedom with respect to these functions, and thus a better overall operation. 

The general mode of operation of a cyclic batch adsorption process is illustrated in Fig. 8. In its simplest form such a process employs two adsorbent beds, each of which is alternately saturated and regenerated. During the saturation or adsorption cycle, adsorption is continued until the mass transfer zone has almost reached the bed outlet. At this point the beds are switched so that the spent bed is replaced by a freshly regenerated bed, while the more strongly absorbed species is removed from the spent bed in... 

---