Cyclic automatic operation

For increasing the capacity of preparative work, two methods have proved to be popular, viz., cyclic automatic operation and increasing the column diameter. These two principles, alone or in combination, should permit the scaling up of production-scale throughputs, but this aim has not yet been realized. 

In the fixed-bed type, the cake of solids remains on the walls of the bowl until removed manually, or automatically by means of a knife mechanism. It is essentially cyclic in operation. In the moving-bed type, the mass of solids is moved along the bowl by the... 

Since elution is basically a batch technique, continuous production requires cyclic batch operation under automatic control. This is achieved, first, by using repetitive automatic... 

Increase of the column diameter. For analytical preparative operation or for cyclic automatic preparative work on analytical columns up to 20 min in diameter], one can make use of analytical instruments. For separations on a larger scale, the scaling-up of the columns and of the chromatographic apparatus must be effected... 

The sulphate adsorption and desorption processes run cyclically by supplying brine and water to the resin column under automatic control. A number of optional operation parameters are available. 

Contrary to catalytic applications, zeolite adsorbents are mostly applied in a fixed-bed operation. A number of columns packed with zeolite adsorbent(s) are interconnected with an automatic valve system to facilitate a continuous flow of the industrial stream being processed. Each bed, however, goes through a stepwise cyclic operation, and during each cycle the adsorbed molecules in the zeolite bed are desorbed by raising the bed temperature, lowering the bed pressure, displacing the adsorbate with another adsorbate, or combination. 

Figure 6.20 illustrates a circuit that has been widely used. SW1 affords choice of anodic or cathodic current, SW2 initiates the experiment, and then SW1 may be used for current reversal. OA-3 is available for differentiating E with respect to t. A more advanced circuit (Fig. 6.21) incorporates an additional feedback loop and a comparator to perform cyclic chronopotentiometry with automatic switching. Operation of this circuit is perfectly analogous to the cyclic voltammetry circuit discussed in Section II.E. 

Repetitive cycle operation. If the operator is required to inject each sample and to wait for the chromatograms to be produced, the task of operating in a repetitive cyclic manner becomes burdensome and the need for an automatic device rapidly becomes apparent. 

These functions must be performed automatically under conditions that ideally should result in a high quality and cost-effective part. Injection molding machines have two principal components to perform the cyclical steps in the injection molding process. These are the injection unit and the clamp unit (Figure 11.4). We now describe the operation of the various units of the injection molding machine... 

Molded-in inserts are commonly used with thermosetting materials. However, since the screw-injection process is automatic, it is desirable to use postassembled inserts rather than molded-in inserts because molded-in inserts require that the mold be held open each cycle to place the inserts. A delay in the manual placement disrupts an automatic cyclic operation, affecting both the production rate and the product quality. 

Filter pressing is a cyclic operation. Different designs enable automatic cake removal. One method is to blow the cake off by sending compressed air tiirough the filtrate tubes. Another method is to make the filter cloth a moving belt. After each operation, the belt is shifted to allow the cake to drop off on either side. 

The air blown into the silo is automatically switched cyclically from sector to sector of the bottom by a special distributing device in conjunction with pneumatically operated valves which are opened and closed as required. 

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