Three-column system

The three-column system is primarily used in basic studies and simple separations. Important parameters and functions are listed in Table 4 while its configuration is shown in Fig. 1. 

Table 4 Column Parameters and Functions of HPIEC Three-Column System...

The five-column HPIEC system, because of the sizable scope of its functions, was used by the authors to study those rare earth separations that were too difficult to examine with the three-column system. The largest rare earth oxide sample employed with it was 50 g. 

Use of the three-column system shown in Fig. 2 has been examined to judge its potential for rare earth separations. The purities of Sm, Eu, and Gd that were obtained from the mixed Sm-Eu-Gd sample used for this basic study were Sm20j 99.5%. EUjOj 99.99%, Gd203 99.5%. The composition of the natural Sm-Eu-Gd sample separated in this study was Nd 13%. Tb 4.5%, Sm 25%, Eu 4.8%, Gd 27.0%, and the other RE elements 25%. Gd and Eu alternatively labeled with Gd-(153, 159) and Eu-(152, 154) were used to determine the displacement curves of these two elements while the displacement curve of Sm was determined by using a spectrophotometric method. 

The record of the method should be brief and in the first person singular. A three column system be used for keeping a record of experiments about the properties of gases etc. The three column be headed Experiment, Observation and Inference. 

In a three column system, on Column One the column operational sequence will be sample, flush, equilibrate, and then on Column Two one will have to equilibrate, sample, flush and to set up Column Three in sequence, one is going to equilibrate through the first two steps and then load sample and then flush. Note that the product is continuously coming out of the system after each sequence. This is different than if one had a single column and one had to wait for longer periods of time between events. It allows optimum utilization of downstream recovery equipment with less batch operation. 

The results verified that the same retention volume for a given solute was obtained on all three column systems. The results from these experiments are depicted in figure 3.7. 

Taymaz [44] developed a direct method for TDI and diphenylmethane diisocyanate in polyurethanes by direct injection of the sample solution on to three-column system (500 +100 +100A) using methylene chloride (lmLmin ) with refractive index detection. A sample of crude MDI was shown to contain about 43% of unreacted MDI when examined by this method. 

In these expressions and Fp are the elution volumes associated with the marker and particle peaks, respectively. As a result of the double-layer effects described earlier, both F and Fp exhibit a dependence on ionic strength. Figure 10.4 shows a typical data set for a three-column system in which either SLS or AMA was used as the stabilizing agent. Experience has shown that, for... 

The Photovac Voyager, a fifth-generation portable GC, is shown in Figure 2. Features of the Photovac Voyager include a three-column system and dual PID-ECD detectors. The Voyager also includes a factory-programmed assay that provides preset instrument operating parameters and compoimd library to simplify operation. 

A combination of Cig reversed phase, Dowex anion-exchange resin, and the chelating resin, chelamine, in a three columns system, was described for the simultaneous preconcentration and differentiation between natural... 

Systems analogous to solvent extraction. A more satisfactory continuous system from the viewpoint of resin utilization would be based upon the counter-current principle as employed so successfully in liquid-liquid extraction processes. Hutcheon describes a three-column system of this type (Fig. 3.6) for separating two components A and B, independent of the type of plant in which it would be operated. The resin passes down column I and then down column II in counter-current flow with two aqueous solutions. The main one of these is the feed solution which enters at the base of column I, but it is mixed with the scrub solution or stripping solution which has passed up column II, again in counter-current flow to the resin. As in a solvent extraction process, chemical compositions of the two solutions are adjusted so that Ea> 1 and <1, where Ea and Eb are the extraction factors applicable in a solvent extraction process, i.e. 

A slower flow rate of the eluent gives better resolution of serum lipoproteins. The effect of flow rate of the eluent on the resolution of LDL and HQL for three column systems is shown in Fig. 6. The flow rate of 0.40 ml/min - 1.0 ml/min is usually used according to column systems (see Section 2.5) due to the balance between the increase in resolution and the time required for analysis. 

RGURE 5 Scheme for performing immunochromatographic analysis in three-column systems including two immunorecognition steps. Symbols as in Fig. 2. ... 

SW amphoterics, however, are not retained by the cation exchanger. In this case use a three-column system, as follows. 

This stand-alone column can be optimized for each selection of the XDl composition. For each XDl, we can go through the same procedure as outlined previously and obtain the optimal design and operating conditions for this overall three-column system. The optimized results can be seen in Figure 8.22. Notice that the ratio of AO flow (2056.01 mol/min) to the bottom IPA product flow (832.50 mol/min) has also been reduced from 3.19 to 2.47. 

Figure 8.22 Optimal design flowsheet for three-column system.

This desirable result is mainly due to the combined pieconcentrator/recovery column dampening the large disturbance from fresh feed, thus making the feed variations to the more sensitive Cl colimin small and easier to handle. The three-column system should also have this desirable feature. However, it requires more process, instrumentation, and control equipment, and the TAC is also higher than the proposed design. 

A method for a more complete analysis of all of the components was developed by Boer and Van Arkel (90). A three-column system with automatic valve switching and cold traps was utilized to determine paraffins, naphthenes, and aromatics. Thus it is commonly referred to as a PNA analysis. A polar column of tris(cyanoethyl)nifromethane was used to retard the aromatics. A 13X molecular sieve column then separated the paraffins and naphthenes. A nonpolar column of UCCW-982 provided further separation of the aromatics and naphthene components. Fignre 13.31 shows a typical chromatogram along with an indication of the column switching involved. 

In the three-column system (Fig. 33) the topping column bottoms passes first to a pressurized refining column and then to an atmospheric refining column. Federal grade AA methanol is withdrawn close to the top of both refining columns. Although the three-column system is more costly, it can reduce the required distillation heat input by 3040% [23]. 

Occasionally a four-column distillation system is used, but most modern processes use either a two- or three-column system to produce U.S. federal grade AA methanol. Multicolumn systems (three or more columns Fig. 33) can generally only be justified when the cost of energy is prohibitively high. 

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