Multi-Column System

Module 1, a column section, represents the section in the main column below tlie draw tray. No separate module is needed at the bottom since no reboiler is used. 

Module 2 models the draw tray and consists of a mixer and an equilibrium stage. Module 3 is a splitter that takes the liquid from the draw tray and splits it into side draw SD and the remaining liquid flowing down to the bottom column section. The side-stripper and the upper column section are modeled with column sections, modules 4 and 5, and the condenser is modeled with an equilibrium stage, module 6. Using computational sequence 1,2, 3,4, 5, 6 requires initialization of streams L3, L5, OH, and R. 

4 Liquid-Liquid Extraction by the Shortcut Column Section Method 

Another application of the shortcut column section method is for solving liquid-liquid extraction problems. The fundamentals of extraction were discussed in Chapter 11, and graphical solution methods were described based on ternary liquid-liquid equilibrium diagrams. These methods are limited to three-component extraction systems. 

A multi-component countercurrent extractor model may be delined for the shortcut column section method in a manner very similar to the vapor-liquid model. The extractor model is developed for liquid-liquid equilibrium stages leading to component flow relationships comparable to the Kremser equation  

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A step forward in simplification of multi-column systems involves the use of anion exchange and cation exchange columns connected in series. Such systems can be readily organized inside a standard isocratic ion chromatograph. In this approach a single eluent is used for separation of anions and cations and ideally the eluted analytes are detected with a single detection unit. In this way Takeuchi et al. [31 separated a mixture of Na+,... 

The principle of the Varicol process consists in a non-synchronous shift of the inlet and outlet ports of a multi-column system on a recycle loop [70]. The Varicol process is characterized by a even more efficient use of the stationary phase than the one achieved in the SMB process. 

Malto-oligosaccharides can be studied by gel chromatography on Bio-Gel P-2 and a multi-column system Bio-Gel P-2 and P-6 at increased temperature [138]. Under these conditions oligosaccharides have different retention volumes and the method is suitable also for preparative separation of hnear and branched oligosaccharides. 

Another example of multi-column analysis has been demonstrated for the determination of impurities in styrene. The marked compounds in the styrene sample (Figure 12.15(a)) were solvent flushed via a splitline, with the analysis being carried out with a cryotrapping separation (CTS) (see Figure 12.15(b)). The first column, was an Ultra-2 (25 m X 0.32 mm i.d., d( = 0.25 p.m) precolumn, while the main column was a DB-WAX (30 m X 0.32 mm, d = 0.25 p.m) with an FID being employed as the detection system. 

An automatic solid phase extraction system was developed by Scott and Kucera (3) for the determination of drug metabolites in blood. The system was basically a multi-column switching system utilizing... 

Figures 6, 7 and 9 show calibration curves using two multi-column combinations and illustrate the degree of "optimization obtained in this system. The mobile phases for Figures 6 and 7 contained 0.025 g polyethylene oxide and ion exclusion and adsorption effects should therefore be largely eliminated. Figure 6 shows that reasonably good resolution can be obtained with a combination of five columns but does exhibit some loss of peak separation at the low cuid high MW ends. In Figure 7 the effect of adding a sixth column of small pore size is illustrated and it is seen that resolution at the low MW end is thereby somewhat improved. This calibration curve is effectively linear with a change of slope at 500,000 MW. It should provide a useful aqueous GPC system for MW and MWD determination of nonionic polyacrylamides.

GL 27] [R 3] [P 29] By means of sulfite oxidation, the specific interfacial areas of the fluid system nitrogen/2-propanol were determined for different flow regimes [5]. For two types of micro bubble columns differing in micro-channel diameter, interfaces of 9800 and 14 800 m m , respectively, were determined (gas and liquid flow rates 270 and 22 ml h in both cases). Here, the smaller channels yield the multi-phase system with the largest interface. 

For the distillation of a multi-component system in a batch column, the established practice leads to sequential removal of products from lower to higher boiling points. A strategy has been suggested, with a proper analysis, which involves the removal of all the products except the heavies, with subsequent fractionation of the mixture. 

Multiple electrodes have been used to obtain selectivity in electrochemical detection. An early example involved the separation of catecholamines from human plasma using a Vydac (The Separation Group Hesperia, CA) SCX cation exchange column eluted with phosphate-EDTA.61 A sensor array using metal oxide-modified surfaces was used with flow injection to analyze multicomponent mixtures of amino acids and sugars.62 An example of the selectivity provided by a multi-electrode system is shown in Figure 2.63... 

A multidimensional gas chromatography system (multi-stage column system) is effective for analysis of difficult samples and can be built up by connecting several column ovens, i.e. tandem GC systems, each of which has independent control functions such as for temperature programming. 

Can equipment sets be combined (e.g., replacing reactive distillation with a separate reactor and multi-column fractionation train installing internal reboilers or heat exchangers) to reduce overall system volume ... 

Treatment of wood with multi-component systems is likely to result in separation of the components when large wood samples are treated. This has been likened to the action of a chromatography column (Schneider, 1995). This is a significant problem that is often only encountered during scale-up of laboratory-based studies, where satisfactory results were previously obtained on small wood samples. Similarly, treatment of large wood samples can often lead to considerable variability in results due to inhomogeneous distribution, which again may not be evident with small samples treated under laboratory conditions. 

Fig. 17.12 MDGC-pyrolysis-IRMS precolumn and main column are connected via the multi-column switching system MCS2 (GERSTEL). Cutting is realised by different gas flows through the MCS2 device [71]...

The simulation of a multi-component system was done with the flow sheeting program Aspen+. An external routine replaced the internal Kj-calculation with a fit function through the experimental Revalues as given in figure 4. The multistage column was split into a cascade of flash modules. Each module is connected to two other... 

Thermally coupled systems can also be devised for multicomponent mixtures. Sargent and Gaminibandara (Optimization in Action, L. W. C. Dixon, ed.. Academic Press, London, 1976, p. 267) presented a natural extension of the Petlyuk column sequence to multi-component systems. Agrawal [Ind. Eng. Chem. Res., 35,1059 (1996) Trans. Inst. Chem. Eng., 78,454 (2000)] presented a method for generating an even more complete superstructure from which all the... 

At the same time, the bioanalysis of LOR and DCL in rat, rabbit, mouse, and dog plasma was reported by others [64]. In order to get more rehable toxicology data, the bioanalysis in these four preclinical species is done simultaneously instead of on separate days. The sample pretreatment was SPE in a 96-well plate format, using a Tomtec Quadra hquid handling system and an Empore Cig 96-well extraction disk plate. Fom-channel parallel LC was done with four 100x2-mm-lD Cg colunms (5 pm) and a mobile phase of 85% methanol in 25 mmol/1 aqueous AmOAc (adjusted to pH 3.5). The mobile phase was delivered at a flow-rate of 800 pl/min and split into 200 pl/min over each of the four colunms. A multi-injector system was apphed with four injection needles. A post-column spht was applied to deliver 60 pEmin per column to a four-channel multiplexed ESI source (Ch. 5.5.3). The interspray step time was 50 ms. Positive-ion ESI-MS was performed in SRM mode with a dwell time of 50 ms for each of the four transitions, i.e., LOR, DCL, and their [DJ-ILIS, with 20 ms interchannel delay. The total cycle time was thus 1.24 s. The LOQ was 1 ng/ml for both analytes. QC samples showed precision ranging from 1 to 16% and accuracy from -8.44 to 10.5%. The interspray crosstalk was less than 0.08% at concentrations as high as 1000 ng/ml. 

Where t is time, z are the axial position in the column, qt is the concentration of solute i in the stationary phase in equilibrium with Cu the mobile phase concentration of solute /, u is the mobile phase velocity, Da is the apparent dispersion coefficient, and F is the phase ratio (Vs/Vm). The equation describes that the difference between the amounts of component / that enters a slice of the column and the amount of the same component that leaves it is equal to the amount accumulated in the slice. The fist two terms on the left-hand side of Eq. 10 are the accumulation terms in the mobile and stationary phase, respectively [109], The third term is the convective term and the term on the right-hand side of Eq. 10 is the diffusion term. For a multi component system there are as many mass balance equation, as there are active components in the system [13],... 

These phenomena may be important for a restricted number of chemical reactor systems, as for example certain industrial multi-phase systems operated in bubble column and fluidized bed reactors. 

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