Countercurrent systems optimization

In contrast to TSP interface, no extensive temperature optimization is needed with APCI. For systems providing a countercurrent drying gas, it is claimed that volatile as well as nonvolatile buffers can be used. Uncharged volatile material is swept away from the nozzle by the countercurrent drying gas, whereas nonvolatile contamination deposited in the source chamber can readily be wiped away without the need to switch off tire vacuum system. 

The distribution ratio of Am(III) is much higher for CyMe4-BTP than for iPr-BTP when mixed with DMDOHEMA in -octanol, and the observed An(III)/Ln(III) selectivity is outstanding for an N-soft-donor ligand SFAm/Eu > 1500 at equilibrium (207). Nevertheless, stripping becomes problematic, and further investigations and optimizations are still required before this system can be applied to countercurrent test implementation. 

Alternatively, one can resort to the use of moving- or fluidized-bed systems in which the adsorbent, and sometimes also the catalyst, is continuously withdrawn from the reactor to undergo an external regeneration. Ideally, one tries to achieve countercurrent adsorbent flow pattern to optimize utilization of the adsorptive capacity. The major problems of such arrangements are those of solids handling (e.g., gas-tight... 

Other Synthesis Problems. One recent synthesis publication by Nishitani and Kunugita (1979) is difficult to classify under the above headings, it deals with selecting the optimal vapor/ liquid flow patterns to use for a multiple effect evaporator system. The two obvious patterns are cocurrent (the liquid and vapor proceed through the system together) and countercurrent. Other patterns are possible and often significantly improve the economics. 

A new potentially exciting development in this area of extractions concerns the use of different reversed micellar systems in countercurrent extractions of different rare earth metals. A mathematical model was developed in order to help optimize the different parameters of this new mode of extraction (364). This should facilitate the further development and utilization of this approach to metal ion separations. 

Countercurrent chromatography utilizes a pair of immiscible solvent phases which have been preequilibrated in a separatory funnel One phase is used as the stationary phase and the other as the mobile phase. A solvent system composed of 12.5% or 16.0% (w/w) PEG 1000 and 12.5% (w/w) potassium phosphate was usually used for the type XL and XLL cross-axis CPCs. These solutions form two layers the upper layer is rich in PEG and the lower layer is rich in potassium phosphate. The ratio of monobasic to dibasic potassium phosphates determines the pH of the solvent system this effect can be used for optimizing the partition coefficient of proteins. 

The fundamental principle of separation for modem DuCCC is identical to classic countercurrent distribution. It is based on the differential partitions of a multicomponent mixture between two countercrossing and immiscible solvents. The separation of a particular component within a complex mixture is based on the selection of a two-phase solvent system, which provides an optimized partition coefficient difference between the desired component and the impurities. In other words, DuCCC and HSCCC cannot be expected to resolve all the components with one particular two-phase solvent system. Nevertheless, it is always possible to select a two-phase solvent system, which will separate the desired component. In general, the crude sample is applied to the middle of the coiled column through the sample inlet, and the extreme polar and nonpolar components are readily eluted by two immiscible solvents to opposite outlets of the column. 

Countercurrent chromatography is a two-phase procedure where the separation is based on the difference in partition coefficients of solutes within the phases. To achieve efficient separation of lipoproteins from human serum, it is essential to optimize the partition coefficient of each component by selecting an appropriate pH for the polymer phase system. 

The countercurrent movement of the mobile and stationary phases is simulated in the following way the stationary phase is divided into several separate chromatographic columns which are connected in a cyclic series. Each column head is equipped with valves that allow the addition of eluent, feed and removal of the raffinate and extract from both component lines. The inlet and outlet lines will be shifted after a given time from one column to a subsequent column in the direction of the mobile phase, thus simulating the movement of the stationary phase in the opposite direction. After a complete cycle, the four lines reach their initial position. The technological parameters for running the SMB system under optimal conditions can be calculated by the available software, based on several analytical runs. 

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