Wicking phase separator

Fig. 7.13 Schematic of a wick-based phase separator sized for a 5-kW PEM fuel cell and demonstrated in both normal and microgravity environments [14].

Mass transfer controlled by diffusion in the gas phase (ammonia in water) has been studied by Anderson et al. (A5) for horizontal annular flow. In spite of the obvious analogy of this case with countercurrent wetted-wall towers, gas velocities in the cocurrent case exceed these used in any reported wetted-wall-tower investigations. In cocurrent annular flow, smooth liquid films free of ripples are not attainable, and entrainment and deposition of liquid droplets presents an additional transfer mechanism. By measuring solute concentrations of liquid in the film and in entrained drops, as well as flow rates, and by assuming absorption equilibrium between droplets and gas, Anderson et al. were able to separate the two contributing mechanisms of transfer. The agreement of their entrainment values (based on the assumption of transfer equilibrium in the droplets) with those of Wicks and Dukler (W2) was taken as supporting evidence for this supposition. 

Another type of tank is the sandwidi unit in which the TLC plate is clamped horizontally b weoi two glass plates separated by gaskets. A wick at one edge of the TLC plate provides the solvoit res oir to develop the plate. The advantage of this system is that it uses less mobile phase, provides a more quickly saturated vapour system, and gives shorter running times. 

Continuous and Multiple Development Although it is possible to separate completely up to 10 compounds using a 10-cm run, a single run will not always separate all the compounds of interest. In these cases, continuous development may be used by running the mobile phase up the plate and removing it from the top by means of a wick, or by evaporating it using an infra-red lamp. 

One simple type of chromatography, paper chromatography, employs a strip of porous paper, such as filter paper, for the stationary phase. A drop of the mixture to be separated is placed on the paper, which is then dipped into a liquid (the mobile phase) that travels up the paper as though it were a wick (see Fig. 1.13). This method of separating a mixture is often used by biochemists, who study the chemistry of living systems. 

Wicke E, Nemst GH (1964) Phase diagram and thermodynamic behaviour of the palladium-hydrogen and of the palladium-deuterium system at normal temperature H/D separation effect. Ber Bunsenges Phys Chem 68 224—235... 

Circular and Anticircular Development. Circular and anticircular development have been accomplished in a number of ways. Because of the need for solvent-delivery control in such systems, chromatography is best carried out in equipment specially designed for the purpose. It is also important that the chamber be kept level. Camag, Analtech, and Anspec all offer chambers for circular development. Samples are applied at the center, and mobile phase is wicked to the surface. Development causes the analyte mixture to separate into a series of concentric rings. Figure 3 illustrates these devices. 

The Vario-KS Chamber and HPTLC-Vario-Chamber (Camag) are horizontal chambers that have a wide variety of operational modes and applications. The plate is placed layer down over a tray with various compartments, which can hold different solvents, humidity-control liquids, and volatile acids and bases whose vapors will impregnate and condition or preload the layer. Developing solvent is in a separate tray and is transferred to the layer by a wick. The Vario chamber can be used to test six mobile phases side-by-side on one plate for solvent optimization, to determine if layer preequilibration (preloading) is advantageous, to ascertain if S- or N-chamber configuration is best, and to test different humidity conditions. 

While the two-phase titration will not determine alkanedisulfonates if monosulfonates are absent, the presence of disulfonate impurities in commercial alkanesulfonate products will cause a variable interference (37). The response of the two-phase titration to molecules containing more than one sulfate or sulfonate group must be determined for each individual case. Lew reports stoichiometric reaction with each functional group for a C22 surfactant with two anionic sulfate groups separated by four carbon atoms (38). Wick-bold suggests addition of 10 mL 20% sodium sulfate solution to eliminate interference from disulfonates, and this was adopted in the ISO procedure (39). Alternatively, modification of the organic solvent to a 93 7 chloroform/l-hexanol mixture will allow complete recovery of disulfonates, regardless of pH (40). 

---