Liquid segments

Figure 1.2 Normal and focused multilamination flow patterns, slug flow composed of gas/liquid segments (Taylor flow ), and ordered foam flow ( hexagon flow ) (from top to bottom).

The non-random two-liquid segment activity coefficient model is a recent development of Chen and Song at Aspen Technology, Inc., [1], It is derived from the polymer NRTL model of Chen [26], which in turn is developed from the original NRTL model of Renon and Prausznitz [27]. The NRTL-SAC model is proposed in support of pharmaceutical and fine chemicals process and product design, for the qualitative tasks of solvent selection and the first approximation of phase equilibrium behavior in vapour liquid and liquid systems, where dissolved or solid phase pharmaceutical solutes are present. The application of NRTL-SAC is demonstrated here with a case study on the active pharmaceutical intermediate Cimetidine, and the design of a suitable crystallization process. 

Chen, C.-C.., Song, Y., 2004, Solubility Modeling with a Non-Random Two-Liquid Segment Activity Coefficient Model, Ind. Eng. Chem. Res., 43, 8354-... 

Figure 6.1. Gibbs free energy curves for Ti (a) a, j9 and liquid segments corresponding to the stable regions of each phase (b) extrapolated extensions into metastable regions (c) characterisation from Kaufinan (1959a) using equation (6.2) and (d) addition of the G curves for u and f.c.c. structures (from Miodownik...

Extraction in liquid/liquid segmented flow has been developed. A continuous-flow extraction system coupled online with an RP-HPLC with C-l 8 and a UV detector was used to study the extraction of fenthion and azinphos methyl in water (82). 

Monodisperse silica nanoparticles of a diameter of 200-500 nm were obtained [329]. This is explained by the well-defined residence time with reduced axial dispersion of the liquid segments [328,329]. In addition, by moving the liquid segments through a tube recirculation flow sets in, which is very effective in liquid mixing. 

Nonrandom two-liquid segment activity coefficient (NRTL-SAC)... 

For a BUBL P calculation, the temperature and the liquid composition are known, and this fixes the location of the PV isotherm for the composition of the liquid phase (solid line). The problem then is to locate a second (dashed) line for a vapor composition such that the line contains a dew point D on its vapor segment that lies at the pressure of the bubble point B on the liquid segment of the solid line. This pressure is the phase equilibrium pressure, and the composition for the dashed line is that of the equilibrium vapor. This equilibrium condition is shown by Fig. 4-9. 

FIGURE 5.6 The segments established in a segmented flow analyser. 1 = tube wall 2 — air bubble 3 = thin liquid film on the tube wall 4 and 5 = liquid segments with indication of the vortices (rounded arrows) large arrow = overall flow movement. 

Another development was to coat the tubing inner wall with a chemically inert liquid species, which was originally perfluorocarbon [20]. This reduces the thickness of the liquid film on the tubing inner wall, minimises the mass transference between successive liquid segments and reduces the frictional forces at the solid—liquid interface. Consequently, carryover is also reduced. The integrity of the air bubbles is better... 

L. Nord, B. Karlberg, Extraction based on the flow-injection principle. Part 6. Film formation and dispersion in liquid liquid segmented flow extraction systems, Anal. Chim. Acta 164 (1984) 233. 

K. Backstrom, L.G. Danielsson, F. Ingman, H.Z. Zhao, Studies of two-phase equilibria by liquid-liquid segmented flow extraction of dithiocarbamic acids into various solvents, Talanta 34 (1987) 783. 

Figure 11. (a) Evolution of tracer concentration in the liquid segment as a function of nondimensional time for various Peclet numbers, (b) Variation of the average tracer concentration as a function of the Peclet number at t =10. 

Fig. 5.18 Innovative hydrodynamic principles of the CHEM-1 autoanalyser. (a) Capsule chemistry technology the fluorocarbon liquid film prevents contact between the segmented flow and the tube walls, (b) Mixing of two liquid segments Li and L2 separated by an air bubble in the vanish zone , (c) Special mixing loop. (Courtesy of Technicon).

Figure 1.2. The parallel between manual and automated operations that have to be performed in the course of a typical colorimetric assay (a) Manual handling (b) a discrete belt-type analyzer (c) a continuous-flow air-segmented analyzer, with a detail of the air and liquid segments, showing a mixing pattern that leads to homogenization of individual liquid segments. Note that all assays aim to perform the measurements at a steady state (stable readout, that is, flat top ).

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