Gas-Liquid Segregation

Gas-liquid phase segregation is typically required following some other separation process, such as distillation, absorption, evaporation, gas-liquid reactions, and condensation. Before separation techniques or equipment can be selected, the parameters of the separation must be defined. Information on volume of gas or liquid, volume ratio of the phases, and disper -phase particle size—that is, drop or bubble size-should be known or estimated. For existing operations, measurements are a possibility, while for new facilities analogies from data on other processes could be used. Laboratory or pilot riant tests may be considered, but it is difficult to maintain all fluid dynamic properties constant while chaining scale and wall effects may be significant on the small scale. 

Methods for estimating quantities of entrainment from gas-liquid contacting devices are also scarce. Distillation tray correlations by Fair are useful for tray-contacting operations (Figs. 3.2-3 and 3.2-4). CsB. Flood is obuined from Fig. 3.2-3 the flooding velocity is calculated by 

FIGURE 3.2-1 Typical vapor stream sampling train configuration. Excerpted by special peimission from Chemical Engineering, August 5, 1985, McGraw-HtU, Inc., New York, NY 10020. 

The percent of flood is calculaled by x 100. The entrainment ratio of liquid/gas is obtamed 

FIGURE 3.2-2 niustiatioo of the need fiir isokinetic sampling. 

Gravity separation occurs by merely reducing the velocity of a stream so that terminal particle settling or rise velocities due to gravity exceed the velocity of the bulk flow. The terminal particle or bubble velocities can be estimated by the methods described in Section 3.1. 

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Gas Partition—segregates gas into small streams and segments when flowing through a liquid or foam. 

Three-phase (solid/liquid/gas) fluidized systems are also of some practical importance. There is again a strong analogy between the rise of gas bubbles in normal liquids and in liquid fluidized beds (Dl, R3), although there is evidence of solid/liquid segregation in wakes (R3, S6) which has no parallel for two-phase systems. 

Most of us think of matter as being segregated into one of three states gas, liquid, or solid. Gases flow easily and expand to fill their container. Liquids also flow, but they take the shape of their container and have a fixed volume. Solids have a fixed shape and do not flow. As a general rule, polymers do not fall neatly into any of these categories. Most uncrosslinked (or lightly crosslinked) polymers do not behave exactly either as liquids or solids. Their behavior has characteristics of both liquid and solid states. We call this state the viscoelastic state, the same term we applied to certain solutions in Chapter 6. 

Structure of Br may not be the same as that of the bulk. Some of the molecular dynamics calculations predict that halide anions in water tend to float on the surface of clusters consisting of water molecules rather than within water. This effect may cause a dissimilar solvation structure to that of the bulk. In addition, if the anion is segregated at the surface by surfactants such as large alkylammonium cations, the anion density at the surface should be high and its environment differ from the bulk. This is a preliminary report of the first experimental study of the solution surface by the EXAFS technique. This technique provides us information on the gas/liquid interface, the structure of Langmuir films, and the effect of the interface on chemical reactions. 

A number of fine reviews have appeared recently which address in part the problems mentioned and the models employed. Rietema (R12) discusses segregation in liquid-liquid dispersion and its effect on chemical reactions. Resnick and Gal-Or (RIO) considered mass transfer and reactions in gas-liquid dispersions. Shah t al. (S16) reviewed droplet mixing phenomena as they applied to growth processes in two liquid-phase fermentations. Patterson (P5) presents a review of simulating turbulent field mixers and reactors in which homogeneous reactions are occurring. In Sections VI, D-F the use of these models to predict conversion and selectivity for reactions which occur in dispersions is discussed. 

The structure of the [CjinimHCl] gas-liquid surface was studied using atomistic simulation [128], A region of enhanced density immediately below the interface in which the cations were oriented with their planes perpendicular to the surface and their dipoles in the surface plane was observed [128], A negligible segregation of cations and anions was also found. The temperature dependence of the surface... 

The carbamatation of CHA in organic solvent (toluene + 10 % by volume of IPA) is usable in rather a large range of concentration 0.2 to 0.7 kmol/m for the determination of gas-liquid interfacial areas (23). Glass beads of small dimension dp = l.lbxlO" m provoke, for small flowrates a segregation between the gas and... 

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