Isothermal displacement

Stokes R H 1994 Isothermal displacement calorimeters So/of/o/ Calorimetry, Experimental Thermodynamics vo IV, ed K N Marsh and PAG O Hare (Oxford Blackwell)... 

If the initial state is one in which the pressure exhibits an extreme value in an isothermal displacement, then =0 and (29.52) shows that since 8/ 4 is chosen to be non-zero,... 

Figure Bl.27.7. Schematic diagram of isothermal displacement calorimeter A, glass calorimeter cell B, sealed heater C, stainless steel stirrer D, thermistor E, inlet tube F, valve G, window shutters H, silver rod ...

Stokes R H 1994 Isothermal displacement calorimeters Solution Calorimetry, Experimental Thermodynamics /o ... 

Figure 14 Isothermal displacement calorimeter with cooling module. A, stainless-steel support tube, B, vent tube C, current and potential leads for heater D, connector for feed tube E, Teflon plug F, vent plug G, heateriwire supports H, baffles I, Teflon support ], heater wires K, stirrer magnet L, stirrer paddle A,feed tube N, thermistor P, Teflon feed cup Q, water inlet tube R, copper heat sink S, 5Q era precision-bore Dewar flask T, 0-rings U, coin-silver cooling rod V, copper cup W, coin-silver support rods X, copper heat shield Y, coin-silver bar Z, cooling module (Reproduced by permission from J. them, and Eng. Data, 1966, 11, 189)...

Stokes, R. H. Marsh, K. N. Tomlins, R. P. Enthalpies of exothermic mixing measured by the isothermal displacement calorimeter for cyclooctane + cyclopentane/. Chem. Thermodyn. 1969,1, 377-379... 

Costigan, M. J. Hodges, L. J. Marsh, K. N. Stokes, R. H. Tuxford, C. W. The isothermal displacement calorimeter design modifications for measuring exothermic enthalpies of mixing Amt. J. Chem. 1980,33.2103-2119... 

The calorimetric techniques for measuring heats of mixing two fluids can be classified into their mode of measurement and their principle of heat detection. The isothermal displacement calorimetry will refer to a static mode and flow calorimetry, to a dynamic mode . The principles of heat detection in the following examples will be power compensation or heat flux determination. 

Fig. 14.6 Enthalpy of solution of CO2 in aqueous solutions of monoethanolamine (MEA) and methyl di-ethanolamine (MDE A) at low loading chaiges using an isothermal displacement calorimeter [19]. Mass fractions of amine solutions <> 0.1, 0.2, o 0.3...

Nonvolatile Solvents. In practice, some gases tend to Hberate such large amounts of heat when they are absorbed into a solvent that the operation caimot be assumed to be isothermal, as has been done thus far. The resulting temperature variations over the tower will displace the equiUbrium line on 2tj—x diagram considerably because the solubiUty usually depends strongly on temperature. Thus nonisothermal operation affects column performance drastically. 

The graphical interpretation of Eq. (16-197) is shown in Fig. 16-37 for the conditions of Example 12. An operating hne is drawn from the origin to the point of the pure displacer isotherm at = cf. For displacement to occur, the operating hne must cross the pure component isotherms of the feed solutes. The product concentrations in the iso-tachic train are found where the operating hne crosses the isotherms. When this condition is met, the feed concentrations do not affect the final product concentrations. 

FIG. 16"37 Schematic showing the intersection of the operating line with the pure-component isotherms in displacement chromatography. Conditions are the same as in Fig. 16-36. 

Scott and Kucera [4] carried out some experiments that were designed to confirm that the two types of solute/stationary phase interaction, sorption and displacement, did, in fact, occur in chromatographic systems. They dispersed about 10 g of silica gel in a solvent mixture made up of 0.35 %w/v of ethyl acetate in n-heptane. It is seen from the adsorption isotherms shown in Figure 8 that at an ethyl acetate concentration of 0.35%w/v more than 95% of the first layer of ethyl acetate has been formed on the silica gel. In addition, at this solvent composition, very little of the second layer was formed. Consequently, this concentration was chosen to ensure that if significant amounts of ethyl acetate were displaced by the solute, it would be derived from the first layer on the silica and not the less strongly held second layer. 

Solutes will interact with the reverse phase surface in much the same way as they do with the silica gel surface. There will be basically two forms of interaction, by sorption and by displacement. Sorption interaction has been experimentally confirmed by Scott and Kucera (10) by measuring the adsorption isotherm of acetophenone on the reverse phase RP18 from a 40%w/v acetonitrile mixture in water. The authors noted that there was no change in the acetonitrile concentration, as the solute was adsorbed. Displacement interactions, although certain to occur, do not appear to have been experimentally demonstrated to date. 

The critical parameters for separation by displacement are the displacer concentration, the loading factor (ratio of the sample size to the column saturation capacity) and the column efficiency. The choice of displacer is probably the most critical step. For correct development to occur the adsorption isotherm of the displacer must overlie those of the feed components. The concentration of the i PlAcer controls the separation time and... 

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