Extraction equilibrium data

Pilot plants can be used to predict solvent dosages and other operating conditions, but such operations are expensive and should be minimized. It is, therefore, desirable to establish correlations of operating variables. Kalichevsky (16) describes correlations of solvent extraction equilibrium data which indicate that the percentage dissolved in the extract layer, L, is related to the solvent dosage, S, by the expression... 

Plot extraction equilibrium data on equilateral- and right-triangular diagrams. 

Extraction equilibrium data are summarized in TABLE IV, together with the reported values of diameter and heat of hydration of alkali and alkaline earth metal cations. The ten-membered cyclic dimer extracted neither monovalent cations nor divalent cations above a detectable limit. On the contrary, the twenty-membered cyclic tetramer and the twenty -five-membered cyclic pentamer bound, more or less, monovalent and divalent cations, the latter showing somewhat higher Kg values than the former for any ions examined. No significant difference in ion extraction ability between racemic and optically active cyclic oligomers was observed. 

The determination of the chemical model from extraction equilibrium data means to determine (1) the number of species, (2) stoichiometry, and (3) formation and extraction constants. Mostly, the trial-and-error method is used for the purpose of trying various combinations of p, q, and r indices, whereas the minimum for U, being the sum of squares of residuals... 

The method used in the EXLET 92 program yields the standard deviations of the stoichiometric indices and thus estimates the uncertainty with which the composition can be calculated from a given set of extraction equilibrium data. 

The efficiencies which may be obtained can consequently be calculated by simple stoichiometry from the equilibrium data. In the ease of countercurrent-packed columns, the solute can theoretically be completely extracted, but equilibrium is not always reached because of the poorer contact between the phases. The rate of solute transfer between phases governs the operation, and the analytical treatment of the performance of such equipment follows closely the methods employed for gas absorption. In the ease of two immiscible liquids, the equilibrium concentrations of a third component in each of the two phases are ordinarily related as follows ... 

Toluene is to be removed from a wastewater stream. The flowrate of the waste stream is 10 kg/s and its inlet composition of toluene is 5(X) ppmw. It is desired to reduced the toluene composition in water to 20 ppmw. Three external MSAs are considered air (S2) for stripping, activated carbon (S2) for adsorption, and a solvent extractant (S3). The data for the candidate MSAs are given in Table 3.6. The equilibrium data for the transfer of the pollutant from the waste stream to the yth MSA is given by... 

Equilibrium data must be obtained for material balance showing raffinate and extracted phases. A simple separation funnel for single-stage extraction using amyl acetate as organic solvent is shown in Figure 7.13. 

Equilibrium data are thus necessary to estimate compositions of both extract and raffinate when the time of extraction is sufficiently long. Phase equilibria have been studied for many ternary systems and the data can be found in the open literature. However, the position of the envelope can be strongly affected by other components of the feed. Furthermore, the envelope line and the tie lines are a function of temperature. Therefore, they should be determined experimentally. The other shapes of the equilibrium line can be found in literature. Equilibria in multi-component mixtures cannot be presented in planar graphs. To deal with such systems lumping of consolutes has been done to describe the system as pseudo-ternary. This can, however, lead to considerable errors in the estimation of the composition of the phases. A more rigorous thermodynamic approach is needed to regress the experimental data on equilibria in these systems. 

Equilibrium data correlations can be extremely complex, especially when related to non-ideal multicomponent mixtures, and in order to handle such real life complex simulations, a commercial dynamic simulator with access to a physical property data-base often becomes essential. The approach in this text, is based, however, on the basic concepts of ideal behaviour, as expressed by Henry s law for gas absorption, the use of constant relative volatility values for distillation and constant distribution coeficients for solvent extraction. These have the advantage that they normally enable an explicit method of solution and avoid the more cumbersome iterative types of procedure, which would otherwise be required. Simulation examples in which more complex forms of equilibria are employed are STEAM and BUBBLE. 

Perry et al. (1997) give a useful summary of solubility data. Liquid-liquid equilibrium compositions can be predicted from vapour-liquid equilibrium data, but the predictions are seldom accurate enough for use in the design of liquid-liquid extraction processes. 

Example 10.3 A feed with a flowrate of 1000 kg-h 1 contains 30% acetic acid by mass in aqueous solution. The acetic acid (AA) is to be extracted with isopropyl ether to produce a raffinate with 2% by mass on a solvent-free basis. Equilibrium data are given in Table 10.11,8. 

The equilibrium data from Table 10.2 are plotted in Figure 10.6a. It can be seen that this does not form a straight-line relationship overall. Figure 10.6a shows the operating line of maximum slope that touches the equilibrium line at xR = 0.1576 kg AA/kg Water. The slope of this line is the ratio of feed to extraction flowrates. If the liquids are immiscible, then the flowrate of solute-free feed (F) is equal to the flowrate of the... 

Table 10.2 Equilibrium data expressed as ratios of feed solvent and extraction solvent.

A batch process produces 5 t of aqueous waste containing 25% wt acetic acid. The acetic acid is to be recovered by extraction with isopropyl ether. Equilibrium data are given in Table 10.1. 

Mackay, D., Shiu, W.Y., Wolkoff, A.W. (1975) Gas chromatographic determination of low concentrations of hydrocarbons in water by vapor phase extraction. ASTM STP 573, pp. 251-258, Am. Soc. Testing and Materials, Philadelphia, Pennsylvania. Macknick, A.B., Prausnitz, J.M. (1979) Vapor pressures of high-molecular-weight hydrocarbons.. /. Chem. Eng. Data 24, 175-178. Mac/ynski. A., Wioeniewska-Goclowska, B., Goral, M. (2004) Recommended liquid-liquid equilibrium data. Part 1. Binary alkane-water systems. J. Phys. Chem. Ref. Data 33, 549-577. 

A 50 per cent solution of solute C in solvent A is extracted with a second solvent B in a countercurrent multiple contact extraction unit. The mass of B is 25 per cent that of the feed solution, and the equilibrium data are ... 

Having established (i) that a meaningful cell emf can only be obtained at equilibrium, (ii) that the emf comprises two electrode potentials, and (iii) that the potential of one half cell can be defined in relation to a reference electrode, we are finally in a position to extract electroanalytical data from cells by using a potentiometric approach. 

The solvent system extractant, diluent, and, if necessary, modifier Equilibrium data extraction and stripping isotherms Kinetic data, as these will govern, to a large extent, the type of contactor required... 

Design of extraction processes and equipment is based on mass transfer and thermodynamic data. Among such thermodynamic data, phase equilibrium data for mixtures, that is, the distribution of components between different phases, are among the most important. Equations for the calculations of phase equilibria can be used in process simulation programs like PROCESS and ASPEN. 

Aguilar, M. Graphical Treatment of Liquid-Liquid Equilibrium Data. In Developments in Solvent Extraction, Ed. Alegret, S. Ed., Ellis Horwood Series in Analytical Chemistry, West Sussex, UK, 1988 p. 87. 

Information about experimental solubility and equilibrium data are important, even when complex mixtures are extracted. Reviews of high-pressure phase-equilibrium data have been published by several authors, for example, by Knapp et al. [38] covering the period 1900 to 1980, by Fomari et al. [39] covering 1978 to 1987, and by Dohm and Brunner [40], between 1988 to 1993. 

Calculations of the relations between the input and output amounts and compositions and the number of extraction stages are based on material balances and equilibrium relations. Knowledge of efficiencies and capacities of the equipment then is applied to find its actual size and configuration. Since extraction processes usually are performed under adiabatic and isothermal conditions, in this respect the design problem is simpler than for thermal separations where enthalpy balances also are involved. On the other hand, the design is complicated by the fact that extraction is feasible only of nonideal liquid mixtures. Consequently, the activity coefficient behaviors of two liquid phases must be taken into account or direct equilibrium data must be available. 

Cryptands of type 7-9 and derivatives thereof carry alkali cations [6.4], even under conditions where natural or synthetic macrocycles are inefficient. The selec-tivities observed depend on the structure of the ligand, the nature of the cation and the type of cotransported counteranion. Designed structural changes allow the transformation of a cation receptor into a cation carrier [6.1, 6.4]. The results obtained with cryptands indicated that there was an optimal complex stability and phase-transfer equilibrium for highest transport rates. Combined with data for various other carriers and cations, they give a bell-shaped dependence of transport rates on extraction equilibrium (Fig. 11), with low rates for too small or too large... 

Solvent extraction Database (SXD) software has been developed by A. Varnek et al.51 Each record of SXD corresponds to one extraction equilibrium and contains 90 fields to store bibliographic information, system descriptions, chemical structures of extractants, and thermodynamic and kinetic data in textual, numerical, and graphical forms. A search can be performed by any field including 2D structure. SXD tools allow the user to compare plots from different records and to select a subset of data according to user-defined constraints (identical metal, content of aqueous or organic phases, etc.). This database, containing about 3,500 records, is available on the INTERNET (http //infochim.u-strasbg.fr/sxd). 

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