The success of modeling mass transfer depends strongly on the accurate description of the physical properties of the system involved. In the case of two liquid phases the knowledge of the liquid-liquid equilibrium is of special importance. This knowledge gains importance when the transfer of multiple species is to be modeled, as more complex interactions have to be considered. These can only be described with advanced mass-transfer models, such as the Stefan-Maxwell model, with a high demand on accuracy in the description of physical properties. The quaternary system toluene + acetone + phenol + water is being considered as a possible new standard test system for the investigation of multicomponent mass transfer in liquid-liquid extraction. Equilibrium data are needed: experimentally determined tie-line data at 20°C are now presented for this system. The results are correlated with the UNIQUAC model using different objective functions. The resulting calculated data sets are compared considering their accuracy and applicability to multicomponent mass-transfer description. The densities of various mixtures of the system have been measured and correlated.
IntroductionThe description of mass transfer in liquid-liquid systems is mostly limited to the case of single-transferred species. But even in the most simple system in liquid-liquid extraction, that is, two solvents and one solute, multicomponent mass transfer is apparent as the solubilities of the solvents change with solute concentration. The investigation of these multicomponent effects on mass transfer in liquid-liquid extraction has been the subject of some recent studies (Zimmermann et al., 1995;Toutain et al., 1998; von Reden, 1998). To increase the value of further studies on the subject, both theoretical and experimental, it seems worthwhile to establish a quaternary standard test system, such as those available for ternary systems (Misek et al., 1985), as its use can significantly increase the comparability of results of different studies (Hartland and Steiner, 1983;Gourdon et al., 1991).A proposed quaternary test system (toluene + acetone + phenol + water) was introduced by von Reden et al. (1996). It is based on the ternary test system toluene + acetone + water recommended by the European Federation of Chemical Engineering (EFCE), which is extended with the second solute, phenol. The solute combination phenol + acetone is involved in phenol/acetone production with the Hock process as well as being relevant to the industrial process of caprolactam manufacture.The system investigated is a type II quaternary system and is represented schematically in Figure 1. Liquid-liquid equilibrium tie-line data are available for the ternary subsystem water + acetone + toluene from Sørensen and Arlt (1980), Vol. 5, Part 2. Binodal curves are available for the system water + acetone + phenol (Schreinemakers, 1900) (note the date!). The binary solubilities of the immiscible pairs toluene + water and phenol + water are also available from Sørensen and Arlt (1980), Vol....
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