Multicomponent systems liquid extraction

There are many types of phase diagrams in addition to the two cases presented here these are summarized in detail by Zief and Wilcox (op. cit., p. 21). Solid-liquid phase equilibria must be determined experimentally for most binaiy and multicomponent systems. Predictive methods are based mostly on ideal phase behavior and have limited accuracy near eutectics. A predic tive technique based on extracting liquid-phase activity coefficients from vapor-liquid equilib-... 

Assuming the liquid phases remain immiscible, the modelling approach for multicomponent systems remains the same, except that it is now necessary to write additional component balance equations for each of the solutes present, as for the multistage extraction cascade with backmixing in Section 3.2.2. Thus for component j, the component balance equations become... 

It is not known whether high-pressure fluids are Newtonian fluids that behave according to the laws given by Eqns. (3.4-1), (3.4-2), and (3.4-3). With regards to diffusion problems, for example, the Fickian nature of diffusion may be rather the exception than the rule. The diffusivity often depends on solute concentration, not only in extraction with a supercritical gas [1] but also in ordinary low-pressure diffusion in the gas phase and in diffusion in a liquid in multicomponent systems and in porous media. 

Originally, extractive distillation was limited to two-component problems. However, recent developments in solvent technology enabled applications of this hybrid separation in multicomponent systems as well. An example of such application is the BTX process of the GTC Technology Corp., shown in Figure 6, in which extractive distillation replaced the conventional liquid-liquid extraction to separate aromatics from catalytic reformate or pyrolysis gasoline. This led to a ca. 25% lower capital cost and a ca. 15% decrease in energy consumption (170). Some other examples of existing and potential applications of the extractive distillations are listed in Table 6. 

The preceding definitions all point out that there are three components involved in liquid-liquid extraction. This is true even if each of these three components is itself a group of multiple components. The concept here is that each group within the multicomponent system plays the role of solute, feed-raffinate, or solvent-extract. The objective is to identify each as a discrete component, even if it is a component mixture, and apply the methodology as given herein. 

Since thermodynamic nonidealities are of the essence for phase separation in liquid-liquid systems, and such nonidealities contribute to multicomponent interaction effects, it may be expected that liquid-liquid extraction would offer an important test of the theories presented in this book. Here, we present some experimental evidence to show the significance of interaction effects in liquid-liquid extraction. The evidence we present is largely based on experiments carried out in a modified Lewis batch extraction cell (Standart et al., 1975 Sethy and Cullinan, 1975 Cullinan and Ram, 1976 Krishna et al., 1985). The analysis we present here is due to Ej-ishna et al. (1985). The experimental system that will be used to demonstrate multicomponent interaction effects is glycerol(l)-water(2)-acetone(l) this system is of Type I. The analysis presented below is the liquid-liquid analog of the two bulb gas diffusion experiment considered in Section 5.4. 

After the optimum additive has been chosen the liquid-vapour equilibria of the ternary or multicomponent systems have to be determined as exactlj- as possible in extractive as well as in azeotropic distillation. For this reason Null and Palmer [76] looked for methods allowing equilibrium values to be obtained from as few experimental data as possible. 

In chemical engineering literature k y is rarely used. But k,i is often used, especially in liquid extraction where the system, in general, is a multicomponent system (see Section 1.2). In distillation and flash separation processes, is used frequently. 

Reactive absorption, distillation, and extraction have much in common. First of all, they involve at least one liquid phase, and therefore the properties of the liquid state become significant. Second, they occur in moving systems, thus the process hydrodynamics plays an important part. Third, these processes are based on the contact of at least two phases, and therefore the interfacial transport phenomena have to be considered. Further common features are multicomponent interactions of mixture components, a tricky interplay of mass transport and chemical reactions, and complex process chemistry and thermodynamics. 

Calculations of multicomponent liquid-liquid equilibrium are needed in the design of liquid (solvent) extraction systems. Since these operations take place considerably below the bubble point, it is not necessary to consider the equilibrium-vapor phase. The equations to be solved are ... 

There is an ever increasing interest in the use of liquid membranes for performing chemical separations. Emulsion liquid membrane (ELM) systems in which the targeted chemical species in an aqueous solution is extracted with a multicomponent emulsion have a variety of applications. These include isolation and concentration of valued or harmful substances in industrial chemistry, separation of substances for determination in analytical chemistry, separation of pollutants in environmental remediation, and detoxification of biological fluids by removal of harmful substances of exogenic and endogenic origins (7). 

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