![]() ![]() In contrast, the feeds for the aqueous and organic phases enter the system at opposite ends in a counter-current setup. In a co-current setup, both the aqueous and organic phases flow in the same direction. The two main patterns at which liquid-liquid extraction is conducted are co-current and counter-current operations. However, it is also relevant to consider that such ratio has to be effective enough to see separation. Furthermore, one aspect to consider as chemical engineer is coming up with the less number of equilibrium stages by changing the aqueous to organic ratio. This ratio comes from the slope of the equilibrium line. ![]() This example shows that eight equilibrium stages are needed to design this liquid-liquid extraction process when the aqueous to organic phase is 2.2 to 1. The blue dots in the operating line come from data collected in experiments. The following picture can be used as a guide to interpreting the McCabe-Thille diagram: Interpreting such diagrams allows to know the operating conditions for the pilot plants. Consequently, the data points collected allow to produce an operating line and the McCabe-Thille diagram. the compound concentration in the organic phase. Once the concentrations for all the ratios tested are known, It is possible to produce a plot of the compound concentration in the aqueous phase vs. Then, the aqueous and organic phases are separated to obtain the target compound concentration in both phases. The McCabe-Thille method relies on conducting several experiments contacting the aqueous solution with the organic solution at different volumetric ratios. This graphical technique optimizes the conditions of an operation unit by identifying the optimal number of cells needed for an effective process and the flow rate ratio between aqueous and organic solutions. McCabe-Thiele diagrams can be used for this calculation. ![]() A convenient place to start the design is to calculate the theoretical number of equilibrium stages for the separation. However, the foundation in its design is somewhat similar. LIquid-liquid extraction is used in several chemical industries. Therefore, it is necessary to make sure the solvent chosen is commercially available and has a reasonable price. However, the solvent only needs to mix with the target compound aimed at being separated.ĭensity: The aqueous and organic phases should present high-density differences for the separation process to be more efficient.Ĭost: Cost represents a relevant aspect in any design decision. Miscibility: The solvent chosen should be immiscible with the aqueous phase in the feed because the two phases (aqueous and organic) have to be contacted in large interfacial areas. ![]() Selectivity: A high selective for the target component will facilitate the operation and design of liquid-liquid separation processes since fewer equilibrium stages will be necessary. Consequently, the organic to aqueous phase ratio also becomes low. The following criteria can be considered as a guide for solvent selection :ĭistribution Coefficient: Having a high distribution coefficient entails that the solvent has a high affinity for the target compound. The physical and chemical properties of the compound are reliable parameters that can tell whether a solvent will be efficient during the separation process. One of the most relevant aspects to consider when conducting a liquid-liquid extraction is selecting the right solvent. ![]()
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