Extraction, partially miscible countercurrent

Some extraction systems are such that the solvent and diluent phases are almost completely immiscible in each other. Hence, separation yields an extract phase essentially free of diluent and a raffinate phase that is almost pure diluent. This greatly simplifies the characterization of the system. When partial miscibility for an extraction process is very low, the system may be considered immiscible and application of McCabe-Thiele analysis is appropriate. It is important to note that McCabe-Thiele analysis for immiscible extraction applies to a countercurrent cascade. The McCabe-Thiele analysis for immiscible extraction is analogous to the analysis for absorption and stripping processes. Consider the flow scheme shown in Figure 5.23,... 

Countercurrent Extraction Cascades for Partially Miscible Systems... 

D19. Many extraction systems are partially miscible at high concentrations of solute, but close to immiscible at low solute concentrations. At relatively low solute concentrations both the McCabe-Thiele and trianglar diagram analyses are applicable. This problem explores this. We wish to use chloroform to extract acetone from water. Equilibrium data are given in Table 13-4. Find the number of equilibrium stages required for a countercurrent cascade if we have a feed of 1000.0 kg/h of a 10.0 wt % acetone, 90.0 wt % water mixture. The solvent used is chloroform saturated with water (no acetone). Flow rate of stream Eq = 1371 k. We desire an outlet raffinate concentration of 0.50 wt % acetone. Assume immiscibility and use a weight ratio units graphical analysis. Conpare results with Problem 13.D43. 

Figure 8.1.39. (a) Countercurrent multistage extraction system for a partially miscible system, (b) Ri t triangular diagram for counter-current multistage extraction, solute C being extracted from feed phase containing primarily A by solvent B (here N = 5). 

Another important application of ethyl lactate is related with the edible oil industry, taking advantage of the partial liquid-liquid miscibility that present the mixtures of ethyl lactate with different lipid type substances. This property could be exploited to develop new separation processes, similar to those mentioned in this chapter, namely the recovery of squalene from olive oil deodorized distillates and the extraction of tocopherols from olive oil. In both applications, the yield and separation factors obtained indicate good selectivity of using ethyl lactate as an extractive solvent, and demonstrate the viability of developing liquid-liquid countercurrent process using green ethyl lactate solvent in edible oil industrial applications. 

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