Extraction with reflux

Fig. 3.1.2 The apparatus used in 1956 for the methanol extraction of Cypridina luciferin. The dried Cypridina (500 g) is extracted at a temperature lower than 40°C with refluxing methanol under reduced pressure for two days. The atmosphere inside the apparatus is completely replaced with hydrogen gas that was purified by its passing through a quartz tube containing red-heated copper fragments. The temperature of the mantle heater is adjusted, the system evacuated, and then all stopcocks are closed. The extraction with refluxing methanol continues for many hours without any further adjustment. From the author s 1957 notebook.

Use of reflux is most effective with Type II systems since then essentially pure products on a solvent-free basis can be made. In contrast to distillation, however, extraction with reflux rarely is beneficial, and few if any practical examples are known. A related kind of process employs a second solvent to wash the extract countercurrently. The requirements for this solvent are that it be only slighly soluble in the extract and easily removable from the extract and raffinate. The sulfolane process is of this type it is described, for example, by Treybal (1980) and in more detail by Lo et al. (1983, pp. 541-545). 

Related Calculations. This basic calculation procedure can be extended to the case of countercurrent multistage extraction with reflux. A schematic of the basic extractor is shown in Fig. 9.5. For this extractor there are N stages in the extracting section, 1E to NE, and there are M stages in the stripping section, 15 to MS. 

Toluene appeared to be the best compromise from the standpoints of volatility, ease of handling, toxicity, and halogen contamination. In all subsequent work, bitumen was extracted with refluxing toluene. Typically, three successive extractions with 100 mL toluene each were used for 10 g... 

Figure 1. The HPLC-graphite furnace atomic absorption (GFAA) analysis of Green River Formation oil shale extracted with refluxing methanol...

When the polymerization is complete, the hot viscous mixture is poured onto a clean aluminium sheet and allowed to cool. A toffee-like solid is formed. This is collected and milled to a powder. The powder is then extracted with refluxing methanol (2 x 150 ml portions) in order to remove the diphenylsulfone. The fine powder that remains is washed with water and then methanol, and dried to give the crude product (3.41 g, 93%). 

Procedure for solving extraction with reflux problems... 

FIGURE 7.3 8 Countercurrent extraction with reflux as in Fig. 7.3-7, showing location of A, and A2. 

A flow diagram for countercurrent extraction with reflux is shown in Fig. 20.14. To emphasize the analogy between this method and fractionation, it is assumed that the cascade is a plate column. Any other kind of cascade, however, may be used. The method requires that sufficient solvent be removed from the extract leaving the cascade to form a raffinate, part of which is returned to the cascade as reflux, the remainder being withdrawn from the plant as a product. Raffinate is withdrawn from the cascade as bottoms product, and fresh solvent is admitted directly to the bottom of the cascade. None of the bottom raffinate needs to be returned as reflux, for the number of stages required is the same whether or not any of the raffinate is recycled to the bottom of the cascade. The situation is not the same as in continuous distillation, in which part of the bottoms must be vaporized to supply heat to the column. 

PRACTICAL EXAMPLES OF EXTRACTION WITH REFLUX. There are few, if any, practical examples of reflux in the simple manner shown in Fig. 20.14. For systems such as aniline-heptane-methylcyclohexane (Fig. 20.11), the ratio of MCH to heptane in the extract is only modestly greater than in the raffinate, so a great many stages would he needed for high-purity products. Furthermore, the low solubility of both solutes in aniline would mean a very large flow of solvent to be handled. However, a modification of the reflux concept has been applied in several industrial processes for extraetive separation. Enrichment of the extract is accomplished by countercurrent washing with another liquid, chosen so that the small amounts of this liquid that dissolve in the extract can be easily removed. The Sulfolane process for extraction of aromatics is an example of this type. 

Figure 7.18 Use of Janecke diagram with auxiliary distribution curve for countercurrent extraction with reflux.

A solution of 143 mg p-(4-carboxy-3-indole)-propionic acid (0.6 mmol) and 15 mg potassium acetate (0.15 mmol) in 5 mL acetic anhydride was maintained at reflux temperature for 16 h. The acetic anhydride was distilled under reduced pressure. The residue was extracted with refluxing benzene. The solution was clarified by filtration and concentrated under diminished pressure. The remainder (125 mg) was recrystallized from a mixture of dichloromethane and ether to give 104 mg l-acetyl-5-keto-l,3,4,5-tetrahydrobenz(ed) indole, m.p. 120-140°C. Further recrystallization from a mixture of dichloromethane and ether gave 90 mg pure product, in a yield of 71%, m.p. 147-152°C. 

Fig. 6.63. Countercurrent extraction with reflux on distribution coordinates.

Fractional Extraction with Reflux. Asselin and Comings (1) describe a process where the A-rich solution removed from stage 1 (Fig. 7.18) is split into two streams, one of which is withdrawn as product, while the other is freed of solvent A by evaporation and the solute taken up by solvent D before it enters stage 1 to provide reflux. Similarly, the D-rich phase leaving stage 1 is split into two streams, one of which is the product while the other is freed of solvent by evaporation and the solute taken up by solvent A as it enters stage 1. At stage 1, let r be the fraction of the A-rich phase whose solute is to be returned as reflux. The reflux ratio is then r/(1 — r) lb. solute returned per pound solute product. Further,... 

A mixture of 50% oleic acid, 50% abietic acid is to be separated with the help of liquid propane as solvent in a countercurrent extraction with reflux. Equilibrium data are available at 81, 91, and 96.7°C. (Hixson and Hixson, Trans. Am. Inst. Cliem. Engrs. 37, 927 (1941). 

Figon IftlS Coimtarcuireht extraction with reflux. 

For purposes of computation, it is easiest to recall the similarity between the adsorption operation and continuous countercurrent extraction with reflux. Solid adsorbent as the added insoluble phase is analogous to extraction solvent, the adsorbate is analogous to the solvent-free extract, and the fluid stream is similar to the raffinate. Computations can then be made using the methods and equations of Chap. 10 [Eqs. (10.31) to (10.34) and (10.39) to (10.50) with Fig. 10.28]. Some simplification is possible, however, thanks to the complete insolubility of adsorbent in the mixture to be separated. 

Figure 8.1.41. Countercurrent multistaged solvent extraction with reflux.

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