Saturated raffinate

Find the saturated extract, saturated raffinate, and conjugate lines on a right-triangular diagram. 

Using the data from Table 7.1, generate a cubic spline interpolation formula for the saturated raffinate curve, one for the saturated extract curve, and one for the tie-line data (see the Mathcad program in Appendix G-l). Equations in the form... 

In Fig. 11.7, the feed is at F and the water-free raffinate product at B. The saturated raffinate is located at B on the saturated raffinate envelope on a line connecting B with the 100% water vertex at S,... 

To find two additional relationships, note that streams and Ej are both leaving equilibrium stages. Thus, the compositions of stream R must be related in such a way that R is on the saturated raffinate curve. This gives a relationship between x and x Similarly, since stream Ep must be a saturated extract, y n and y, related. If the saturated extract and saturated raffinate relationships are known in analytical form, these two equations can be added to the three mass balances, and the resulting five equations can be solved simultaneously for the five unknowns. 

To develop a fourth relation we must realize that stream R2 is a saturated raffinate stream. Thus, it will be located on the saturated raffinate line, and x 2 and x, 2 are related by the relationship describing the saturated raffinate line. With four equations and four unknowns we can now solve for the variables Ej, ... 

These stage-by-stage calculations can be done anal5 cally and can be programmed for spreadsheet solution if equations are available for the tie lines and the saturated extract and saturated raffinate curves. If the equations are not readily available, either the equilibrium data must be fitted to an analytical form or a data matrix with a suitable interpolation routine must be developed. Graphical techniques can be employed and have the advantage of giving a visual interpretation of the process. 

In a graphical procedure for countercurrrent systems the equilibrium calculations can easily be handled by constructing tie lines. The relation between x j and x j is already shown as the saturated raffinate curve. All that remains is to develop a method for representing the mass balances graphically. 

One further inportant point should be stressed with respect to Figure 13-23. If two equilibrium stages were used with F/S = 2 as in the original problem statement, the saturated extract would not be located at the value E2 shown on the graph and saturated raffinate would not be at the value shown. The streams Rj and E2 do not satisfy the external mass balance for this system The values R and Ejvj do, but R and E2 do not. The exact conpositions of the product streams for a two-stage system require a trial-and-error solution. 

A. Define. The system is similar to that of Figure 14-4 with streams Eq and specified. In addition, weight fraction x = 0.04 and is a saturated raffinate. We wish to find the composition... 

A4. In leaching the final saturated raffinate often contains a significant amount of solvent. This is the case for Exanple 14-3 and for Problems 14.E1 to 14.E3. How do you recover this solvent ... 

Stages / + 1 through n constitute the raffinate stripping section of the cascade, where the raffinate solution is exhausted of its C content. The primary raffinate product Rn is divided into two streams Pr, the saturated raffinate product, may be further treated to remove solvent and to provide the finished raffinate and operation not concerned with the extraction operation and which when mixed with the extracting solvent S, provides the raflSnate reflux Pn, Bn, and Pr are of the same composi-... 

One hundred pounds per hour of a solution containing 50% pyridine (C), 50% water (A) are to be reduced to a saturated raffinate containing 1% pyridine with benzene as solvent in a countercurrent multiple contact system. Equilibrium data are available at 25 C. (Woodman, J. Chem. Soc. 1926, 2461). Calculate... 

A feed of 200 Ib./hr. containing 50% acetone (C), 50% water (B), is to be extracted in a countercurrent multiple-contact plant with 50 Ib./hr. of 1,1,2-trichloroethane (B) as solvent. The final saturated raffinate is to contain 2% acetone, and an intermediate saturated raffinate containing as nearly 25% acetone as possible is to be withdrawn from... 

Example 13-5 A solvent extraction system (countercurrent multistage contact process) is to reduce a 50 percent pyridine and 50 percent water (mass percents) to a 1 percent pyridine solution (i.e., saturated raffinate) by using pure benzene... 

Feed is a saturated raffinate (83 percent A, 17 percent B, both solvent-free basis). Solvent-free percents in extract and raffinate are 83 percent A, 17 percent B, 10 percent A, 90 percent B. Find the required stages at twice minimum reflux rate. 

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