Ponchon fractionation

The composition of a typical system is satisfactorily presented in the form of a diagram. Those diagrams most frequently employed are a right-triangular plot of mass fraction of solvent against mass fraction of solute (Fig. 18-92(i) and a plot suggestive of a Ponchon-Savarit dia-... 

Marcel Ponchon Graphical Study of Fractional Distillation, Tech. Moderne, 13 20 (1921). 

An equimolal mixture of carbon tetrachloride and toluene is to be fractionated so as to produce an overhead containing 4 mole% toluene and a bottoms containing 4 mole% carbon tetrachloride. Calculate by the Ponchon method the theoretical minimum reflux ratio, the theoretical minimum number of stages, and the number of theoretical stages when LID = 2.5. The thermal condition of the feed is saturated liquid, which is sent to the optimum stage. 

Figure 7.7. Ponchon-Savarit and McCabe-Thiele diagrams for the fractional crystallization of lead and barium nitrates from aqueous solution. After Matz, 1969)...

Fig. 2-10. Enthalpy-concentration diagram of Merkel and Ponchon. h Enthalpy of the binary mixture w Mass fraction of the k r component in the binary mixture...

The required number of stages for fractional crystallization are determined by methods given in [7.1]. The Ponchon-Savarit and the McCabe-Thiele diagram are both commonly used. 

The major difference between the McCabe-Thiele method and the Ponchon-Savarit method is that the liquid and vapor flow rates in the latter method are not assumed constant throughout the column. Because of this, the Ponchon-Savarit method is a more general and accurate method. Since the method is based on enthalpy values of fluid mixtures throughout the column, an enthalpy-concentration diagram is used in conjunction with a vapor-liquid equilibrium plot to determine the number of theoretical plates required for a specific separation. Units based on either moles (and mole fractions) or mass (and mass fractions) are acceptable as long as they are consistent. 

Mole Fraction in Liquid and Vapor Fig. 6.18. Ponchon-Savarit analysis for a rectifying column. 

Complete Fractionation Columns. A complete fractionation column, as shown in Fig. 6.11, may also be analyzed using the Ponchon-Savarit technique. In the McCabe-Thiele analysis, equations for two operating lines were found. These correspond to the A points in the Ponchon-Savarit analysis, where one A point represents the difference between passing streams in the column above the feed plate and the other A point represents the difference between passing streams below the feed plate. Assume that the reflux ratio, along with the composition and enthalpy of the feed, overhead distillate, and bottom product are known. Then points F, B, D, and A i may be located on... 

Ponchon Method. A weakness of the McCabe-Thiele method, as outlined heretofore, is the fact that the transfer of heat is not directly introduced. Heat must be transferred on each plate, reboiler heat must be supplied at the base of the fractionator, and cooling by reflux must be accomplished at the top. The method devised by Ponchon does not ignore these relationships, and although space is not available for an explanation of the Ponchon method, Example 16-11 will indicate its general usefulness. 

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