Robinson and Gilliland

The benzene-toluene example of Robinson and Gilliland [59] has been elaborated on and expanded after the advanced distillation course of Holland [25], Figure 8-26. 

If the operating and equilibrium lines are straight, and they usually can be taken as such when the concentrations are small, the number of stages required can be calculated using the equations given by Robinson and Gilliland (1950). 

Figure 11.45 shows a composition profile for the azeotropic distillation column in the process shown in Figure 11.44. This is taken from a solution presented by Robinson and Gilliland...

The general method of stage-by-stage calculation for multicomponent systems was first shown by Lewis and Matheson (LI) and by Underwood (Ul) in 1932. The method of Lewis and Matheson was further improved by Robinson and Gilliland (Rl), but substantially unchanged. In its most basic form, the concept of the method is simple. Consider the example cited above. If the amounts of each component in both of the products could be exactly calculated, it would only be necessary to start at one end and calculate until a stage was reached at which the composition matched that of the other product. 

However, the products cannot be calculated exactly and the procedure outlined is difficult to accomplish. Instead, calculations are made from both ends of the column to a match on an internal stage, perhaps first neglecting certain components, and later correcting the calculation by adding those components. The method has been well described by Robinson and Gilliland, and is certainly useful for simple distillation columns. Greenstadt et al. (Gl) have shown its application to computers. 

Although these specifications lead to only moderate tray and reflux requirements, in practice distillation with only two towers and the assistance of an azeotropic separating agent such as benzene is found more economical. Calculation of such a process is made by Robinson and Gilliland (1950, p. 313). 

Figure 13.12. Concentration profiles in two kinds of distillations, (a) Purifying column for fermentation alcohol small streams with high concentrations of impurities are withdrawn as sidestreams (Robinson and Gilliland, Elements of Fractional Distillation, McGraw-Hill, New York, 1939 edition), (b) Typical concentration profiles in separation of light hydrocarbon mixtures when no substantial inversions of relative volatilities occur (Van Winkle, Distillation, McGraw-Hill, New York, 1967).

Figure 13.29. Composition profiles and flowsketches of two azeotropic distillation processes (adapted by King, 1980). (a) Separation of ethanol and water with benzene as entrainer. Data of the composition profiles in the first column were calculated by Robinson and Gilliland, (1950) the flowsketch is after Zdonik and Woodfield (in Chemical Engineers Handbook, McGraw-Hill, New York, 1950, p. 652). (b) Separation of n-heptane and toluene with methylethylketone entrainer which is introduced in this case at two points in the column (data calculated by Smith, 1963).

Robinson and Gilliland (1950), Abrams et al. (1987) and Hasebe et al. (1992, 1995), Sorensen and Skogestad (1996a), Barolo et al. (1998), Furlonge et al. (1999) reported simulation results using inverted, batch distillation columns with middle vessel and multi-effect batch distillation, respectively. Mujtaba (1997) simulated batch distillation operation using a continuous distillation model. 

The features and modelling issues of IBD columns with or without chemical reaction are presented in Chapter 2 and 4 respectively. Simulation of IBD columns without chemical reactions is also presented in Chapter 4. After Robinson and Gilliland (1950) had introduced IBD columns, Abrams et al. (1987), Mujtaba and Macchietto (1994) and Sorensen and Skogestad (1996) used such columns for batch distillation and compared their performances with conventional columns. While Mujtaba and Macchietto (1994) studied simultaneous chemical reaction and separation using IBD columns, Sorensen and Skogestad (1996) presented the most comprehensive study on IBD columns. Some examples from these works are presented below. 

Using an H-x diagram to derive pseudo molecular weights and pseudo latent heats of vaporization for the components. These pseudo properties are then applied to construct an x-y diagram. This method is described in detail by Robinson and Gilliland (6),... 

Only a brief review of the fundamental principles that underlie the design procedures will be given a fuller discussion can be found in Volume 2, and in other text books Robinson and Gilliland (1950), Norman (1961), Oliver (1966), Smith (1963), King (1980), Hengstebeck (1961), Kister (1992). 

This new method is based on the equation given by Robinson and Gilliland [6 ] for the minimum reflux ratio for binary mixtures, for the limiting condition X/j = = 1,0 ... 

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