Multicomponent distillation profiles

The existence of a methane peak is not considered a phenomenon that will always occur with intermediately permeable gases in multicomponent mixtures. Rather, the peak is thought to be the result of a combination of factors. These factors include composition of the feed mixture, pure-gas permeabilities, and the internal reflux ratio. For instance. Figure 3 indicates that the intermediate-gas composition profile will steadily decrease in a stripper 1.0 m long, but otherwise identical to the column used in this study, fed with a 63.6% N2 - 32.3% CH - 4.1% CO2 mixture under similar total reflux conditions. The presence of an intermediate peak, however, is reminiscent of multicomponent distillation profiles and raises the possibility of withdrawing a side stream enriched with an intermediate gas. 

When data of activity coefficients of all pairs of components are known, including those with the solvent, any of the standard calculation procedures for multicomponent distillation, which include ternaries, may be used. Composition profiles found by tray-by-tray calculations in two cases appear in Figure 13.24. 

Figure 2.16 Composition profiles in multicomponent distillation, Example 2,4, (a) Liquid <6,1 vapor, (Prom C. J. King , Separation Processes. 2d ed, Copyright by McGraw-Hill, hie. Reprinted by permission.)...

Multicomponent distillation, 393 absorption factor method, 398 azeotropic, 420-426 bubblepoint (BP) method, 406-409 computer program references. 404 concentration profiles, 394 distribution of non-kevs. 395 Edmister method, 398,399 extractive, 412, 417-422 feed tray location, 397 free variables, number of 395 Lewis-Matheson method 404 MESH eauations. 405-407 molecular, 425-427 nomenclature, 405 number of theoretical trays, 397 packed towers, 433-439 petroleum, 411-415 reflux, minimum, 397 reflux, operating, 397 SC (simultaneous correction) method, 408-411... 

Explain the flow, temperature, and composition profiles for multicomponent distillation... 

Multicomponent Differential Distillation 494 Dissolved Oxygen and BOD Profiles in a River 572... 

For single separation duty, Mujtaba and Macchietto (1993) proposed a method, based on extensions of the techniques of Mujtaba (1989) and Mujtaba and Macchietto (1988, 1989, 1991, 1992), to determine the optimal multiperiod operation policies for binary and general multicomponent batch distillation of a given feed mixture, with several main-cuts and off-cuts. A two level dynamic optimisation formulation was presented so as to maximise a general profit function for the multiperiod operation, subject to general constraints. The solution of this problem determines the optimal amount of each main and off cut, the optimal duration of each distillation task and the optimal reflux ratio profiles during each production period. The outer level optimisation maximises the profit function by... 

Many industrial columns use temperatures for composition control because direct composition analyzers can be expensive and unreliable. Although temperature is uniquely related to composition only in a binary system (at known pressure), it is still often possible to use the temperatures on various trays up and down the column to maintain approximate composition control, even in multicomponent systems. Probably 75 percent of all distillation columns use temperature control of some tray to hold the composition profile in the column. This prevents the light-key (LK) impurities from dropping out the bottom and the heavy-key (HK) impurities from going overhead. 

FIG. 13-106 Distillate-composition profile for the multicomponent-batch-distillation example. 

FIG. 13-109a Responses after a 30 percent increase in the feed flow rate for the multicomponent-dynamic-distillation example of Fig. 13-100. Profiles of liquid mole fractions at several times. 

In multicomponent separations, the sensitivity of temperature to the key components is important. Figure 18.2a and b shows composition and temperature profiles for a depropanizer separating propane (C3) and lighter components from butane (C4) and heavier components. The temperature is sensitive to the composition of the keys between tray 3 and tray 13. Below tray 3 and above tray 13 the temperature is more sensitive to the concentration of nonkeys than to the concentration of the keys. Trays 8 to 10 show some tendency toward retrograde distillation (recognized by the maximum in the C4 concentration curve) and are best avoided. Moczek et al. (287) provide a detailed demonstration of the anomaly in temperature response in the retrograde distillation region. This leaves trays 3 to 7 and trays 11 to 13 as those suitable for temperatime control. 

The differences in the composition profiles for multicomponent and binary distillation for relatively ideal VLE with no azeotropes can be summarized as follows ... 

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