McCabe-Thiele diagrams column distillation

Fig. 5.9 shows the geometric representation of these balances in the McCabe-Thiele diagram. The distillate composition xP is located at the intersection of the condenser operating line and the operating line of the RD section. By specifying xP, the number of reactive trays can be estimated from the classical staircase construction. From the intersection of the operating line of the column section with that of the reboiler line, the bottom composition is determined. 

The system material balance from Treybal [129] using a heated kettle and distillation column following a McCabe-Thiele diagram, using reflux, but having only a batch (kettle) charge ... 

Both modes usually are conducted with constant vaporization rate at an optimum value for the particular type of column construction. Figure 13.10 represents these modes on McCabe-Thiele diagrams. Small scale distillations often are controlled... 

FIG. 13-57 McCabe-Thiele diagram for nonideal distillation column. 

Both modes usually are conducted with constant vaporization rate at an optimum value for the particular type of column construction. Figure 13.9 represents these modes on McCabe-Thiele diagrams. Small scale distillations often are controlled manually, but an automatic control scheme is shown in Figure 13.9(c). Constant overhead composition can be assured by control of temperature or directly of composition at the top of the column. Constant reflux is assured by flow control on that stream. Sometimes there is an advantage in operating at several different reflux rates at different times during the process, particularly with multicomponent mixtures as on Figure 13.10. 

Once one has proposed alternative configurations for systems of separation devices to effect a desired separation, one must then design these devices so the various alternatives may be compared. For a distillation column, the first set of design decisions is to choose the number of trays, the feed tray location, and the reflux ratio at which to operate it. For a binary separation, the McCabe-Thiele diagram (or the concepts behind it) is an indispensable aid in making these decisions. 

Figure 30. McCabe-Thiele diagram for a column distillation.

Composition and temperature profiles are shown in Figures 14.13 and 14.14. In this example we see that the vapor and liquid temperatures are rather different. This result is quite typical of absorption columns indeed, it is possible for temperature differences to be over the order of 20 K. The McCabe-Thiele diagram is shown in Figure 14.15 and the component efficiencies in Figure 14.16. The efficiencies tend to be lower than in the distillation operations considered above. 

The operation of a batch still and column can be analyzed using a McCabe-Thiele diagram, with the same operating-line equation that was used for the rectifying section of a continuous distillation ... 

The McCabe-Thiele diagram below refers to the usual distillation column. What is the significance of x, (algebraic value and physical significance) ... 

A batch column with plates above a still pot functions as a rectifier, which can provide a sharper separation than differential distillation. If the reflux ratio is fixed, distillate and still bottoms compositions will vary with time. Equation (9-2) applies with yo = Xo- Its use is facilitated with the McCabe-Thiele diagram as described by Smoker and Rose. ... 

McCabe-Thiele diagrams for adsorption, 320 for binary distillation, 326, 329, 330, 332, 334 for countercurrent multistage separator, 309 for extraction, 317 for ion exchange, 322 for rectifying column, 314 McCabe-Thiele method for distillation, 310-315, 322-340... 

If a constant distillate composition is required, this can be achieved by increasing the reflux ratio as the system is depleted in the more volatile material. Calculations are again made with the McCabe-Thiele diagram as described by Bogart and illustrated by the following example. Other methods of operating batch columns are described by Ellerbe. ... 

Dissolution of the HCl in water sets free a large amount of heat of absorption (approximately as high as the latent heat of evaporation of water). Hence, the liquid in the absorber reaches boiling temperature and, in turn, some water is evaporated by the absorption of HCl. Hence, the conditions in the absorber are quite similar to those in a distillation column. The equilibrium curve of a boiling HCI/H2O liquid is shown in the McCabe-Thiele diagram of Fig. 11.1-6. The presence of the inert gases only reduces the effective pressine of the HCI/H2O system. 

Geelen and Wijffels (19) investigated the reaction of vinyl acetate with stearic acid in a distillation column to form vinyl stearate and acetic acid. A modified form of the McCabe-Thiele diagram was employed to obtain the number of theoretical plates for a given conversion. This was tested experimentally using a bubble-cap Oldershaw column for the distillation reactor followed by a packed column for separation of top products (vinyl acetate acetic acid). Theoretical considerations agreed reasonably well with experimental findings. 

D26. A distillation column with a partial condenser and a total reboiler is separating acetone and ethanol. There are two feeds. One feed is 50.0 mol% acetone, flows at 100.0 mol/min, and is a superheated vapor where approximately 1 mole of liquid will vaporize on the feed stage for each 20 moles of feed. The other feed is a saturated liquid, flows at 150.0 mol/min and is 35.0 mol% acetone. We desire a distillate product that is = 0.85 mole fraction acetone and a bottoms product that is Xg = 0.10 mole fraction acetone. The column has a partial condenser and a total reboiler. Boilup is returned as a saturated vapor. Column operates at a pressure of 1.0 atin. Assume CMO and use a McCabe-Thiele diagram. VLE data are given in Problem 4.D7. 

D6. We are separating 1,000 mol/h of a 40% benzene, 60% toluene feed in a distillation column with a total condenser and a partial reboiler. Feed is a saturated liquid. CMO is valid. A distillate that is 99.3% benzene and a bottoms that is 1% benzene are desired. Use the Fenske equation to find the number of stages required at total reflux, a McCabe-Thiele diagram to find (L/D), and the Gilliland correlation to estimate the number of stages required if L/D = 1.15(L/D)n. Estimate that the relative volatility is constant at a x = 2.4. Check your results with a McCabe-Thiele diagram... 

D17. A distillation column is separating toluene and xylene, a = 3.03. Feed is a saturated liquid and reflux is returned as a saturated liquid, p = 1.0 atm F = 100.0 kmol/h. Distillate mole fraction is Xp) = 0.996 and bottoms Xg = 0.008. Use the Underwood equation to find (L/D)j and at feed mole fractions of z = 0.1, 0.3, 0.5, 0.7, and 0.9. Gheck your result at z = 0.5 with a McCabe-Thiele diagram What are the trends for Qc,minl Qr nim toluene feed concentration increases ... 

Figure 8-4. Binary heterogeneous azeotrope (A) two-column distillation system, (B) McCabe-Thiele diagram for column 1. (C) McCabe-Thiele diagram for column 2 with expanded coordinates.

The batch distillation column can also be operated with variable reflux ratio to keep x constant. The operating Eq. 19-261 is still valid. Now the slope will vary, but the intersection with the y=x line will be constant at Xp,. The McCabe-Thiele diagram for this case is shown in Figure 9-7. This diagram relates Xs to Xp). Since Xp, is kept constant, the calculation procedure is somewhat different. 

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