Examples batch distillation, constant reflux

Batch with Constant Reflux Ratio, 48 Batch with Variable Reflux Rate Rectification, 50 Example 8-14 Batch Distillation, Constant Reflux Following the Procedure of Block, 51 Example 8-15 Vapor Boil-up Rate for Fixed Trays, 53 Example 8-16 Binary Batch Differential Distillation, 54 Example 8-17 Multicomponent Batch Distillation, 55 Steam Distillation, 57 Example 8-18 Multicomponent Steam Flash, 59 Example 8-18 Continuous Steam Flash Separation Process — Separation of Non-Volatile Component from Organics, 61 Example 8-20 Open Steam Stripping of Heavy Absorber Rich Oil of Light Hydrocarbon Content, 62 Distillation with Heat Balance,... 

Figure 11.37. Batch distillation-constant reflux ratio (Example 11.13)...

Example 8-14 Batch Distillation, Constant Reflux Following the Procedure of Block [133]... 

If the same batch as in Example 11.12 is distilled with a constant reflux ratio of R = 2.1, what will be the heat required and the average composition of the distillate if the distillation is stopped when the composition in the still has fallen to 0.105 mole fraction of ethanol ... 

Hence the reflux ratio, the amount of distillate, and the bottoms composition can be related to the fractional distillation time. This is done in Example 13.4, which studies batch distillations at constant overhead composition and also finds the suitable constant reflux ratio that enables meeting required overhead and residue specifications. Although the variable reflux operation is slightly more difficult to control, this example shows that it is substantially more efficient thermally—the average reflux ratio is much lower—than the other type of operation. 

Robinson (1969) considered the following example problem. A binary feed mixture with an initial amount of charge, B0 = 100 kmol and composition xB0 = <0.50, 0.50> molefraction, having constant relative volatility of 2.0 was to be processed in a batch distillation column with 8 theoretical stages. The aim was to produce 40 kmol of distillate product (D) with composition (xd) of 0.5 molefraction for component 1 in minimum time (tF) using optimal reflux ratio (/ ). 

Figure S.2 Batch distillation of benzene-toluene at constant reflux ratio, Example 5,3, ia-e) McCabe-Thiele diagram for progressively reducing still concentration to 0.13 mole fraction benzene.

A batch distillation column with four theoretical stages (first stage is the still pot) is charged with 100 kmol of a 50 mol% benzene in toluene mixture at atmospheric pressure. At a constant reflux ratio R = 1.5, how many moles of the charge must be distilled if an average product composition of 84 mol% benzene is required If the boil-up ratio is 15 kmol/h, calculate the distillation time. The equilibrium distribution curve at column pressure is given in Example 6.4. 

As stated earlier, the basic batch distillation column satisfies the Rayleigh equation. Therefore we can use the same equation to calculate the total amount of distillate, as was done for the constant reflux condition. Values of xb,xd— b, f/xn — xb are obtained for each operating line. Values of xb versus 1/xd — xb are plotted from which the right hand side of the Rayleigh equation is obtained as the area under the curve and is found to be 0.5108, which corresponds to ln[ ]. Hence the total amount of distillate given by (1 — is equal to 40 moles, which is what we obtained in the variable reflux and constant reflux operations in Examples 4.2 and 4.3. 

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. ... 

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