Batch distillation, rectification

Although batch distillation is covered in a subsequent separate section, it is appropriate to consider the application of RCM and DRD to batch distulation at this time. With a conventional batch-rectification column, a charge of starting material is heated and fractionated, with a vapor product removed continuously. The composition of the vapor prodiic t changes continuously and at times drastically as the lighter component(s) are exhausted from the stiU. Between points of drastic change in the vapor composition, a cut is often made. Successive cuts can be removed until the still is nearly diy. The sequence, number, and limiting composition of each cut is dependent on the form of... 

For a constant reflux ratio, the value can be almost any ratio however, this ratio affects the number of theoretical plates and, consequently, actual trays installed in the rectification section to achieve the desired separation. Control of batch distillation is examined in Reference 134. 

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,... 

Batch Distillation Evaporation and Condensation Continuous Distillation Fractionation Rectification Reflux Distillation Vacuum Distillation Steam Distillation Azeotropic Extractive Distillation Destructive Distillation Molecular Distillation Distillation by Compression and Sublimation)... 

Experimental verification of the separation of the mixture u-hexane-ethyl acetate by heteroazeotropic batch distillation in a bench scale rectification column... 

Gentilcore [Chem. Eng. Progr, 98(1), 56 (Jan. 2002)] describes an alternative strategy of constant-level batch distillation where the replacement solvent is added at a rate to keep the volume of liquid in the pot constant. For simple distillation without rectification the analog of Eq. (13-126) is... 

See destructive distillation batch distillation extractive distillation rectification dephlegmation flash distillation continuous distillation simple distillation reflux fractional distillation azeotropic distillation vacuum distillation molecular distillation hydrodistillation. 

For the production of relatively pure products by batch distillation, the stillpot is usually augmented by a multistage rectification column with reflux. Shown in Figure 12.19 is a flow diagram for a typical batch distillation process. The feed in this example contains components A, B, and... 

Shortcut methods for handling multicomponent batch distillation have been developed for the two cases of constant reflux and constant distillate composition (Diwekar and Mandhaven, 1991 Sundaram and Evans, 1993). Both methods avoid tedious stage-by-stage calculations of vapor and liquid compositions by employing the Fenske-Underwood-Gilliland (FUG) shortcut procedure for continuous distillation, described in Section 6.8, at succesive time steps. In essence, they treat batch distillation as a sequence of continuous, steady-state rectifications. As in the FUG method, no estimations of compositions or temperatures are made for intermediate stages. 

Multistage batch distillation (i.e., batch rectification) is governed by the Rayleigh equation... 

Fig. 2-54. Batch distillation unit. S Still C Condenser TC Top product cooler TR Top product receiver RC Rectification column...

The simple distillation curve is the temperature as a function of the per cent distilled in a simple or Rayleigh type of distillation. This type of distillation is approximated by the laboratory A.S.T.M. distillation which is widely used to characterize petroleum fractions. The A.S.T.M. procedure gives some reflux and rectification, and the results are not exactly equal to the simple batch distillation, although the difference is not large. The temperature normally measured is the condensation temperature of the vapor flowing from the still to the condenser. Curve A of Fig. 11-1 is typical for the simple distillation of a complex mixture. The temperature at any point is the averaged result of a large number of components and includes all the effects of nonideality in the solutions. Thus in most cases it is impossible to relate such a curve to the volatility of the individual components involved. As a result, such simple distillation curves are not of much direct value for the solution of rectification problems. 

A batch distillation with rectification involves charging the still with the material to be separated and carrying out the fractionation until the desired amount has been distilled off. The overhead composition will vary during the operation, and usually a number of cuts will be made. Some of the cuts will be the desired products, while others will be intermediate fractions that can be recycled to subsequent batches to obtain further separation. 

The batch distillation of binary mixtures will be considered fpr the cases of (1) no rectification, (2) rectification without liquid holdup in the column, and (3) rectification with holdup. 

Ho Rectification Batch distillation without rectification corresponds to the simple distillations of Chap. 6, and the calculations of the concentrations as a function of the amount distilled can be made by Eqs. (6-8) and (6-7). 

This mode of batch rectification requires the continuous adjustment of the reflux to the colunrn in order to achieve a steady overhead distillate composition. Starting with a kettle obviously rich in the more volatile component, a relatively low reflux ratio will be required to achieve the specified overhead distillate composition. With time, the reflux ratio must be continuously increased to maintain a fixed overhead composition. Ultimately, a practical maximum reflux is reached and the operation normally would be stopped to avoid distillate contamination. 

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