Packed Batch Distillation

Nad and Spiegel (1987) carried out experimentation in a conventional packed batch distillation column using a cyclohexane-heptane-toluene mixture. The column consists of 20 theoretical stages (equivalent) including the condenser and reboiler. The feed to the column was 2.93 kmol of which 1.9% was total column holdup and 1.2% was condenser holdup. The column underwent an initial total reflux operation for about 2.54 hr before any product was collected. After then the mixture was separated into 3 main-cuts with 2 off-cuts in between, leaving a final product in the reboiler. 

Wajge et al. (1997) attempted to develop rigorous PDAE model for packed batch distillation with and without chemical reaction and used finite difference and orthogonal collocation techniques to solve such model. The main purpose of the study was to investigate the efficiencies of the numerical methods employed. The authors observed that the collocation techniques are computationally more efficient compared to the finite difference method, however the order of approximating polynomial needs to be carefully chosen to achieve a right balance between accuracy and efficiency. See the original reference for further details. 

Simple Batch Distillation Constant a, with Trays or Packing, Constant BoUup, and with Reflux [129] Using x-y Diagram... 

In batch distillation the mixture to be distilled is charged as a batch to the still and the distillation carried out till a satisfactory top or bottom product is achieved. The still usually consists of a vessel surmounted by a packed or plate column. The heater may be incorporated in the vessel or a separate reboiler used. Batch distillation should be considered under the following circumstances ... 

Packed fractional distillation columns run in the batch mode are often used for low-pressure drop vacuum separation. With a trayed column, the liquid holdup on the trays contributes directly to the hydraulic head required to pass through the column, and with twenty theoretical stages that static pressure drop is very high, e.g., as much as 100-200 mm Hg. 

During the batch distillation of a binary mixture in a packed column the product contained 0.60 mole fraction of the more volatile component when the concentration in the still was 0.40 mole fraction. If the reflux ratio used was 20 1, and the vapour composition y is related to the liquor composition x by the equation y = 1.035x over the range of... 

To increase product recovery in batch distillations, as a result to the lower liquid holdup in a packed column. 

Batch distillation. Because of the smaller liquid holdup of packing, a higher percentage of the liquid can be recovered as top product. 

As a means of preparing high percentages of diesel fuels with good quality from the hydrocracked oil, a batch distillation of the oil was made in a packed laboratory distillation column in which a first fraction was removed at a corrected column head... 

A batch distillation column with a diameter of 100 mm and a reactive packing height of 2 m (MULTIPAK I ) in the bottom section and an additional meter of conventional packing (ROMBOPAK 6M ) in the top section was used. The flow sheet of the column is shown in Figure 22. 

Figure 5.27. Cont d. (c) Composition control. Top product take-off and boil-up controlled by feed, (d) Packed column, differential pressure control. Eckert (1964) discusses the control of packed columns, (e) Batch distillation, reflux flow controlled based on temperature to infer composition.

A batch distillation apparatus consists of a reboiler attached to the bottom of a trayed or packed column with a condenser at the top. A batch of feedstock is charged to the reboiler, and then the mixture in the reboiler is gradually vaporized. The vapor flows up the column, is condensed in the condenser, and part of the condensate is returned to the column as reflux, flowing countercurrent to the vapor. The rest of the condensate is collected over a period of time as a single distillate product or a series of distillate fractions. Generally, there are no side feeds or side products and the entire column acts as a rectifier. 

Eor batch distillation size based on cycle time fill, distill, discharge bottoms, clean, for = 2, NTS = 10 reflux ratio 20 1 Op,p = 4, NTS = 6 reflux ratio 12 1 Op,p = 10, NTS = 3 reflux ratio 7.5 1 To convert TS to height of packing ... 

Tray colunms operate with about 40 mm of liquid on the tray and for this reason have a higher hold-up than packed columns. This is not an important handicap in continuous distillation, where ideally the composition is constant in any part of the system once equilibrium is established. In batch distillation a high inventory in the column makes a sharp separation more difficult to achieve. 

Step-Ill The organic layer is transferred to a batch distillation still equipped with a packed tower. The mixture is distilled. As the water-n-butanol system forms a heterogeneous azeotrope, the condensate separates into two layers in the receiver. The organic layer is refluxed, and the water layer is drawn as distillate and discharged as effluent. 

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