Batch distillation inverted

A Develop the equations describing an inverted batch distillation column. This system has a large reflux drum into which the feed is charged. This material is fed to the top of the distillation column (which acts like a stripper). Vapor is generated in a reboiler in the base. Heavy material is withdrawn from the bottom of the column. 

This type of column is inherently very flexible in the sense that it can be easily converted to a conventional or inverted batch distillation column by changing the location of the feed and by closing or opening appropriate valves in the product lines. 

Robinson and Gilliland (1950), Abrams et al. (1987) and Hasebe et al. (1992, 1995), Sorensen and Skogestad (1996a), Barolo et al. (1998), Furlonge et al. (1999) reported simulation results using inverted, batch distillation columns with middle vessel and multi-effect batch distillation, respectively. Mujtaba (1997) simulated batch distillation operation using a continuous distillation model. 

Referring to Figure 4.12 for inverted batch distillation column, the intermediate plate equations in model types III, IV and V presented in section 4.2 will remain the same. The model equations for the condenser and for the reboiler for types III, IV and V models are presented below. 

A liquid binary mixture with B0 = 10 kmol (Hc) and xB0 = <0.6, 0.4> (xj) molefraction is subject to inverted batch distillation shown in Figure 4.12. The relative volatility of the mixture over the operating temperature range is assumed constant with a value of (a-) 2. The number of plates is, N= 10. The vapour boilup rate is, V = 10.0 kmol/hr. The total plate holdup is 0.3 kmol and the reboiler holdup is 0.1 kmol. The total batch time of operation is 4 hr with two time intervals. The first interval is of duration 1 hr and the column is operated with a reboil ratio of 0.8. The second interval is of duration 3 hrs when the column is operated with a reboil ratio of 0.9. The column operation is simulated with the type III model (section 4.3.2.1). 

Referring to Figure 2.2 for MVC column configuration, the model equations for the rectifying section are the same (except the reboiler equations) as those presented for conventional batch distillation column (Type III, IV, V in section 4.2). The model equations for the stripping section are the same (except the condenser equations) as those presented for inverted batch distillation column (Type III, IV, V in section 4.3.2). However, note that the vapour and liquid flow rates in the rectifying and stripping sections will not be same because of the introduction of the feed plate. 

Conventional batch distillation is not suitable when all reaction products have higher boiling temperatures than those of the reactants. Inverted batch distillation is suitable for such situation. If all the reaction products are valuable, as the reaction proceeds, the products will be separated from the bottom of the column in different main bottom cuts in sequential order. 

For cases where some of the reaction products have higher and some lower boiling points than those of the reactants, then neither the conventional nor the inverted batch distillation are suitable. For such reaction schemes, the MVC column will be the most suitable one because the light and heavy products can now be... 

Another alternative is called inverted batch distillation (Diwekar. 1995 Pratt. 1967 Robinson and Gilliland. 1950) because bottoms are withdrawn continuously while distillate is withdrawn only at the end of the distillation (see Figure 9-8 and Problem 9.C21. In this case the charge is placed in the accumulator and a reboiler with a small holdup is used. Inverted batch distillation is seldom used, but it is useful when quite pure bottoms product is required. 

The feed into the column is F kg moles of mole fraction Xp of the more volatile conponent. The final moles in the reboiler at the end of the batch is of mole fraction fjjjap The symbol W is used since the material left in the reboiler is often a waste. is the total kilogram moles of distillate of average concentration Xq a g. Equations (9-1) and (9-2) are applicable to sinple batch and normal multistage batch distillation. Some minor changes in variable definitions are required for inverted batch distillation. 

C2. Assume that holdup in the column and in the total reboiler is negligible in an inverted batch distillation tFigure 9-RL... 

E3. In inverted batch distillation the charge of feed is placed in the accumulator at the top of the column fFigure 9-8). Liquid is fed to the top of the column. At the bottom of the column bottoms are continuously withdrawn and part of the stream is sent to a total reboiler, vaporized and sent back up the column. During the course of the batch distillation the less volatile component is slowly removed from the liquid in the accumulator and the mole fraction more volatile component increases. Assuming that holdup in the total reboiler, total condenser and the trays is small compared to the holdup in the accumulator, the Rayleigh equation for inverted batch distillation is. 

The column shown in figure Id can be visualised as an inverted batch distillation column placed on top of a regular batch column, the two being connected at the withdrawal stage. Hence, feasibility studies for the regular and inverted batch distillation columns may be applied to the novel process provided that the concentration of the withdrawal tray lies on the column s profile. Therefore, it is possible to obtain pure intermediate-boiling product b from an infinite column operated at infinite reflux ratios, only if the distillate and sump vessels contain the binary mixtures a-b (light-intermediate boilers) and b-c (intermediate-heavy boilers), respectively. 

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