Batch distillation binary

Distillation at constant reflux ratio but varying top product composition. 

Distillation at constant top product composition but varying reflux ratio. 

Compared to this a solution approach based on digital simulation is much more realistic. 

Consider the binary batch distillation column, represented in Fig. 3.58, and based on that of Luyben (1973, 1990). The still contains Mb moles with liquid mole fraction composition xg. The liquid holdup on each plate n of the column is M with liquid composition x and a corresponding vapour phase composition y,. The liquid flow from plate to plate varies along the column with consequent variations in M . Overhead vapours are condensed in a total condenser and the condensate collected in a reflux drum with a liquid holdup volume Mg and liquid composition xq. From here part of the condensate is returned to the top plate of the column as reflux at the rate Lq and composition xq. Product is removed from the reflux drum at a composition xd and rate D which is controlled by a simple proportional controller acting on the reflux drum level and is proportional to Md- 

For simplicity the following assumptions are made, although a more general model could easily be derived, in which these assumptions could be relaxed. 

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FIG. 13-98 Typical variation in distillate and reboiler compositions with amount distilled in binary batch distillation at a constant-reflux ratio. 

CONSTANT HOLDUP BINARY BATCH DISTILLATION COLUMN EQUILIBRIUM PLATE BEHAVIOUR... 

Bubble Point Calculation Binary Batch Distillation Column... 

Process Modes for a Bioreactor 538 Binary Batch Distillation Column 490 Bubble Point Calculation for a Batch Distillation Column 504... 

Table 5 displays the quantity and composition of the main streams of the process. -Hexane is drawn of as distillate product with a molar purity of 96.8%. Another binary batch distillation step is required to obtain n-hexane with a highest purity. Ethyl acetate with 99.6% of purity is recovered in the still at the end of the process, while the acetonitrile-rich phase obtained from decanter can be reused in the next batch distillation process. The make-up of fresh entrainer for the next cycle of n-hexane-ethyl acetate separation is approximately 52%. 

Attarwala, F.T., and Abrams, H.J., Optimisation techniques in binary batch distillation. IChemE Annual Research Meeting, London, 1974. 

Figure 7.1. State Task Network for Binary Batch Distillation with One Main-Cut and One Off-cut. [Mujtaba and Macchietto, 1993]a...

Figure 8.2. Quasi-steady State Off-cut Recycle Strategy in Binary Batch Distillation...

The one level optimal control formulation proposed by Mujtaba (1989) is found to be much faster than the classical two-level formulation to obtain optimal recycle policies in binary batch distillation. In addition, the one level formulation is also much more robust. The reason for the robustness is that for every function evaluation of the outer loop problem, the two-level method requires to reinitialise the reflux ratio profile for each new value of (Rl, xRI). This was done automatically in Mujtaba (1989) using the reflux ratio profile calculated at the previous function evaluation in the outer loop so that the inner loop problems (specially problem P2) could be solved in a small number of iterations. However, experience has shown that even after this re-initialisation of the reflux profile sometimes no solutions (even sub-optimal) were obtained. This is due to failure to converge within a maximum limit of function evaluations for the inner loop problems. On the other hand the one level formulation does not require such re-initialisation. The reflux profile was set only at the beginning and a solution was always found within the prescribed number of function evaluations. 

Mujtaba and Hussain (1998) implemented the general optimisation framework based on the hybrid scheme for a binary batch distillation process. It was shown that the optimal control policy using a detailed process model was very close to that obtained using the hybrid model. 

The graphical procedure is applicable to any binary batch distillation process and is not limited to operations at constant reflux ratio or constant distillate composition. 

The graphical-based shortcut methods for binary batch distillation may be applied to multicomponent distillation only when the separation is between two key components to produce one distillate product and the residue. In this case the calculations may be approximated by lumping the other components with either of the key components and treating the system as a pseudo-binary. 

In a binary batch distillation process with no reflux (differential distillation), constant relative volatility is assumed throughout the process, a = 2. If the initial liquid composition X° = 0.4, what is the initial distillate composition What is the composition of the liquid remaining in the boiler when 50% of the original liquid has been distilled When 99% has been distilled ... 

Develop the state model for an ideal binary batch distillation column with N ideal plates (Figure PII. 12). At t = 0, the composition of the initial mixture is cA and cB (molar fractions), and its total mass is M (moles). 

Binary Batch Distillation with Constant Reflux... 

Consider the binary batch distillation of Example 6.3. For this system, n-heptane with n-octane at 1 atm, the average relative volatility is a = 2.16 (Treybal, 1980). The mixture will be batch distilled until the average concentration of the distillate is 65 mol% heptane. Using equation (6-117), derived in Problem 6.7, compute the composition of the residue and the fraction of the feed that is distilled. 

Fig. 5.1-13 Graphical determination of product concentrations of binary batch distillation...

The mass balances for batch distillation are somewhat different from those for continuous distillation. In batch distillation we are more interested in the total amounts of bottoms and distillate collected than in the rates. For a binary batch distillation, mass balances around the entire system for the entire operation time... 

In the simple binary batch distillation system shown in Figure 9-1 the vapor product is in equilibrium with liquid in the still pot at any given time. Since we use a total condenser, y = Xp,. Substituting this into Eq. 

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