Distillation period

The highly interactive nature of the balance and equilibria equations for the distillation period are depicted in Fig. 3.66. An implicit, iterative algebraic loop is involved in the calculation of the boiling point temperature at each time interval. This involves guessing the temperature and calculating the sum of the partial pressures, or mole fractions. The condition required is that Zyi + yw = 1. The iterative loop for the bubble point calculation is represented by the five interconnected blocks in the lower right hand corner of Fig. 3.66. The model of Prenosil (1976) also included an efficiency term E for the steam heating, dependent on liquid depth L and bubble diameter D. 

Figure 3.66. Information flow diagram for the distillation period.

The model involves first a heating period and, when the boiling temperature is reached, and then a distillation period. 

The heating period begins with FLAG set initially to zero. When Xy > 1 then FLAG becomes 1, and the distillation period begins at statement 10. At each time interval the subroutine TCALC is used to make the iterative bubble point calculation. The component mass balance determines the removal of volatiles in the vapour, where the total molar flow rate, V, is determined from the energy balance. 

Figure 5.235. Temperature and water mass variations during the heating and distillation periods.

You now have steam going through your distillation setup, and as soon as product starts to come over, you ll be doing an external steam distillation. Periodically open the steam trap drain (Caution — HOT ) and let the condensed steam out. 

When the reduction takes place in a jacketed reducer, a fflgnificant improvement is realized. This is due to the fact that the jacket cuts down the dilution during the reduction period. Furthermore, some of the ensuing distillate is fortunately consumed in the reduction of the next charge. Finally, less steam is required during the distillation period, owing to the increased aniline concentration in the reducer charge. 

The integral in Eq. (2-3) can only be evaluated if the vapor concentration y(x) is known as a function of the concentration x, in the still during the distillation period. Numerical results from experiments are generally used. 

In the distillation period the heat required to heat the contents of the still to the boiling point, and the actual heat Q required for the distillation, are provided by the heating system of the still ... 

Nawar (23) has commented that the apparatus shown in Fig. 1 la may present problems if the sample contains water. He suggested the apparatus shown in Fig. 1 lb. Vacuum is applied at point A, and vessel L is filled wifh liquid nifrogen during the 1-hour distillation period. At the end of the distillation, the cold trap is disconnected and the coolant is discarded. The condenser is inverted, the ice melted, and condensed volatiles and water extracted with a solvent. He reported greater than 80% recovery of high-boiling hydrocarbons in a model system study. 

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