Open distillation

The evaporation velocity at ambient pressure and, say, 60 °C, which corresponds to a mole fraction in the sweep gas of about 30 % water vapor, is about uuq = IO-5 m s-i. This results in Kj , = 0.904 which is rather close to 1, so that the effect of the liquid phase mass transfer resistance on the selectivity of an open distillation process with a free gas-liquid interface in most cases can be ignored. If, however, kuq becomes very small (as in the pervaporation process described in the next example), Kuq might become very small and thus reduce the selectivity of the open distillation process practically down to zero. 

In open distillation the vapor generated by a supply of heat is immediately removed from the liquid. Therefore, the content of the low boiler in the vapor product is higher than in closed distillation. 

In countercirrrent distillation the vapor product has the highest content of low-boiling constituents. The vapor is, in a first approximation, in equilibrium state with the hquid feed. In industrial practice only the operation modes closed distillation and open distillation are used. All operation modes can be performed continuously or... 

In open distillation the vapor generated in the reboiler is steadily removed from the residual liquid. In practice this process is preferably performed as a discontinuous process, called batch distillation. 

In discontinuous simple open distillation discontinuous partial distillation, Rayleigh Distillation) the distillation still is charged with a liquid mixture. Slow heating to the boiling point partially vaporizes the liquid. The vapor becomes enriched with the more volatile components and is withdrawn from the distillation still. After condensing in a condenser the distillate is stored in a distillate receiver (Fig. 2-3). 

Figure 11.11 Composition as a function of time for two ternary systems in the case of open distillation at atmospheric pressure. Ideal ternary system with a low, intermediate and high-boiling compound (a). Ternary system acetone-benzene-cyclohexane (b).

Figure 1.3. Open evaporation process (open distillation), x, y, composition of liquid and equrtibrium vapor phases L, amount of liquid dL, infinitesimal amount of evaporated hquid.

Zharov, V. T, Serafimov, L. A. (1975). Physico-Chemical Foundations of Bath Open Distillation and Distillation. Leningrad Khinaiya (Rus.). 

Also like distillation, the thermal profile of evaporators can be manipulated by changing the pressure. However, the degrees of freedom in evaporator design open up more options. 

When constructing a manometer of the type shown in Fig. 12(c), it is impor tant to apply a very high vacuum (e.g., with a Hy-Vac pump) to the manometer while the mercury in the left-hand (sealed) limb is heated until it boils unless this is done, traces of air will remain in this limb and cause inaccurate readings. During a distillation, the tap I should be kept closed except when a pressure reading is being taken if it is left open indefinitely, a sudden default by the distillation apparatus or by the pump may cause the mercury in the sealed limb of G to fly back and fracture the top of the limb. 

In order to save the cost of the distilling-flask (which after the above treatment is useless for further work), the mixture may be distilled from a small retort made by blowing a suitable bulb on the end of a rather thick-walled tube of about 8-10 mm. internal diameter the tube is then bent through almost 90° a few cm. above the bulb, cut to a suitable length, and the Open end fitted into the boiling ube as before. 

Steaming-out the steam distillation apparatus. After the cleaned steam -distillation apparatus (Fig. 88) has been assembled, it is essential to pass steam through it for some time to remove readily soluble alkali. All the taps on the apparatus are opened and the water in the steam generator boiled vigorously. The steam will gradually pass into the apparatus. After a few minutes, the tap of the tap-funnel C may be closed and soon afterwards the tap Ti of the steam-trap finally the tap Tj of the funnel G may be closed, Steaming-out should then be continued for not less than one hour, the receiver J not being in place. 

Distillation of the ammonia. The ammonia which has been liberated quantitatively in the bulb F must now be distilled completely into the receiver J. The tap Ti on the steam-trap is therefore closed and tap T2 opened so that the steam is delivered into the bulb F, which at the same time is heated directly with the flame of a micro-Bunsen... 

Liquids by liquids. The apparatus represented by Fig. 11, 58, 3 is employed for the extraction of aqueous solutions by solvents lighter than water, such as ether or benzene. The solvent distilled from the flask (attached to the lower end) and condensed by the reflux condenser (fltted to the upper end) passes through the funnel down a narrow tube, partially open at the lower end, into the aqueous solution, then rises to the surface and returns to the flask, having during its passage extracted some portion of the dissolved material from it. To improve the efficiency of the process. 

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