Distillation constant level

Ether. The most satisfactory method for the removal of (diethyl) ether is either on a steam bath fed from an external steam supply or by means of an electrically-heated, constant-level water bath (Fig. 77, 5, 1). If neither of these is available, a water bath containing hot water may be used. The hot water should be brought from another part of the laboratory under no circumstances should there be a free flame under the water bath. It caimot be too strongly emphasised that no flame whatsoever may be present in the vicinity of the distillation apparatus a flame 10 feet away may ignite diethyl ether if a continuous bench top lies between the flame and the still and a gentle draught happens to be blowing in the direction of the flame. 

To avoid salt accumulation in the basin, brine is intermittently or continuously withdrawn, and salt water is supplied to maintain a reasonably constant level in the distiller basin. Because distillate and brine are warmer than the feed water, a heat exchanger may be used for heat conservation and higher yield. 

The liquid used to scrub the vapors is previously condensed deodorizer distillate that is chilled, recycled, and drawn off as necessary to maintain a constant level in the scrubber. The condensate may entrap vapors of pesticides if they get this far in the refinery. Deodorizer distillate is rich in tocotrienols or tocopherols, some of which have vitamin E... 

Gentilcore [Chem. Eng. Progr, 98(1), 56 (Jan. 2002)] describes an alternative strategy of constant-level batch distillation where the replacement solvent is added at a rate to keep the volume of liquid in the pot constant. For simple distillation without rectification the analog of Eq. (13-126) is... 

The vapor leaving the exhausting column to pass to the heater is substantially in equilibrium with the liquid on the top plate of the column. It is partially condensed in the heater, enriched in its alcohol content, and then passes to the condenser where it is completely condensed. The portion of the vapor condensed in the heater is returned to the top plate of the column together with a controlled portion of the vapor condensed in the condenser, from the regulating bottle E. The distillate flows, through the tester F where its quantity and specific gravity may be measured, to the storage tank G. The water supply for the condenser is obtained from the constant level feed tank N. ... 

Table 1. Changes of outlet sulphur level depending on end of distillation (constant inlet sulphur 430 ppm)...

Water supply, 2 = Distilled -water apparatus, 3 = Flow meter, 4 — Constant level device, 5 = Feed line, 6 = Overflow, 7 = Column, 8 = Boiler, 9 - Product line, 10 = 1-inch copper pipe between boiler and column, 11 = Beflux cooler, 12 13 = Main condensers, 14 = Stock tank, 15 = Drain, 16 = Boiler manometer, 17 = Differential manometer, 18 - Manostat, 19 = Magnetic valve, 20 = To pump, 21—23 — Piping... 

Equipment can be arranged in a variety of configurations. In sinple batch distillation (Figure 9-11. the vapor is withdrawn continuously from the reboiler. The system differs from flash distillation in that there is no continuous feed input and the liquid is drained only at the end of the batch. An alternative to sinple batch distillation is constant-level batch distillation where solvent is fed continually to the still pot to keep the liquid level constant tGentilcore. 20021. 

For a constant-level batch distillation the general mole balance is... 

For the total mole balance this is In - Out = 0, since the moles in the still pot are constant. Thus, if dS moles of the second solvent are added, the overall mole balance for a constant-level batch distillation is... 

Since vapor and liquid are assumed to be in equilibrium, y is related to by the equilibrium relationship. Equation (9-17) can be integrated graphically or numerically in a procedure that is quite similar to that used for simple batch distillation. Problem 9.D17 will lead you through these calculations for constant-level batch distillation. 

Gentilcore 2002 presents a constant relative volatility sanple calculation that illustrates the advantage of constant-level batch distillation when it is used to exchange solvents. 

Solve problems for constant-level batch distillation... 

D17. A nonvolatile solute is dissolved in 1.0 kmol of methanol. We wish to switch the solvent to water. Because the solution is already concentrated, a first batch distillation to concentrate the solution is not required. We desire to have the solute in 1.0 kmol of solution that is 99.0 mol% water and 1.0 mol% methanol. This can be done either with a constant-level batch distillation or by diluting the mixture with water and then doing a sinple batch distillation. VLE data (ignore the effect of the solute) are in Table 2-7. Do a constant-level batch distillation fromxjyf jj i = 1.0 (pure methanol) to Xj = 0.01. Find the moles of water added during the constant-level batch... 

This process is analogous to constant level batch distillation fsection 9.3.1 and the analysis for immiscible extraction is very similar to the analysis in that section. If we assume that the level in the mixed tank is constant, then the overall mass balance becomes in = out, and for dS kg of entering solvent,... 

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