Distillation tower pressure, decrease

An example of pressure-swing distillation, described by Van Winkle (1967), is provided for the mixture, A-B, having a minimum-boiling azeotrope, with the T-x-y curves at two pressures shown in Figure 7.36a. To take advantage of the decrease in the composition of A as the pressure decreases from Pj to P[, a sequence of two distillation towers is shown in... 

Distillation of Ammonium Bicarbonate Solutions. Vapor-liquid equilibrium data for ammonium bicarbonate solutions at the boil are apparently not available in the literature. The data in the literature, however, do indicate that when the temperature of such a solution is increased, or the pressure on it decreased, the gas that is evolved is predominantly carbon dioxide. Thus, it appears that such a distillation would be two consecutive processes first, a steam stripping of the carbon dioxide in the solution, followed by a distillation of ammonia from an ammonia-water mixture containing perhaps some carbon dioxide. Possibly the ammonia, carbon dioxide, and water in the distillate product would recombine completely in the condenser to form an ammonium bicarbonate solution. Perhaps an absorption tower would be necessary to effect the recombination. 

Lower distillation temperatures can be obtained by the use of steam. In this case the steam does not usually condense in the tower, and the plates contain only the high boiling organic material. The steam acts as an inert carrier that is easily condensed and does not have to pass through the vacuum pump. In some cases the temperature gradient in the distillation column may be so great that the steam will condense in the upper portions, and it should be withdrawn. If too much water collects on a plate, it may seriously interfere with the fractionation if the water runs down the tower, it will vaporize on the lower plates and this steam recycle in the tower can overload the unit and seriously interfere with the fractionation. Theoretically it is possible to fractionate a material with a very low vapor pressure by the use of steam distillation, but the steam consumption increases as the vapor pressure on the component decreases. Reduction of the total pressure reduces the steam consumption, but if the vapor pressure of the com-... 

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