Membranes Minimum reflux

Ultrafiltration, 631 applications, 633 membranes, 637-639 Underwood minimum reflux binaty, 387 multicomponent, 397 Units, conversion of, 671, 672 UMQUAC equation, 475 Upflow fixed beds, 609 Uranium recovery, 515 Utilities, typical characteristics, 15... 

Distillation to 90-volZ ethanol requires multistage operation. The process calculations were performed according to the Ponchon-Savarit method.(12) Assuming the concentration of the ethanol bottoms stream to be 1 volZ, and a reflux ratio of 1.5 times the minimum, the heat input to the reboiler corresponds to an energy requirement of 3.2 kWh/gal of 90-volZ product as distillate, or about 2.7 times that of a CCRO process employing the hypothetical, improved membrane. 

Usually in an enricher or the enriching section of the membrane column, the more permeable component is steadily concentrated from the feed inlet to the compressor. However, some of the results show that the shell-side and even the tube-side composition profiles can pass through a minimum. Note the experimental data in Figures 7 and 8. In these cases the feed flow is relatively slow and reflux action, rather than bulk flow, is predominant. Figure 8 Illustrates that a composition minimum can also occur dinring operation of the total column when the residue flow rate from the enriching section is too slow. 

In a given application, 100 mol/s of a saturated liquid containing 37 mol% ethanol and 63 mol% water must be separated to yield a product which is 99 mol% ethanol, and a residue containing 99 mol% water. The solution will be fed to a distillation column operating at atmospheric pressure, with a partial reboiler and a total condenser. The reflux ratio will be 1.5 times the minimum. The distillate will enter a membrane with parameters am = 70 and 0 = 0.6. The membrane boosts the concentration so that the permeate stream is the ethanol-rich product (xp = 0.99). The retentate stream is returned as a saturated liquid to the column to the tray at the nearest liquid concentration. 

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