Column distillation, with partial condenser

The first distillation column has 32 trays, with the feed on tray 12, being operated at a reflux rate of 50 000 kg/h. The column has a partial condenser and delivers 1000 kg/h vapor distillate (sent to the absorption column) and 32 000 kg/h liquid distillate. The liquid distillate contains mainly ethanol (77% weight) and water (20% weight), with furfural the main impurity. The recovery of ethanol is almost 100%. The bottoms stream (2.9 x 10s kg/h) consists mainly of water, the concentration of dissolved organic compounds being around 7% (weight). 

A stage in a separation process could, for instance, be a tray in a distillation column, a section in a packed absorption column, or a partial condenser or reboiler. An equilibrium stage is a contacting device—a vessel—in which two or more phases can mix thoroughly and interact with each other for a sufficient length of time until the number of moles of any component moving from one phase to another equals the number of moles of that component moving in the opposite direction, that is, until no more net mass transfer takes place between the phases. The composition of each phase is then the equilibrium composition. 

A column with partial condenser and reboiler is to be used for the separation of benzene (1) from toluene (2), giving a distillate with 0.95 mole fraction benzene and a bottoms product with 0.10 mole fraction benzene. The column will operate at 105 kPa pressure and a reflux ratio of 4. The feed, at 55°C and a flow rate of 100 kmol/h containing 45 mol% benzene and 55 mol% toluene, enters the column at the fifth theoretical stage from the top. The estimated average relative volatility (benzene relative to toluene) is assumed constant, and estimated at 2.41. Based on the column conditions and thermodynamic properties, the predicted q-value is 1.2. It is required to determine the number of theoretical stages below the feed to complete the separation. 

A distillation column is designed to separate a 70-30 mole percent mixture to produce a distillate product with 97.5% mole component 1 and a bottoms product with 20% mole component 1. The column has a partial condenser and reboiler and operates at 1 atm pressure. Determine the required number of theoretical trays and the optimum feed location at a reflux ratio of 1.5. Calculate the recovery of component 1 in the distillate. Calculate the recovery at the same distillate purity and reflux ratio if the feed is introduced three trays below the optimum feed tray. Use thermodynamic data from Problem 6.1. 

Figure 12.8 shows a model of a main column and a side-stripper. Vapor feed F goes to the bottom of the main column, which is steam-stripped with stream 51, using no reboiler. The column has a partial condenser with vapor distillate D. Side draw SD is taken from around the middle of the main column and steam-stripped in the side-stripper, with the overhead vapor, OH, returned to the draw tray in the main column. The side-stripper is steam-stripped with stream 52. 

The stream defined below is sent to a column at a fixed pressure. The column has a partial condenser with a vapor distillate product and a partial reboiler with a liquid bottoms product. Assuming total reflux and constant relative volatilities, calculate by the Fenske equations the minimum number of trays and the product rates and compositions to meet the following specifications ... 

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. ... 

CONVENTIONAL DISTILLATION COLUMNS WITH PARTIAL CONDENSERS... 

Control Structure CS1. Figure 8.9a shows the control structure that is probably most commonly used for distillation columns with partial condensers. The main features of this structure are pressure controlled by manipulating vapor distillate flow rate and reflux drum level controlled by manipulating condenser heat removal. Reflux flow rate is fixed or ratioed to feed. 

Some distillation columns with partial condensers are constructed with the condenser installed at the top of the column inside the shell. There is usually no reflux drum. Vapor flows upward through the tubes of the condenser. The condensate liquid flows downward and drops into a liquid distributor above the top tray. These dephlegmatoi systems are frequently used when very toxic or dangerous chemicals are involved because it avoids potential leak problems with pumps and extra vessels and fittings. 

D26. A distillation column with a partial condenser and a total reboiler is separating acetone and ethanol. There are two feeds. One feed is 50.0 mol% acetone, flows at 100.0 mol/min, and is a superheated vapor where approximately 1 mole of liquid will vaporize on the feed stage for each 20 moles of feed. The other feed is a saturated liquid, flows at 150.0 mol/min and is 35.0 mol% acetone. We desire a distillate product that is = 0.85 mole fraction acetone and a bottoms product that is Xg = 0.10 mole fraction acetone. The column has a partial condenser and a total reboiler. Boilup is returned as a saturated vapor. Column operates at a pressure of 1.0 atin. Assume CMO and use a McCabe-Thiele diagram. VLE data are given in Problem 4.D7. 

E5. A distillation column is separating a feed that is 30 mol% acetone and 70 mol% ethanol. The column has a partial condenser. Operation is at p = 1 atm The feed flow rate is 1000 kmol/day, the feed is a saturated liquid, and feed is input at the optimum location. We desire a distillate that is 90 mol% acetone and a bottoms that is 10 mol% acetone. Use a boilup ratio of V/B = 1.25. On the fourth stage above the partial reboiler, a vapor sidestream with flow rate S = 200 kmol/day is withdrawn and then condensed to a saturated liquid, which is returned to the column as feed at the optimum location. Assume CMO. Find the mole fraction of vapor side stream y, optimum feed... 

Nonadiabatic rectification (thermal rectification, redistillation) is a thermally gentle separation process of high-boiling liquid mixtures, using a combination of partial distillation and partial condensation. The fractionator is a special thin-layer evaporator, with externally heated columns and an externally cooled rotor (Fig. 2-84). 

There are a number of additional modes of operating a distillation column. These include partial condenser open steam introduced at the column bottom without a reboiler enriching distillation column stripping distillation column operation with a side stream, etc. We will briefly describe each one of these in the context of equilibrium stages/ plates and constant molal overflow. 

A 250-cc. round-bottomed flask is fitted with a thermometer reaching nearly to the bottom (Note 1) and a 3- or 4-bulb fractionating column without a side arm, at the upper end of which is attached a partial condenser (Fig. 3) (Note 2). The side arm (A) of the latter carries a no° thermometer and is connected to a condenser set for downward distillation. The inside container (B) of the partial condenser is filled halfway with toluene, a chip of porous plate is added, and the top is attached to a reflux condenser. 

Starting with superheated vapour represented by point H, on cooling to D condensation commences, and the first drop of liquid has a composition K. Further cooling to T gives liquid L and vapour N. Thus, partial condensation brings about enrichment of the vapour in the more volatile component in the same manner as partial vaporisation. The industrial distillation column is, in essence, a series of units in which these two processes of partial vaporisation and partial condensation are effected simultaneously. 

As an illustration of this method of determining variables, consider a distillation column with a partial condenser. The complete set of equations for this column is shown in Table I. The equations are self-explanatory, but a few points about them should be noted. First, even if written... 

More elaborate means have been described for removing the acetone by distillation with relatively little isopropyl alcohol. These include various columns such as a Vigreux13 or a modified Widmer column.10 They are to be recommended when the aldehyde or ketone boils Within 50° of isopropyl alcohol, but are unnecessary under other circumstances. A reflux condenser maintained at constant temperature by boiling methanol has been suggested.6 More convenient than this is the simple but effective partial condenser designed by Hahn.49 An easily constructed modification is illustrated in Fig. 3 (adapted from Organic Syntheses).60 The partial condenser is attached directly to the round-bottomed flask, and ethanol is placed in the inner condensing tube. The... 

Distillation with vapor product. When a partial condenser is used, the flash drum plays the role of a vapor/liquid separator. In the setup known as a stabilizer there is only vapor distillate, while the liquid is returned as reflux. The column has a pasteurization section when a gaseous stream leaves at the top, while the... 

The separation section receives liquid streams from both reactors. For assessment the residue curve map in Figure 5.7 is of help. The first separation step is the removal of lights. This operation can take place in a distillation column operated under vacuum (200mmHg) with a partial condenser. Next, the separation of the ternary mixture cyclohexanone/cyclohexanol/phenol follows. Two columns are necessary. In a direct sequence (Figure 5.15) both cyclohexanone and cyclohexanol are separated as top products. The azeotrope phenol/cyclohexanol to be recycled is the bottoms from the second split In an indirect sequence (Figure 5.16) the azeotropic phenol mixture is a bottom product already from the first split. Then, in the second split cyclohexanone is obtained as the top distillate, while cyclohexanol is taken off as the bottom product The final column separates the phenol from the heavies. 

The chlorine stream is interrupted, and the reaction mixture is allowed to stand for a short time, then it is poured into a separatory funnel and washed thoroughly with hydrochloric acid, soda solution, and water. If part of the mixture has not already precipitated as a white crystalline solid, the mixture is transferred to a beaker until part of it solidifies, then it is filtered, cooled to about 10°, and centrifuged. About 95 grams of practically pure m-nitrochlorobenzene is obtained. The filtrate and the liquid from the centrifuge are combined and subjected to hractional distillation in vacuo. For this purpose, a column should be used which is about 80 cm. in length and provided with a partial condenser. Approximately the following fractions are collected ... 

For a reasonable topology for the residue map, we next can discover that the points between P and F may not be products from any column for which F is a feed. The construction in Fig. 53 illustrates. This figure corresponds either to a total condenser with a liquid top product or to a partial condenser with a vapor top product. If the top product is two-phase, the distillation curve passes through... 

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