Two-stage distillation column

The added separation power of a two-stage distillation column (Figure 3.3) over a single stage results from the fact that the two stages can be maintained at two different temperatures. For a binary system, the compositions are given by Equations 3.3 and 3.4 or 3.5 and 3.6. These equations indicate that separation, expressed in terms of mole fractions of the products, is a function of F-values. In this simple model, the F-values are a function of temperature only. Hence, the temperature effect is the only active one in binary distillation. 

In the two-stage distillation column (Figure 3.3), the operating pressure and the feed... 

The effect of reflux ratio on the performance of a two-stage distillation column is demonstrated numerically for a binary system in Example 3.2. 

The propane-butane equimolar mixture of Example 3.1 at 38°C and 590 kPa is fed at a rate of 100 kmol/h at the bottom stage of a two-stage distillation column as in Figure 3.3. The liquid rate, ij, is specified at 50 kmol/h, and it is desired to determine the effect of reflux ratio, L /Vy, on the products composition and stage temperatures. 

FIGURE 3.4 Performance of two-stage distillation column (Example 3.2). 

A two-stage distillation column consists of a partial condenser, stage 1, and a partial reboiler, stage 2, with no trays in between. A 100 mol/s stream consisting of a binary equimolar mixture of components 1 and 2 is fed to the reboiler. It is required to obtain online compositions of the distillate and the bottoms for control purposes. Online analyzers are not available, but the flow rates of the distillate and reflux rates can be measured in real time. The X-values of the lighter component, component 1, and the measured distillate rate, V, and reflux rate, Lj, are as follows ... 

A two-stage distillation column similar to the colunm in Example 3.2 (Figure 3.3) is to be used for separating a mixture of 60 mol/hr propane and 40 mol/hr butane. The feed stream, at lOOT and 100 psia, is sent to the bottom stage, the reboiler. It is desired to recover 65% of the propane in the distillate with a purity of 75%. 

The still pictured in Fig. 1.3 is acting as a two-stage distillation column—that is, a fractionator that has two fractionation trays. 

The still pictured in Fig. 1.3 is acting as a two-stage distillation column— that is, a fractionator that has two fractionation trays. The bottom tray is the big can. The top tray is the 12-oz can. If I wanted to build a similar facility in a chemical plant, I would have ... 

The (9-xylene [95-47-6] in Eigure 8 is recovered by a two-stage distillation. Eirst it is separated (or spHt) from / -xylene [108-38-3] and the other Cg aromatics in a superfractionating column, the xylene spHtter, (Unit H). The bottoms, a mixture of o-xylene and Cg aromatics, is redistilled (or remn) in Unit I to recover o-xylene of 96-H% purity. 

It has been established on previous occasions (Sections 3.2.2 and 5.2.1) that a conventional two-product distillation column with a hxed feed and conhguration and operating at a given pressure has two degrees of freedom. The conhguration is dehned by the number of stages, type of condenser and reboiler, and the feed location. The feed is of hxed how rate, composition, and thermal conditions. 

The dephenolated raffinate is then fed to the top of the solvent stripper to recover the solvent by stripping with gas. To remove the solvent from the stripper overhead gas, the latter is washed with raw phenol, and the solvent-free gas is recycled to the stripper. The extract from the mixer/settler, containing the phenols and other extracted components, is fed to a two-stage distillation unit to produce highly pure ether overhead and solvent-free raw phenol at the bottom. Depending on the bottom temperature of the distillation column, the raw phenol may contain up to S % water. The raw phenol is partly exported as a product and partly used as wash liquor for the solvent scrubber. The ether-laden bottmn product from the solvent scrubber is recycled to the lower stage of the distillation column to expel the ether. 

Water is continuously added to the last extraction bath and flows countercurrenfly to filament travel from bath to bath. Maximum solvent concentration of 15—30% is reached in the coagulation bath and maintained constant by continuously removing the solvent—water mixture for solvent recovery. Spinning solvent is generally recovered by a two-stage process in which the excess water is initially removed by distillation followed by transfer of cmde solvent to a second column where it is distilled and transferred for reuse in polymer manufacture. 

A distillation column is composed of two types of stages. Those above the inlet of fresh material terminate in a condenser, and are called tire rectifying ... 

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