Extractive distillation diagram

Extractions or extractive distillations with supercritical solvent need to be performed at as high as possible a solubility of oil in the extract or vapor phase in order to reduce the solvent or carrier gas requirement. From our lemon oil-carbon dioxide phase diagrams, it appears that the highest practical solubility level is 0.9 mole % (2.8 wt ) essential oil. This is obtainable at 313 K. At lower temperature, sensitivity of solubility to pressure requires that solubility be lower (e.g., 0.3 mole % at 308 K). 

Fig. 10.21. Simplified diagram of the Sohio acrylonitrile process (a) fluidized-bed reactor (b) absorber column (c) extractive distillation column (d) acetonitrile stripping column (e) lights fractionation column (f) product column. (Patrick IV. Langvardt, Ullmann s Encyclopedia of Industrial Chemistry, IV. Gerhartz (Ed.), 5lh ed. Vol. A1, p.179, 1985. Copyright Wiley-VCH Verlag GmbH Co KG. Used with permission of the copyright owner and the author.)...

As a consequence of these restrictions, separation of binaiy mixtures by extractive distillation corresponds to onfy two possible three-component distillation region diagrams, depending on whether the binary mixture is pinched or close-boiling (DRD 001), or forms a minimumboiling azeotrope (DRD 003). The addition of high-boiling solvents... 

The fundamental flow diagram for an extractive distillation process is shown in Figure 1. The feed enters the extractive distillation column (primary column) in which the solvent is added near the top. The component (or components) whose volatility is the greatest in the presence of the solvent is driven overhead in this column. The bottoms consist of the solvent and the other component (or components) these are fed to the solvent recovery column (secondary column). The regenerated solvent is cooled and fed back to the primary column. 

Figure 1 Schematic diagram of an extractive distillation process (example separation of aliphatics from aromatics)...

Extraction and extractive distillation can also be accomplished using N-Forylmorpholin (NFM) as the solvent. Krupp Uhde offers an extractive distillation process for license that employs NFM as the solvent. N-Forylmorpholin is employed in the extractor and in the distillation column to lower the vapor pressure of the aromatics relative to nonaromatics of a similar boiling point. In this way aromatics can be separated from nonaromatics in a very small and simple distillation column. N-Forylmorpholin has properties that make it an excellent solvent for this application. It is highly selective, thermally stable and has a boiling point in the range of the products to be separated. A flow diagram for this extractive distillation process is given in Fig. 3. 

Acetone and methanol are impossible to separate by simple distillation due to the presence of an azeotrope. However, the addition of water near the top of a column allows these two components to be separated. Five sets of steady-state operating data for the extractive distillation of an acetone-methanol azeotrope in a laboratory scale column have been provided by Kumar et al. (1984). A schematic diagram of the column is provided in Figure 14.19. The column had a diameter of 15 cm and was fitted with 13 bubble cap trays, a total condenser and a thermosiphon (equilibrium) reboiler. Unlike many experimental distillation studies, these experiments were not carried out at total reflux the acetone-methanol feed entered the column on the eleventh stage from the top (the condenser counts as the first stage) and the water was introduced on stage six. The column was operated at atmospheric pressure for all five runs. Additional details of the column, operational specifications, and computed product compositions for one of these experiments can be found in Table 14.9. 

Figure 14.19. Schematic diagram of extractive distillation operation.

Section, which appears every month. It also has a special section on Patents which lists new patents according to their classification. The Process Issue of the Petroleum Refiner is now carrying a special section on Petrochemical Processes. In the September 1952 issue for example, Extractive Distillation for Aromatic Recovery, Modified SO2 Extraction for Aromatic Recovery, Udex Extraction, Ethylene Manufacture by Cracking, Ethylene Production, Hypersorption, Hydrocol, Dehydrogenation (for butadiene), and Butadiene Process, were described. These descriptions include the main essentials of the process, simplified flow diagrams, and the name of the company offering it. Formerly these processes were described under the Process Section. 

The low distribution coefficients, the attendant requirement of recycling CO2 containing very little ethanol in order to achieve a high recovery of ethanol from the feed stream, and the inability to achieve the separation of ethanol from the extract stream by pressure letdown required the development of this SCF extraction-distillation process. The diagram shown in figure 8.14 pictorially summarizes that an old distillation technique can be combined with new supercritical CO2 extraction to solve the separation problem supercritical CO2 can extract the ethanol from the feed stream, distillation can separate and regenerate the solvent for recycle, and vapor compression can achieve energy efficiency. 

FIGURE 53-5 Flow diagram for the extractive distillation separation of toluene from medtylcyclohexane (MCH), using phanol as the solvent. 

Outadiene is one of the most valuable chemicals produced in the mod-em chemical refining complex. The pure monomer is recovered from crude C4 streams by liquid-liquid extraction or extractive distillation with a selective solvent. A simplified diagram of an extractive distillation process is shown in Figure 1. The C4 feed is separated into two product streams in the extractive distillation column—a butane-butene stream which goes overhead from the column and a butadiene concentrate which is carried out the bottom of the column dissolved in the solvent. The butadiene concentrate contains cis- and trans-2-butene, and after being stripped from the solvent, it is subjected to normal distillation. Butadiene is distilled overhead at 99+% purity. 

---