Extractive distillation with liquid solvent

Extractive distillation with liquid solvent is used commercially for the production of anhydrous ethanol from ethanol-water mixtures. This method uses a relatively nonvolatile liquid solvent, such as ethylene glycol, which is fed into a distillation column some trays above the ethanol feed tray. The presence of the solvent at relatively high concentration in the liquid on the trays alters the volatility of one of the feed components more than the other, so a separation of the feed components can be made in the column. 

UOP/Shell BTX, purification Reformate, pyrolysis gasoline Shell Sulfolane process liquid extraction and/or extractive distillation with sulfolane solvent 123 1998... 

Complete recovery of aromatics. liquid-liquid extraction is the first choice, but extractive distillation with high-performance solvents is also applicable. 

In all cases, the selective solvents (entrainers) have the task of altering the partition coefficients in a way that high separation factors and selectivities for the different phase equilibria (extractive distillation vapor-liquid equilibrium (VLE), extraction liquid-liquid equilibrium (LLE), absorption gas-liquid equilibrium (GLE)) are achieved, resulting in a separation of compounds. The required partition coefficients, separation factors and selectivities can be calculated with the help of thermodynamic models (g -models, equations of state). 

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. 

Such a process depends upon the difference in departure from ideally between the solvent and the components of the binary mixture to be separated. In the example given, both toluene and isooctane separately form nonideal liquid solutions with phenol, but the extent of the nonideality with isooctane is greater than that with toluene. When all three substances are present, therefore, the toluene and isooctane themselves behave as a nonideal mixture and then-relative volatility becomes high. Considerations of this sort form the basis for the choice of an extractive-distillation solvent. If, for example, a mixture of acetone (bp = 56.4 C) and methanol (bp = 64.7°Q, which form a binary azeotrope, were to be separated by extractive distillation, a suitable solvent could probably be chosen from the group of aliphatic alcohols. Butanol (bp = 117.8 Q, since it is a member of the same homologous series but not far removed, forms substantially ideal solutions with methanol, which are themselves readily separated. It will form solutions of positive deviation from ideality with acetone, however, and the acetone-methanol vapor-liquid equilibria will therefore be substantially altered in ternary mixtures. If butanol forms no azeotrope with acetone, and if it alters the vapor-liquid equilibrium of acetone-methanol sufficiently to destroy the azeotrope in this system, it will serve as an extractive-distillation solvent. When both substances of the binary mixture to be separated are themselves chemically very similar, a solvent of an entirely different chemical nature will be necessary. Acetone and furfural, for example, are useful as extractive-distillation solvents for separating the hydrocarbons butene-2 and a-butane. 

Y-Phenylbutyric acid. Prepare amalgamated zinc from 120 g. of zinc wool contained in a 1-litre rovmd-bottomed flask (Section 111,50, IS), decant the liquid as completely as possible, and add in the following order 75 ml. of water, 180 ml. of concentrated hydrochloric acid, 100 ml. of pure toluene (1) and 50 g. of p benzoylpropionic acid. Fit the flask with a reflux condenser connected to a gas absorption device (Fig. II, 8, l,c), and boil the reaction mixture vigorously for 30 hours add three or four 50 ml. portions of concentrated hydrochloric acid at approximately six hour intervals during the refluxing period in order to maintain the concentration of the acid. Allow to cool to room temperature and separate the two layers. Dilute the aqueous portion with about 200 ml. of water and extract with three 75 ml. portions of ether. Combine the toluene layer with the ether extracts, wash with water, and dry over anhydrous magnesium or calcium sulphate. Remove the solvents by distillation under diminished pressure on a water bath (compare Fig. II, 37, 1), transfer the residue to a Claisen flask, and distil imder reduced pressure (Fig. II, 19, 1). Collect the y-phenylbutyric acid at 178-181°/19 mm. this solidifies on coohng to a colourless sohd (40 g.) and melts at 47-48°. 

To a solution of 0.35 mol of allenyllithium in 240 ml of hexane and 200 ml of THF (see Chapter II, Exp. 13) were added 25 g of dry HMPT at -80°C. Subsequently 0.30 mol of l-bromo-3-chloropropane were added in 10 min. The reaction was very exothermic, but could be kept under control by occasional cooling in a bath with liquid nitrogen. After an additional 10 min the cooling bath was removed and the temperature was allowed to rise to -30°C. The solution was then poured into 500 ml of water. The organic layer and three ethereal extracts were dried over magnesium sulfate. The solvents were distilled off as thoroughly as possible at... 

A mixture of 0.20 mol of the adduct from cyclooctene and dibromocarbene (note 1) and 250 ml of dry diethyl ether was cooled to -65°C. A solution of 0.23 mol of ethyllithium (note 2) in 200 ml of diethyl ether (see Chapter II, Exp. 1) was added in 15 min with cooling between -60 and -50°C. The reaction was very exothermic (note 3). After the addition the cooling bath was removed and the temperature was allowed to rise to about -10°C and the reaction mixture was poured into 200 ml of ice-water. The aqueous layer was extracted twice with diethyl ether. After drying, the solvent was removed in a water-pump vacuum and the remaining liquid was distilled through a 40-cm Vigreux column. 1,2-Cyclononadiene, b.p. 62°C/22 mmHg, 1.5059, was obtained in 86 yield. 

The choice of separation method to be appHed to a particular system depends largely on the phase relations that can be developed by using various separative agents. Adsorption is usually considered to be a more complex operation than is the use of selective solvents in Hquid—Hquid extraction (see Extraction, liquid-liquid), extractive distillation, or azeotropic distillation (see Distillation, azeotropic and extractive). Consequentiy, adsorption is employed when it achieves higher selectivities than those obtained with solvents. 

Hydrolysis of the ester is achieved by refluxing in aqueous N or 2N NaOH solution until the insoluble ester dissolves. The solution is then cooled, and the alcohol is extracted into a suitable solvent, e.g. ether, toluene or alcohol-free chloroform. The extract is dried (CaS04, MgS04) and distilled, then fractionally distilled if liquid or recrystallised if solid. (The p-nitrobenzoic acid can be recovered by acidification of the aqueous layer.) In most cases where the alcohol to be purified can be readily extracted fi-om ethanol, the hydrolysis of the ester is best achieved with N or 2N ethanolic NaOH or 85% aqueous ethanolic N NaOH. The former is prepared by dissolving the necessary alkali in a minimum volume of water and diluting with absolute alcohol. The ethanolic solution is refluxed for one to two hours and hydrolysis is complete when an aliquot gives a clear solution on dilution with four or five times its volume of water. The bulk of the ethanol is distilled off and the residue is... 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

N-Cyclohex-l-enylpyrrolidine (9 g 0 06 mol) was dissolved in pentane with A -ethyldiisopropylamine (7.8 g 0.06 mol). Perfluorohexyl iodide (13.4 g, 0.03 mol) IS added to the solution. Aprecipitate of A-ethyldiisopropylamine hydroiodide IS formed instantly After 3 h, the precipitate is filtered off, and the solution is evaporated The crude liquid is hydrolyzed with 6 mL of 40% sulfuric acid The mixture is stirred for 3 h and extracted with ether. The ether layer is neutralized with aqueous sodium hydrogen carbonate, washed with water, and dried over magnesium sulfate. The solvent is evaporated, and the residue is distilled. A second distillation with a spinning-band column yields 7 9 g (63%) of pure 2-(perfluoro-hexyl)cyclohexanone (bp, 71 -73 °C at 0 4 mm of Hg). 

After the suspension was cooled under nitrogen, the solvent was distilled off under vacuum. The residue was taken up in 200 ml water and the milky emulsion extracted exhaustively with ether. From the organic phase, the excess butylglycidyl ether was extracted with diluted potassium hydroxide solution. The ether phase was washed neutral with water and the solvent removed after drying with sodium sulfate. The remaining oily residue was distilled under vacuum there was obtained a colorless liquid of BP 123.5°C/0.07 mm. Yield 81.8 g (91.1% of the theory). 

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