Extractive Distillation by Salt Effects

The research programs on extractive distillation by salt effect and on salt effect in vapor-liquid equilibrium at the Royal Military College of Canada are supported by the Defence Research Board of Canada, Grant No. 9530-142. 

Literature pertaining to salt effect in vapor-liquid equilibrium and to extractive distillation using salt effect was recently reviewed by Furter and Cook (10), and the theory and technical aspects were reviewed by Furter (II). Vapor-liquid equilibrium data for 188 systems containing salt were previously compiled by Ciparis (12), who has also published a recent book with Dobroserdov and Kogan on the theory and practice of extractive distillation by salt effect (13). 

The topic covered in the 10 papers of the first section is commonly referred to as salt effect in vapor-liquid equilibrium and is potentially of great industrial importance. This salt effect leads to extractive distillation processes in which a dissolved salt replaces a liquid additive as the separating agent the replacement often results in a greatly improved separating ability and reduced energy requirements. Two papers in this volume, those by Sloan and by Vaillancourt, illustrate the use of such processing to concentrate nitric acid from its aqueous azeotrope. Nevertheless, the effect has not been exploited by industry to nearly the extent that would seem to be merited by its scientific promise. 

Solvents used for extractive distillation vary considerably, but in almost all cases solvent selection presents a trade-off between its selectivity and solvency (194). The effectivity of the solvent can sometimes be improved by the addition of a salt (195). 

Furter [91] has analyzed the state of the art from the point of view of employing the salt effect in industrial processes, especially in extractive distillation. In addition, he ha.s made up a list of references covering the years 1966 to 1977 [91 a]. Schubert et al. [92] investigated the effect of some metal chlorides and other salts on the isothermal = 60°C) phase equilibrium behaviour of the systems n-propanol-water, n-butanol-water and methanol-water. Using CH30H/H20/NaBr as an example, the method of predicting salt effects for vapour-liquid equilibria as developed by Schuberth has been extended to uusaturated solutions [92a]. 

Furter, W. F., Production of Fuel-Grade Ethanol by Extractive Distillation Enploying the Salt Effect, Separ. Purific. Methods, 22,1 (1993). 

Another method used in industry, which can be categorized as extractive distillation, is to use a dissolved salt (e.g., calcium chloride) as a separating agent to altCT the relative volatility of the two components in the mixture. This behavior, known as salt effect, is due to the preferential salvation of the ions (formed when the salt dissociates in solution) by the less volatile component of the solvent mixture. The bottom product of this saline extractive distillation column is the mixture of the salt and the less volatile component (e.g., water). The separation of this bottom stream may require an evaporative crystallizer and a spray dryer for recovery of the anhydrous salt. A sahne extractive distillation method is usually more expensive than conventional extractive distillation. 

Highly Nonideal Systems. Highly nonideal systems are of principal concern the nonideality may be caused by the components present and/or by the operating conditions. This category includes subjects like critical phenomena, extractive/azeotropic distillation, solvent selection guidelines, salt effects, high molecular... 

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). 

The mixture is decanted into an Erlenmeyer flask, the residual green salts are washed with two 15-ml portions of acetone, and the washings are added to the main acetone solution. Cautiously, sodium bicarbonate (approx. 13 g) is added to the solution with swirling until the pH of the reaction mixture is neutral. The suspension is filtered, and the residue is washed with 10-15 ml of acetone. The filtrate is transferred to a round-bottom flask and concentrated on a rotary evaporator under an aspirator while the flask temperature is maintained at about 50°. The flask is cooled and the residue transferred to a separatory funnel, (If solidification occurs, the residue may be dissolved in ether to effect the transfer.) To the funnel is added 100 ml of saturated sodium chloride solution, and the mixture is extracted with two 50-ml portions of ether. The ether extracts are combined, washed with several 5-ml portions of water, dried over anhydrous magnesium sulfate, and filtered into a round-bottom flask. The ether may be distilled away at atmospheric pressure (steam bath) or evaporated on a rotary evaporator. On cooling, the residue should crystallize. If it does not, it may be treated with 5 ml of 30-60° petroleum ether, and crystallization may be induced by cooling and scratching. The crystalline product is collected by filtration and recrystallized from aqueous methanol. 4-r-Butylcyclohexanone has mp 48-49° (yield 60-90 %). 

Finely chop the glands with a razor blade or pulverize in a blender. Extract the adrenalin into a small excess of hot H2O concentrate in a vacuum. Remove the salts and proteins (if proteins are not removed, they will give the same effect as blood poisoning from a rattle snake bite, but worse) by precipitating with alcohol and remove this precipitate by filtration. The filtrate is then distilled in vacuo to remove the adrenalin (1 would perform the filtration above, at room temp). Add a little ammonia to precipitate the active compound and filter from the water. The amount of ammonia depends on the amount of substance. To experiment, to get the proper amount, add a very little amount of ammonia to the distillate and filter off any precipitate if any forms. Add a little more ammonia and filter. Repeat until no more precipitate is formed, remember the amount of ammonia used and use this amount on the same amount of filtrate during the extraction of the next batch. 

Ice-acetone bath. The bottle is closed with a rubber stopper which is clamped or wired securely in place (Note 3) and is shaken mechanically at room temperature until the suspended malonic acid dissolves (Note 4). The bottle is chilled in an ice-salt bath and opened then the contents are poured into a separatory funnel containing 250 ml. of water, 70 g. of sodium hydroxide, and 250 g. of ice. The mixture is shaken (carefully at first), the layers are separated, and the aqueous portion is extracted with two 75-ml. portions of ether. The organic layers are combined, dried over anhydrous potassium carbonate, and filtered into a dropping funnel attached to the neck of a 125-ml. modified Claisen flask (Note 5). The flask is immersed in an oil bath at about 100°, and the excess isobutylene and ether are removed by flash distillation effected by allowing the solution to run in slowly from the dropping funnel. The dropping funnel is then removed, and the residue is distilled at reduced pressure. The fraction boiling at 112—115°/31 mm. is collected. The yield of colorless di-tert-butyl malonate is 60.0 62.0 g. (58-60%), 1.4158-1.4161,... 

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