Distillation of volatile solvents from

Distillation of volatile solvents from solutions, 86-89, 105 fire hazards attending, 90 Distillation under diminished pressure, 103-108... 

Fig. 5.3. Wayda-Dye greaseless vacuum line. This apparatus makes extensive use of metal bellows tubing and O-ring seals. Thus the reaction vessels, filters, and other items can be tilted and manipu lated like Schlenk ware, and high vacuum conditions can be achieved for the removal of atmospheric gases and for baking out residual moisture. Trap to-trap distillation of volatile solvents such as NH) or SO is readily accomplished with this apparatus. This version is not designed for the measurement of volatiles or trap-to-trap separation. (Reproduced from A.L. Way da and J. L. Dye, J. Chent. Educ. 62, 356 (1985) by permission of the copyright owner the Division of Chemical Education of the American Chemical Society.)...

A. Vacuum Line Filtration. For their work on the diammoniate of dibo-rane. Parry, Schultz, and Girardot24 devised a versatile vacuum line filtration apparatus which is useful when small quantities of solid are handled and when the solvent is sufficiently volatile to be distilled on the vacuum line. The filter is attached to the vacuum system through a standard taper joint which allows it to be rocked or inverted (Fig. 9.21). Prior to filtration, any volatile contents are frozen down and the apparatus is thoroughly evacuated (Fig. 9.21a). By inversion of the apparatus, the solution is then poured onto the frit, and the solvent vapor pressure is employed to effect a suction filtration by closing the stopcock in the equalizing arm and cooling the lower tube (Fig. 9.21b). The precipitate is washed by distillation of the solvent from the lower receiver into the upper portion of the apparatus (with the stopcock in the sidearm open) and repetition... 

This method, which is also known as rotary evaporation or rovap , is the technique of choice for the removal of large volumes of volatile solvents from solutions, e.g. from extractions and column chromatography (p. 217). Rotary evaporators are now standard communal pieces of equipment in the laboratory and the operating principle is that of a reduced-pressure distillation except that the evaporation flask can be rotated. This rotation reduces the risk of bumping , inherent in all reduced-pressure distillations, and spreads the solution in a thin film on the walls of the flask. This effectively increases the surface area of the solution and increases the rate of evaporation, which is further enhanced by the use of a vacuum. 

It is very common to combine methods in obtaining aroma isolates. The simultaneous distillation/extraction method previously described is an example. Another popular combination method initially involves the solvent extraction of volatiles from a food and then high-vacuum distillation of the solvent/aroma extract to provide a fat-free aroma isolate. This technique is broadly used today to provide high-quality aroma extracts for numerous purposes. The apparatus used in solvent removal has been improved upon to reduce analysis time and efficiency the modified method is termed solvent-assisted flavour extraction (SAFE) [16]. 

Selective solvent extraction of volatiles will remove volatiles with very high yields although the extracts are always contaminated with non-volatile components. For example, acetonitrile extraction followed by co-extraction with pentane was used by Vemin (38). In our experiments the direct extraction of crushed crackers with Freon 113 or ethyl acetate contained too much residual lipid. Distillation of the solvent yielded a lipid concentrate low in aroma volatiles. Attempts to use gel filtration (Bio-Beads S-X12 from Bio-RAD) to remove the lipids but retain the odorous substances were also unsuccessful. 

However, in 1972, one year before Manassen s and Joo s first publications, Parshall working at Dupont in Delaware reported that the hydrogenation and alkoxycarbonylation of alkenes could be catalysed by PtCL when dissolved in tetraalkylammonium chloride/tin dichloride at temperatures of less than 100°C/5] It was even noted that the product could be separated by decantation or distillation. Parshall recognised the separation problem associated with homogeneous catalysis and in this paper states, An approach that seems under utilised is the use of molten salts as stable, non-volatile solvents from which organic products are readily separated by distillation. .. or decantation . An even earlier report by a group working for the U S. 

The recovery of actinide chlorides from ammonium chloralumi-nate by distillation of the solvent at 400°C resulted in very little of the uranium or thorium being carried over with the distillate. The aluminum/nitrogen ratios in the bottoms indicated a non-volatile compound that contained aluminum but not nitrogen. This latter compound may have been aluminum oxychloride. 

The solvent could depress the volatility of either the lighter or the heavier of the components to be separated. Thus, it is not unusual for the relative volatilities of the components in the feed to be reversed by the addition of the solvent. Since the solvent in extractive distillation is considerably less volatile than the feed components, no azeotropes are formed, and the separation of the solvent from the bottoms product is relatively easy. 

Professor Robinson, a native of Massachusetts, received his BS degree in Chemical Engineering from M.I.T. in 1909 and, after five years in industry, returned to complete a master s degree, joining the staff as an instructor in industrial chemistry in 1915. His Elements of Fractional Distillation, published in 1922, one of the first U.S. texts in this area, was revised through 1950 by Professor Gilliland. Another 1922 text in the field was The Recovery of Volatile Solvents, In 1923 he collaborated... 

The volatilities of ABC extractants are low, and they are practically insoluble in the aqueous streams (lower than those of the corresponding amine). As a result, extractant losses are low, and contamination of the exiting streams is avoided. Low volatility becomes a drawback in the purification of the extractant from impurities that may accumulate in it. Unlike in the case of volatile solvents, such as C4—C5 alkanols, that can be purified through distillation, in the case of ABC extractants, some feed pretreatment or partial treatment of the regenerated extractant by NaOH might be required. 

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