Vacuum distillation in laboratory

Presence of traces of sodium hydroxide probably caused formation of the acetylenic sodium salt, which exploded dining high-vacuum distillation in a metal still [1], A laboratory investigation which duplicated the explosion, without revealing the precise cause, was also reported [2],... 

This subject is discussed in the section entitled Vacuum Distillation in the Laboratory and Plant (page 341). 

The so-called hydro-vac pump, shown in Fig. 11, 22, 2 (the upper half of the mercury reservoir and the column above it are insulated by a layer of asbestos), is an inexpensive, all-glass, mercury diffusion pump, which can be used in series either with an oil pmnp or with a water Alter pmnp (compare Fig. 11,21, 1) capable of producing a vacuum of at least 2 mm. It is accordingly of particular value in the organic laboratory for vacuum distillations, fractionations, sublimations and pyrolyses as well as for molecular distillations (see Section 11,26). The hydro-vac... 

Fractional vacuum distillation is the method used to separate terpene mixtures into their components. The terpene chemist usually has in the laboratory a range of columns with differing numbers of theoretical stages. Experimental distillation in the laboratory is useful in providing data for manufacturing plants that produce commercial quantities of terpene products. 

The chloride is mixed on a laboratory scale with xs Ca (powder or chips) in an Fe tube in a high-T glass distillation vessel. The Fe tube protects the glass from corrosive attack by the alkali-metal vapors. The vessel is inclined and evacuated while slowly heating to 700-800°C. The liberated Rb or Cs distills onto the cooler upper walls of the vessel and runs into integral glass ampules, which are sealed under vacuum for storage. Further purification is achieved by repeated. vacuum distillation at 300°C. Yields arc theoretical. 

Rubber stoppers are frequently employed in the laboratory in vacuum distillation assemblies (compare Section 11,19) for distillations under atmospheric pressure bark corks are generally used. Many organic liquids and vapours dissolve new rubber stoppers slightly and cause them to swell. In practice, it is found that rubber stoppers which have been previously used on one or two occasions are not appreciably attacked by most organic solvents, owing presmnably... 

Zero-headspace procedures involve the collection of a soil sample with immediate transfer to a container into which the sample fits exactly. The only space for gases is that within the soil pores. The volume of sample collected depends on the concentration of volatiles in the soil. It is imperative that the container employed can be interfaced directly with the gas chromatograph. Several commercial versions of zero-headspace sampling devices are available. The sample is transported to the laboratory at 4°C, where it is analyzed directly by purge-and-trap gas chromatography (EPA 5035) or other appropriate techniques, such as vacuum distillation (EPA 5032) or headspace (EPA 5021). 

The analysis involves gas chromatographic methods such as purge and trap, vacuum distillation, and headspace (Askari et al., 1996). On the other hand, samples for the determination of semi- and nonvolatile hydrocarbons need not be collected in such a rigorous manner. On arrival at the laboratory, they require extraction by techniques such as solvent or supercritical fiuid. Some cleanup of... 

When sodium ethoxide is made from ethanol, dried by distillation from sodium in vacuum, and vacuum-distilled sodium, the product is always yellow. The author believes that he heard the method of obtaining the pure, colourless product in M. Szwarc s laboratory and that it is unpublished the following description is adapted from a Keele thesis. 

Triphenyl phosphite (Aldrich, 97%) is purified by fractional vacuum distillation (bp 181-183 °C, 1 torr) and stored in the dark under nitrogen. A 2 M solution of CH3MgBr in dibutyl ether may be purchased from Alfa Inorganics, or prepared according to the following procedure. If the CH3MgBr solution is prepared in the laboratory, bromomethane (Air Products) is used without further purification. 

The equipment used for the laboratory tests included a 650-mL round-bottomed flask, a Liebig condenser, and a 200-mL receiving flask, all constructed of Teflon. Two hundred and fifty milliliters of acid solution were placed in a still the solution heated slowly and the temperatures of both bottoms and overhead streams recorded as distillation proceeded. Fractions of distillate were collected in the receiving flask and titrated to determine the total H+ concentration. In addition, the temperatures of the bottoms and overhead streams, changes in the volume of the bottoms stream, and concentration of F, NOj, and S04 in the overhead stream were determined. Because laboratory tests were conducted at atmospheric pressure, operating temperatures were higher than would be expected in actual vacuum distillation. Ion chromatography (IC) was vised to detect F", NOj, and S04 in successive distillate fractions. 

MOLECULAR DISTILLATION, A special form ol disiillation conducted al pressures of I -7 micriunelers ni the laboratory and X - TO micro meters in industrial applications. Compared with conventional laboratory vacuum distillations carried out bciween I and ID millimeters of mercury... 

Investigations in our laboratories have been concerned with characterizing odor components produced by irradiating approximately 15-pound batches of ground, raw, lean beef, vacuum-packed in sardine cans and enzyme-inactivated 4). Irradiation at 5 megarads was carried out either in the M.I.T. cobalt-60 source before removing volatile constituents by distillation, or concurrent radiation-distillation at 5 megarads was carried out by procedures described elsewhere 15,17). 

Vacuum distillation on the semimicro scale (1-8 ml) is conveniently carried out using the apparatus illustrated in Fig. 2.111. Although this design is not now available commercially, many research laboratories still have this useful piece of... 

The environmental site investigated for this study was at the US Environmental Protection Agency s National Exposure Research Laboratory on the University of Nevada Las Vegas (UNLV) campus. The VOCs monitored in this study were those that are persistent in the environment, that tended to bioconcentrate in an organic phase (hydrophobic), and that could easily be detected in air and leaves. Nine different plant species found on the UNLV campus were analysed by using vacuum distillation coupled with GC-MS to determine concentrations of VOCs. Grab air samples were taken before and immediately after collection of leaves to determine the concentration of VOCs in air. 

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