Vacuum distillation technique

The reaction of Na with Hg to form an amalgam that can then be separated from the NajO for oxygen analysis has been compared with the vacuum distillation technique . Ion-exchange techniques in which the sample is dissolved in a suitable solvent and the resulting separation of elements is achieved by an ion-exchange resin is less common. This technique is particularly suited to separating the volatile impurities such as K, Rb and Co. ... 

Attempted isolation of diethyl hydroxymethyl phosphonate by standard vacuum distillation technique is accompanied by extensive decomposition. The use of Kugelrohr apparatus allows the isolation to be accomplished at a lower temperature, and therefore the product is obtained in higher yield. Alternately, the checkers found that distillation using a 2 wiped-film molecular still (Pope Scientific, Inc.) significantly raised product yields, especially when the reaction was performed on a larger scale (Notes 3 and 6). 

Another vacuum distillation technique, including for water removal in large-scale operations, is evaporation. Thin-film evaporators are designed to expose large surface areas of liquid to heat and/or vacuum in order to speed the evaporation process. The design principle is illustrated in Figure 5. 

Phosphaalkynes 9 are obtained almost exclusively by P-elimination of hexa-methyldisiloxane from appropriately substituted phosphaalkenes 8 (for their synthesis, see Protocol 3). The original elimination from 8 (R = f-Bu)31 performed in solution at room temperature in the presence of sodium hydroxide was optimized (solid NaOH, temperatures between 160 and 180°C, vacuum distillation techniques) and also generalized. In particular cases, aluminium trichloride in dichloromethane has proved to be a useful reagent for the elimination.32... 

For the above-mentioned products, critical fluid technology faces stiff competition from molecular (vacuum) distillation techniques, a time-honored technique, although greater selectivity is potentially available utilizing critical-fluid-based methods. This, coupled with the fact that C02-derived extracts exhibit, in many cases, extended shelf-lives due to the prophylactic action of the residual, nonoxidative CO2 atmosphere, as well as micro-organism de-... 

A vacuum distillation technique was employed for the separation of the crude into three temperature cuts plus the high boiling asphalt residue. These temperature cuts are ... 

Environmental aspects, as well as the requirement of efficient mixing in the mixed acid process, have led to the development of single-phase nitrations. These can be divided into Hquid- and vapor-phase nitrations. One Hquid-phase technique involves the use of > 98% by weight nitric acid, with temperatures of 20—60°C and atmospheric pressure (21). The molar ratios of nitric acid benzene are 2 1 to 4 1. After the reaction is complete, excess nitric acid is vacuum distilled and recycled. An analogous process is used to simultaneously produce a nitrobenzene and dinitrotoluene mixture (22). A conversion of 100% is obtained without the formation of nitrophenols or nitrocresols. The nitrobenzene and dinitrotoluene are separated by distillation. 

Most aroma chemicals are relatively high boiling (80—160°C at 0.4 kPa = 3 mm Hg) Hquids and therefore are subject to purification by vacuum distillation. Because small amounts of decomposition may lead to unacceptable odor contamination, thermal stabiUty of products and by-products is an issue. Important advances have been made in distillation techniques and equipment to allow routine production of 5000 kg or larger batches of various products. In order to make optimal use of equipment and to standardize conditions for distillations and reactions, computer control has been instituted. This is particulady well suited to the multipurpose batch operations encountered in most aroma chemical plants. In some instances, on-line analytical capabihty is being developed to work in conjunction with computer controls. 

One of the most frequent techniques for analyzing 1,4-dioxane is gas chromatography. Birkel et al. [319] proposed in 1979 a gas chromatographic method based on partial vacuum distillation of the sample, analyzing polysorbate 60 and 80 with sensitivity to the 0.5 ppm. Stafford et al. [320] proposed a direct injection GC method which meant an improvement to the Birkel s technique. Robinson and Ciurczak [321] described a direct GC method for the analysis of... 

Multicycle vacuum distillations have been assessed ". The distillations were effected at 700°C. Data on the effect of distillation rate and of fraction distilled on the purity of the sample are collected in Table 1. These data show that the technique is effective in removing the less volatile impurities As, Co, Cu, Cr, Fe, Ga, Mn and Sb from Mg but has little effect on more volatile species, Ba, Zn and Zr. Increase of the distillation rate or the fraction distilled leads to a decrease in the effective purification. Double (99% fraction) distillation gives a product of similar purity to that of a single (72% fraction) distillation . Single (78% fraction) distillation of a Mg sample (assay 99.9%) unusually rich in Mn (300 fig g" ) at 3.5 g h gave a decrease (Xl0 ) in Mn content (to 0.025 fig g ) a similar value (0.04 fig g" ) was obtained from a doubly (99% fraction) distilled sample. This technique gives Mg with assays of 99.9995%... 

There is a great number of separation and purification processes to choose from in process development, but classical separations such as crystallization, filtration, drying, liquid-liquid extraction and distillation are still predominantly used. For solid products crystallization, filtration, and drying are the first options although vacuum distillation and extraction combined with the other techniques are also possible. For liquid products, liquid-liquid... 

Equally precise and meticulous as an experimentalist, he devoted time during his days at Pittsburgh to write comprehensive articles on such practical techniques as crystallization, vacuum distillation, and sublimation, which were published in the Weissberger Techniques of Organic Chemistry series. His preoccupation with careful experimental techniques and then-accurate recording in the literature remained with him always. He abhorred vague descriptions of procedures, speculative interpretations not based on... 

Methylene dichloride [6] and perchloric acid [7] were purified and dosed as described. Silver perchlorate (BDH) was treated in vacuo for a few hours before use. 1-Phenylethyl bromide (Eastman-Kodak) was fractionally distilled under high vacuum and the middle fraction was collected into breakable phials since this compound undergoes a slow decomposition, yielding hydrogen bromide and styrene, when kept in bulk, solutions of it in methylene dichloride were prepared from the original phials by the tipping technique [7]. Styrene was purified [8], dried, and stored [9] as described. Shortly before use it was vacuum-distilled into breakable phials from a microburette. 

Phials of anhydrous perchloric acid in methylene dichloride were made up as described [11]. Sodium ethoxide was prepared i.vac. from purified ethanol and sodium purified by cascade fusion . Solutions of it in diethyl ether were prepared and filled into phials [11,12] by standard techniques on a tapless, jointless high-vacuum system. These solutions were colourless, whereas those prepared i.vac. from vacuum-distilled sodium were always yellow or brown. 

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... 

Fuels and other petroleum products are derived from crude oil through the use of a variety of different refining process techniques. Distillation, however, is the first significant processing step taken in crude oil refining. Both atmospheric and vacuum distillation can be utilized to process crude oil into fuels and other products. 

Since fermentation takes place in a dilute aqueous solution, the reaction continues until the alcohol concentration approaches about 14%. At higher concentrations, the process becomes self-inhibitory. By-products from starch fermentation to ethanol can include higher-molecular-weight alcohols, glycerine, and ethers. Usually no more than 10% starch is converted to these compounds. Atmospheric distillation, vacuum distillation, and membrane separation techniques can be used to recover ethanol from the final fermented product. The distillate bottoms, called stillage, are recovered as a by-product for animal feed. A biomass fermentation flow diagram is provided in FIGURE 12-2. 

In hot-climate viticulture it is a common practice to lower the high ethanol content of wines made from overripe fruit by partial dealcoholisation. This objective can be achieved by vacuum distillation, where the spinning cone column technique allows even more viscous liquids to be processed. Alternatively, a water-ethanol fraction can be separated from wine by reverse osmosis, followed by distillation of the water-ethanol permeate to yield high-grade ethanol and pure water. The latter will be added back to the treated wine. 

Fig. 18.2 Aroma-isolation techniques based on distillation. Left simultaneous distillation/extrac-tion right high-vacuum distillation with cryotrapping. (Reprinted with permission from [15]. Copyright 1998 American Chemical Society)...

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]. 

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