Steam distillation advantages

Place 45 g. (43 ml.) of benzal chloride (Section IV,22), 250 ml. of water and 75 g. of precipitated calcium carbonate (1) in a 500 ml. round-bottomed flask fltted with a reflux condenser, and heat the mixture for 4 hours in an oil bath maintained at 130°. It is advantageous to pass a current of carbon dioxide through the apparatus. Filter off the calcium salts, and distil the filtrate in steam (Fig. II, 40, 1) until no more oil passes over (2). Separate the benzaldehyde from the steam distillate by two extractions with small volumes of ether, distil off most of the ether on a water bath, and transfer the residual benzaldehyde to a wide-mouthed bottle or flask. Add excess of a concentrated solution of sodium bisulphite in portions with stirring or shaking stopper the vessel and shake vigorously until the odour of benzaldehyde can no longer be detected. Filter the paste of the benzaldehyde bisulphite compound at the pump... 

The common impurities found in amines are nitro compounds (if prepared by reduction), the corresponding halides (if prepared from them) and the corresponding carbamate salts. Amines are dissolved in aqueous acid, the pH of the solution being at least three units below the pKg value of the base to ensure almost complete formation of the cation. They are extracted with diethyl ether to remove neutral impurities and to decompose the carbamate salts. The solution is then made strongly alkaline and the amines that separate are extracted into a suitable solvent (ether or toluene) or steam distilled. The latter process removes coloured impurities. Note that chloroform cannot be used as a solvent for primary amines because, in the presence of alkali, poisonous carbylamines (isocyanides) are formed. However, chloroform is a useful solvent for the extraction of heterocyclic bases. In this case it has the added advantage that while the extract is being freed from the chloroform most of the moisture is removed with the solvent. 

An absolutely scientific definition of the term essential cr volatile oils is hardly possible, but for all practical purposes they may be defined as odoriferous bodies of an oily nature obtained almost exclusively from vegetable sources, generally liquid (sometimes semi-solid or solid) at ordinary temperatures, and volatile without decomposition. This definition must be accepted within the ordinary limitations which are laid down by the common acceptation of the words, which will make themselves apparent in the sequel, and show that no more restricted definition is either advantageous or possible. Many essential oils, for example, are partially decomposed when distilled by themselves, and some even when steam distilled. 

From the completion of addition of the sodium ethoxide solution to the steam distillation, fast work is advantageous, and all equipment should be in readiness before the addition is started. Allowing the solution to stand before addition of the tartaric acid may cause darkening and formation of gummy material. It is important that the solution should remain slightly acid during the steam distillation. 

At the completion of the reaction, the aniline is separated from the iron oxides by steam distillation and the umeacted iron removed. The pigment is washed, filtered and dried, or calcined in rotary kilns to hematite (Plate 20.1, see p. XXXIX). Considerable control over pigment properties can be achieved in this process by varying the nature and concentration of the additives and the reaction rate the latter depends on pH, the rate of addition of iron and nitrobenzene and the type and particle size of the iron particles. Two advantages of this method are that a saleable byproduct, aniline, is produced and that there are no environmentally, harmful waste products. 

Another important group is the essential oils which are manufactured mainly from herbs and spices mostly by steam distillation. The advantage of steam distillation is the fact that a clean and powerful oil can be isolated after the distillation step without waxes and other non-volatile compounds but with an odour... 

The impurities present in aromatic nitro compounds depend on the aromatic portion of the molecule. Thus, benzene, phenols or anilines are probable impurities in nitrobenzene, nitrophenols and nitroanilines, respectively. Purification should be carried out accordingly. Isomeric compounds are likely to remain as impurities after the preliminary purifications to remove basic and acidic contaminants. For example, o-nitrophenol may be found in samples of p-nitrophenol. Usually, the o-nitro compounds are more steam volatile than the p-nitro isomers, and can be separated in this way. Polynitro impurities in mononitro compounds can be readily removed because of their relatively lower solubilities in solvents. With acidic or basic nitro compounds which cannot be separated in the above manner, advantage may be taken of their differences in pKg values. The compounds can thus be purified by preliminary extractions with several sets of aqueous buffers of known pH (see for example Table 19, p. 43) from a solution of the substance in a suitable solvent such as ethyl ether. This method is more satisfactory and less laborious the larger the difference between the pK value of the impurity and the desired compound. Heterocyclic nitro compounds require similar treatment to the nitroanilines. Neutral nitro compounds can be steam distilled. 

Volatile ginger oil obtained from steam distillation has been the subject of many research studies (5-12). However, the thermal degradative effects of steam distillation upon volatile and nonvolatile components of ginger were seldom discussed. Recently, Moyler (1) compared the advantages of liquid carbon dioxide extraction over conventional methods such as solvent extraction or steam distillation by showing reconstructed GC chromatograms which clearly displayed the differences. However,quantitative results showing the differences were not mentioned. 

The above development raises conceptually the problem of steam distillation versus reboiled stripping. The first has the advantage of simpler equipment, but the disadvantage of contamination. With the second the situation is reversed. The choice depends largely on local conditions. 

Certain compounds present in the essential oil can be changed by the steam. This can be ill strated by comparing a steam-distilled extract with that of the solvent extract. In rose extracts compounds such as phenylethyl alcohol make up a major proportion of the solvent-extracted material, but this is practically all lost in the steam distillation extract as it dissolves in the water. However, the process can be advantageous in German chamomile, where matricin is decomposed to form the characteristic blue compound chamazulene. 

The researches have dealt with each phase of the pentosan determination. Many modifications have been introduced in the distillation procedure, in attempts to obtain ma.ximal yields of furfural. For e.xample, some workers prefer to distil with 23 % hydrobromic acid, rather than with the conventional 12% hydrochloric acid. Others distil in the presence of added sodium chloride, to avoid changes in acid concentration. Steam distillation has been used by a number of workers, who claim theoretical yields of furfural from pentoses, but Launer and Wilson found no advantage either in salts or in steam in the analysis of pulps and papers. Interfering substances are of two types materials other than pentosans which form furfural in the pentosan analysis, and substances which yield products which may be determined as furfural. TJronic acids and polyuronides yield furfural, although not quantitatively, and, in the case of materials containing appreciable quantities of these substances, it is usual to make a correction. The value of the correction to be applied has been determined experimentally by several workers, with somewhat differing results. 

This process appears to provide considerable economic and practical advantages over alternative cholesterol reduction technologies, such as steam distillation and supercritical carbon dioxide fluid extraction. For instance, there is no absorption of vitamins, it is a low-temperature operation, and it has a low capital cost. The only economic concern is that the ratio of the addition of p-cyclodextrin to the cholesterol removed is high, creating the potential for a high-cost process. Even so, the Europeans have commercialized the process, and reduced-cholesterol butter and cheese products have been introduced into the marketplace (49). 

Some high-boiling substances decompose before the boiling point is reached and, if impure, cannot be purified by ordinary distillation. However, they can be freed from contaminating substances by steam distillation at a lower temperature, at which they are stable. Steam distillation also offers the advantage of selectivity, since some water-insoluble substances are volatile with steam and others are not, and some volatilize so very slowly that sharp separation is possible. The technique is useful in process-... 

The advantage of steam distillation over other methods of volatile oil extraction lies principally in its wide applicability and speed of operation. Most plants or plant parts, with the exception of the flowers in some few cases, may be extracted most readily and most expeditiously and with a minimum amount of labor by the steam distillation method. The simplicity of the operation is obvious. The removal of the oil is much more complete than by any other process. Furthermore, there is produced as a by-product during the distillation an aqueous distillate which is completely saturated with the oil. The aqueous distillate may in many instances be utilized and sold as an aromatic water of commerce, especially in such cases as lavender, orange flowers, rose, etc. The aromatic waters possess excellent odors, largely because of the extreme dilution of the odorous compounds held in solution, and are useful in the perfumery and toilet-preparation industries. When the aqueous distillate from the plant has no marketable value, it may be profitably collected and returned to the boiler. In case of a further distillation of the same plant it will materially add to the yield of oil, since the distillate is a saturated solution of the oil. Many oils are extremely soluble in water. Distillates from oils of this class usually augment considerably the yield of oil when returned to the boiler and transformed into steam and oil vapors. 

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