Separation of alcohols

The most common hydrophobic adsorbents are activated carbon and siUcahte. The latter is of particular interest since the affinity for water is very low indeed the heat of adsorption is even smaller than the latent heat of vaporization (3). It seems clear that the channel stmcture of siUcahte must inhibit the hydrogen bonding between occluded water molecules, thus enhancing the hydrophobic nature of the adsorbent. As a result, siUcahte has some potential as a selective adsorbent for the separation of alcohols and other organics from dilute aqueous solutions (4). 

Figure 3. Chromatogram showing separation of alcohol derivatives of Reagent V. Conditions as described in the text under HPLC Separation Conditions."...

The approach by Brennan with collaborators led to notable improvement in the biocompatibility of sol-gel processing. However, there are some disadvantages. Their approach does not exclude the hydrolytic separation of alcohol. Its presence is detrimental for sensitive biopolymers. Furthermore, the two-stage synthesis is accompanied by the significant shrinkage of sol-gel derived nanocomposites. This leads to a decrease in the pore size that sometimes can restrict the accessibility of enzymes to substrates. 

The use of silicones in membrane applications is relatively new. It is, however, a rapidly growing area as evidenced by a number of original papers and reviews published recently. Pervaporation with the use of polymer membranes has been recognized as a versatile separation process in the chemical industry.458 A study of PDMS as an active layer in the composite pervaporation membranes for separation of alcohols and esters has been reported.459 Two-dimensional... 

Asaeda, M. and L. D. Du. 1986. Separation of alcohol/water gaseous mixtures by thin ceramic membrane. J. Chem. Eng. Japan 19(1) 72-77, 84-85. 

Farhadpour, F.A., Bono, A., and Tuzun, U. (1984) Separation of alcohol-water mixtures by liquid phase adsorption. Monogr. Eur. Brew. Conv., 9, 203. 

Separation of alcohol. Turn the stopcock R3 toward volumetric flask E, and stop circulation of cooling water thru condenser C, while continuing to cool the condenser D. This will permit the alcohol to be distilled, pass thru C to D to be condensed in it together with water, into the flask E. After collecting about 150ml of distillate in E, filter tt into another 200ml volumetric flask (to remove DPhA) and complete to the mark with distd w... 

It is of interest to note that though the Latin manuscript in which appear these notices of the separation of alcohol both contain evidence of Arabic influences, yet thus far no such definite knowledge of the process has been found in any Arabian manuscripts of earlier or even contemporary dates. It is probable that its separation was effected by Italian or Spanish chemists who, while they served as mediators between Arabia and Latin scholars, were themselves originators of much that was later attributed to Arabian chemists. 

The separation of alcohol from different raw materials like cider [13], wine fermentation broth [14], alcohol-water mixtures [15-18] and wine [19-22] is an interesting alternative to distillation processes especially if heat sensitive substances are present. Separex company separated the aroma substances out of whisky and cognac, which gives a very interesting product for food industry. 

In most cases, the separation of alcohols, usually methanol, ethanol, and glycerol, is carried out contemporaneously with the separation of sugars and organic acids, and almost always the desire is to quantify all these analytes. It is seen, therefore, that the mobile phase is often an aqueous acid solution, even though only water may be used (5,9). Sulphuric acid is the one most frequently used, although phosphoric acid is preferred by some, since it is less corrosive on the components of the HPLC system (10). The concentration of sulphuric acid normally varies between 0.004 N and 0.01 N or more. The choice of acid may, however, be dictated by other considerations. This is the case, for example, with the use of a conductivity detector, which requires an appropriate conductivity suppressor system. If such a device is not available for a particular... 

Fig. 1 Optimized separation of alcohols. Column, HPX-87 H (300 X 7.8-mm ID) column temperature, 50°C mobile phase, 0.01 N sulphuric acid flow rate, 0.7 ml/min refractive index detection. For peak identification, see Table 1. (Reprinted from Ref. 13 with the kind permission of Elsevier Science—NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

Since, as has already been said, the separation of alcohols is performed very often together with other analytes, such as organic acids and sugars, the choice of the type of detector also takes into account their chemical-physical properties. Usually, the choice is the ultraviolet detector (UV), the refractive index detector (RI), or the electrochemical detector (EC). Of the last, various types exist, which we shall describe briefly. 

The dimer-rich fractions were adsorbed on 30 parts of Woelm alumina, activity grade IV (i.e., alumina containing 10% water) and eluted first with mixtures of chloroform and cyclohexane and on a second pass with benzene and cyclohexane. Occasionally, acetone-cyclohexane mixtures were used for better separation of alcohols and dimers and nylon powder chromatography for ultimate purification. Even at a 30 1 (alumina lignin) weight... 

Pervaporation is a membrane separation process where the liquid feed mixture is in contact with the membrane in the upstream under atmospheric pressure and permeate is removed from the downstream as vapor by vacuum or a swept inert gas. Most of the research efforts of the pervaporation have concentrated on the separation of alcohol-water system [1-20] but the separation of acetic acid-water mixtures has received relatively little attention [21-34]. Acetic acid is an important basic chemical in the industry ranking among the top 20 organic intermediates. Because of the small differences in the volatility s of water and acetic acid in dilute aqueous solutions, azeotropic distillation is used instead of normal binary distillation so that the process is an energy intensive process. From this point of view, the pervaporation separation of acetic acid-water mixtures can be one of the alternate processes for saving energy. 

T. Matsuura and S. Sourirajan, Physiochemical Criteria for Reverse Osmosis Separation of Alcohols, Phenols, and Monocarboxylic Acid in Aqueous Solutions Using Porous Cellulose Acetate Membranes, J. Appl. Polym. Sci. 15, 2905 (1971). 

In an alternate process, enantioselective enzymatic acylation of racemic a-methyl-l,3-benzodioxole-5-ethanol (55, Fig. 17) was developed using Amano lipase PS-30 (lipase from Pseudomonas cepacia) with vinyl acetate as acylating agent in n-hexane benzene (2 1). This process gave (+)-56 in 54% yield with 80% ee and (-)-57 in 46% yield with 96% ee After separation of alcohol (+)-56 from acetate (-)-57 by methanolysis in the presence of K2CC)3, the acetate was converted to alcohol (-)-56 in 95% yield with 96% ee Mitsunobu inversion of (-)-56 provided (+)-56 in 94% yield with 96% ee The conversion of (.S )-alcohol 56 to (-)-talampanel was carried out in 54% overall yield (Easwar and Argade, 2003). 

The applications of liquid chromatography to terpenoids have been reviewed.32 Rapid separation of alcohols (e.g. geraniol-nerolidol, geraniol-citronellol) by metal complex formation has been re-examined.33... 

Asaeda M., Du L.D. and Fuji M., Separation of alcohol/water gaseous mixtures by improved ceramic membranes, 7. Chem. Eng. Jpn. 79 84 (1986). 

A good example of separation on the basis of affinity is the separation of alcohol/ water mixtures using a hydrophobic, silicalite membrane. Pervaporation of an ethanol/ water mixture through such a membrane resulted the removal of the alcohol from the mixture [16]. The separation selectivities achieved are between 10 and 60, depending on temperature and the alcohol content in the feed. In this way azeotropes can be broken. The reason for this is that the principle of separation, namely, differences in adsorptive behavior, is different from separation based on vapor pressure differences, used in distillation. Another example of such a separation is the pervaporation of an acetic acid/water mixture through a silicalite membrane, resulting in the removal of acetic acid [17]. 

If the product finally obtained is an individual compound it will distil at approximately a constant temperature which is the boiling-point of the compound. If the product is a mixture of two compounds that can be separated by fractional distillation, this method is then used as in the case of the separation of alcohol and water, which is a common laboratory exercise illustrating this process. It usually results that compounds so separated are only partially pure, each being mixed with a little of the other. In some cases, two compounds can not be separated in this way, because their boiling-points are too close together. By conversion into derivatives, e.g., esters, the boiling-points of which lie farther apart, fractional distillation may be made possible. The conditions of distillation may also vary as some compounds must be distilled under diminished pressure. 

Selective removal of phenol from industrial wastewater Separation of alcohols and aqueous organic liquids Recovery of VOC from surfactant containing aqueous solutions... 

Huang RYM, Moon GY, and Pal R. N-acetylated chitosan membranes for the pervaporation separation of alcohol/toluene mixtures. J. Memb. Sci. 2000 176(2) 223-231. 

Piera E, Giroir-Fendler A, Moueddeb H, Dalmon JA, Coronas J, Menendez M, and Santamarfa J. Separation of alcohols and alcohols/02 mixtures using zeohte MFI membranes. J Membr Sci 1998 142 97-109. 

Fig. 4-10. Typical vapor-phase chromatography record for the separation of alcohols. (Wilkins Instrument and Research Co.)...

Besides normal-phase TLC, reversed-phase TLC was used by impregnating the silica gel layer with paraffin or silicone oil and using hydrophilic solvents as mobile phases. By this method, it is possible to achieve a good separation of alcohols belonging to groups with the same number of carbon atoms. 

The second section refers to polyelectrolyte membranes prepared by alternating electrostatic layer-by-layer assembly of cationic and anionic polyelectrolytes on porous supports. Mass transport across ultrathin polyelectrolyte multilayer membranes is described. The permeation of gas molecules, liquid mixtures, and ions in aqueous solution has been investigated. The studies indicate that the membranes are excellently suited for separation of alcohol/water mixtures under pervaporation conditions and for ion separation, e.g. under nanofiltration conditions. 

While the droplets are falling down in the continuous dense gas phase, which is moving in countercurrent mode from the bottom to the top, some components are dissolved and carried out as extract into the separator whereas the insoluble part is collected and withdrawn from the bottom of the column as raffinate. This is illustrated in Fig. 2.28 as trickle flow mode. Examples are the deterpenation of citrus oils, the deacidification of vegetable oils, the separation of alcohol and water and the enrichment of carotenes or of EPA- and DHA-fatty acid esters from fish oils. 

The introduction of ion-exclusion chromatography is attributed to Wheaton and Bauman [1], It serves, above all, for the separation of weak inorganic and organic acids. In addition, ion-exclusion chromatography can be utilized for the separation of alcohols, aldehydes, amino acids, and carbohydrates. Due to Donnan exclusion, fully dissociated acids are not retained at the stationary phase, eluting therefore within the void volume as a single peak. Undissociated compounds, however, can diffuse into the pores of the resin, since they are not subject to Donnan exclusion. In this case, separations are based on non-ionic interactions between the solute and the stationary phase. 

In comparison, Fig. 4-15 shows the simultaneous separation of alcohols and aldehydes on IonPac ICE-AS 1 using pure water as the mobile phase. 

Fig. 4-15. Simultaneous separation of alcohols and aldehydes on IonPac ICE-AS1. - Eluent water flow rate 1 mL/min detection RI injection volume 50 pL solute concentrations 100 ppm each of glyoxal (1), glycerol (2), formaldehyde (3), ethylene glycol (4), glutaric dialdehyde (5), methanol (6), ethanol (7), 2-propanol (8), and 1-propanol (9).

---