Solvents azeotropic mixtures

The cmde wax is refined by extracting at 90—100°C with an azeotropic mixture of benzene and a mixture of alcohols, typically 85% benzene and 15% methanol (see Distillation, azeotropic and extractive). Distilling the solvent leaves a wax too daddy colored to be used without added refining. 

Obviously, the use of a nonvolatile ionic liquid simplifies the distillative workup of volatile products, especially in comparison with the use of low-boiling solvents, where it may save the distillation of the solvent during product isolation. Moreover, common problems related to the formation of azeotropic mixtures of the volatile solvents and the product/by-products formed are avoided by use of a nonvolatile ionic liquid. In the Rh-catalyzed hydroformylation of 3-pentenoic acid methyl ester it was even found that the addition of ionic liquid was able to stabilize the homogeneous catalyst during the thermal stress of product distillation (Figure 5.2-1) [21]. This option may be especially attractive technically, due to the fact that the stabilizing effects could already be observed even with quite small amounts of added ionic liquid. 

The carotenoid extract obtained by extraction of fresh food with a water-soluble solvent contains large amounts of water from the sample. In order to remove the water and solvent, in the case of acetone, carotenoids are transferred to petroleum ether, diethyl ether, or a mixture by adding small portions of the solvent extract and a large amount of water in a separatory funnel. The remaining traces of water can be removed either by addition of anhydrous Na2S04 or ethanol to form the azeotropic mixture. 

A procedure that has been widely used for spray residues is the separation of the residue from the sample by extraction with an organic solvent, usually benzene. After most of the solvent has been removed, the residue is treated with sodium and isopropyl alcohol and the chloride ion is estimated by standard methods. Carter 10) has determined in this manner DDT residues on a number of crops, and he has recommended the adoption by the Association of Official Agricultural Chemists of the method as a tentative one for DDT 11). Koblitsky and Chisholm 42) have determined DDT in soil samples by the sodium-isopropyl alcohol procedure after removing the DDT by extraction with an azeotropic mixture of two volumes of benzene and one volume of isopropyl alcohol. 

Chloro-hydrogen disilanes H6 nClnSi2 are obtained by chlorination of Si2H6 or by reaction of phenylated disilanes with HCI/AICI3. The synthesis of these compounds in a pure form is difficult because of equilibration reactions and the formation of azeotropic mixtures with the solvents. Eq.(3) shows all disilanes formed from 1,2-diphenyl-disilane and HCI/AICI3 [8]. 

Figure 4.9) to synthesize isopropyl myristate. This is enabled by a continuous feed of 2-propanol to the reactor, which forms an azeotropic mixture with water. This mixture is distilled, thereby removing the water produced. Afterwards, the immobilized enzyme used can be easily removed by filtration. The feasibility of this technique is also illustrated within the synthesis of glucose stearate. A mixture of ethyl methylketone and hexane as solvent is used, forming an azeotropic mixture with the water produced [42],... 

Hydrogen transfer reactions are highly selective and usually no side products are formed. However, a major problem is that such reactions are in redox equilibrium and high TOFs can often only be reached when the equilibria involved are shifted towards the product side. As stated above, this can be achieved by adding an excess of the hydrogen donor. (For a comparison, see Table 20.2, entry 8 and Table 20.7, entry 3, in which a 10-fold increase in TOF, from 6 to 60, can be observed for the reaction catalyzed by neodymium isopropoxide upon changing the amount of hydrogen donor from an equimolar amount to a solvent. Removal of the oxidation product by distillation also increases the reaction rate. When formic acid (49) is employed, the reduction is a truly irreversible reaction [82]. This acid is mainly used for the reduction of C-C double bonds. As the proton and the hydride are removed from the acid, carbon dioxide is formed, which leaves the reaction mixture. Typically, the reaction is performed in an azeotropic mixture of formic acid and triethylamine in the molar ratio 5 2 [83],... 

As can be seen from the data in Table 35.1, the maximum reaction rate is achieved at the 5 2 formic acid triethylamine ratio that is the commonly used azeotropic mixture known as TEAF. When more acid is present, the catalyst may be less active, but equally there may be less formate anion (i.e., the active reagent). The concentration of the latter also depends upon the solvent being used. When there is more triethylamine present the reaction rate also decreases, and there are some indications that triethylamine may deactivate the catalyst. However, the use of formic acid mixtures with ammonia, ethylamine or diethy-lamine is less effective than triethylamine. 

Hydrophilic membranes with a preferential permeation of water are mainly used for the dehydration of organic solvents with an emphasis on azeotropic mixtures. Membranes for the removal of small alcohol molecules like methanol and ethanol are also of a hydrophilic nature. 

The ratio of 70/30 (v/v) MeCl2/HFIP was chosen because it is a mlnlmum-bolllng (37 C) azeotropic mixture. The exact composition can be reproduced by distillation from a mixture of approximately the correct ratio, and one can easily reclaim >90% of the solvent used by simple distillation. In view of the cost of HFIP the ability to reclaim solvent is an Important consideration. 

Some solvent mixtures can be very difficult and energy intensive to separate because of the closeness of boiling points and the formation of azeotropic mixtures [45]. Azeotropic or extractive distiUation can be used for azeotropic solvent mixtures and solvents which have very low relative volatihties ]43, 45]. Azeotropic and extractive distillation involves the addition of another solvent, known as an entrainer, which will form its own azeotrope with one of the components to be separated ]45]. However, the additional solvent required for azeotropic and extractive distillation can also generate more wastes depending on how easily the entrainer itself can be recycled and reused. 

Transport through the membrane can be considered to occur by a solution-diffusion mechanism under the influence of a chemical potential driving force [48, 49]. The primary benefit of using PV systems is that they are essentially independent of the vapor-liquid equihbrium of solvent mixtures. Therefore PV can be used to overcome the separation barriers created by many azeotropic mixtures [48, 50]. 

Data of Azeotropes. The choice of azeotropic entrainer for a desired separation is much more restricted than that of solvents for extractive distillation, although many azeotropic data are known. The most extensive compilation is that of Ogorodnikov, Lesteva, and Kogan (Handbook of Azeotropic Mixtures (in Russian), 1971). It contains data of 21,069 systems, of which 1274 are ternary, 60 multicomponent, and the rest binary. Another compilation Handbook of Chemistry and Physics, 60th ed., CRC Press, Boca Raton, FL, 1979) has data of 685 binary and 119 ternary azeotropes. Shorter lists with grouping according to the major substances also are available in Lange s Handbook of Chemistry... 

Allyl alcohol is a colorless liquid having a pungent odor its vapor may cause severe irritation and injury to eyes, nose, throat, and lungs. It is also corrosive. Allyl alcohol is freely miscible with water and miscible with many polar organic solvents and aromatic hydrocarbons, but is not miscible with n-hexane. It forms an azeotropic mixture with water and a ternary azeotropic mixture with water and organic solvents. Allyl alcohol lias both bacterial and fungicidal effects. Properties of allyl alcohol are shown in Tabic 1. 

Forms azeotropic mixture with 3 mol of water, boiling at 92-93°C volatile with steam miscible with water, alcohol, acetone, ether, petroleum ether, oils, and many organic liquids solvent for many organic and inorganic compounds.1,4... 

The synthesis of chlorohydrogendisilanes by reaction of phenylhydrogendisilanes with HC1 in benzene has been complicated by equilibration reactions in the cases of mono-and dichlorodisilanes and by the formation of azeotropic mixtures of the chlorodisilanes with the solvent and the by-product benzene54. This could be overcome by the use of the larger mesityl (Mes) substituent55 (equation 31). 

Tran and Mujtaba (1997) and Mujtaba et al. (1997) highlighted the operating features and limitations of BED processes for close boiling and azeotropic mixtures. However, the works were limited to the separation of only one key component in the distillate without due regard to the recovery of solvent or the separation of other components in the feed mixture. 

Mujtaba (1999) considered the conventional configuration of BED processes for the separation of binary close boiling and azeotropic mixtures. Dynamic optimisation technique was used for quantitative assessment of the effectiveness of BED processes. Two distinct solvent feeding modes were considered and their implications on the optimisation problem formulation, solution and on the performance of BED processes were discussed. A general Multiperiod Dynamic Optimisation (MDO) problem formulation was presented to obtain optimal separation of all the components in the feed mixture and the recovery of solvent while maximising the overall profitability of the operation. 

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