Water entrainment, azeotropic

Dean-Stark apparatus, -separator, - trap (s. a. Water entrainment, azeotropic)... 

Water entrainment, azeotropic 16, 234, 241/2, 432, 937 Water scavenger, ethyl propionate as — 16, 795 Water-solubilization 16, 501 Wieland s. Barbier Wiligerodt-Kindler reaction 16, 507... 

Anhydrous Acetic Acid. In the manufacture of acetic acid by direct oxidation of a petroleum-based feedstock, solvent extraction has been used to separate acetic acid [64-19-7] from the aqueous reaction Hquor containing significant quantities of formic and propionic acids. Isoamyl acetate [123-92-2] is used as solvent to extract nearly all the acetic acid, and some water, from the aqueous feed (236). The extract is then dehydrated by azeotropic distillation using isoamyl acetate as water entrainer (see DISTILLATION, AZEOTROPIC AND EXTRACTIVE). It is claimed that the extraction step in this process affords substantial savings in plant capital investment and operating cost (see Acetic acid and derivatives). A detailed description of various extraction processes is available (237). 

When using propanols for esterification, the alcohol and water form azeotropes making necessary secondary recovery and recycling of alcohol. An industrial process that is conducted in this way makes use of homogeneous catalyst (para-toluene sulfonic acid) lost after reaction [5]. A more efficient solution can found by employing an entrainer for breaking the azeotrope water/alcohol and superacid solid catalyst. Besides, the entrainer has a beneficial effect on the reaction rate, by increasing the amount of alcohol recycled to the reaction space [3]. 

Figure 2. Flow sheet for removing emulsified water by azeotropic distillation using a vapor feed of the reflux of a fixed amount of entrainer...

In the conventional reactive distillation combined with azeotropic distillation an azeotropic distillation takes place in the second column. An entrainer is fed in order to obtain pure isopropanol at the bottom and a water/entrainer mixture at the top. The entrainer is chosen such that it forms an... 

FIGURE 5.5-1 Dehydration of alcohol by azeotropic distillation, using benzene as entrainer to form a low-boiling eihanol-water-benzene azeotrope. 

A convincing application of two columns sequence is the split of the azeotrope ethanol (A) / water (B) with tetrahydrofurane (C), as proposed by Stichlmair (1999). Figure 9.19 depicts qualitatively the split sequencing. The entrainer is a low-boiler forming a minimum azeotrope with water (az nbp 64.2 C) below the boiling point of the original water-ethanol azeotrope (azj, nbp 78.2 °C). There is also an azeotrope tetrahydroftirane-ethanol (az, nbp 65.9 C), but this is not essential. Water and ethanol,... 

Pyridine Forms fully miscible, water-rich azeotrope, easily split by pervaporation or vapor permeation. Final dehydration feasible. Avoids entrainers and messy salt/alkali solutions. Tetrahydrojuran Easily dehydrated by pervaporation down to a few hundred ppm of water. No messy chemicals. 

Oxalic acid esters. Anhydrous oxalic acid refluxed with -heptanol and p-toluene-sulfonyl chloride as catalyst in benzene with azeotropic water entrainment > di- -heptyl oxalate. Y 91%. F. e. s. P. P. Rodionov, V. M. Nakonechnaya, and A. P. Yarkova, Izv. Vyssh. Ucheb. Zaved., Khim. Khim. Tekhnol. 11, 615 (1968) C. A. 69,76571. 

A mixture of 5-nitrofurfural diacetate, abs. ethanol, some coned. H2SO4, and benzene refluxed 30 hrs. with azeotropic water entrainment -> 5-nitrofurfural diethyl acetal. Y 82%. F. e. s. W. Weuffen and H. Tiedt, Arch. Exp. Veterinaermed. 21 (1), 267 (1967) C. A. 68, 21758. 

LiH added under Ng to a dry mixture of ethyl malonate and Li-iodide in benzene, and refluxed 26 hrs. with azeotropic water entrainment, while 1-o-tolylaziridine in benzene is added dropwise during the first 8 hrs. -> crude ethyl y -o-toluidino-ethylmalonate. Y 50%. F. e. s. H. Stamm, A. 716, 121 (1968). 

A soln. of homopiperonal, piperidine, and a trace of p-toluenesulfonic acid refluxed 3 hrs. in benzene with azeotropic water entrainment, the resulting crude enamine mixed with triethylamine and dry chloroform, ice-cooled, stirred, and treated dropwise with a soln. of 2-acetoxy-4-methoxybenzoyl diloride in the same solvent, stirring continued 6 hrs., and allowed to stand overnight at room temp. 

A soln. of o-benzoylbenzaldehyde and ethylenediamine in toluene refluxed 18 hrs. with azeotropic water entrainment -> 2,3-dihydro-5-phenyl-5H-imidazo[2,l-a]iso-indole. Y 43% as the sulfate. W. Metlesics et al., J. Org. Chem. 33, 2874 (1968). 

For all these reasons, the separation stage is important when selecting an entrainer. The various settling characteristics of possible ternary azeotropes formed in the ethanol/water/entrainer combination illustrate the problems (Table 7.4). 

Table 7.4 Settling characteristics of water entrainers in ternary azeotropes with ethanol Density of...

Water entrainer B.P. (°C) Azeotropic b.p. (°C) Water (% w/w) Equivalent reflux ratio... 

Entrainer Water in azeotrope (% w/w) Solubility of water in entrainer (% w/w) Net water removed (% w/w)... 

DIPE is comparatively non-toxic and, provided that it is kept inhibited, it is not difficult to handle so that its use as an entraining agent for removing water by azeotropic distillation is straightforward and it can be very effectively dehydrated itself because its water azeotrope (4.6% w/w water) splits into two phases... 

As the VLB diagram (Fig. 16.28) shows, the water/ dioxane azeotrope is separated easily from both water and from the solvent. However, the laboratory techniques used for drying (molecular sieves, barium oxide, magnesium sulphate and potassium hydroxide) are all rather expensive without a recovery system. Chloroform is an effective azeotropic entrainer and its toxicity is not an automatic disqualification because dioxane itself needs to be handled with very great care. 

Azeotropic water entrainment. A mixture of phosphorous acid, -decanol, and toluene refluxed under argon with removal of the resulting water -> mono- -decyl phosphite. Y 82%. F. e., also phosphinic acid monoesters, s. E. E. Nifant ev, V. R. KiPdisheva, and I. S. Nasonovskii, Zh. Prikl. Khim. 42, 2590 (1969) C. A. 72, 100835. 

Carboxylic acid aryl esters from carboxylic acids and phenols Azeotropic water entrainment... 

Azeotropic water entrainment s. 18, 454 cyclic 1,3-dienamines s. I. Seki, Chem. Pharm. Bull. 18, 671 (1970)... 

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