Dehydration of aqueous ethanol mixtures

Dehydration of Aqueous Ethanol Mixtures by Extractive Distillation... 

For the azeotropic dehydration of aqueous ethanol mixtures approaching the constant boiling mixture, a brief comparison is shown for the entrainers, n-pentane, benzene, and diethyl ether. Since water is most non-ideal in n-pentane, the driest ethanol is expected to be produced if n-pentane is used. 

C. Black and D. E. Dilsler. Dehydration of Aqueous Ethanol Mixtures by Extractive Distillation. 

C. Black and D. E. Ditsler, Dehydration of Aqueous Ethanol Mixtures by Extractive Distillation, in Extractive and Azeotnqnc Distillation, Chap. I, American Chemical Society Advances in Chemistry NO. 115. Washington, DC, 1972. 

S. Kato, K. Nagahama, H. Noritomi and H. Asai, Permeation rates of aqueous alcohol solutions in pervaporation through Nation membrane, J. Membr. Sci., 1992, 72, 31-41 V Freger, E. Korin, J. Wisniak and E. Komgold, Transport mechanism in ion-exchange pervaporation membranes Dehydration of water-ethanol mixture by sodium polyethylene sulphonate membranes, J. Membr. Sci., 1997, 133, 255-267. 

The use of digital computers to carry out complete calculations in the design of separation processes has been the goal of many. To do this effectively, suitable methods for phase equilibria and tray-to-tray distillation calculations are required. Results calculated by the application of such methods to dehydrate aqueous ethanol mixtures using ethylene glycol as the extractive distillation solvent is discussed below. A brief review of the methods used for phase equilibria and enthalpies is followed by a discussion of the results from distillation calculations. These are compared for extractive distillation with corresponding results obtained by azeotropic distillation with n-pentane. 

For the separation of toluene/cyclohexane mixtures for a 550-h test, the permeation rate was determined by the aromatic component, and the separation factor reached 15-25 at 40 °C. Owing to the low organic solvent composition in the feed, the fluxes of the organic compounds were relatively small. When the same SLM was used for the dehydrations of aqueous 1-propanol and of aqueous ethanol, water was found to be the preferential permeation component (Wang et al., 2009). 

For example, the reaction of nitronates (123) with a zinc copper pair in ethanol followed by treatment of the intermediate with aqueous ammonium chloride a to give an equilibrium mixture of ketoximes (124) and their cyclic esters 125. Heating of this mixture b affords pyocoles (126). Successive treatment of nitronates (123) with boron trifluoride etherate and water c affords 1,4-diketones (127). Catalytic hydrogenation of acyl nitronates (123) over platinum dioxide d or 5% rhodium on aluminum oxide e gives a-hydroxypyrrolidines (128) or pyrrolidines 129, respectively. Finally, smooth dehydration of a-hydroxypyrrolidines (128) into pyrrolines (130f) can be performed. 

The dehydration of the dioxindoles can be achieved by treatment with a mixture of HC1 and AcOH424,425. The 3-methyleneoxindoles can be selectively reduced at the carbon-carbon double bond using Na2S2C>4 in aqueous ethanol (Scheme 97). 

Another option is extractive crystallisation. Here, the tendency of particular aqueous-solvent mixtures such as water-propanol, water-amines, water-micelles, water-polar polymers to split into two liquid phases upon small variations in temperature is used to dehydrate solutions of crystallisable solutes. At low temperatures, these systems form homogeneous mixtures, whereas at high temperatures, a solvent rich phase is created. The aqueous solute becomes concentrated in a smaller volume and consequently crystallises, whereas the pure solvent is recycled. Also, alternative schemes may be used depending on the exact phase behaviour of the component. For instance, a solute such as amino acids and peptides may crystallise from an aqueous solution upon introducing a fully miscible component, such as in water-ethanol mixtures. In a second stage, after the separation of the crystals, the conditions may be altered to induce an L - L phase split that allows easy recovery of the auxiliary component. Maurer and co-workers [25] described the use of high pressure CO2 in water-alkanol systems. At low pres-... 

Cyclohept-2-enone and cyclo-oct-2-enone undergo ring-contraction to 1-acetyl-cyclopentene and 1-acetylcyclohexene, respectively, in aqueous ethanol containing triethylamine at 140 Treatment of eucarvone with sodium hydride and methyl iodide gave a mixture of products including the bicyclic compounds 3-methylcar-4-en-2-one and l,3-dimethylcar-4-en-2-one. Attempts to dehydrate cycloheptene (237) gave mixtures of dimethylisopropylbenzenes. ... 

Vane LM, Alvarez FR, Rosenblum L, Govindaswamy S. Hybrid vapor stripping-vapor permeation process for recovery and dehydration of 1-butanol and acetone/butanol/ethanol from dilute aqueous solutions. Part 2. Experimental validation with simple mixtures and actual fermentation broth. J Chem Technol Biotechnol 2013 88 1448-58. 

In liquid mixtures of type (2), the solutions of primary interest are azeotropic and other mixtures containing variable amounts of water in organics dehydration of organic solvents containing very small amounts of water. Removal of water from azeotropic mixtures of ethanol-water, isopropanol-water, etc., is extensively practiced using polymeric membranes (of crosslinked polyvinyl alcohol) that are highly polar and selective for water. On the other hand, the membranes that are used to remove VOCs selectively from aqueous solutions are usually highly nonpolar rubbery polymeric membranes, e.g. dimethyl siloxane (silicone rubber). 

Ethanol (EtOH) [5h] Commercial products are pure enough for most purposes. The impurities are MeOH, PrOH, Ac, water, etc. In order to reduce 2000 ppm of water in absolute EtOH, about 5% of hexane or cyclohexane is added to the EtOH and the mixture is fractionated to remove the aqueous azeotrope. By this step, the water content is reduced to < 500 ppm. The dehydrated EtOH is then slowly passed through a column of dry molecular sieves (4A) to reduce the water content to 7 ppm. 

Protection for primary amines. Sheehan and Guziec1 have introduced this reagent for replacement of both hydrogens of a primary amine function by incorporation into the very stable 4,5-diphenyl-4-oxazoline-2-one ring system (3).2 These Ox-protected derivatives are obtained by treatment of a primary amine or amino acid tetramethyl-ammonium salt with (1) in DMF. After stirring for 0.5 hr., the mixture is acidified (HC1) and extracted with ethyl acetate to obtain a diastereomeric mixture of hydroxy-oxazolidinoncs (2). The mixture is dehydrated to the Ox derivative (3) by trifluoroacetic acid (TFA). Ox derivatives are stable to aqueous base, refluxing ethanolic hydrazine,... 

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