Water azeotropic mixtures

Suspension (co)polymerization is carried out in aqueous solutions of monomers dispersed in the form of 0.1-5 mm diameter droplets by stirring in nonmixed water-organic liquids in the presence of initiators. The organic liquids that are not dissolving monomers and (co)polymers are represented by solvents that either form azeotropic water mixtures (toluene, heptane, cy-... 

Solvent Recovery The largest current industrial use of pei vapo-ration is the treatment of mixed organic process streams that have become contaminated with small (10 percent) quantities of water. Pei vaporation becomes vei y attractive when dehydrating streams down to less than 1 percent water. The advantages result from the small operating costs relative to distillation and adsorption. Also, distillation is often impossible, since azeotropes commonly form in multicomponent organic/water mixtures. 

Example 4.5 2-Propanol (isopropanol) and water form an azeotropic mixture at a particular liquid composition that results in the vapor and liquid compositions being equal. Vapor-liquid equilibrium for 2-propanol-water mixtures can be predicted by the Wilson equation. Vapor pressure coefficients in bar with temperature in Kelvin for the Antoine equation are given in Table 4.113. Data for the Wilson equation are given in Table 4.126. Assume the gas constant R = 8.3145 kJ-kmol 1-K 1. Determine the azeotropic composition at 1 atm. 

Pervaporation. Pervaporation differs from the other membrane processes described so far in that the phase-state on one side of the membrane is different from that on the other side. The term pervaporation is a combination of the words permselective and evaporation. The feed to the membrane module is a mixture (e.g. ethanol-water mixture) at a pressure high enough to maintain it in the liquid phase. The liquid mixture is contacted with a dense membrane. The other side of the membrane is maintained at a pressure at or below the dew point of the permeate, thus maintaining it in the vapor phase. The permeate side is often held under vacuum conditions. Pervaporation is potentially useful when separating mixtures that form azeotropes (e.g. ethanol-water mixture). One of the ways to change the vapor-liquid equilibrium to overcome azeotropic behavior is to place a membrane between the vapor and liquid phases. Temperatures are restricted to below 100°C, and as with other liquid membrane processes, feed pretreatment and membrane cleaning are necessary. 

Figure 12.33 Separation of isopropyl alcohol (IPA) and water mixture using di-isopropyl ether (DIPE) as entrainer in heterogeneous azeotropic distillation.

Ketone synthesis, 72 173-174 73 667-668 Ketone-water azeotropes, 74 563 Ketone-water mixture properties, 74 568-569t Ketose, 4 696... 

The answer is like fighting fire with fire—another azeotrope is formed. When benzene is added to ethyl alcohol and water a ternary azeotrope, a mixture of three compounds that boil at a single temperature, is formed. The ternary azeotrope has the composition of 68% benzene, 24% ethyl alcohol, and 6% water, and it boils at a temperature lower than the binary ethyl alcohol/water azeotrope. So, when a little benzene is added to the ethyl alcohol/water mixture and then put through a distillation column, the ternary azeotrope, in a 68-24-6 composition will come off the top, talcing with it all the benzene, all the water, but just some of the ethyl alcohol. Out the bottom comes whats left, the rest of the ethyl alcohol in nearly pure form. Slick. None of this, by the way, is shown in Figure 13—2. 

The catalytic esterification of ethanol and acetic acid to ethyl acetate and water has been taken as a representative example to emphasize the potential advantages of the application of membrane technology compared with conventional distillation [48], see Fig. 13.6. From the McCabe-Thiele diagram for the separation of ethanol-water mixtures it follows that pervaporation can reach high water selectivities at the azeotropic point in contrast to the distillation process. Considering the economic evaluation of membrane-assisted esterifications compared with the conventional distillation technique, a decrease of 75% in energy input and 50% lower investment and operation costs can be calculated. The characteristics of the membrane and the module design mainly determine the investment costs of membrane processes, whereas the operational costs are influenced by the hfetime of the membranes. 

The step 6 product (3.80 mmol), 4,4 -difluorodiphenylsulfone (3.58 mmol), and K2C03 (14.6 mmol) were added to the reaction flask and treated with 10 ml DMSO and 5 ml toluene and then stirred at 150°C for 6 hours with azeotropic water removal. The mixture was treated with additional step 6 product (1.84 mmol)... 

Pervaporation (PV) is a membrane-based process used to separate aqueous, azeotropic solvent mixtures. This is done using a hydrophihc, non-porous membrane that is highly selective to water. Figure 3.9 shows a typical PV system that produces a dehydrated solvent stream (retentate) from a solvent/water feed. 

HC1 and water distill as an azeotrope (a mixture) whose composition ( 6 M ) depends on pressure. The composition is tabulated as a function of the pressure during distillation. See Problem 11-55 for more information. 

Azeotropic and Partially Miscible Systems. Azeotropic mixtures are those whose vapor and liquid equilibrium compositions are identical. Their x-y lines cross or touch the diagonal. Partially miscible substances form a vapor phase of constant composition over the entire range of two-phase liquid compositions usually the horizontal portion of the x-y plot intersects the diagonal, but those of a few mixtures do not, notably those of mixtures of methylethylketone and phenol with water. Separation of azeotropic mixtures sometimes can be effected in several towers at different pressures, as illustrated by Example 13.6 for ethanol-water mixtures. Partially miscible constant boiling mixtures usually can be separated with two towers and a condensate phase separator, as done in Example 13.7 for n-butanol and water. 

By the reaction of concentrated solutions of nickel acetate and Hacac in an ethanol-water mixture the bis-aqua adduct [Ni(acac)2(H20)2] is obtained. An improved synthesis of the same compound has been devised starting from NiO(OH) which was reduced with Hacac at room temperature.1549 The green anhydrous Ni(acac)2 derivative is obtained by azeotropic distillation with toluene of the aqua complex or by its sublimation in vacuo. 

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. 

Fig. 4.7 shows a temperature versus composition diagram for an ethanol-water mixture. It is slightly idealized to make a pedagogical point. If one starts with initial composition Q in the liquid (point A in Fig. 4.7), the vapor mixture will have the composition B. If this vapor is condensed, the liquid mixture will have composition C2 at point C the vapor phase will have the composition C3 at point D. Further cycles will achieve ever smaller increases in ethanol liquid content until the azeotrope (constant-boiling) composition is reached at 95.6 mass% and 78.2°C... 

As it is well known, fermentation processes generally produce aqueous solutions of ethanol, the separation of which necessitates a series of distillation processes. Distillation, however, is a very expensive operation and in addition, ethanol-water mixture forms an azeotrope which further increases the cost of purification. Therefore, novel separation methods must be investigated to make the process more feasible and economical. 

FIG. 13-52 Azeotropic distillation tower for distillation of an ethanol-water mixture using benzene as a mass separating agent. [Ajier Prokopakis and Seider (op. cit.).]... 

This study was undertaken to obtain the necessary vapor-liquid equilibrium data and to determine the distillation requirements for recovering solvent for reuse from the solvent-water mixture obtained from adsorber regeneration. Previous binary vapor-liquid equilibrium data (2, 3) indicated two binary azeotropes (water-THF and water-MEK) and a two phase region (water-MEK). The ternary system was thus expected to be highly nonideal. 

Catalyst Preparation. The potassium siloxanolate catalyst was prepared by charging finely crushed potassium hydroxide, D4, and toluene to a flask equipped with an overhead stirrer and an attached Dean-Stark trap with condenser. Argon was bubbled through the solution from below the level of the liquid to promote the elimination of water via a toluene azeotrope as the reaction proceeded. Typically, a D4/KOH molar ratio of 3 1 was used with enough toluene to form an approximately 50% (wt/vol) solution. The catalyst was allowed to form at 120 °C for 24 h, during which time the toluene-water mixture was eliminated and collected in the Dean-Stark trap. The clear catalyst was then diluted to an —35% (wt/vol) solution with dry toluene and stored in a desiccator until use. 

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