Ternary azeotropes ethyl acetate

Podebush Sequence forPthanol—Water Separation. When ethyl acetate is used as the entrainer to break the ethanol—water azeotrope the residue curve map is similar to the one shown in Figure 21d, ie, the ternary azeotrope is homogeneous. Otherwise the map is the same as for ethanol—water—benzene. In such... 

Esters of medium volatility are capable of removing the water formed by distillation. Examples are propyl, butyl, and amyl formates, ethyl, propyl, butyl, and amyl acetates, and the methyl and ethyl esters of propionic, butyric, and valeric acids. In some cases, ternary azeotropic mixtures of alcohol, ester, and water are formed. This group is capable of further subdivision with ethyl acetate, all of the ester is removed as a vapor mixture with alcohol and part of the water, while the balance of the water accumulates in the system. With butyl acetate, on the other hand, all of the water formed is removed overhead with part of the ester and alcohol, and the balance of the ester accumulates as a high boiler in the system. 

Ethyl Acetate. The production of ethyl acetate by continuous esterification is an excellent example of the use of azeotropic principles to obtain a high yield of ester (2). The acetic acid, concentrated sulfuric acid, and an excess of 95% ethyl alcohol are mixed in reaction tanks provided with agitators. After esterification equilibrium is reached in the mixture, it is pumped into a receiving tank and through a preheater into the upper section of a bubblecap plate column (Fig. 5). The temperature at the top of this column is maintained at ca 80°C and its vapor (alcohol with the ester formed and ca 10% water) is passed to a condenser. The first recovery column is operated with a top temperature of 70°C, producing a ternary azeotrope of 83% ester, 9% alcohol, and 8% water. The ternary mixture is fed to a static mixer where water is added in order to form two layers and allowed to separate in a decanter. The upper layer contains ca 93% ethyl acetate, 5% water, and 2% alcohol, and is sent to a second recovery or ester-drying column. The overhead from this column is 95—100% ethyl acetate which is sent to a cooler and then to a storage tank. This process also applies to methyl butyrate. 

Entrainer bp (°C) Binary azeotrope with n-hexane (68.7°C) Binary azeotrope with ethyl acetate (77.1 °C) Ternary azeotrope... 

Nitromethane shows the simplest residue curve map with one unstable curved separatrix dividing the triangle in two basic distillation regions. Methanol and acetonitrile give rise two binary azeotropic mixtures and three distillation regions that are bounded by two unstable curved separatrices. Water shows the most complicated residue curve maps, due to the presence of a ternary azeotrope and a miscibility gap with both the n-hexane and the ethyl acetate component. In all four cases, the heteroazeotrope (binary or ternary) has the lowest boiling temperature of the system. As it can be seen in Table 3, all entrainers except water provide the n-hexane-rich phase Zw as distillate product with a purity better than 0.91. Water is not a desirable entrainer because of the existence of ternary azeotrope whose n-hexane-rich phase has a water purity much lower (0.70). Considering in Table 3 the split... 

Ester manufacture is a relatively simple process in which the alcohol and an acid are heated together in the presence of a sulfuric acid catalyst, and the reaction is driven to completion by removing the products as formed (usually by distillation) and employing an excess of one of the reagents. In the case of ethyl acetate, esterification takes place in a column that takes a ternary azeotrope. Alcohol can be added to the condensed overhead liquid to wash out the alcohol, which is then purified by distillation and returned to the column to react. 

It is evident that this procedure gives a satisfactory method of converting a given amount of acetic acid completely to ethyl acetate. It also can be seen that, if the ester is removed as rapidly as it is formed, esterification must go on even in the presence of a considerable proportion of water. To form the ternary azeotrope, a small excess of alcohol must be added. 

As can be readily seen from the above, the manufacture of ethyl acetate becomes a matter of distillation. With proper adjustments of rates of addition and distillation, the esterification can be carried out as a continuous process. ActuaUy, the liquor containing acetic acid and the proper amount of sulfuric acid is fed into the column at the proper plate where it meets the alcohol. Esterification takes place on the plates in the nolumn, and the ternary azeotrope of ester, alcohol, and water comes out at the top continuously. The distillate is washed with water and the ester passed to another column. The dilute alcohol obtained by washing the ternary azeotrope goes to a still for the recovery of the alcohol, which is returned to make more ester. 

In a nonideal system such as ethyl acetate/water/ ethanol, for instance, there exists considerable complexity from a phase equilibrium point of view because of the presence of a liquid liquid-equilibrium (LLE) envelope, as well as the presence of three binary azeotropes and a single ternary azeotrope. Attempts have been made to... 

Furzer, I. A., Critical distillation experiments in a region near the homogeneous ternary azeotrope in the system ethyl acetate ethanol water. 2001. Industrial and Engineering Chemistry Research, 40(3) 990 992. 

Not only must the ethyl acetate be recovered from water but also the hydrolysis products, which have been formed during the heating of the ethyl acetate in the presence of a large excess of water, must be removed before the solvent is fit for reuse. Although this can be done by fractionation it involves separating a two-phase ternary azeotrope and the unstable nature of ethyl acetate is also a problem since the fractionation must be done at a low pressure. 

The ternary azeotrope is only just two-phase at low temperature (Fig. 16.32), so there is no practical way of using a phase separation to remove water even if it were acceptable to recover ethyl acetate with ethanol present. 

Fig. 16.32 Ternary solubility diagram showing the temperature dependence of the phase behaviour of ethyl acetate/ water/ethanol, indicating that the ternary azeotrope is two phase at 20 °C and single phase at 70 °C.

The boiling points of the pure components at atmospheric pressure are as follows ethyl acetate (ETAC) 77.2 C ethanol (ETOH) 78.3 C water (H20) 100.0 C acetic acid (HAG) 118.0 G. There are three binary azeotropes and one ternary azeotrope summarized in Table 10.2, with respective boiling points at atmospheric pressure. The normal boiling points for the pure components as well as the compositions of the azeotropes are obtained from ASPEN Properties Plus using UNIQUAG and show satisfactory agreement with the data available elsewhere [105]. 

Ma, Xu, Liu, and Sun (2010) used perfluorosulfonic acid-poly(vinyl alcohol)-Si02/ poly(vinyl alcohol)/polyacrylonitrile (PFSA-PVA-Si02/PVA/PAN) bifunctional hollow-fiber composite membranes. The catalytic and the selective layer of the membrane were independently optimized. These membranes were synthesized by dipcoating. The performance of these bifunctional membranes was evaluated by dehydrating the ternary azeotropic composed of a water, ethanol, and ethyl acetate system (top product of a reactive distillation process of esterification of acetic acid with ethanol), obtaining separation factors of water/ethanol up to 379. An extensive assessment on the esterification reaction of ethanol-acetic acid was later published (Lu, Xu, Ma, Cao, 2013). In this case, the reaction equilibrium was broken in less than 5 h, and a 90% conversion of acetic acid was achieved after 55 h. 

In the main esterification process for acetic acid ethyl ester (ethyl acetate) a mixture of acetic acid and ethanol with a small amount of sulphuric acid is preheated and fed to an esterifying column where it is refluxed. The mixture removed goes to a second refluxing column where a ternary azeotrope containing 85% ethyl acetate is removed. Water is mixed with the distillate after which it separates into two layers. The top layer is fed to a refluxing column from which the residue containing 95% ethyl acetate is distilled to remove any impurities. Ethyl acetate and ethyl lactate are used as solvents. Some ethyl esters of carboxylic acids are used as flavor and aroma substances. 

Three candidate acetates will be studied in detailed process simulations to demonstrate the factors needed to be considered in determining the suitable entrainer for this system. The three candidate acetates to be considered are ethyl acetate (Tanaka and Yamada and Siirola ), isobutyl acetate (iBuAc) (Costantini et al. and Patten and Ure ), and w-butyl acetate (Othmer °). The important experimental physical properties of these three acetates at atmospheric pressure are listed in Table 9.1. The azeotropic data are from Horsley and Gmehling, the VLB data are from Gmehling and Onken, with the VLB data for acetic acid-isobutyl acetate system from Christensen and Olson. " The binary and ternary BBB data are from Sprensen and Arlt. ... 

The set of NRTB parameters used provides a good match between predicted and experimental data binary and ternary VBB and BBB. The sets of NRTB parameters for the ternary systems of acetic acid-water-ethyl acetate, acetic acid-water-isobutyl acetate, and acetic acid-water-M-butyl acetate are listed in Tables 9.2 to 9.4. The NRTB model parameters are obtained by htting all binary and ternary VBB and BBB data while trying to get a good prediction of the azeotropic temperature and composition. The pure component parameters used in the Hayden-O Connell model are shown in Table 9.5 while the association parameters... 

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