Acetic acid binary azeotropes

Methyl Vinyl Ketone. Methyl vinyl ketone [78-94-4] (3-buten-2-one) is a colorless Hquid with a pungent odor. It is stable only below 0°C, and readily polymerizes on standing at room temperature. It can be inhibited for storage and transportation by a mixture of acetic or formic acid and hydroquinone or catechol (266). This ketone is completely soluble in water, and forms a binary azeotrope with water (85 MVK 15 H2O vol %) at 75.8°C. 

Formic acid can be dehydrated with propyl formate as entrainer. Small contents of formic acid and water in acetic acid can be entrained away with chloroform which forms binary azeotropes with water and formic acid but no other azeotropes in this system. 

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. 

The high boiling reactant is fed as feed 1 and the low boiling reactant as feed 2. Between the two feeds, there is the reaction zone. As a special application, feed 1 can serve as an extractive agent, e.g. in the case of the production of methyl acetate, acetic acid serves as an entrainer for the binary azeotropic mixture methanol and methylacetate. The ensemble is then a reactive extractive distillation column. 

Liquid with pungent odor. bp7 81.4. tig 1.4086. dj 0.8636 dj5 0 8407. Easily soluble in water, methanol, ethanol, ether, acetone, glacial acetic acid. Slightly sol in hydrocarbons. Forms a binary azeotrope with water, bp 75 (12% water), uv spectrum and electric moments Rogers, J. Am. Chem. Soc. 69, 2544 (1947). Polymerizes on standing, LDm in mioe and rats 35 mg/kg, C.A. 72, 124809b 0970). 

For the second mixture, water/acetic acid, UNIFAC predicts an azeotrope, but the comparison with experimental data reveals that the prediction is completely wrong There is no azeotrope, although the binary shows a high non-ideal behaviour toward diluted acid solutions. We may try with Wilson, changing the option for the vapour phase to Hayden-O Connell method. Now the estimation is very accurate (not shown). We may retry to use UNIFAC with Hayden-O Connell. In fact, the azeotrope disappears, but the accuracy is rather modest. 

The next mixture contains formic acid (11.9 %), acetic acid (31.4%) and water (56.7%). The difference of freezing points of water and acids is too close (9 and 16 °C respectively), so that the separation by crystallisation is not feasible. If distillation is applied, one can separate two binary mixtures, formic acid/water and acetic acid/water. The separation of these mixtures is known, and it can be solved by standard techniques. Figure 7.23 shows the final sequencing that will consists from a flash, a distillation column, and a special device of extractive azeotropic distillation. 

Diagram of the four distillation areas of the ternary system water-formic acid-acetic acid, having a binary and a ternary azeotrope, and position of composition R [39]... 

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]. 

Acidity as acetic acid 0.01% max. ISOAMYL ALCOHOL FORMS BINARY AZEOTROPES WITH ... 

As shown in Figure 8.44, the predicted ternary phase equihbria at 1 atm show three homogeneous azeotropes. T vo are binary (water/formic acid and water/acetic acid) and... 

Many investigations of the extraction of ethanol from water have postulated that a very high selectivity is needed to enrich the solvent-free extract to an ethanol content near or above the binary azeotrope with water. However, this degree of enrichment is not necessary. The extraction step can be followed by an extractive-distillation dewatering step similar to the process shown for acetic acid recovery in Fig. 15.2-3. 

We examine separation of the mixtures, concentration space of which contains region of existence of two hquid phases and points of heteroazeotropes. It is considerably easier to separate such mixtures into pure components because one can use for separation the combination of distillation columns and decanters (i.e., heteroazeotropic and heteroextractive complexes). Such complexes are widely used now for separation of binary azeotropic mixtures (e.g., of ethanol and water) and of mixtures that form a tangential azeotrope (e.g., acetic acid and water), adding an entrainer that forms two liquid phases with one or both components of the separated azeotropic mixture. In a number of cases, the initial mixture itself contains a component that forms two liquid phases with one or several components of this mixture. Such a component is an autoentrainer, and it is the easiest to separate the mixture under consideration with the help of heteroazeotropic or heteroextractive complex. The example can be the mixture of acetone, butanol, and water, where butanol is autoentrainer. First, heteroazeotropic distillation of the mixture of ethanol and water with the help of benzene as an entrainer was offered in the work (Young, 1902) in the form of a periodical process and then in the form of a continuous process in the work (Kubierschky, 1915). 

We now discuss a more complicated task separation of five-component mixture water(l)-methanol(2)-acetic acid(3)-acetone(4)-pyridin(5) with three binary azeotropes 15, 24, 35 (Petlyuk et al., 1985). Figure 8.12 shows seg-... 

For the second example, separation of mixture water(l)-methanol(2)-acetic acid(3)-aceton(4)-pyridin(5), both possible splits in first column with one feeding without distributed component 2,4 1,3,5 and 1,2,4 3,5, are not expedient because one of the products is binary mixture with azeotrope. 

---