Methanol acetone azeotrope

FIG. 13-60 Residue curves for acetone-chloroform-methanol system suggesting a ternary saddle azeotrope. 

As a result of the study of these systems, it has been found that the methanol-acetone azeotrope exhibits the unusual phenomenon of becoming nonazeotropic at both low and high pressures—that is, below 200-mm. pressure the system is nonazeotropic with methanol as the more volatile product, while above 15,000 mm. the system is nonazeotropic with acetone the more volatile component. 

Figure 3.10 shows typical RCM for nonideal mixtures involving azeotropes. For the mixture ace tone/heptane /benzene (plot a) there is only one distillation field. The problem seems similar to a zeotropic system, except for the fact that the minimum boiler is a binary azeotrope and not a pure component. With the mixture acetone/chloroform/toluene (plot b) there is one distillation boundary linking the high-boiler with the low-boiler azeotrope. Consequently, there are two distillation regions. Similar behavior shows the plot c, with two azeotropes. The mixture acetone/chloroform/methanol (plotd) has four azeotropes (3 binaries and 1 ternary) displaying a behavior with four distillation regions. 

Schematic DRDs are particularly useful in determining the implications of possibly unknown ternary saddle azeotropes by postulating position 7 at interior positions in the temperature profile. Also note that some combinations of binary azeotropes require the existence of a ternary saddle azeotrope. As an example, consider the system acetone (56.4°C), chloroform (61.2°C), and methanol (64.7°C) at 1-atm pressure. Methanol forms minimum-boiling azeotropes with both acetone (54.6°C) and chloroform (53.5°C), and acetone-chloroform forms a maximum-boiling azeotrope (64.5°C). Experimentally there are no data for maximum- or minimum-boiling ternary azeotropes for this mixture. Assuming no ternary azeotrope, the temperature profile for this system is 461325, which from Table 13-18 is consistent with DRD 040 and DRD 042. However, Table 13-18 also indicates that the pure-component and binary azeotrope data are consistent with three temperature profiles involving a ternary saddle azeotrope, namely, 4671325, 4617325, and 4613725. All three of these temperature profiles correspond to DRD 107. Calculated residue curve trajectories for the acetone-chloroform-methanol system at 1-atm pressure, as...

Donald F. Othmer while at Eastman Kodak during the 1920 s experimented using salts to concentrate acetic acid (14). He also developed an industrial process for distilling acetone from its azeotrope with methanol by passing a concentrated calcium chloride brine down the rectification column (15). Pure acetone was condensed overhead, and acetone-free methanol was recovered in a separate still from the brine which was then recycled. The improved Othmer recirculation still (16) has been the apparatus generally favored by investigators who have studied the effects of salts on vapor-liquid equilibrium. 

Since pentane and water exhibit immiscibility, we might consider decantation as the first step. If it worked, it would be an inexpensive one to carry out. But a rigorous three-phase equilibrium calculation predicts that, in the presence of acetone and methanol, the small water fraction in the feed does not form a second liquid phase so we reject this idea. The calculation also reveals that the feed mixture is almost at the azeotropic composition for the pentane/methanol binary pair. 

Figure 37 shows the results from carrying out a rigorous simulation for this option. Because pentane forms azeotropes with acetone and methanol, these species appear in both products. Noting that although F31 is a much smaller stream than F21. it has similar compositions, we decide to recycle it back to the extractor feed also. The bottom product of column DI-3 consists of acetone, methanol, and water-with no pentane. 

Physiological Activity of Aleksinac Shale Constituents. Quite recently, physiological activity of the polar constituents of Aleksinac shale bitumen, extracted with an azeotropic mixture of chloroform, acetone and methanol, was investigated (28). This preliminary study was based on an assumption that some of the biological... 

Acetone and methanol are impossible to separate by simple distillation due to the presence of an azeotrope. However, the addition of water near the top of a column allows these two components to be separated. Five sets of steady-state operating data for the extractive distillation of an acetone-methanol azeotrope in a laboratory scale column have been provided by Kumar et al. (1984). A schematic diagram of the column is provided in Figure 14.19. The column had a diameter of 15 cm and was fitted with 13 bubble cap trays, a total condenser and a thermosiphon (equilibrium) reboiler. Unlike many experimental distillation studies, these experiments were not carried out at total reflux the acetone-methanol feed entered the column on the eleventh stage from the top (the condenser counts as the first stage) and the water was introduced on stage six. The column was operated at atmospheric pressure for all five runs. Additional details of the column, operational specifications, and computed product compositions for one of these experiments can be found in Table 14.9. 

The use of a polar and a nonpolar solvent to separate acetone and methanol from a mixture of tetramethylene oxide and other oxides has been described by Hopkins and Fritsch.17 A schematic drawing of this purification process is shown in Fig. 6-1. The ternary azeotrope of acetone, methanol, and tetramethylene, a cyclic ether, may be broken by an extractive distillation using the highly polar solvent, water. The volatility of the methanol is lowered by the water to such an extent that the azeotrope of acetone and tetramethylene oxide may be distilled overhead in the extractive distillation column, and the methanol is withdrawn with the water from the bottom of the column. A second column is used to separate the azeotropic mixture of acetone and tetramethylene oxides by use of the relative nonpolar solvent, pentane. An azeotrope of pentane and acetone boiling at 32°C, is removed from the top of the column. The azeotrope is broken by adding water which results in the formation of two phases, a pentane phase and an acetone-water phase. 

Finally, Figure 9.4d illustrates a more complex situation, the mixture acetone/ chloroform/methanol, with four azeotropes (three binaries and one ternary). There are four distillation regions. Note that the ternary azeotrope is a saddle. 

Figure 9.6 shows the RCM for the mixture acetone/chloroform/methanol, for which the class is 311-S. The first digit represents the max-azeotrope acetone/chloroform, the second the minimum-azeotrope chloroform/methanol, the third the minimum-azeotrope acetone/methanol. The letter S signifies the ternary saddle azeotrope. More RCMs are presented in Perry (1997), from a total of 125 configurations. 

The method has been successfully applied to numerous systems, four of which are shown in Figure 2. The azeotrope methanol-methyl ethyl ketone became nonazeotropic at 3000 mm. of mercury after it was predicted that this would occur at 2000 to 4000 mm. The azeotrope methanol-acetone was studied in detail after it was predicted that the azeotropism would disappear at both low and high pressures. This system is nonazeotropic below 200 mm. of mercury and above 15,000 mm. compared to predicted limits of 200 to 500 mm. and 10,000 to 20,000 mm. While this is the only azeotropic system known to become nonazeotropic at both low and high pressures, there are indications that the phenomenon occurs in several other systems, contrary to the conclusions of Lecat that such systems probably do not exist (3). 

The binary azeotrope between acetone and methanol is the point with the lowest temperature on the map, and all profiles originate from this point. 

Comparing the two plots in Figure 2.8a and b, it can be seen that the composition of the low-boding binary azeotrope that exists between acetone and methanol has a strong dependence on pressure, moving from about 80 mol% acetone at 1 atm to 40mol% at 10 atm. More importantly, however, is to notice the change in the node type at pure acetone at 1 atm, pure acetone is a saddle point, while at 10 atm, this point becomes a stable node. Further, there is now also a saddle node in the form of a binary azeotrope between acetone and ethanol at 10 atm that never existed at 1 atm. 

A very interesting mixture is presented in Figs. 5.2-18 and 5.2-19. The mixture acetone/chloroform/methanol exhibits two binary minimum azeotropes, one binary... 

Fig. 5.2-19 Distillation lines of the system acetone/chloroform/methanol at a pressure of 1 bar. The boundary distillation lines, which run between the minimum and the maximum azeotropes, respectively, divide the mixture into four fields with different starting and endpoints of distillation lines...

An example of extractive distillation is the separation a binary mixture of acetone and methanol. These two components form a binary homogeneous minimum-boiling azeotrope. The normal boding points of acetone and methanol are 329 and 338 K, respectively, so acetone is the light-key component. The boding point of the azeotrope (328 K) is lower than the boding point of the pure light component. The composition of the acetone/methanol... 

Determine the azeotropic points of the system acetone (l)-methanol (2) at 50,100, and 150 ""C by the ratio of the activity coefficients and vapor pressures using the Wilson equation with the interaction parameters given in the table below. 

Figure 5.50 Ratio of the activity coefficients y]/y2 and ratio of the vapor pressures P /P of the system acetone (1)-methanol (2) for the determination of the azeotropic points at 50, 100, and 150 "C.

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