Methanol binary azeotropes

Figure 5.3 gives the ternary diagram for the system. The acetone/methanol binary azeotrope is shown on the ordinate axis. The residue curves originate from this minimumboiling azeotrope and move to the heaviest component DMSO comer. Figure 5.4 shows the location of the distillate (D) and bottoms (B) products. The straight component-balance... 

The distillate D2 is fed to the C5-recovery column C3. This column operates at a pressure of 10 bar, which shifts the azeotropic composition so that the distillate stream from this column D3 has a composition of 34.2 mol% methanol. Note that this is slightly above the composition of the iCs-methanol binary azeotrope, but remember that there is a mixture of a number of C5 components in this system. Higher and lower pressures were explored to see their effect on the economics. The 10 bar pressure seems to be about the optimum since going above this pressure does not shift the azeotrope significantly and raises the base temperature, which would require higher-temperamre energy input. 

Isoprene [78-79-5] (2-methyl-1,3-butadiene) is a colorless, volatile Hquid that is soluble in most hydrocarbons but is practically insoluble in water. Isoprene forms binary azeotropes with water, methanol, methylamine, acetonitrile, methyl formate, bromoethane, ethyl alcohol, methyl sulfide, acetone, propylene oxide, ethyl formate, isopropyl nitrate, methyla1 (dimethoxymethane), ethyl ether, and / -pentane. Ternary azeotropes form with water—acetone, water—acetonitrile, and methyl formate—ethyl bromide (8). Typical properties of isoprene are Hsted in Table 1. 

Schematic DRD shown in Fig. 13-59 are particularly useful in determining the imphcations of possibly unknown ternary saddle azeotropes by postulating position 7 at interior positions in the temperature profile. It should also be noted that some combinations of binary azeotropes require the existence of a ternaiy saddle azeotrope. As an example, consider the system acetone (56.4°C), chloroform (61.2°C), and methanol (64.7°C). 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 ternaiy azeotropes. The temperature profile for this system is 461325, which from Table 13-16 is consistent with DRD 040 and DRD 042. However, Table 13-16 also indicates that the pure component and binary azeotrope data are consistent with three temperature profiles involving a ternaiy saddle azeotrope, namely 4671325, 4617325, and 4613725. All three of these temperature profiles correspond to DRD 107. Experimental residue cui ve trajectories for the acetone-...

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... 

The low equilibrium constant and the strongly nonideal behavior that causes the forming of the binary azeotropes methyl acetate/methanol and methyl acetate/ water make this reaction system interesting as a possible RD application (33). Therefore, methyl acetate synthesis has been chosen as a test system and investigated in a semibatch RD column. Since the process is carried out under atmospheric pressure, no side reactions in the liquid phase occur (146). 

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. 

As an example. Van Dongen (Ph.D. Thesis, University of Massachusetts, 1983) considered the separation of a methanol-methyl acetate mixture, which forms a homogeneous azeotrope, using n-hexane as an entrainer. The distillation boundaries for this system (Fig. 13-87a) are somewhat curved. A separation sequence that exploits this boundary curvature is shown in Fig. 13-87b. Recycled methanol—methyl acetate binary azeotrope and methanol-methyl acetate—hexane ternary azeotrope are added to the original feed FO to produce a net feed com-... 

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. 

The quantity of hexane necessary to entrain water, methanol, ethanol, acetone, and acetaldehyde dimethyl acetal to the top was estimated as the sum of the hexane quantities required to form the binary azeotropes with the quantities of water, methanol, ethanol, acetone, and acetaldehyde dimethyl acetal in the mixture. 

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. 

Properties Colorless liquid etherlike odor. Fp -88.68C, bp 63.2-65.6C, d 0.913 (20/4C), refr index 1.4320 (20C), flash p -22F (-30C). Insoluble in water 0.3 g/100 g water. Miscible with most organic solvents. Forms a binary azeotrope with methanol, a ternary azeotrope with methanol-water. 

The composition of the binary azeotrope of benzene and methanol is 60.5% benzene, 39.5% methanol. 

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). 

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. 

As an example, the separation of a butene/methanol/MTBE system is investigated. Methyl tertiary-butyl ether (MTBE) is the desired product, and hence needs to be efficiently recovered from a reactor output. Difficulty arises when separating such a mixture with conventional distillation processes, because of the binary azeotropes that exist between methanol and MTBE, as well as between methanol and butene. The driving force for separation in membrane processes differs from that in distillation, thus a membrane process will not exhibit the same azeotropic behavior. Thus, the limitations on distillation processes can be overcome by using a membrane unit. 

The D-RCM for the butene/methanol/MTBE system is shown in Figure 9.11a. The D-RCM reveals the presence of two binary azeotropes, which in turn create a distillation boundary, suggesting that separation by distillation only is a complex matter. 

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