Acetone/methanol equilibria

Acetic acidMBK/water extraction, 468 Acetic acid purificatibn, 547 Acetic anhydride reactor, 573 Acetone/methanol equilibria, 416 Acetone/water equilibria, 423 Acetonitrile... 

Many papers concerning salt effect on vapor-liquid equilibrium have been published. The systems formed by alcohol-water mixtures saturated with various salts have been the most widely studied, with those based on the ethyl alcohol-water binary being of special interest (1-6,8,10,11). However, other alcohol mixtures have also been studied methanol (10,16,17,20,21,22), 1-propanol (10,12,23,24), 2-propanol (12,23,25,26), butanol (27), phenol (28), and ethylene glycol (29,30). Other binary solvents studied have included acetic acid-water (22), propionic acid-water (31), nitric acid-water (32), acetone-methanol (33), ethanol-benzene (27), pyridine-water (25), and dioxane-water (26). 

Differences in results can occur between tests in a liquid and a gaseous medium. This is often because different times are required to reach equilibrium temperature, and if crystallisation is occurring, for example, the stiffness will be dependent on time of conditioning. It is also essential that if a liquid medium is used the liquid does not affect the rubber by swelling it or removing extractables, as either process can have a considerable effect on low temperature behaviour. Ethanol is most widely used but acetone, methanol, butanol, silicone fluid and n-hexane are all suggested in ISO 2921. Not all of these will be suitable for all rubbers and the suitability of any proposed liquid must be checked by preliminary swelling tests. 

Table 5 Equilibrium Constants (K, ), Relaxation Times (t) and Intersystem Crossing Rate Constants (kx, k t in Equation 21) For Some [Fe(X-salmeen)] f Complexes in Acetone/Methanol Solution1...

VER chart, 372 Vapor-liquid equilibrium data acetone/methanol, 416 acetone/water, 416,423 butadiene, 420... 

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 boiling point-equilibrium data for the system acetone-methanol at 760 mm Hg are given in Table 18.7. A column is to be designed to separate a feed analyzing 25 mole percent acetone and 75 mole percent methanol into an overhead product containing 78 mole percent acetone and a bottom product containing 1.0 mole percent acetone. The feed enters as an equilibrium mixture of 30 percent liquid and 70 percent vapor. A reflux ratio equal to twice the minimum is to be used. An external reboiler is to be used. Bottom product is removed from the reboiler. The condensate (reflux and overhead product) leaves the condenser at 25°C, and the reflux enters the column at this temperature. The molal latent heats of both components are 7700 g cai/g mol. The Murphree plate efficiency is 70 percent. Calculate (a) the number of plates required above and below the feed (b) the heat required at the reboiler, in Btu per pound mole of overhead product (c) the heat removed in the condenser, in Btu per pound mole of overhead product. 

Potentiometric measurements with a silver-silver chloride and glass electrode pair in liquid junction-free systems have proved suitable for equilibrium studies in solutions prepared with various non-aqueous solvents (e.g. dimethyl sulphoxide, acetonitrile, acetone, methanol, ethylene glycol) [Bu 75a]. 

Such a process depends upon the difference in departure from ideally between the solvent and the components of the binary mixture to be separated. In the example given, both toluene and isooctane separately form nonideal liquid solutions with phenol, but the extent of the nonideality with isooctane is greater than that with toluene. When all three substances are present, therefore, the toluene and isooctane themselves behave as a nonideal mixture and then-relative volatility becomes high. Considerations of this sort form the basis for the choice of an extractive-distillation solvent. If, for example, a mixture of acetone (bp = 56.4 C) and methanol (bp = 64.7°Q, which form a binary azeotrope, were to be separated by extractive distillation, a suitable solvent could probably be chosen from the group of aliphatic alcohols. Butanol (bp = 117.8 Q, since it is a member of the same homologous series but not far removed, forms substantially ideal solutions with methanol, which are themselves readily separated. It will form solutions of positive deviation from ideality with acetone, however, and the acetone-methanol vapor-liquid equilibria will therefore be substantially altered in ternary mixtures. If butanol forms no azeotrope with acetone, and if it alters the vapor-liquid equilibrium of acetone-methanol sufficiently to destroy the azeotrope in this system, it will serve as an extractive-distillation solvent. When both substances of the binary mixture to be separated are themselves chemically very similar, a solvent of an entirely different chemical nature will be necessary. Acetone and furfural, for example, are useful as extractive-distillation solvents for separating the hydrocarbons butene-2 and a-butane. 

We now illustrate the above statements by considering the results of barrier height calculations for six prototype (three dimethyl and three single methyl) molecules ethane, dimethyl ether (DME), acetone, methanol, acetaldehyde, and propene. The equilibrium and metastable top-of-barrier conformers are shown in Figures 1 and 2 and Table 2. These systems, because... 

Yan, W. Topphoff, M. Zhu, M. Gmehling, J. Measiu ment and correlation of isobaric vapor-liquid equilibrium data for the system acetone + methanol + zinc chloride. J. Chem. Eng. Data 1999, 44, 314-318. 

Kurihara, K. Hori, H. Kojima, K. Vapor-liquid equilibrium data for acetone + methanol + benzene, chloroform + methanol + benzene, and constituent binary systems at 101.3 kPa. J. Chem. Eng. Data 1998, 43, 264-268. 

Application of the algorithm for analysis of vapor-liquid equilibrium data can be illustrated with the isobaric data of 0th-mer (1928) for the system acetone(1)-methanol(2). For simplicity, the van Laar equations are used here to express the activity coefficients. 

Vapor-Liquid Equilibrium Data Reduction for Acetone(1)-Methanol(2) System (Othmer, 1928)... 

In some instances, distinct polymorphic forms can be isolated that do not interconvert when suspended in a solvent system, but that also do not exhibit differences in intrinsic dissolution rates. One such example is enalapril maleate, which exists in two bioequivalent polymorphic forms of equal dissolution rate [139], and therefore of equal free energy. When solution calorimetry was used to study the system, it was found that the enthalpy difference between the two forms was very small. The difference in heats of solution of the two polymorphic forms obtained in methanol was found to be 0.51 kcal/mol, while the analogous difference obtained in acetone was 0.69 kcal/mol. These results obtained in two different solvent systems are probably equal to within experimental error. It may be concluded that the small difference in lattice enthalpies (AH) between the two forms is compensated by an almost equal and opposite small difference in the entropy term (-T AS), so that the difference in free energy (AG) is not sufficient to lead to observable differences in either dissolution rate or equilibrium solubility. The bioequivalence of the two polymorphs of enalapril maleate is therefore easily explained thermodynamically. 

The effect of inert solutes, such as calcium chloride, magnesium chloride and sucrose, can also be employed judiciously and efficaciously in the development of solutions to difficult extraction problems by allowing efficient extractions from the water into such solvents as acetone, ethanol and methanol that are found to be completely miscible with water in the absence of salt. Matkovitch and Cristian found the above three inert solutes to be the best agents for salting acetone out of water. It has been observed that the acetone layer that separated from a saturated aqueous solution of CaCl2 exclusively contained 0.32 0.01% water (v/v) and 212 ppm salt (w/w) at equilibrium. 

This interconversion can also be performed in solvents, and the rate of the isomerization is dependent on the solvent used. In the dipolar aprotic solvent DMSO the rate of the reaction is fast, but in methanol, acetone, or dioxane the rate is low. However, the value of the equilibrium constant is scarcely influenced by the solvent ( 134/133 = 6-10) (75JHC985).This is not too surprising, since the equilibrium position is controlled by the relative thermodynamic stability of the isomers, which is a function of their heats of formation and of solvation. Undoubtedly, the heat of formation is the more important factor to the thermodynamic stability (75JHC985). 

In each case, the products other than acetaldehyde must be recycled to reform the substrate. For example, 2,2-dimethoxypropane yields acetaldehyde, acetone, and methanol according to Equation 12. The reaction is carried out at 135 C and 2250 psig with a cobalt catalyst. Iodide promoters are not required. The acetaldehyde rate is typically 4.0 M/hr and the selectivity is 60-70%. The co-produced acetone and methanol are recycled in a separate step via the equilibrium represented by Equation 14. 

The following abbreviations are used in Tables I and II A = acetone, B = benzene, C = chloroform, D = dichloromethane, E = ethanol, M = methanol, P = pyridine, W = water, eq = equilibrium rotation value, / = furanoside, p = pyranoside, and R = 2-acetamido-2-deoxy-D-glucose see also Ref. 99. 

Maher, P. J., and B. D. Smith, Vapor-liquid equilibrium data for binary systems of chlorobenzene with acetone, acetonitrile, ethyl acetate, ethylbenzene, methanol and 1-pentene , J. Chem. Eng. Data, 24, 363-377 (1979). 

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