Methanol phase equilibria

A mixture of cyclohexane and cyclopentane is to be separated by liquid-liquid extraction at 25°C with methanol. Phase equilibria for this system may be predicted by the van Laar equation with constants given in Example 5.11. Calculate, by the ISR method, product rates and compositions and interstage flow rates and compositions for the conditions below with ... 

Relative to our phase equilibrium study in Chapters 4 and 5, the above three techniques are illustrated on the phase diagram of Figure 7.18, as AT = 0, AT = 0, and 10% methanol, for depressurization, thermal stimulation, and inhibitor injection, respectively. Additional explanation is given in the figure caption. 

Taken from K. Roth, G. Schneider, and E. U. Franck, Liquid-Liquid and Liquid-Solid Phase Equilibriums in Cyclohexane-Methanol and Phenol-Water Systems up to 6000 Bars , Ber. Bunsenges. Physik. Chem., 70, 5-10 (1966). 

The experimental and predicted results for the ternary system carbon dioxide-methanol-water are listed in Table 7. Chang and Rousseau [47] have measured the solubilities of carbon dioxide in methanol-water mixtures at differents pressures and at temperatures below the critical temperature of carbon dioxide while Yoon [51] have measured the liquid and vapor phase equilibrium composition but overestimates shightly these of carbon dioxide in the liquid phase. 

For a first approximation to the solution, we will assume that essentially all the methanol condenses, with only trace amounts appearing in the recycle line. We will also assume that most of the water condenses and that very small amounts of carbon monoxide, carbon dioxide, hydrogen, methane, and nitrogen dissolve in the condensate. To account for methanol and water vapor in the recycle gases and the solubility of the gases in the crade methanol, we would have to include phase equilibrium relationships in the analysis. As stated earlier, several condensable byproducts, high and low-boiling compounds in the cmde methanol, are present in small amounts, as shown in Table 3.5.1. We will not consider these compounds in the synthesis-loop analysis. 

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. 

Of particular interest to those in the natural gas industry is the phase diagram of hydrate systems in the presence of inhibitors. Fig. 3 shows the phase diagram for methane hydrates in the presence of methanol and a NaCl and KCl mixture. The solid line is the three-phase equilibrium curve for methane in pure water. As seen from Fig. 3, forming hydrates in the presence of either an alcohol or salt increases the pressure required for gas hydrate formation, at a given temperature. 

Of the above-mentioned techniques, thermodynamic inhibitors, which include alcohols, salts, and glycols, are by far the most prevalent. For example, adding methanol to a natural gas will shift the equilibrium conditions so that a higher pressure is required to form hydrates, at a given temperature, as illustrated for methane in Fig. 3. Methods for estimating the saturation water content of natural gases and amounts of methanol or glycol required to suppress hydrate formation are discussed by Katz, Sloan,and Campbell. Current practice for the estimations is to use computer software based on phase equilibrium calculations. ... 

Using the H-X Diagram. Fnthalpy and phase equilibrium data for the methanol (l)/water (2) mixture are given below ... 

Robinson, D. B., D. Y. Peng, and S. Y.-K. Chung. 1985. The development of the Peng-Robinson equation and its application to phase-equilibrium in a system containing methanol. J. Fluid Phase Equil. 24 25-41. 

Special consideration is given to the effect of completely miscible cosolvents such as methanol and ethanol. A new approximate method of predicting cosolvent effects is presented. The results should be useful in supplying necessary phase equilibrium data to complex computer programs for modeling transport and fate of sparingly soluble organics in the environment. 

In this study, the phase equilibrium in the binary mixtures that are expected to be found in the flash distillation was modeled with the Predictive Soave-Redlich-Kwong (PSRK) equation of state [4], using modified molecular parameters r and q. Five binary ethanol + congener mixtures were considered for new yield values for parameters r and q. The congeners considered were acetic acid, acetaldehyde, furfural, methanol, and 1-pentanol. Subsequently, the model was validated with the water + ethanol binary system, and the 1 -pentanol + ethanol + water, 1-propanol + ethanol + water, and furfural + ethanol + water ternary systems. 

Furter [91] has analyzed the state of the art from the point of view of employing the salt effect in industrial processes, especially in extractive distillation. In addition, he ha.s made up a list of references covering the years 1966 to 1977 [91 a]. Schubert et al. [92] investigated the effect of some metal chlorides and other salts on the isothermal = 60°C) phase equilibrium behaviour of the systems n-propanol-water, n-butanol-water and methanol-water. Using CH30H/H20/NaBr as an example, the method of predicting salt effects for vapour-liquid equilibria as developed by Schuberth has been extended to uusaturated solutions [92a]. 

FIGURE 5.20 A feasible design for the acetone/wato/methanol system showing unique distillation regions, using the NRTL phase equilibrium model at 1 atm. 

Figure 7.40 Transformed compositions for isobutene, methanol, and MTBE in chemical an) phase equilibrium. (Reprinted from Doherty and Buzad, 1992).

Figure 9.13 gives a ternary diagram for the isopentane-methanol-TAME system at 4 bar. The phase equilibrium of this system is complex because of the existence of azeotropes. The UNIFAC physical property package in Aspen Plus is used to model the VLB in all units except the methanol/water column where the van Laar equations are used because of their ability to accurately match the experimental data. 

Scharfer et al. set up a multi-component transport model to describe the diffusion driven mass transport of water and methanol in PEM [170]. For a PEM in contact with liquid methanol and water on one side and conditioned air on the other, the corresponding differential equations and boundary conditions were derived taking into account the polymers three-dimensional swelling. Phase equilibrium parameters and unknown diffusion coefficients for Nafion 117 were obtained by comparing the simulation results to water and methanol concentration profiles measured with confocal Raman spectroscopy. The influence of methanol concentration, temperature and air flow rate was predicted by the model. Although there are indications for an influence of convective fluxes, the measured profiles are ascribed to a Fickean diffusion. Furthermore, the assumption to describe the thermodynamic phase equilibrium as liquid-type equilibrium also at the lower surface of the membrane, which is in contact with a gas phase, can be confirmed by their results. 

Assuming that 1000 compounds are of technical interest, phase equilibrium information for about 500000 binary systems are required to fit the required binary parameters to describe aU possible binary and multicomponent systems. Although more than 64500 VLE data sets for nonelectrolyte systems have been published up lo now, VLE data are available for only 10300 binary systems, since for a few systems a large number of data sets were published, for example, for the systems ethanol-water, ammonia-water, water-carbon dioxide, methanol-water, methane-nitrogen more than 150 data sets are available. This means that only for 2% of the required systems at least one VLE data set is available. If only... 

Figure 11.14 Phase equilibrium behavior of the ternary system acetone-chloroform-methanol at atmospheric pressure calculated using modified UNIFAC. (a) Tx-behavior (b) lines of constant separation factors (ofi2 = 1, 0fi3 = 1, of23 = l)l...

Formaldehyde is a low-boiling substance with a normal boiling point of approx. 254 K. It is not stable in its pure form, so it usually occurs in aqueous or methanolic solutions. Mixtures of formaldehyde and water or alcohols are not binary solutions in the usual sense, as formaldehyde reacts with both of them to a wide variety of species which are not stable as pure compounds themselves. Therefore, the standard procedure for building up a thermodynamic model by setting up the pure component properties and the binary interaction parameters fails in this case. The formaldehyde-water-methanol system is a good example freactive phase equilibrium, where a special model has to be developed. This has been done by the group of Maurer [2-6]. 

The equilibrium constants, the UNIFAC interaction parameters, and the vapor pressure parameters of the components which do not exist in pure form have to be fitted simultaneously to phase equilibrium data and reaction equilibrium data obtained from spectroscopic measurements for the systems formaldehyde-water, formaldehyde-methanol, and the ternary system formaldehyde-water-methanol, for which large amounts of data are available. To keep the significance of the particular parameters, a number of simplifying assumptions are made. 

High pressure fluid phase equilibrium data of polyglycerol in carbon dioxide and methanol... 

Horstmann, S. Mougin, P. Lecomte, F. Fischer, K. Gmehling, J. Phase equilibrium and excess enthalpy data for the system methanol + 2,2 -diethtmolamine -t water/. Chem. Eng. Data 2002,47,1496-1501... 

Kontogeorgis, G.M., Yakoumis, I.V., Meijer, H., Hendriks, E.M., Moorwood, T. Multicomponent Phase Equilibrium Calculations for Water Methanol Alkane Mixtures. Fluid Phase EquiUbr. 1999 158 201. 

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