Dilution VLE Data

PBAD Acetone PBMA Methyl Ethyl Ketone 

PBAD Benzene PBMA Methyl Isobutyl Ketone 

PBAD Methyl Ethyl Ketone PBMA n-Propanol 

PMMA o-Dichlorobenzene PPeMA Methyl Ethyl Ketone 

PMMA Ethylene Glycol PPM A Methyl Ethyl Ketone 

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There are no thermodynamic consistency tests that can be applied to the data. For each system in the infinite dilution VLE data base, the weight fraction activity coefficients were plotted as a function of temperature. In many cases considerable scatter was observed. Some data were found that were significantly outside the anticipated range or which showed contradictory behavior with temperature from that expected. These points were kept in the data base but are indicated by an "R", for Rejected, if they were judged to be clearly erroneous or by an "N", for Not recommended, if they appeared questionable but not obviously incorrect. Similarly, in the finite concentration VLE data base some points were judged to be significant outliers and are indicated accordingly. 

Van Ness and Abbott, Int. DATA Ser., Ser. A, Sel. Data Mixtures, 1978 67 (1978)] and excess enthalpy data [Morris et al.,/, Chem. Eng. Data 20 403-T05 (1975)] are available. The VLE data are well correlated by the Margules equations. As noted in connection with Eq. (4-270), parameters Ai and A i relate directly to infinite dilution values of the activity coefficients. Thus, we have from the VLE data at 323.15 K ... 

Where K a is the mass transfer coefficient, C is the VOC concentration in the solvent in equilibrium with the vapor phase, C is the actual solvent VOC concentration, and J is the flux of the VOC. Raising the temperature will cause C to approach zero. For the dilute VOC in the solvent, small values of C cause the flux to approach zero and separation does not occur. By using membranes with their large area to volume ratio, the mass transfer coefficient can be increased by an order of magnitude or more compare to a conventional packed column (33). This increase in area will enhance flux despite small values of C, thus making the separation more feasible. The VLE data needed to evaluate the MASX/MADS process are currently being collected. It is expected that this process wiU perform well. 

Figure 3.5.7. VLE correlation of the methyl acetate and cyclohexane binary system at 313 K with the 2PVDW mixing rule and the PRSV equation of state. Solid lines are model predictions obtained by direct correlation of VLE data, and the dashed lines are predictions using infinite dilution activity coefficient data. See text for details. (Points are experimental data from the DECHEMA Chemistry Series, Gmehling and Onken 1977, Vol. 1, Pt. 5, p. 392 the data file for this system on the accompanying disk is MAC640.DAT.)...

Torress-Marchal, C., Cantalino, A. L., and De Brito, R. M., 1989. Prediction of vapor-liquid equilibria (VLE) from dilute systems data using the SRK equation of state Industrial applications. Fluid Phase Eq., 52 111-117. 

This equation is also a solution to the Gibbs-Duhem equation. The constants may be calculated from infinite dilution activity coefficients or from a single VLE data point. 

Polymer-solvent VLE Vapor-hquid data, both at intermediate concentrations and at the infinite dilution of the solvent, are available in two extensive databases DECHEMA and DIPPR Polymer Project. - These databases are also available in electronic form. The data are restricted to single solvent systems and often cover various temperatures. A more recent compilation of VLE has been published by Wohlfarth. Basically low-pressure VLE data are available. Very few high-pressure VLE data exist for polymer-solvent systems (with nongasesous solvents), e.g., the work by Surana et al. ... 

If one has no access to experimentally determined VLE data it is possible to calculate (using Van Laar, Wilson or UNIQUAC equations) activity coefficients throughout the composition range from values available in the literature for activity coefficients of the two components at infinite dilution (y ) in each other. 

Column 5 of Table 13.8 is mostly drawn from the Dechema VLE data series and from the Dechema activity coefficients at infinite dilution series. The references, which are drawn from the latter, are identified by starting with lx. This group is mostly recorded at 25 °C and is more useful for LLE calculations. The values of y drawn from VLE data are derived from distillation experiments and are therefore more relevant to y information taken at or near the boiling point of the system. However, there are a great many pairs of solvents for which the value of y has not been published and for these the UNIFAC system has been used to give a calculated value. For a smaller number, there are no UNIFAC interaction parameters available and for these an estimate has been made. 

Equation-of-state approaches are preferred concepts for a quantitative representation of polymer solution properties. They are able to correlate experimental VLE data over wide ranges of pressure and temperature and allow for physically meaningful extrapolation of experimental data into unmeasured regions of interest for application. Based on the experience of the author about the application of the COR equation-of-state model to many polymer-solvent systems, it is possible, for example, to measure some vapor pressures at temperatures between 50 and 100 C and concentrations between 50 and 80 wt% polymer by isopiestic sorption together with some infinite dilution data (limiting activity coefficients, Henry s constants) at temperatures between 100 and 200 C by IGC and then to calculate the complete vapor-liquid equilibrium region between room temperature and about 350 C, pressures between 0.1 mbar and 10 bar, and solvent concentration between the common polymer solution of about 75-95 wt% solvent and the ppm-region where the final solvent and/or monomer devolatilization process takes place. Equivalent results can be obtained with any other comparable equation of state model like PHC, SAFT, PHSC, etc. 

D17. A nonvolatile solute is dissolved in 1.0 kmol of methanol. We wish to switch the solvent to water. Because the solution is already concentrated, a first batch distillation to concentrate the solution is not required. We desire to have the solute in 1.0 kmol of solution that is 99.0 mol% water and 1.0 mol% methanol. This can be done either with a constant-level batch distillation or by diluting the mixture with water and then doing a sinple batch distillation. VLE data (ignore the effect of the solute) are in Table 2-7. Do a constant-level batch distillation fromxjyf jj i = 1.0 (pure methanol) to Xj = 0.01. Find the moles of water added during the constant-level batch... 

In the case of complete data, this means VLE data, where P, T, x, y,- is given, also the deviation between the experimental and predicted activity coefficients or excess Gibbs energies can be used to fit the required binary parameters. Furthermore the parameters can be determined by a simultaneous fit to different properties to cover properly the composition and temperature dependence of the activity coefficients. For example, the deviation of the derived activity coefficients can be minimized together with the deviations of the activity coefficients at infinite dilution, excess enthalpies, and so on. Accurate activity coefficients at infinite dilution measured with sophisticated experimental techniques are of special importance, since they deliver the only reliable information about the real behavior in the dilute range [23], for example, at the top or the bottom of a distillation column. Excess enthalpies measured using flow calorimetry are important too, since they provide the most reliable information about the temperature dependence of the activity... 

VLE data, the results of two thermodynamic consistency tests, and the parameters of different -models, such as the Wilson, NRTL, and UNIQUAC equation. Additionally, the parameters of the Margules [28] and van Laar [29] equation are listed. Furthermore, the calculated results for the different models are given. For the model which shows the lowest mean deviation in vapor phase mole fraction the results are additionally shown in graphical form together with the experimental data and the calculated activity coefficients at infinite dilution. In the appendix of the data compilation the reader will find the additionally required pure component data, such as the molar volumes for the Wilson equation, the relative van der Waals properties for the UNIQUAC equation, and the parameters of the dimerization constants for carboxylic acids. Usually, the Antoine parameter A is adjusted to A to start from the vapor pressure data given by the authors, and to use the -model parameters only to describe the deviation from Raoult s law. Since in this data compilation only VLE data up to 5000 mm Hg are presented, ideal vapor phase behavior is assumed when fitting the parameters. For systems with carboxylic acids the association model is used to describe the deviation from ideal vapor phase behavior. 

Figure 5.31 Result of the fit of temperature-independent Wilson parameters to consistent isobaric VLE data at 1 atm of the system ethanol (l)-n-decano (2) and calculated results for the excess enthalpies and activity coefficients at infinite dilution for...

To obtain the correct values at infinite dilution and the correct temperature dependence resp. excess enthalpies, besides VLE data further reliable thermodynamic information should be taken into account for fitting temperature-dependent... 

The calculated separation factor is shown in Figure 11.6 together with the experimental values derived from the VLE data published by different authors, the calculated results using the default model parameters from different g -models, and the mean separation factor (dashed line) calculated from the scattering experimental VLE data. It can be seen that the most reliable separation factor is obtained using the activity coefficient at infinite dilution for fitting the binary parameters. 

In Section 11.4, it was shown how suitable solvents can be selected with the help of powerful predictive thermodynamic models or direct access to the DDB using a sophisticated software package. A similar procedure for the selection of suitable solvents was also realized for other separation processes, such as physical absorption, extraction, solution crystallization, supercritical extraction, and so on. In the case of absorption processes or supercritical extraction instead of a g -model, for example, modified UNIFAC, of course an equation of state such as PSRK or VTPR has to be used. For the separation processes mentioned above instead of azeotropic data or activity coefficients at infinite dilution, now gas solubility data, liquid-liquid equilibrium data, distribution coefficients, solid-liquid equilibrium data or VLE data with supercritical compounds are required and can be accessed from the DDB. 

A better method of calculation for multicomponent mixtures has been developed by Wilson [3]. The binary parameters still must be determined from experimental VLE data. This method applies to mixtures of polar and nonpolar molecules (such as n-hexane and ethanol) that are strongly nonideal. Also, this method has the ability to model nonideal systems, even in dilute regions. However, this method does not predict curves exhibiting maximum or minimum values of y, nor will it predict immiscibility. 

Much of the early work was conducted with dilute (-15 wt%) MEA solutions because such solutions were commonly used in commercial plants at the time since higher concentrations were considered too corrosive. With the advent of corrosion inhiUted solutions and a better understanding of corrosion mechatusms, more concentrated solutions have become popular. This is reflected in the recent VLE data, which typically covers both 15 and 30 wt% solutions. More data are provided for MEA than for the other amines because of its widespread and long time commercial use. Also, many of the conclusions for MEA, such as the general effects of temperature, amine concentration, and the presence of other acid gases are also applicable to other amines. 

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