UNIFAC parameters

Chemical Thermodynamics for Process Simulation. First Edition. 

Jurgen Gmehling, Barbel Kolbe, Michael Kleiber, and Jlirgen Rarey. 

Further parameters were published in the following reference 

The following internet site www.ddbst.com contains the entire list of the published UNIFAC group interaction parameters. The revised and extended UNIFAC group interaction parameter matrix is only available for the sponsors of the UNIFAC consortium www.unifac.org.  

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Magnussen, T., Rasmussen, P. and Frednenslund, A. (1981) Ind. Eng. Chem. Proc. Des. and Dev. 20, 331. UNIFAC parameter table for prediction of liquid-liquid equilibria. 

In contrast to the NRTL-SAC model, the UNIFAC model developed by Fredenslund et. al. [29] divides each molecule into a set of functional groups that interact with each other on a binaiy basis and whose interactions are combined together to describe the global liquid phase interaction between molecules. Because the segments in UNIFAC are based on functional groups it is possible to model a system provided that all of the molecular structures are known. The problem with pharmaceutical sized molecules is that existing UNIFAC parameter tables do not contain many of the group interaction parameters that are necessary, and even when they do, the interactions are fitted to a database of chemicals that are much smaller and simpler than pharmaceuticals, and typically fail to represent them adequately. 

Magnussen, T., P. Rasmussen, and A. Fredenslund. 1981. UNIFAC Parameter Table for Prediction of Liquid-Liquid Equilibria. Ind. Eng. Chem. Process Des. Dev. 20 331-339. 

The application of UNIFAC to the solid-liquid equilibrium of sohds, such as naphthalene and anthracene, in nonaqueous mixed solvents provided quite accurate results [11]. Unfortunately, the accuracy of UNIFAC regarding the solubility of solids in aqueous solutions is low [7-9]. Large deviations from the experimental activity coefficients at infinite dilution and the experimental octanol/water partition coefficients have been reported [8,9] when the classical old version of UNIFAC interaction parameters [4] was used. To improve the prediction of the activity coefficients at infinite dilution and of the octanol/water partition coefficients of environmentally significant substances, special ad hoc sets of parameters were introduced [7-9]. The reason is that the UNIFAC parameters were determined mostly using the equihbrium properties of mixtures composed of low molecular weight molecules. Also, the UNIFAC method cannot be applied to the phase equilibrium in systems containing... 

The application of UNIFAC to the solubility of naphthalene in nonaqueous mixed solvents provided satisfactory results when compared to experimental data (Acree, 1984). However, the UNIFAC was inaccurate in predicting the solubilities of solids in aqueous solutions (Fan and Jafvert, 1997). Furthermore, the application of the traditional UNIFAC to mixtures containing a polymer or another large molecule, such as a drug, and low molecular weight solvents is debatable (Fredenslund and Sprensen, 1994). The reason is that the UNIFAC parameters were determined mostly... 

Less success has been obtained to date in predicting Ue as compared with vie data. The absolute mean deviation between experimental and calculated mole fractions for 17 ternary lie test systems is found to be 9.22 mole %. To improve fitting of data, UNIFAC parameters have been redetermined based on lie data, and a new table of interaction parameters has been prepared by Magnussen et al. [12] while keeping the pure-component parameters/ and Q unchanged. Using the lie parameters, the fitting of data is improved. The absolute mean deviation between data and calculations is reduced to 1.73 mole % for the same 17 text mixtures. 

Of course, all the calculations here are approximate. In particular, we have used UNIFAC, which is not meant to be applicable to liquid-liquid equilibrium, and further, —25°C is below the temperature at which the UNIFAC parameters were obtained, so. the results we have obtained are not expected to be accurate. Therefore, all the conclusions should be checked against experimental data. As examples of the uncertainty of such predictions, from experimental data it is found that the amount of ethylene glycol required to result in a mixture freezing point of —25°C is closer to 45 wt % than the - 57 wt % estimated here, and that -pentanol is actually only soluble in water to about 2 j wt %, rather than the complete miscibility found here. This should serve as a warning concerning the use of any completely predictive method, even the UNIFAC model, which is currently the best. 

UNIFAC is not reliable for LLE, which is more difficult for modelling than VLE. Note that VLE and LLE make use of different UNIFAC parameters. 

Modem software has built-in UNIFAC automatic decomposition algorithms. Check the availability of the UNIFAC parameters when the molecule decomposition is not obvious, or it contains less common atoms. Note also that there are several updates of UNIFAC parameters. 

First the activity coefficients at infinite dilution of n-hexane in water and water in n-hexane at 25 ""C have to be calculated. Using the modified UNIFAC parameters given in Appendix I an activity coefficient at infinite dilution of 6618 for n-hexane in water and a value of 135.9 for water in n-hexane is obtained. With these values directly the solubilities can be calculated ... 

Original UNIFAC parameters Q Published PSRK parameters... 

In order to apply this algorithm to the technical side of mathematics, the parameters of the technological factual situation to be improved must be recorded in terms of mathematical models (Fig. 3.1). In doing so, generally speaking a distinction can be drawn between sequential and parameter optimizations. The task of determining the UNIFAC parameter set happens to be a sequential optimization. 

Macedo, E. A. Mendonca, J. M. Medina, A. G. Vapor-hquid equilibrium of the systems ethyl formate-methyl ethyl ketone, ethyl formate-toluene and ethyl formate-methyl ethyl ketone-toluene new UNIFAC parameters for interactions between the groups ACHmCOO, ACCH2mCOQ and CH2CQ/HCOO Fluid Phase Equilib. 1984,18,197-210... 

Kassmann, K.-D. Knapp, H. Design of a differential pressure cell. VLE of aldehyde systems and new UNIFAC parameters. Fluid Phase Equilib. 1986, 29, 241-248. 

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