(181d) Application of An Association Model to Complex Fluids

The SAFT equation of state (EoS) was originally proposed thirty years ago, and much work has been done to improve and extend the application of SAFT since then. There are however still several issues regarding associating fluids which needs to be addressed. One of these issues is how we should treat large complex associating chemicals. Alcohols, amines, water and glycols have all been more or less satisfactorily modeled with SAFT and the time has therefore come to extend the models to compounds with multiple/different functional groups, e.g. alkanolamines or amino acids. In this work we use a simplified SAFT method (the CPA EoS [1]) where the repulsive, dispersion and chain terms are substituted by SRK.

We apply the CPA EoS to three alkanolamines; monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA), using a so-called first-level approach where the capabilities of the model have been investigated under certain simplifying assumptions. No special treatment of polarity is used, only the association term of CPA/SAFT is employed. We use existing association schemes, like 2B and 4C [2] as well as two new schemes within the same framework. Two different association schemes are investigated for each alkanolamine; one with which we make no distinction between O and N, and one where we ignore the amine group and only consider the association of the hydroxyl group, which is known to associate stronger. The parameters, where the association of the amine group has been included, seem to give more satisfactory results than the others.

Pure component parameters are usually fitted to pure component vapor pressure and liquid density, but we find that additional data is necessary in order to obtain reliable parameters, e.g. binary LLE data with an inert compound.

The parameters obtained in this way provide satisfactorily results for LLE and for alkanolamine-water VLE. Large negative values are, however, typically needed for the interaction parameter in the latter case, which is in agreement with previous results for other aqueous cross-associating mixtures, e.g. water-alcohols and water-glycols [3-5]. Comparisons with other models will be included.

References

[1] G.M. Kontogeorgis, E.C. Voutsas, I.V. Yakoumis, D.P. Tassios, Ind. Eng. Chem. Res. 35 (1996) 4310-4318.

[2] S.H. Huang, M. Radosz, Ind. Eng. Chem. Res., 29 (1990) 2284-2294.

[3] G.K. Folas, J. Gabrielsen, M.L. Michelsen, E.H. Stenby, G.M. Kontogeorgis, Ind. Eng. Chem. Res, 44 (2005) 3823-3833

[4] S.O. Derawi, G.M. Kontogeorgis, M.L. Michelsen, E.H. Stenby, Ind. Eng. Chem. Res, 42 (2003) 1470-1477

[5] M. Kaarsholm, S.O. Derawi, M.L. Michelsen, G.M. Kontogeorgis, Ind. Eng. Chem. Res, 44 (2005) 4406-4413