Phase-equilibrium calculations for n-alkane + alkanol systems using continuous thermodynamics |
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| Institution: | 1. Departamento de Ingeniería Electromecánica, Escuela Politécnica Superior, Universidad de Burgos, E-09006 Burgos, Spain;2. Institut Supérieur des Professions Infirmières et Techniques de Santé Tétouan – Annexe Tanger, 93040 Tétouan, Morocco;3. Ecole Nationale des Sciences Appliquées d’El Jadida, Université Chouaib Doukkali-El Jadida, 24002 El Jadida Plateau, Morocco;1. Multimedia and Computer Vision group, School of Computer and Systems Engineering, Universidad del Valle, Ciudad Universitaria Meléndez, Cali, Colombia;2. Computer Vision and Image Processing group, School of Science and Engineering (Computing), University of Dundee, Queen Mother Building, Dundee DD1 4HN, Scotland, UK;3. Coal Science and Technology group, Chemical Engineering School, Universidad del Valle, Ciudad Universitaria Meléndez, Cali, Colombia;1. LATA2M, Laboratoire de Thermodynamique Appliquée et Modélisation Moléculaire, University of Tlemcen, Post Office Box 119, Tlemcen 13000, Algeria;2. Research Group TERMOCAL, Thermodynamics and Calibration, University of Valladolid, Escuela de Ingenierias Industriales, Paseo del Cauce 59, E-47011 Valladolid, Spain;1. Department of Chemical Engineering. Brigham Young University, Provo, UT 84604, USA;2. Distinguished Professor, Aalborg University, Aalborg, Denmark |
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| Abstract: | A new association model based on continuous thermodynamics is introduced and applied to six systems of the type n-alkane (n-hexane, n-heptane, n-octane) + alkanol (methanol, ethanol). The alkanol is considered to be a mixture of chain associates with the composition described by a continuous distribution function. This distribution function is derived as an analytical expression from the mass action law applied to the association equilibrium. To consider the entropic contribution originating from the size differences of the molecules (associates) activity coefficients based on Flory–Huggins model are included in the mass action law. Unlike the molecular-mass distribution of a polymer the chain-length distribution of the associates depends on the temperature and on the mole fraction of the alkanol. The treatment of vapor–liquid equilibrium and liquid–liquid equilibrium is similar to that of an oil system or of a polymer solution using continuous thermodynamics. Different to other chemical models of association there is no additive split into a physical and a chemical contribution. The equilibrium constants of association were fitted to vapor-pressure data of methanol and ethanol. The model needs only one interaction parameter being independent of temperature and taking the same value for all systems studied. Considering the simplicity of the model, both the liquid–liquid equilibrium of the three methanol systems and the vapor–liquid equilibrium of all six systems are predicted with reasonable accuracy. |
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