Phase Behaviour in Certain CO2 + n-Alkane + 1-Alkanol Systems Experiments and Modelling

Phase Behaviour in Certain CO2 + n-Alkane + 1-Alkanol Systems Experiments and Modelling

Smits, J.C.

Gauter, K. (mentor)
Peters, C.J. (mentor)
de Swaan Arons, J. (mentor)

Applied Sciences

Chemica! Technology and Materials Science

Applied Thermodynamics and Phase Equilibria

1996-05

In the experimental part of this study, critical endpoints in the ternary systems carbon dioxide (CO2) + n-tridecane + 1-pentanol and carbon dioxide + n-tridecane + 1- hexanol were determined. These critical endpoints were determined in a so-called Cailletet apparatus. All experiments were carried out at constant CO2 mole fractions of 0.95. In the system carbon dioxide + n-tridecane + 1-pentanol, the transition from type II to type IV fluid phase behaviour was observed, coming from the CO2 + 1-pentanol side. This transition is characterized by the occurrence of a tricritical point with coordinates x* = 0.819, T = 318.85 K, P = 9.45 MPa. x* refers to the tridecane mole fraction on a CO2-free basis. In the system carbon dioxide + tridecane + 1-hexanol, transitions from type III -> type IV -> type II -> type IV fluid phase behaviour were observed, coming from the CO2 + 1-hexanol side. The transitions between type II and type IV are characterized by the occurrence of two tricritical points with coordinates x* = 0.855, T = 318.40 and P = 9.339 MPa and x* = 0.216, T = 319.81 and P = 9.356 MPa. The transition between type III and type IV is characterized by a double critical end point with coordinates x* = 0.029, T = 295.43 and P = 6.11 MPa. The experimentally observed phenomena are consistent with the already presented transitions in CO2 + n-alkane + 1-alkanol systems. The observed transitions in phase behaviour can qualitatively be explained by a global phase diagram originally developed by Van Konynenburg and Scott. In the modelling part of this study, phase behaviour of CO2 + alkane + 1-alkanol systems was calculated as a function of the average solute chain length in the mixture. In these calculations it was assumed that ternary CO2 + n-alkane + 1-alkanol systems are congruent to CO2 + n-alkane systems, when taking alkanol aggregation into account. Alkanol aggregation has been calculated by two models, the first assuming a mono-disperse aggregate distrubution and the second a poly-disperse distribution. Six CO2 + n-alkane + 1-alkanol systems were modelled. For some observed phase transitions in carbon dioxide + n-alkane + 1-alkanol systems, the modelling is quantitative and for others, only a qualitative description was obtained. The results calculated with the mono-disperse model were in general slightly better than those obtained by the more complex poly-disperse model. The system CO2 + tridecane + hexanol was an exception. The polydisperse model yielded better results for this system. Model values for the aggregation number and equilibrium constant, estimated from fitting to the experimental results, were found to be almost equal to literature values obtained from IR spectroscopy.

http://resolver.tudelft.nl/uuid:ab0a04f3-3491-4314-a95c-a943aff2f955

Student theses

master thesis

J.C. Smits