Measurement and prediction of vapour pressures of 2,6,10,14-tetramethylpentadecane (pristane)Experimental and Monte Carlo simulation results

Abstract

This work presents results obtained in the characterization of a long branched alkane, the 2,6,10,14-tetramethylpentadecane (pristane), by establishing vapour pressures following two ways of investigation. First, an experimental study has been done in order to perform measurements of low vapour pressures (from 300 to 450 K and from 0.3 to 2300 Pa) using an original apparatus described in a previous work [I. Mokbel, E. Rauzy, H. Loiseleur, C. Berro, J. Jose, Fluid Phase Equilib. 108 (1995) 103]. Then, molecular simulations have been performed, in order to predict, using Monte Carlo techniques, vapour pressures of pristane from 298 to 688 K. Two types of algorithm have been used: Gibbs Ensemble Monte Carlo to predict vapour pressures at high temperatures, and thermodynamic integration to extend the prediction to lower temperatures. Simulations have been performed using the branch point sampling technique (BPST) proposed by [M.D. Macedonia, E.D. Maginn, Mol. Phys. 96 (1999) 1375] and the anisotropic united atom (AUA) potential optimised in a previous work [E. Bourasseau, P. Ungerer, A. Boutin, A.H. Fuchs, J. Phys. Chem. B 97 (2002) 1985]. Both methods are presented, and comparison of the results shows good agreement. It is concluded that simulated results well reproduce experimental results obtained with the apparatus used to measure low vapour pressures of such heavy compounds. Intermolecular potentials, previously optimised on the basis of short alkanes, can be used directly to predict equilibrium properties of long branched alkanes by Monte Carlo simulation. Finally, this type of work appears really interesting for petroleum industry, because of the current lack of experimental data concerning branched alkanes containing more than 10 carbon atoms.