The phase equilibria of binary and ternary mixtures of light/heavy hydrocarbons is crucial for the design and optimization of various process in chemical and petrochemical industry. Such mixtures are the binaries of methane with tetradecane, hexadecane, eicosane and many others. The higher the difference in the carbon number the higher the divergence of the critical and melting temperatures. The vapor-liquid equilibrium region for each mixture of methane with a heavy alkane spans from temperatures higher than the normal melting temperature of the heavy component up to its critical temperature. Thus, methane is always supercritical and therefore the constant temperature phase diagram should close to the critical point of the mixture. Despite the importance of light/heavy mixtures, the availability of vapor-liquid equilibria data from experiments or simulations is scarce. Traditionally, cubic (e.g Peng-Robinson) or higher order (e.g SAFT) equations of state are utilized for such phase equilibria calculations. However, the predicting ability of cubic equations of state is often poor for mixtures that the asymmetry is high and also many adjustable parameters are needed in order to be in fairly good agreement with the experiments. Alternatively, molecular simulations have been used extensively during the last two decades for VLE calculations and they are proven to be a reliable and accurate tool. To that extent a great number of molecular models, describing the intra- and inter-molecular interactions, were developed.
This study aims in performing phase-equilibria calculations for important light/heavy mixtures of hydrocarbons by employing well established Monte Carlo (MC) simulations techniques, such as Gibbs Ensemble (GEMC), Configurational Bias (CBMC) and Fractional Component Monte Carlo (CFCMC)[1,2]. The accuracy and predicting ability range of various force fields[3,4] to reproduce pure component and mixture properties is assessed. To that extent, the data obtained from our Monte Carlo simulations are compared with available experimental data and EOS modeling (e.g. PC-SAFT). For mixtures lacking experimental data, the obtained MC data can be used to fit EOS parameters and to guide experimentalists to choose state points.
[1] A. Z. Panagiotopoulos, Mol. Phys. 61, 813-826 (1987).
[2] A. Torres-Knoop, S. P. Balaji, T. J. H. Vlugt and D. Dubbeldam, J. Chem. Theory Comput. 10, 942-952 (2014).
[3] M. G. Martin and J. I. Siepmann, J. Phys. Chem. B 102, 2569-2577 (1998).
[4] C. Herdes, T. S. Totton and E. A. Muller, Fluid Phase Equil. 406, 91-100 (2015).
