Phase Equilibria Predictions of Binary Mixtures of Light/Heavy Hydrocarbons by Monte Carlo Simulations

Abstract

For the design and optimization of different processes and technologies in the chemical and petrochemical industry, the knowledge of the accurate vapor-liquid phase equilibrium of hydrocarbons and their binary mixtures is fundamental. The main focus of this thesis is the binary mixtures of methane with various n-alkanes and the binary mixture of methane and toluene, at temperatures ranging from 400 to 650 K and pressures ranging from 2 MPa to 50 MPa. Despite the currently increased importance of these asymmetric binary mixtures of methane and long n-alkanes due to Enhanced Oil Recovery technologies and depletion of old, easily accessible and highly profitable hydrocarbon reservoirs, the available vapor-liquid equilibrium (VLE) data from experiments are scarce or unknown.Currently, the most common practice for volumetric and phase behavior calculations in the industry is based on different cubic, such as Peng-Robinson, SRK or on higher order equations of state like PC-SAFT . However, the predicted data by equations of state are not accurate enough, due to the lack of experimental data. This is more pronounced for high temperature and pressure conditions or in the vicinity of the critical point. This thesis aims to produce vapor-liquid phase equilibrium data for binary mixtures of methane with various long n-alkanes by performing Monte Carlo molecular simulations in the Gibbs ensemble with TraPPE force field. The simulation results are used to validate the applied TraPPE force field by comparing its results to available experimental data. At extrapolated conditions, the new data are compared to PC-SAFT predictions in order to assess the performance of the CBMC technique and to highlight the deviations between the CBMC and PC-SAFT results. Additionally, this new data could be used to adjust the parameters of the applied PC-SAFT equation of state to achieve better predictions at extrapolated conditions.