Direct calculation of bubble points for alkane mixtures by molecular simulation

A Force Field for Poly(oxymethylene) Dimethyl Ethers (OMEn)

A united atom force field for the homologous series of the poly(oxymethylene) dimethyl ethers (OMEn), H₃C-O-(CH₂O)_n-CH₃, is presented. OMEn are oxygenates and promising new synthetic fuels and solvents. The molecular geometry of the OMEn, the internal degrees of freedom, and their electrostatic properties were obtained from quantum mechanical calculations. To model repulsion and dispersion, Lennard-Jones parameters were fitted to the experimental liquid densities and vapor pressures of pure OMEn (n = 1-4). The critical properties of OMEn (n = 1-4) were determined from the simulation data. Additionally, the shear viscosity of pure liquid OMEn is evaluated and compared with literature data. Finally, the solubility of CO₂ in OME2, OME3, and OME4 is predicted using a literature model for CO₂ and the Lorentz-Berthelot combining rules. The results agree well with experimental data from the literature.

Molecular simulations of the n -alkane liquid-vapor interface: interfacial properties and their long range corrections

Monte Carlo simulations have been performed to study the interfacial properties of the liquid-vapor interface of alkanes. We highlight the chemical equilibrium of the liquid-vapor interface by calculating a local chemical potential including the appropriate long-range corrections profiles. We extend the "test-area" (TA) technique developed by Gloor [J. Chem. Phys. 123, 134703 (2005)] on Lennard-Jones and square-well fluids to molecular systems. We establish both operational expressions of the TA approach for the calculation of the surface tension profile and the corresponding long-range corrections by underlining the approximations used. We compare the results between the different operational expressions of the surface tension and focus on the truncation procedures to explain the difference between the different techniques using either the potential or force equations. We make the results of surface tension identical between the different methods by using consistent potential and force equations. In the case of a relatively small cutoff, we propose to show that the Irving-Kirkwood definition and TA methods lead to the same value of the surface tension under condition that appropriate long-range corrections be included in the calculation. We end this paper by calculation of the entropy change profile and a comparison with experiments.