Browsing by Author "Fouad, Wael A."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Application of molecular modeling to the vapor–liquid equilibrium of alkyl esters (biodiesel) and alcohols systems
    (Elsevier, 2015) Corazza, Marcos L.; Fouad, Wael A.; Chapman, Walter G.
    This work is focused on the thermodynamic modeling of systems related to biodiesel processing using the Perturbed Chain form of the Statistical Associating Fluid Theory (PC-SAFT). Different binary ester + ester and methanol or ethanol + ester systems were investigated. The PC-SAFT equation of state was able to predict the vapor–liquid equilibrium and solid–liquid equilibrium of different esters + esters binary systems. Furthermore, using a transferable cross-association parameters approach, the phase behavior of alcohols + alkyl esters of biodiesel was successfully predicted for a wide range of pressure and temperature conditions. Polar interactions seem to play a minor role in determining the phase behavior of mixtures considered in this work.
  • Thumbnail Image
    Item
    High pressure measurements and molecular modeling of the water content of acid gas containing mixtures
    (Wiley, 2015) Fouad, Wael A.; Yarrison, Matt; Song, Kyoo Y.; Cox, Kenneth R.; Chapman, Walter G.
    Water content of three carbon dioxide containing natural gas mixtures in equilibrium with an aqueous phase was measured using a dynamic saturation method. Measurements were performed up to high temperatures (477.6 K = 400°F) and pressures (103.4 MPa = 15,000 psia). The perturbed chain form of the statistical associating fluid theory was applied to predict water content of pure carbon dioxide (CO2), hydrogen sulfide (H2S), nitrous oxide (N2O), nitrogen (N2), and argon (Ar) systems. The theory application was also extended to model water content of acid gas mixtures containing methane (CH4). To model accurately the liquid-liquid equilibrium at subcritical conditions, cross association between CO2, H2S, and water was included. The agreement between the model predictions and experimental data measured in this work was found to be good up to high temperatures and pressures.
  • Thumbnail Image
    Item
    Isolating the non-polar contributions to the intermolecular potential for water-alkane interactions
    (AIP Publishing LLC., 2014) Ballal, Deepti; Venkataraman, Pradeep; Fouad, Wael A.; Cox, Kenneth R.; Chapman, Walter G.
    Intermolecular potential models for water and alkanes describe pure component properties fairly well, but fail to reproduce properties of water-alkane mixtures. Understanding interactions between water and non-polar molecules like alkanes is important not only for the hydrocarbon industry but has implications to biological processes as well. Although non-polar solutes in water have been widely studied, much less work has focused on water in non-polar solvents. In this study we calculate the solubility of water in different alkanes (methane to dodecane) at ambient conditions where the water content in alkanes is very low so that the non-polar water-alkane interactions determine solubility. Only the alkane-rich phase is simulated since the fugacity of water in the water rich phase is calculated from an accurate equation of state. Using the SPC/E model for water and TraPPE model for alkanes along with Lorentz-Berthelot mixing rules for the cross parameters produces a water solubility that is an order of magnitude lower than the experimental value. It is found that an effective water Lennard-Jones energy εW/k = 220 K is required to match the experimental water solubility in TraPPE alkanes. This number is much higher than used in most simulation water models (SPC/E—εW/k = 78.2 K). It is surprising that the interaction energy obtained here is also higher than the water-alkane interaction energy predicted by studies on solubility of alkanes in water. The reason for this high water-alkane interaction energy is not completely understood. Some factors that might contribute to the large interaction energy, such as polarizability of alkanes, octupole moment of methane, and clustering of water at low concentrations in alkanes, are examined. It is found that, though important, these factors do not completely explain the anomalously strong attraction between alkanes and water observed experimentally.