(425b) Towards a Generalized Molecular Model for Upstream and Downstream Applications

Authors: 
Fouad, W. A., Rice University
Wang, L., Rice University
Haghmoradi, A., Rice University
Cox, K. R., Rice University
Chapman, W. G., Rice University

Phase equilibrium experiments, Fourier-transformed infrared (FT-IR) spectroscopy measurements, molecular dynamic (MD) simulations and the Perturbed Chain form of the Statistical Associating Fluid Theory (PC-SAFT) were used to understand the interactions in water + alkane, alcohol + alkane, alcohol + aromatic and water + alcohol binary systems. Modeling water + alkane mixtures has been a long standing challenge. Using molecular simulation, it was found that an effective water Lennard-Jones energy of 220 K is required to match the experimental water solubility in TraPPE alkanes. A similar value of dispersion energy was required when PC-SAFT was applied. These numbers are significantly higher than that used in most of the water simulation models (78.2 K for SPC/E). The reason behind such discrepancy is yet to be found. Nevertheless, the application of the new SAFT water model was extended to predict water content of sweet and sour natural gas mixtures in equilibrium with an aqueous or a hydrate phase. In general, alcohols and water exhibit similarities in terms of structure and physical interactions. As a result, studying the interactions in alcohol + alkane systems might provide insight into the water + alkane problem.  The Polar PC-SAFT equation of state was used to model the system vapor-liquid equilibrium (VLE), activity coefficients and extents of association. The model showed a good agreement with spectroscopic and simulation data on the fraction of free alcohol monomers. Moreover, the alcohol model was used to predict the thermodynamics of weak hydrogen bonds formed between alcohols and the π-electrons of the aromatic rings. Results were compared with spectroscopic data and showed an acceptable agreement. Finally, using the knowledge gained in understanding water interactions, cluster formation in alcohol + water binary systems was studied using molecular theory and MD simulations.