| Petroleum mixtures contain numerous types of hydrocarbon molecules. Characterizations of such complex mixtures are critical to kinetic modeling during refining, but providing such characterizations is a challenge. The isomeric lump in homologous series sets up the analytical limit for characterizing the composition of heavy petroleum oil. By minimizing the Gibbs free energy of the whole isomeric lump, subject to the stoichiometric constraint and the measured averaged boiling point of that lump, an optimization approach has been proposed to quantify the compositional distribution among the isomers. This thesis presents a computer-assisted deterministic approach for automatically generating hydrocarbons, optimizing the molecular geometry on-line, selecting the most possible molecules, distributing them within a measured isomeric lump, predicting the physical and thermodynamic properties of each molecule using Quantitative-Structure-Property-Relationship (QSPR) models, and, consequently, processing them to predict the properties of a mixture. The simulated results were compared with five diesel samples of measured properties for molecular weight, density, refractive index, and simulated distillation curves. Good agreements were found between predicted bulk properties and measured ones for all five diesel samples, and thus, these results indicated the proposed methodology could be used to derive the detailed molecular representation for middle distillates.; A new approach has been proposed to quantify the compositional distribution of different hydrocarbon isomers in an "isomeric lump" determined using gas chromatography - mass spectrometry (GC-MS) methods. It appears that by minimizing the Gibbs free energy of the mixture of the major isomers, subject to the stoichiometric constraint and the measured average boiling point of that isomeric lump, the concentration distribution of various isomers can be determined with good accuracy. The simulated compositions of the heptane isomers were compared with the reported analytical results for 18 crude oils. The correspondence between predicted and measured distributions was found to be good. The reported distributions of the heptane isomers are far from the thermodynamic equilibrium distribution, so the introduction of an average boiling point constraint helps these distributions match. With this delumping approach, the petroleum mixtures can be characterized at a molecular level, which is beyond the analytical limitations. |
