No abstract

No abstract

The molecular representation of hydrocarbon mixtures is critical to the advanced kinetics modeling of refining conversion processes; however, the achievement of such a representation is considered a significant challenge. The isomeric lump in a homologous series sets the analytical limit in analytical characterization of middle and heavy distillates. This paper proposes a new procedure for de-lumping detailed analytical information generated using a gas chromatography−field-ionization mass spectrometry (GC−FIMS) method into a molecular representation. As a result, concentration distributions of the various molecules in the sample of interest are calculated. This paper presents a deterministic computer-assisted procedure that automatically (i) generates hydrocarbon molecules according to literature-based set of rules, (ii) selects the hydrocarbon molecules that are most thermodynamically stable (likely to exist), (iii) optimizes the three-dimensional geometry of those molecules and calculates their thermodynamic properties, and (iv) calculates the concentration distributions of those molecules. A separate validation calculation involves (i) prediction of the physical properties for pure hydrocarbons using quantitative structure−property relationship (QSPR) correlations; and (ii) prediction of bulk physical properties of this mixture using the calculated concentrations, properties of its pure hydrocarbon components, and suitable mixing rules. This procedure was applied to find molecular representations of five middle-distillate samples and the results were validated through the estimation and comparison of such simulated and measured physical properties as density, refractive index, and simulated distillation curves (the latter of which are used as a consistency check). Good agreement was observed between the predicted and measured properties for all five middle-distillate samples. This agreement validates the molecular characterization algorithm, at least for the purpose of bulk property prediction in middle distillates.

This paper proposes a new approach to quantify the compositional distribution of different hydrocarbon isomers in an “isomeric lump” of a crude oil, determined using gas chromatography−mass spectrometry (GC-MS) methods. The concentration distribution of isomers can be determined with good accuracy by minimizing the Gibbs free energy of the mixture containing a set of isomers, subject to the stoichiometric constraint and the measured average boiling point of that isomeric lump. The simulated compositions of the hexane and heptane isomers were compared with the reported analytical results for 18 crude oils. The correspondence between predicted and measured distributions was found to be satisfactory. The experimental distributions of hexane and heptane isomers in those crudes are far from the thermodynamic equilibria, but the introduction of additional experimental information, in the form of the average boiling point of the lump, made it possible to model its isomeric distributions. This finding is important for the derivation of molecular representation for distillates in advanced kinetics modeling of refinery conversion processes.

A model for particle settling velocities in polydisperse suspensions is proposed alongside normalized particle self and interaction mobilities. The model predictions are compared with other models (Davis and Gecol, 1994; and Al‐Naafa and Selim, 1989), as well as published experimental data. A general agreement was found between the current model and the existing data for binary dispersed particle systems except for one case where ΦL is fixed. For ternary dispersed particle systems, predictions from both the A‐S model and the current model agree well with the existing data. With the improved sedimentation coefficients, the D‐G model also produces satisfactory results.