(537g) Molecular-Level Composition Model for Heavy Petroleum Resid Supercritical Fluid Extraction Fractions
The utilization of an increasing content of heavy petroleum feedstocks forms a challenge for refineries around the world. The high content of aromatic and heteroatom species in resids leads to fouling and catalysts deactivation during catalytic processing. Prior separation will improve the ability to handle these feedstocks and permit obtaining maximum yields of the valuable liquid product by removing contaminates. Supercritical fluid extraction (SFE) technology, developed 20 years ago, separates heavy petroleum resid into several deep cuts by adjusting the solubility of supercritical solvent. Selectively processing different fraction in heavy petroleum resid based on their property can thus be achieved. Compositional variation during SFE is important for organizing the separation/reaction processes networks. However, due to the complexity of heavy petroleum molecules, this is not yet well understood.
In the present work, we developed a molecular-level composition model for heavy petroleum resid supercritical fluid extraction fractions. In the first stage, a structural attribute (core, inter-linkage and sidechain) library was built by the knowledge of heavy petroleum chemistry. Molecular identities in the fraction were determined by juxtaposition of the structural attributes from the library. The concentrations of constructed molecules were calculated by sampling probability density functions (PDFs) for the attributes. The properties of the fractions were then calculated from group contribution methods and structure-property correlations. The PDFs parameters were tuned by a global optimization algorithm to fit the experimental data points to obtain quantitative results. There were ~20,000 molecules in compositional model, including aromatic hydrocarbon and heteroatom species.
Molecular compositions for a series of heavy petroleum resid SFE fractions were thus calculated. The overall solubility parameters show good agreement with experimental measurement. By comparing the solubility parameters distribution, the separation efficiency of the extraction unit was obtained. Molecular distribution for different SFE fractions was also discussed and compared with mass spectrometry results. The present model will provide understanding of heavy petroleum processing and lead to optimization of its use.