Adam T. Pauli

RELATIONSHIPS BETWEEN ASPHALTENES, HEITHAUS COMPATIBILITY PARAMETERS, AND ASPHALT VISCOSITY

ABSTRACT Historically, asphalt rheology has been described in terms of a colloidal model, which depicts asphalts as dispersions of asphaltenes in petrolenes (maltenes). The model leads to a classification of asphalts into sol, gel, or intermediate categories. Sol and gel type asphalts exhibit differences in physical and chemical behavior. Sol asphalts also are described as compatible, while gel asphalts are described as non-compatible. The relative viscosity of an asphalt, defined as the quotient of the viscosity of the whole asphalt divided by the viscosity of the n-heptane soluble maltene fraction at a given temperature and rate of shear is one measure of asphalt compatibility. Based on this definition of compatibility, asphalts with low values of relative viscosity are designated as compatible and higher values of relative viscosity are designated as incompatible. Asphalt compatibility is also related to the asphaltene content, where asphalts with low asphaltene content are designated as compatible. It...

Predicting coke formation tendencies

New coking indexes were developed to measure how near a pyrolysis system is to coke formation during the coke formation induction period. These are based on an asphaltene flocculation titration and the cyclohexane soluble portion of heptane asphaltenes. Coking indexes were determined for five residua before and after pyrolysis for 60 and 90 min at 400°C. The coking indexes appear to be universal for all the materials studied. The theoretical basis is based on the dispersed particle solution model of residua structure. Coking onset is coincidental with the destruction of the ordered structure and the formation of a bimodal system. Nuclear magnetic resonance (NMR) imaging showed the presence of two and three phase systems in the toluene soluble portions of residua pyrolyzed for 90 min. Results also show that initial coke formation can be related to the free solvent volume. A relationship was observed between free solvent volume and the amount of initial coke make at 400°C. The results provide a new tool for ranking residua, gauging proximity to coke formation, predicting initial coke make tendencies.

Molecular weight polarity map for residua pyrolysis

Abstract A new molecular weight/polarity map was developed for petroleum residua based on the Scatchard–Hildebrand solubility equation. A series of extractions is performed with solvents of increasing solubility parameter, and the fractions are analyzed by vapor pressure osmometry for number average molecular weight, and analytical scale size exclusion chromatography for molecular weight spread. The results are diagnostic of the layers of solvation by resin-type molecules around a central asphaltene core. As thermal treatment progresses, the solubility parameter of the components of residua fractions increases, and the apparent molecular weight decreases. Coking onset appears to coincide with the depletion of resin-type asphaltene solubilizing components of residua and the formation of a bimodal system.