Supercritical refining of asphalts

Abstract

Supercritical (SC) pentane and cyclohexane provided fractionation of reduced crudes and asphalts from three sources. The gas oils present during reduced crude fractionation reduced solvent selectivity and contaminated the fractions. Subsequently, vacuum distillation or propane deasphalting must precede reduced crude SC separation for satisfactory results. Cyclohexane separations required high temperatures that caused thermal degradation of some feed constituents due to high solubility and poor heat transfer. Asphalts separated more efficiently and produced ten SC fractions. The whole asphalts and SC fractions were analyzed using Corbett fractionation, infrared analysis, gel permeation chromatography (GPC), atomic absorption, and mechanical spectroscopy. Corbett analyses demonstrated that the asphaltenes concentrate in the heaviest fractions and most of the saturates reside in the lightest fractions. Infrared analysis showed increasing aromaticity with fraction number, which correlated well with the viscosity for all asphalts and fractions investigated. GPC refractive index chromatograms indicated that the SC process separates roughly according to hydrodynamic volume. The nickel and vanadium concentrate in the heaviest fractions more than the iron, most of which results from processing contamination. Asphalts produced from the SC fractions proved far superior in aging characteristics than the original asphalts. Also, the aging properties of blends from the three refineries indicate reduced dependence on crude source. Analysis of the aging data acquired on the whole asphalt, asphalt blends, and selected SC fractions revealed that the reduction in metals during the supercritical refining of the asphalts was responsible for the improvement in aging performance. The metal content, especially nickel, correlated with the hardening susceptibility and hardening rates of the asphalts, blends, and SC fractions independent of crude source...