Studies on large crude oil alkanes. I. High temperature liquid chromatography

Isolation of very large alkane components from heavy oil fractions and solid deposits was achieved by high temperature medium pressure liquid chromatography (MPLC). n-Heptane and silicagel were the selected solvent and adsorbent employed for routine analysis. Preadsorption of the sample proved to be the most convenient injection technique. Porosity of adsorbents and stepwise temperature gradients were assessed to influence the generation of diverse-multimodal solid phases. Total elution of complex mixtures was possible if high temperature was adopted during the entire experiment and, this behavior was rationalized on the basis of mutual cosolvency of very broad alkane distributions. Isolated fractions were characterized by high temperature size exclusion chromatography (SEC), technique that allowed to detect very large alkanes preconcentrated during the stepwise separations. Porosity of solid asphaltenes was inferred and diffusional plus crystallization effects were proposed to explain all these findings.