Observation of Liquid Crystals in Heavy Petroleum Fractions

Abstract

In this work, we report for the first time the observation of naturally occurring discotic liquid-crystalline domains of ca. 100 μm in diameter in unreacted heavy fractions of petroleum. Precipitated solids from several bitumen and heavy oil samples exhibited the characteristic optical patterns of liquid crystals when observed under cross-polarized light. Samples included asphaltenes precipitated from Athabasca and Cold Lake bitumen (Canada), Maya heavy crude oil (Mexico), and Safaniya crude oil (Saudi Arabia) and a maltene fraction of Athabasca bitumen. The liquid-crystal domains appeared in asphaltene solids at ∼330 K in a nitrogen atmosphere and disappeared at ∼430 K. Upon cooling and subsequent reheating, the domains did not reappear. Liquid-crystal domains also appeared and then disappeared in the presence of toluene vapor at room temperature. Because the liquid crystals exhibit both thermotropic and lyotropic behavior, they are amphotropic. While amphotropic liquid crystals are known to arise in biological systems, the specific attributes of the liquid-crystal structures observed here are the first reported occurrence of such behavior in nature. The presence of liquid crystals in petroleum solids enriches our understanding of the complex phase and interfacial behavior of these materials and may provide new opportunities for partitioning petroleum.