Study of colloidal nature of petroleum with an automated Bonse–Hart X-ray small-angle scattering unit

A Bonse–Hart small-angle X-ray diffractometer was interfaced to an automated X-ray diffraction system and used to study the colloidal nature of crude oil. Asphaltic colloids, which have a radius of gyration of 20 to 40 Å in many oils, were found to grow in size to several thousand Å on addition of straight and branched-chain aliphatic hydrocarbons. Addition of cyclic and aromatic hydrocarbons produced little change in colloid size. Two types of large colloids, having radii of gyration of several hundred to several thousand Å, were found in some crude oils in addition to the mentioned asphaltic ones. One of the larger colloids is wax. The other seems closely associated with the asphaltene colloids and is present in the asphaltene fraction on precipitation of the asphaltene with pentane. The use of ultracentrifugation, deasphalting, and temperature variation allowed mixtures of colloids to be studied in more detail than could be single oil samples.