Characterizing the wax-asphaltene interaction and surface morphology using analytical spectroscopy and microscopy techniques

Abstract

In this study, the effect of wax-asphaltene molecular interaction and crude oil property on the amount of wax appearance temperature (WAT) along with the size and morphology of the wax crystals were investigated. For this purpose, three crude oil samples selected, and their WAT value is determined using a cross-polarized microscope (CPM) method. The spectroscopy analysis of crude oil samples demonstrated that the morphology of wax crystals in CPM images depends mainly on the functional groups existing in crude oil. The presence of polar functional groups such as hydroxyl, increasing the aliphatic compounds, and reducing the percentage of aromatics in crude oil leads to wax crystals to become rounded, and their uniformity rise. The size of the wax crystals is associated with the crude oil aromaticity index. Increasing the aromatic rings in the structure of crude oil creates larger wax crystals. However, the amount of WAT depends on the molecular structure of the wax and asphaltene besides their interaction. If the wax molecule is mainly paraffinic and the percentage of cyclic compounds is low, the interaction between the poly-aromatic asphaltene molecule with the wax molecules significantly decreases; thus, the asphaltene cannot act as a nucleation point for the wax particles, and the WAT value reduces. The shape of the wax particles in SEM images is closely related to its molecular structure. If the wax constituent of crude oil is microcrystalline, the interaction between the wax and asphaltene increases. Therefore, the wax particles will be observed rounded under SEM. If the wax has both cyclic and paraffinic compounds, its crystals will be seen in the plate-type form. Furthermore, if the wax constituent is macrocrystalline, the wax particles will have a hive-type shape and cover the entire surface of the image.