Electrodeposition of Asphaltenes. 1. Preliminary Studies on Electrodeposition from Oil−Heptane Mixtures

We investigated the behavior of asphaltic solids in an unstable crude oil Y3, its mixtures with heptane, and its isolated asphaltenes with respect to electrodeposition onto metal electrodes in direct current (DC) electric fields. Asphaltic material from the neat oil Y3 was found to possess a net negative charge, whereas its isolated asphaltene had a net positive charge when suspended in heptane.

The negative charge of the deposit from the oil reversed to positive when the electrodes with the deposit were transferred from the oil to heptane, which was manifested in the movement of the particles from the anode to the cathode. Mixing the oil with heptane prior to application of a DC electric field resulted in a gradual decrease of the amount of anodic deposit and an increase of the amount of cathodic deposit upon increasing the heptane/oil ratio, but that trend did not hold when small amounts of oil were added to heptane under a DC electric field.

Fourier transform infrared (FTIR) spectroscopy and high-performance liquid chromatography−size-exclusion chromatography (HPLC−SEC) data for electrode deposits obtained in the latter experiments showed that the cathodic material was more aromatic and appeared richer in carbonyl and sulfoxide groups than the anodic material.

Nevertheless, structural properties of cathodic as well as anodic deposits were distinct from those of resins and asphaltenes isolated from the crude oil Y3. Application of a DC electric field did not cause flocculation of asphaltenes in either a stable oil or a solution of asphaltenes in toluene.