Electrokinetic behavior of asphaltene particles

The effect of electrostatic field on the aggregation rate and aggregate size of asphaltene particles precipitated from three different crude oil samples suspended in a mixture of toluene and n-heptane (a model oil) was investigated. An electrode-embedded glass micro-model utilizing a high-voltage direct current power supply was utilized in this study. The asphaltene particle size and the rate of aggregation under the electric field were monitored using a high-resolution optical microscope and the average aggregate size for asphaltene particles was estimated using image processing software. To investigate the effects of structural parameters on asphaltene aggregation rate, aggregate size and electro-deposition, the elemental analyses for the three asphaltene samples were carried out and the mass ratios for C, H, N, S and O elements present in the asphaltene samples were determined. Also, the functional groups of asphaltene molecules were analyzed using the FTIR technique. Asphaltene molecules with larger chromophore and higher complexity exhibited faster aggregation behavior under the electrical field. The asphaltene aggregation rate was found to be directly proportional to the number of hetero-atoms on asphaltene molecules. The effects of parameters such as the electric field intensity, exposure time, asphaltene concentration, the amount of precipitant, and the asphaltene molecular structure on the asphaltene aggregation rate and aggregate size under the electrostatic field were also investigated. The electrostatic field strongly affected the aggregation rate of asphaltene particle; under an electrostatic field, asphaltene particles tended to aggregate faster and this may have resulted in faster and a larger quantity of asphaltene particles that precipitated out of the quiescent mixture of toluene and n-heptane. It should be also stated that for higher voltage applied to the mixture, a higher aggregation rate and larger aggregate size of asphaltene particles were observed.