Characterization of the Charge Carriers in Bitumen

Abstract

This work aims to identify the nature of the charge carriers in Athabasca bitumen to better understand the mechanisms of emulsion stabilization and electrically induced separations. A quartz crystal microbalance (QCM) with nanogram sensitivity is used to determine the electrodeposited mass in toluene-based systems. The use of low voltages for the first time allows a small amount of deposited material to be determined accurately. The method consists of applying a DC voltage between two gold-coated QCM crystals immersed in toluene solutions of asphaltenes, maltenes, or solid-free bitumen. Application of a 250 V/cm electric field strength produces an electrocollection of cationic and anionic species at the negatively and positively charged QCM crystals, respectively. A small fraction of the electrocollected material eventually electrodeposits and forms a transparent colorless film at the electrode surfaces. The specific mass (i.e., mass over charge) is found to be higher for the positive species than it is for the negative species. With this method, the characteristic time of relaxation of the bituminous solutions is estimated during the early stage of voltage application. This time could be used to establish a minimum frequency criterion for the critical field methods of water electrocoalescence in oil. Solids separated from bitumen are mainly negatively charged, and their specific mass is relatively high. This study shows that electrodeposition can efficiently separate solids and solid-stabilized water droplets from bitumen. Thus, an electrostatic treatment processes could be successful in removing solids and water from diluted bitumen systems.