Effect of ultrasonic frequency on separation of water from heavy crude oil emulsion using ultrasonic baths

In this work, a comprehensive study was performed for the evaluation of ultrasound (US) frequency for demulsification of crude oil emulsions. Experiments were performed using ultrasonic baths operating at the following frequencies: 25, 35, 45, 130, 582, 862 and 1146 kHz. Synthetic water-in-oil emulsions with 12%, 35% and 50% of water and medians of droplet size distribution (DSD, D(0.5)) of 5, 10 and 25 μm were prepared using a heavy crude oil (API density of 19). Crude oil demulsification was achieved at frequencies in the range of 25–45 kHz for all tested emulsions. When frequencies higher than 45 kHz were applied, no changes in the characteristics of the crude oil emulsions were observed. Demulsification efficiencies of about 65% were achieved at a frequency of 45 kHz after 15 min of US application (emulsions with original water content of 50% and D(0.5) = 10 μm). An important aspect is that no addition of chemical demulsifiers was performed, and the demulsification efficiency was considered high, taking into account that the results were obtained using a non-conventional crude oil. Contrary to the normal application of low-frequency US that has been used for emulsification, the proposed approach seems to be a promising technology for water removal from crude oil emulsions.