Efficient water removal from water-in-oil emulsions by high electric field demulsification

Following hydrothermal liquefaction (HTL), microalgae bio-crude products contain approximately 5-20% water. High electric field (HEF) demulsification can separate water from settled oil based on electrostatic charge. In this study, we investigated the effect of HEF demulsification on water-in-oil (W/O) emulsions as a model bio-crude emulsion using a batch-type coalescer. Three W/O emulsions of soybean oil, medium-chain triglyceride (MCT) oil, and castor oil (10 wt% water content) were prepared and exposed to an alternating current electric field at different voltages (1000-4000 V) and frequencies (50-2000 Hz) for 1 h. Water content in castor oil samples declined to 9.6-8.6 wt% from the initial 10 wt% as the applied voltage increased at 50 Hz after 1 day storage. A noticeable difference in the remaining water in the oil occurred between samples exposed to 50 Hz and 500 Hz at 4000 V. The water content declined to 1.8 and 1.4 wt% (MCT oil); 4.3 and 1.8 wt% (soybean oil); and 8.4 and 8.1 wt% (castor oil) at 50 Hz and 500 Hz, respectively, at 4000 V. Moreover, HEF demulsification consumed negligible energy compared to centrifugation (1.37 x 10(3) J/kg versus 2.71 x 10(10) J/kg).