Coalescence behavior of aqueous drops in water-in-oil emulsions under high-frequency pulsed AC fields

High-frequency pulsed alternating current field (HFPACF) has attracted attentions owing to its excellent performances of eliminating short circuit, saving energy and reducing environmental pollution. To study the coalescence mechanism of aqueous drops in water-in-oil (W/O) emulsions under HFPACF, micro behavior of dispersed drops for W/O emulsion was monitored by using a self-designed micro-visual model and coalescence mechanism was analyzed by discussing effects of pulse amplitude, pulse frequency, pulse width ratio, demulsifier concentration, aqueous mass ratio of emulsion, and different model oil emulsions. The results show that the dispersed drops coalesce under the action of electric field, and the particle size of dispersed drops increases with the increase of pulse frequency and amplitude. When the pulse frequency or amplitude reach to a critical value, aqueous drops are driven to form water string or water channel between two electrodes which hinders further drops coalescence in other areas. However, with the increase of pulse width ratio, the size of dispersed drops increases slowly. The optimum pulse frequency and pulse amplitude are obtained at 3.9 kV and 4.21 kHz, respectively, the optimal pulse width range is 54.9%-84.4%. When the concentration of demulsifier is 60 mg/L, the synergistic demulsification effect achieves the highest performance. When the aqueous mass ratio of emulsion reaches a high level (over 30%), which means the drops in emulsion have big size, the coalescence performance under the same electric field strength is great. Also, it is discovered that the dispersed drops in Yongping model oil emulsion have difficulty in forming water chains, since there are much asphaltenes and resins in the water-oil interface leading to high strength of film. For Shuanghe oil emulsion drops are prevented from coalescing, because it contains a mass of paraffin, which can stabilize emulsion at low temperature. (C) 2020 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.