Electrocoalescence in non-uniform electric fields: An experimental study

• Prospects of the non-uniform electric fields over a uniform field in phase separation operations are investigated.
• Effectiveness of the different symmetric as well as asymmetric electric fields in electrocoalescence is elucidated.
• Coalescence behavior in the water-in-oil as well as oil-in-oil emulsions is studied.
• The findings will be useful in design of fast and compact desalters and demulsifiers.

The method of electrostatic force-assisted phase separation is widely used in the chemical industry. The fast and clean separation capabilities make electrocoalescence a favorite among the other competing phase separation techniques. In the present study, we experimentally investigated the relative merits of symmetric and asymmetric non-uniform and uniform electric fields in electrocoalescence. Three different types of emulsions are studied: (i) a perfectly conducting (PC) phase dispersed in a perfectly dielectric (PD) medium, (ii) a leaky dielectric (LD) phase dispersed in another LD phase of higher electrical conductivity, and (iii) a LD phase dispersed in another LD phase of lower electrical conductivity. The coalescence behavior of each emulsion in the non-uniform electric fields is analyzed and the results are compared with that in a uniform field. The observations show that a non-uniformity as well as asymmetry of electric field can affect electrocoalescence in a nontrivial way and is sensitive to the drop-medium system, specifically pin-plate, quadrupole and annular electrode configurations are found to be advantageous over uniform field in PC drops in PD medium, less conducting LD drops in more conducting LD medium and more conducting LD drops in less conducting LD medium, respectively.