Effect of electrode configurations on phase equilibria with applied electric fields

Applying an electric field to some boiling binary mixtures has been shown experimentally to increase the separation factor by as much as 10%. In this work, an electric field was applied across the interface of boiling mixtures of 2-propanol-water via electrodes located in the vapor and the liquid. The shape and separation of the electrodes and the strength and polarity of the electric field were altered to investigate their effect on the vapor mole fraction, the current, and the vapor temperature. The results show that greater voltage differences, in the absence of excessive electrical current, lead to higher concentrations of 2-propanol in the vapor. However, it was found that varying the electrode separation at a given potential difference, and thus the electric field strength, has little effect on the vapor composition. The effects of the applied potential difference are reduced with elevated current and under conditions where liquid dynamics such as dripping, splashing, or jetting provide an opportunity for charge to be transferred between the electrode in the vapor and the liquid. It is also shown that directing the electric field from the vapor to the liquid produces a lower current, and the effect on the composition is larger. These findings, in combination with calculations of the interface charge density, suggest that improvements in the separation efficiency achieved by an applied potential difference are not due to effects of the electric field in the bulk fluids, but rather are induced by charge accumulation at the vapor-liquid interface.