Study of the Cation and Salinity Effect on Electrocoalescence of Water/Crude Oil Emulsions

摘要

The resolution of water-in-crude oil (W/O) emulsions formed during extraction or desalinaton processes of crude oil is still a problem for the oil industry. Among the main separation processes used today, electrostatic separation induced by the application of DC or AC electric fields is the most interesting because it is ecologically correct. However, the electroseparation efficiency is still limited by the current lack of knowledge concerning the mechanism that is behind this process. Stabilization of the water/crude oil emulsion is guaranteed, mainly, by resins and asphaltenes that are present at the W/O interface, forming a rigid cross-linked film that wraps the droplets. The influence of salts and the salinity of the aqueous phase on the stability of emulsions is poorly known because most researchers use, as the aqueous phase, a complex saline solution composed of a mixture of chlorides and sulfates of mono- and divalent cations to simulate the composition of seawater. Thus, the isolated effect of each type of cation may not be known. In this work, we used the rheology technique to study the effect of cation type and salinity of the aqueous phase on the stability of water/oil emulsions, under application of a DC electric field. It was verified mat the stability of the emulsions follow this order: H_2O ? Na~+ ～ K~+ < Ba~(2+). It was also observed that the presence of salts increases the stability of the emulsions up to a critical value of ionic strength (～0.1-0.3 mol L~(-1), depending on the system), above which the stability decreases, tending to that observed for the emulsion produced with water.