Electrophoretic separation

Abstract

For the electrophoretic separation of a dispersed phase or contaminant (solid, liquid, or gaseous) from a continuous liquid phase under conditions of intrinsic ionic conductivity due to intrinsic bipolar ions in the continuous phase, especially for conductivities of the continuous liquid phase in excess of about 10.sup.-8 (.OMEGA..m).sup.-1 for which known electrofiltration processes are relatively ineffective or unworkable, a voltage is applied to the dispersed phase-containing liquid phase. The dispersed phase has a field-dependent mobility, and the applied voltage is such as to establish, within the liquid to be treated, a periodic asymmetric electric field E(t), conveniently comprising alternate positive and negative rectangular pulses, having the properties that the time-averaged amplitude of E(t) over one complete period, T, is zero but the average amplitude of each positive feature of the periodic waveform is unequal to that of each negative feature. These conditions give rise to a net electrophoretic migration of dispersed phase which causes dispersed phase to accumulate in a collection region, for example on one or more collector surfaces or within the liquid bulk. In the former case, the collector surfaces are periodically cleaned or regenerated (for deposited solids) or, for liquid or gaseous contaminants, the dispersed phase separates by settling or floatation from the collector surfaces. In the latter case the collected dispersed phase can be mechanically filtered off (with a solid dispersed phase) or allowed to settle or float (for solid, liquid or gaseous dispersed phases). The process is of particular practical importance for the electrofiltration of contaminated petroleum liquids.