Removal of Emulsified Oil Particles by Dissolved Air Flotation

Abstract

Dilute emulsified particles (~300 mg dm 3, da-% fJtm) of heavy oil A were removed in a 50 x 50 mm-square and 0.32 m-deep column by flotation using small bubble swarms (da0 pm) generated by a rapid depressurization of supersaturated liquid. Pressure at which air was dissolved was varied within 2-4.5 x 105 Pa. The flotation efficiency is best at 3 x 105 Pa and decreases at higher pressure in spite of higher bubble holdup, probably because of excessive liquid disturbance. The flotation is also influenced significantly by the chemical species added and their concentrations. A solution of pH 4 shows the best flotation in the pH range investigated (pH 2-10). A microelectrophoresis measurement shows that the zeta potential of both oil particle and bubble shifts from positive to negative with increasing pH through a PZC (point of zero charge, C=0) around pH 4 and the best flotation at pH 4 can be explained by the great reduction in repulsive interaction of the electric double layer. Flotation efficiencies are improved in CaCl2 and A1C13 solutions with increasing concentration (10~5-10~2 mol dm 3) while they decrease [slightly in NaCl solution. This trend is discussed semiquantatively in the light of the variation of zeta potential with concentration. © 1979, The Society of Chemical Engineers, Japan. All rights reserved.