Removal of Oil From Dilute Aqueous Emulsions By
Autocoacervation and Coalescence in Carbon-Metal
Granular Beds
WILLIAM P. BROWN, Technical Services Representative
Nalco Chemical Company
Chicago, Illinois 60601
MRIGANKA M. GHOSH, Associate Professor
Department of Civil Engineering
University of Maine
Orono, Maine 04473
INTRODUCTION
Separation of finely divided mineral oil droplets from oil-in-water (O/ W) emulsions is
of major concern in the treatment of oily wastes from automotive plants, chemical
processing plants, oil refineries, and steel mills. Existing treatment facilities employing
dissolved air flotation units or clarifiers remove most of the large oil droplets present in the
wastewater but very little of those having a diameter of 20/J or less. Chemical treatment with
acid, alum, and lime removes much of the oil but alum treatment creates voluminous
sludges that need to be hauled away at a considerable cost. Treatment with organic
"emulsionbreaker" chemicals can achieve the same effluent quality at about the same
chemical cost but the sludge produced is only a fraction of that generated by treatment with
inorganic chemicals. Other methods for oil removal include sand filtration, heat treatment,
reverse osmosis, fibrous-mat filtration, and electrostatic precipitation.
The main objective of this research was to study the feasibility of using bimetallic,
porous-bed coalescers in the separation of oil from dilute oil-in-water emulsions commonly
encountered in many industrial wastewaters. In particular, the effect of several operational
variables, namely the depth of bed, superficial velocity and the porosity of the granular
medium as related to packing of bed material, on the efficiency of removal was determined.
The effect of the size of dispersed oil on its removal was also studied but only in a qualitative fashion.
Two types of mixed granular media, namely carbon-aluminum and carbon-iron were
used in an effort to determine the effect of the net electromotive force (e.m.f.) of the
electrochemical cell on the separation of the two liquid phases present in the emulsion.
It is hoped that rational design criteria for bimetallic coalescers can be developed from
available theories of coalescence and the experimental data obtained from this study.
LITERATURE REVIEW
A stable oil emulsion can be described as a colloidal system consisting of negatively
charged oil droplets surrounded by an ionic atmosphere. Clayton (1) has given an excellent
review of the early theories of the formation and stability of emulsions. According to these
theories the formation of stable emulsions depends on two major conditions, first, the oil
must be divided into droplets small enough to remain suspended and second, there must be
a film separating the droplets from the continuous phase (water) so that coalescence of oil
droplets will be inhibited. Once the emulsion is formed adsorption or ionization of organic
radicals or particular matter will keep the suspended droplets in a stable state. Canevari(2)
has evaluated the various factors influencing the rise rate of suspended oil droplets using
Stokes' equation
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