CHAPTER 11 EMULSION BREAKING

1 CHAPTER 11 EMULSION BREAKINGAn EMULSION is an intimate mixture of two liquid phases, such as oil and water,in which the liquids are mutually insoluble and where either phase may be dis-persed in the other. In water chemistry, two types of emulsions are commonlyfound, oily wastewater (oil emulsified in water or O/W emulsions) and waste oilemulsions (water emulsified in oil or W/O emulsions).Oily waste and waste oil emulsions can usually be differentiated EMULSION appears to be just oily, dirty water; a drop of the EMULSION addedto water disperses (Figure a). A W/O EMULSION is usually thick and viscous;a drop of this EMULSION added to water does not disperse (Figure ).

2 QIL-IN-WATER EMULSIONSAn oily waste EMULSION , in which oil is dispersed in the water phase, may containany of various types of oil in a wide range of concentrations. These oils are definedas substances that can be extracted from water by hexane, carbon tetrachloride,chloroform, or fluorocarbons. In addition to oils, typical contaminants of theseemulsions may be solids, silt, metal particles, emulsifiers, cleaners, soaps, sol-vents, and other residues. The types of oils found in these emulsions will dependon the industry. They may be fats, lubricants, cutting fluids, heavy hydrocarbonssuch as tars, grease, crude oils, and diesel oils, and also light hydrocarbons includ-ing gasoline, kerosene, and jet fuel.

3 Their concentration in the wastewater mayvary from only a few parts per million to as much as 5 to 10% by stable O/W EMULSION is a colloidal system of electrically charged oil dropletssurrounded by an ionic environment. Violent mixing and shearing of oily waste-water in transfer pumps disperses these minute oil droplets throughout the stability is maintained by a combination of physical and chemicalmechanisms. These emulsions are similar in behavior to the colloidal systemsencountered in swamps (color) and rivers (silt).One such stabilizing mechanism, ionization, is brought about by the additionof surface-active agents, such as organic materials or cleaners, which aid in main-taining a stable colloidal system.

4 These molecules usually carry an electric chargeand seek out the oil/water interface of the emulsified droplet. Here, the accumu-lated charges cause the EMULSION to be stabilized through repulsion of the com-monly charged droplets. Neutral (nonionic) surfactants can also stabilize an emul-sion, since these molecules are bifunctional: one end is soluble in water, and theother end in hydrocarbon, so the molecule bridges the interface and stabilizes (a) If a few drops of oily water (O/W EMULSION ) are added to water, they disperse inthe water. This is a test to distinguish O/W from W/O emulsions, (b) A few drops of this emulsionadded to water remained as a separate phase floating on the surface, showing it to be a , solid particles may stabilize an EMULSION if they are of correct size andabundance.

5 In this case, stabilization occurs because the solid particles adsorbedat the oil/water interface tend to reinforce the interfacial film. The dispersed drop-lets cannot coalesce because of the interference or blocking effect caused by thesolids (Figure ).Emulsions can also be stabilized by friction between the oil and water phasescreated by vigorous mechanical or physical agitation. Static electric charges devel-oped by this action tend to collect at the oil/water emulsifier is usually a complex molecule, often having a hydrophilic(water-loving) group at one end and a lyophilic (oil-loving) group at the other(Figure ). Emulsifiers disperse oil droplets in the water phase because theyhave an affinity for both water and oil that enables them to overcome the naturalforces of emulsifiers are surfactants having either anionic or nonionic polargroups.

6 Petroleum sulfonates and sulfonated fatty acids are common anionicemulsifiers, and ethoxylated alkyl phenols are common nonionic of naturally occurring surfactants are organic sulfur compounds, var-ious simple esters, and metal complexes. Alkaline cleaners containing surfactantsFIG. Physical EMULSION stabilization by finely dividedsolids, illustrated with O/W charged oil dropletsSolid particles prevent contactof oil dropletsWaterWaterOilOilWater SOFT bank EBook Center Tehran, Phone: 66403879,66493070 (a) Oil-in-water EMULSION ( b) Water -in-oil emulsionNOTE; Emulsifier molecule shown in simplified form:/~xWater-soluble end/ ^Oil-soluble end(Hydrophilic group) (lipophilic group)FIG.

7 Chemical stabilization of emulsions by surfactants having hydrophilic andlipophilic emulsify free oil are present in many wastewaters. Table lists a varietyof emulsifiers for both O/W and W/O Oil-in-Water EmulsionsEmulsions may be broken by chemical, electrolytic, or physical methods. Thebreaking of an EMULSION is also called resolution, since the result is to separate theTABLE Emulsifying AgentsOil-in-water type1. Formation when soaps are colloidallydispersed in water phase2. Ionic emulsifiersa. Sodium, potassium soaps andsulfidesb. Sodium naphthenes and cresylatesc. Precipitated sulfides plussurfactantsd. organic amines3. Electrolytes which favor stabilitya.

8 Salts of univalent cationsb. Salts of di- and trivalent cationsWater-in-oil type1. Formation when soaps are precipitatedfrom aqueous phase2. Ionic emulsifiersa. Multivalent metal soapsb. Sulfide ion plus carbon particlesc. Multivalent metal oxidesd. Mercaptanse. Naphthenic or cresylic acids3. Electrolytes which favor stabilitySalts of di- and trivalent cations SOFT bank EBook Center Tehran, Phone: 66403879,66493070 FIG. The action of a cationic EMULSION breaker in neutralizing surface charges on acolloidal oil droplet in oily mixture into its parts. Chemicals are commonly used for the treatmentof oily wastewaters, and are also used to enhance mechanical treatment. In break-ing emulsions, the stabilizing factors must be neutralized to allow the emulsifieddroplets to coalesce.

9 The accumulated electric charges on the emulsified dropletare neutralized by introducing a charge opposite to that of the droplet ( ). Chemical EMULSION breakers provide this opposite charge. The dielectriccharacteristics of water and oil cause emulsified oil droplets to carry negativecharges. Therefore, to destabilize an oil-in-water EMULSION , a cationic (positivecharge) EMULSION breaker should be resolution of an O/W EMULSION should ideally yield an oil layer and awater layer. However, such a clear resolution is seldom achieved: there is often ascum, called a rag, at the interface where solids and neutralized emulsifier treatment of oily wastewater is normally divided into two Coagulation: This is destruction of the emulsifying properties of the surface-active agent or neutralization of the charged oil Flocculation: This is agglomeration of the neutralized droplets into large,separable , sulfuric acid has been used in oily waste treatment plants as thefirst step in EMULSION BREAKING .

10 Acid converts the carboxyl ion in surfactants tocarboxylic acid, allowing the oil droplets to agglomerate. Chemical coagulatingagents, such as salts of iron or aluminum, can be used in place of acid, with theadditional benefit that these aid in agglomeration of the oil droplets. However,the aluminum or iron forms hydroxide sludges that are difficult to dewater. Acidsgenerally break emulsions more effectively than coagulant salts, but the resultantacidic wastewater must be neutralized after oil/water oildropletsEmulsionbreaker(cationic) SOFT bank EBook Center Tehran, Phone: 66403879,66493070 FIG The use of organic EMULSION breakers in place of alum or salts which form hydrousfloes greatly reduces sludge volume.