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THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
lating agent before a satisfactory emulsion can be produced; but a powerful flocculating agent will usually prevent emulsification. 5-Certain finely divided solids, such as carbon black and silica, are mutually antagonistic so far as the formation of emulsions is concerned, and in this respect are analogous to sodium and calcium oleates.
Vol. 13, No. 11
terial more easily wetted by oil acting as emulsifier. The character of this emulsifier may most easily be shown by the actions of the emulsions under certain conditions of test. It has been shown by the author that the water particles are negatively charged electrically, and indeed both alternating and direct current electrical treatment have been used to discharge these emulsions. As a matter of fact we have found that a static charge is sufficient toprecipitate the water. The water particles may be made to coalesce and preEmulsifying Agents in Oil-Field cipitate by the addition of certain electrolytes, such as acids Emulsions and iron salts. Such an effect may be due to the preferential adsorption of certain ions, but it is rather hard to believe By J. L. Sherrick that these emulsions, ranging from 10 to 60 per cent in conMELLON INSTITUTE OF INDUSTRIAL. RESEARCH, PITTSBURGH, PA. Since publishing the reeults of a research on oil-field tent of dispersed water phase, owe their stability to ion ademulsions1 carried on in the winter of 1918 to 1919, the writer sorption alone. Even though Ellis has prepared emulsions has received many inquiries from widrspread sources. stabilized by ion adsorption, these were extremely dilute Although the subject matter of the present contribution emulsions and were of the oil-in-water type. Certain water-soluble colloids, such as sodium oleate and represents no additional laboratory research, certain points the sodium salts of certain sulfonic acids render these emultherein have been developed in discussion with associates and are offered in the hope that they will encourage further sions unstable and precipitate the water if added in proper proportion. This is indeed what one might expect if the discussion. Before considering the question as to the substance in original emulsifying agent were an oil-soluble colloid as the crude oil which serves as the emulsifying agent, it is first action of two such colloids must be antagonistic, the one necessary to review briefly the general conditions for emul- tending to form a water-in-oil and the other tending to form an oil-in-water emulsion. The precipitating colloid must, sion formation. however, be added in exactly sufficient quantity to neutralEMULSIFYING AGENTS ize the effect of the original emulsifying colloid. If tQ0 large The necessity for the presence of some third component an excess is added it may bring about simply a phase reversal, to serve as an emulsifying agent has been recognized by changing the emulsion from the water-in-oil type to the oilalmost all workers in emulsions. The substances, which in-water type. function as emulsifiers, by collecting a t the interface of the The action of certain organic solvents upon these emulsions two liquids to form protective films for the dispersed phase probably throws more light on the nature of the emulare, however, quite varied in their nature. sifying agent present than any of the other reactions. A The most common emulsifying agents are the emulsoid standard method among oil men for determining the percolloids like soap, gelatin, gums, starches, beeswax, etc. centage of water in an emulsion consists in adding light gasoIt seems certain also that suspensoid colloids may so serve, lene to the emulsion and centrifuging the mixture when the although they are not generally used. Pickering2 however, amount of water in the sample can be read off from the gradhas gone a step beyond this and used finely divided solids for uated centrifuge glass. It has been found that ether serves such a purpose. It has been claimed that ions adsorbed even better than gasoline for this test. on the surface of liquid particles may serve as emulsifiers, The effect of these organic solvents in breaking the emuland Ellis has prepared an emulsion which owes its stability sions was thought to be due to the fact that the solvent mixto ion adsorption. It is probable, however, that for the for- ing with the oil phase increased the difference in density mation of emulsions of relatively high concentration of dis- of the two phases to such an extent that the emulsifier was persed phase, say 50 per cent or more, the presence of an no longer powerful enough to hold the emulsion. It was emulsifier which will form a relatively tough and elastic film found, however, that a mixture of ether and carbon bisulfide by collecting at the interface is necessary. of the same density RS the emulsion served to break the emulTYPES OF EMULSIONS sion more easily even than the light liquid ether. Emulsions may be classified according to the position of THEEMULSIFYING AGENT the several phases. Thus we have oil-in-water emulsions, The substances, other than water and oil, present iu these in which the oil is dispersed as small particles in a con- emulsions are the following: tinuous water phase, and water-in-oil emulsions, in which Electrolytes in solution in the water phase. the water is dispersed as small particles in a continuous Hydrated earthy material. oil phase. Heavy hydrocarbons, such aa aspllalt, asphaltenes, etc., probably The type of emulsion formed by any given oil with water present in colloidal solution in the oil. depends primarily upon the nature of the emulsifying subThe ions of the electrolytes present in the water phase stance. Bancroft has explained this from the standpoint probably affect both the magnitude and nature of the elecof surface tension. I n a general way, however, the following e on the water particles but, as previously stated, applies: An oil-in-water emulsion is formed by the use of a ow they could stabilize such concenwater-soluble colloid as emulsifier; a water-in-oil emulsion all, it seems hardly likely that ions is formed by the use of an oil-soluble colloid. With finely could stabilize a water-inemulsion, even granting that divided solid material, the liquid which more easily wets the they might be effective for an emulsion of the opposite type. solid material will be the continuous phase. We would expect hydrated earthy matter to be wetted OIL-FIELD EMULSIONS more easily by water khan by oil and, if a colloid, to be Oil-field emulsions belong to the water-in-oil type and as water-soluble. We seem to recall, however, having read that such must be formed by an oil-soluble colloid or a solid ma- precipitated hydrous ferric oxide would occlude or adsorb small amounts of oil or grease contained in the solution from 1 THISJOURNAL, 12 (1920),133. which it was precipitated. 2.T. Chcm. Soc., 91 (1907),2001.
Nov., 1921
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T H E J O U R N A L OF. I N D U X T R I A L A N D ENGINEERING CHEMIXTRY
There seems to be little doubt as to the fact that some of the asphalt-like bodies are present in crude oil as oil-soluble colloids. However, if such were effective as emulsifiers, it would seem that all of the asphalt base oils should emulsify very easily, but this is not the case. It seems entirely probable, then, that the hydrated earthy matei-ial, adsorbing the heavy asphalt-like bodies of the crude oil in a manner similar to hydrous ferric oxide, becomes an oil-soluble colloid, and as such forms tough elastic membranes about the drops of water. Richardson1 has found such an oil-soluble colloid in Trinidad asphalt and has even reproduced such a colloid by mixing a water solution of colloidal clay with asphalts and asphalt oils and driving off most of the water with heat. It is probable that some such process took place during the formation of the crude petroleums, leaving them charged with such an oil-soluble colloid which later served as an emulsifier when the crude came in contact with water under conditions favorable for emulsion formation. Since the earthy material is an oil-soluble colloid in virtue of the fact that it carries adsorbed asphalt, when such asphalt is removed by organic solvents, the earthy matter is no longer oil-soluble and cannot therefore protect a waterin-oil emulsion. In June 1918 the writer went from Houston up into northern Texas to investigate some “bottom settlings” which resisted an electrical treatment that was a t the time very successful in breaking oil-field emulsions. This material which reprwented sedimentary accumulations from pipe line storage tanks was stiff and very sticky. It would not respond to electric treatment except when it was diluted with more than an equal quantity of good crude oil. Evidently the crude oil phase was much more firmly held in this emulsion than in those occurring in the oil fields but even it responded to organic solvents. This “B, S.” contained about 50 or 60 per cent water, but was much stiffer tha? the regular oilfield emulsions containing a like percentage of water. It would readily serve to emulsify a clean crude oil with water and seemed to represent exactly such an emulsifier as we have assumed to be responsible for the formation of emulsions in the oil fields.
Common Characteristics of Crude Petroleum Emulsions By E. E. Ayres, Jr. SHARPLES SPECIALTY Co.,PHILADELPHIA, PA.
What do we mean by the “resolution of emulsions?” The man in the field who is responsible for production of crude petroleum considers his emulsion resolved when the water globules have settled, leaving the bulk of his oil homogeneous. The research chemist is often content with a proper degree of coalescence, for with the globules large enough, subsidence may be taken for granted. Subsidence and coalescence should be regarded as of equal importance, for subsidence unaided may be too slow, and must leave an incomplete resolution in any case, while a Coalescence technique which would leave the settling of the water beyond doubt might be too costly. Except with the least stable of emulsions, centrifugal engineers have found it profitable (usually by a correct use of heat) to increase the average size of the water globules before attempting centrifugal subsidence. The people who have been interested in commercializing the use of reagents and electricity for crude petroleum emulsions have found it necessary to facilitate (usually by an efficient gravity system) the settling that must, of course, follow coalescence to yield a practical resolution. J . P k s Chrm , 19 (1915),246.
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GRAVITYAND CENTRIFUGAL SUBSIDENCE Really efficient gravity systems are rare. Throughout the Middle West there are expensive continuous-flow basins that violate the first principles of subsidence. Gravity costs nothing except time, and it is therefore used injudiciously for easily accomplished subsidence, and is discarded as useless when the elapsed time seems too great. A few years ago centrifugal force was squandered in like manner. But centrifugal force is expensive, and centrifugal engineers were compelled to look for the fundamental principles which must be obeyed. The modern centrifuge probably secures as efficient subsidence as the mechanical limitations of the machine permit. FACTORS INVOLVED I N SUBSIDENCE Centrifugal and gravity subsidence are dependent, of course, upon differences in specific gravities. It is natural, therefore, that our first question should be “Is the absolute density of the suspended particle great enough for separation?” The answer is “yes” in every case. If we were to find a case in which the gravity of crude petroleum were exactly the same as the gravity of the suspended water, the equality could not exist a t all temperatures because of differences in coefficients of expansion. An inspection of the form of Stokcs’ law which controls the motion of such particles will show the relative unimportance of absolute density. The centrifugal engineer considers two points: If the particle is too small, subsidence is impossible; if the viscosity of the continuous phase is too high, subsidence may be too slow. I n the case of crude petroleum emulsions the particles are never too small for subsidence. Viscosity varies widely, but not so widely as might be supposed. The extremely viscous emulsions so often encountered may comprise a continuous phase of low-viscosity oil, in which case subsidence will take place as readily as though the emulsion itself had a low viscosity. I n other words, we may disregard the viscosity of the emulsion, and inquire only into the viscosity of the oil of the emulsion. To get a clear idea of what gravity and centrifugal force will do to a crude petroleum emulsion let us consider a body of oil containing 15 per cent of water dispersed as small globules. If this oil is permitted to stand a sufficient time the emulsion will reach a state of equilibrium. The time will he dependent upon the size of the globules, the viscosity of the oil, and, in lesser degree, the difference between the specific gravity of the oil and the water. Bt equilibrium, all of the globules of water, except a small percentage of the smallest, have settled to the bottom. The supernatant oil will therefore be reasonably free from water. Let us assume that one third of the settled globules are large enough to coalesce when brought into contact by subsidence. The coalescrd globules will form a water layer a t the bottom of the container. The other two thirds of the globules are too small for gravity coalescence, and remain as globules closely packed together in viscous formation. It is of interest that the highest centrifugal force will cause no greater degree of coalescence than gravity. The above example, if correct for a specific case of gravity separation, will apply with equal correctness to centrifugal separation. Furthermore, the small globules in the settled emulsion are packed into as small a space by gravity as they can be packed by the highest centrifugal force. This indicates that the globules may be brought into contact by subsidence with relative eaRe. There are many emulsions that cannot be concentrated by gravity to contain more than 30 per cent of dispersed phase. The concentrated crude petroleum emulsions contain rarely more than 55 per cent m t e r , which would indicate that the globules are of rather uniform size. Other much more stable emulsions
