Nor., 1921
THE J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Recovering Petroleum from Emulsions by Chemical Treatment By Ralph R. Matthews and Philip A. Crosby ROXANAPETROLEUM CORPORATION, Woon RIVER, ILLINOIS
One of the most serious problems that producers of petroleum have encountered, from the time the first well was drilled, has been the emulsion of petroleum and water. This probably did not cause much trouble before the development of fields outside of Pennsylvania, because the petroleum produced there was of low specific gravity and water readily separatcd from the oil. The discovery of the asphalt base petroleum in California, and that in the mid-continent field with the so-called mixed base, furnished oils which emulsified easily and produced emulsions which were exceedingly hard to break. The oil man has various names for petroleum emulsions, such as B. S., roily oil, cut oil, and tank bottoms, but all refer to a mixture of water (generally a brine), oil, and finely divided silt or sediment. Tank bottoms generally contain quite a proportion of crude wax or petrolatum which apparently separates from the petroleum stored in the tanks. The oil content of such emulsions varies considerably, but will run from 10 per cent up to 98 per cent. The latter figure is given because pipe lines will accept oil with not over 2 per cent B. S. & W., and while this is not considered emulsified oil it is often exceedingly difficult to reduce much below 2 per cent. I n early days the oil producer found the easiest way to get rid of such oil was to burn it, and each had his sump in which he collected and burned emulsions. As oil became of more value, attention was turned to methods of recovering it. Various methods of heating and settling were evolved, cal treatment was brought forward, various chemlso used, and the latest development is the application of the centrifuge. I n 1917 the World War had increased the value of oil to such an extent that a serious effort was made in the midcontinent oil fields to recover emulsified oil. At that time the writers had considerable experience with a so-called chemical treatment for recovery of oil from emulsions.
RESULTSWITH SOLIDCoiwoum This chemical was known as “Tret-0-Lite” and the composition was approximately as follows-
...................... .................... ..................... .................... Paraffin.. ............................ Water.. .............................
Sodlum oleate.. Sodium resinate.. Sodium silicate.. Phenol..........
Per cent 83.0 5.5
5.0
1015
oil films and allowed the tiny drops of water to collect and finally to separate from the oil. Analyses which the writers have made of brines from the mid-continent field lead to the belief that the above theory is probably correct, since they are uniformly of very low alkalinity and in some cases slightly acid, the result probably of hydrolysis of magnesium chloride. In fact, oil emulsions have often been “broken” by merely adding sodium carbonate and agitating thoroughly. The B. S. (55 W. results in the accompanying table are typical of what was done by using the compound with tank bot toms. Before Tredtina Per cent 20 8 4
i2
14 8
.s
Av.
9
Alter Treating Per cent 1.0 1.0 0.6 0.5 1.0
Amount of Chemical Per cent by W t . 0.7 0.7 0.5
0.5 0.9 0.9 0.8
0.6 0.8
0.7 0.6 0.8 0.8
Temp.
F.
130 130 130 130 130 142 142 142 134
Time of Settling Hrs. 26 48 20 la 24 72 28
27 32
These figures show that the compound does break the emulsions readily and results in an oil recovery. The oil recovered from tank bottoms is generally not of much value for refining because of the absence of lighter hydrocarbons, and the wax content usually makes it of too high a flowing point to use as fuel oil in even moderately cold weather. The best method of handling it was found to be as a mixture with a considerable quantity of petroleum which was pumped to the refinery and handled in the usual manner. Because petroleum is more easily refined with a minimum water content, experiments were also conducted with a view of reducing the B. S. Rr W., as determined by centrifuge, to below 0 . 1 per cent. This was done by pumping the oil from one closed tank to another, heating to not over 110” F., and adding the required chemical by a small proportional pump as the oil was moved. The oil was sampled each day, but after standing for 17 days the B. S. & W. content had dropped only from 1 . 5 to 0.8 per cent, and the oil showed about 0.8 per cent loss of gasoline during the settling period. Some other tests were made, but it was eventually decided that the introduction of the aqueous solution might even have a tende3cy to increase thd B. S. & -W. content of petroleum which already had a low percentage. Prolonged settling probably would not bring the amount much below 0 . 5 per cent, and as shown above, would result in a loss of gasoline. LIQUID
COMPOUND
After considerable experimental work, the manufacturers of this compound have developed a liquid compound. This is an aqueous solution containing about 25 per cent of sulTOTAL 100.0 fonated oleic acid. I n its manufacture the excess acids are It was colored blue by a very small amount of ultramarine neutralized with caustic soda. This gives a more convenient blue which was added as an indicator during manufacture. compound to handle in the field and one which is more effiAn aqueous solution of this compound (later work has cient in breaking the surface tension of the oil films surroundshown a 1per cent solution is best) was added to the emulsion ing the tiny drops of water; otherwise its action appears to in the proportion of 0.1 to 1per cent by weight, and an inti- be the same as noted above. mate mixture was obtained by agitation with air or natural I n the field the compound was diluted to a 1 per cent gas. This was allowed to stand until the emulsion “broke.” solution with a soft water, and was then fed into the oil as it T o hasten this, the mixture was generally heated to about was pumped. In order to get a thorough mixing of the emul150” F., depending on the character of the emulsion. The sion and solution it was found necessary to put it through equipment usually consisted of wooden tanks of the desired a t least 1500 ft. of 2-in. pipe. From the 2-in. pipe the mixture capacity and a portable steam boiler. Thus the equipment discharged into a 250-bbl. wooden tank. The tank concould be moved readily from place to place. tained about 6 ft. of water, through which the discharge The patentee claimed that the compound acted as a water bubbled, removing any free water and allowing the separation softening agent and allowed the silt and sediment, to precipi: to take place so that pipe line oil could be drawn off from the tate along with the insoluble soaps formed. The oil-soluble top. -4steam coil was placed in the tank so the water could portion of the compound decreased the surface tension of the .. be heated if necessary. 4.0 1.5
1.0
1016
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
This compound has been used very effectively in the El Dorado, Arkansas, oil field where a large amount of emulsified oil has been produced. As a typical example the following may be cited: An emulsion which could not be broken by whirling in a centrifuge was treated as outlined above with 0.03 per cent by weight at a temperature of 100’ to 120’ F. The yield was 75 per cent of oil with a B. S. & W. content below 2 per cent, and 25 per cent water. Working in the West Columbia, Texas, field an oil which showed 75 per cent B. S. and 25 per cent water (by centrifuge) was treated a t approximately 90” F. with 0.02 per cent by weight. The yield was 60 per cent of pipe line oil and 40 per cent water. ADVANTAGES OF
AN
OIL-SOLUBLE COMPOUND
The emulsions encountered in the various oil fields ha~7ein each case been found to be individual problems. The fact that it has been necessary to vary the treatment so often has led to research seeking to develop a universal compound which would break any emulsion. A t the present time field experiments are being made with an oil-soluble compound with indications that>it will be satisfactory. Such a compound would have the following advantages over the liquid water-soluble compound: 1-A smaller quantity would be necessary 2-It could probably be used without heat. 3-Would not require dilution with water. &Would mix with oil readily. 5-Would be more convenient to handle. 6-Could probably be more universally applied.
ACKNOWLEDGMENT Acknowledgment is made to Messrs. W. S. Rarnickel and H. L. Barthels of W. S. Barnickel and Company for valuable assistance in the preparation of this paper.
DISCUSSION ON ELECTRICAL DEHYDRATION OF CRUDE OIL
By W. G . and H.C. Eddy 927 HIGGINS BUILDING, Los ANGELES, CALIFORNIA
A more appropriate title of’this discussion wguld be, “The Electrical Process of De-emulsification.” A new era dawned on the oil industry when Dr. Cottrell proved that emulsion is essentially oil and water-an intimate mixture to be sure but nevertheless nothing but a mechanical mixture that can be broken down electrically and separated into pipe line oil and oil-free water. When an emulsion is subjected to the influence of a high potential alternating field the minute water particles, electrically charged by the field, rupture the enveloping oil films and coalesce, forming larger water droplets. This action of stress and strain, attraction and repulsion, on the conducting water particles continues until all the microscopic drops of water in the original emulsion have broken the bonds of the entrapping oil films, the larger droplets serving as nuclei until t h e entire water content is freed into large drops which readily settle out. The action of the electric current is easily followed in the micro moving picture film, and under the microscope the breaking up of the emulsion is accomplished in a few seconds. The low power requirements of the process, from the records of commercial plants, substantiate the theory that the phenomenon is that of a multitude of series condensers rather than of conducting paths. The minute water particles serve as the electrodes or poles of the condensers and the separating oil acts as the dielectric which is ruptured by the high voltage, allowing adjacent positively and negatively charged droplets to neutralize themselves by uniting.
Vol. 13,No. 11
THEELECTRIC DEHYDRATOR The dehydrator consists of the electrical treater and a settling trap. The treater is a galvanized steel tank approximately 3 ft. in diameter and 8 ft. high: in the center of this is suspended a vertical Shaft which carries a number of circular disks. This shaft is supported by an insulated bearing and rotated a t a slow speed by a small electric motor. A potential of approximately 11,000 volts alternating current of any commercial frequency is impressed between the revolving electrode and the tank shell which constitutes the other electrode, and is grounded. The usual supply circuit is one of 220 voltage and the current passes through a suitable switchboard and regulating coil and is stepped up by a transformer to the required high potential. The emulsified oil is fed continuously to the treater, passing into and through the annular electric fields formed between the edges of the disks and the treater shell, where the de-emulsification takes place. The freed oil and water pass into the trap tank where they separate, the oil flowing from the top to the shipping tanks, while from the bottom flows the liberated water, together with the salts in solution. A plant utilizing a single transformer, motor and trap may consist of any number of treaters from one to eight in even multiples. The capacity zverages from 300 to 1000 bbls. per day per treater depending on the character of the emulsion, some treaters having demonstrated a capacity over 1600 bbls. The electric power consumption ranges from 5 to 75 watt hours per bbl. of cleaned oil, the cost of electricity averaging one cent for 20 to 50 bbls. The fundamental process on which Dr. Cottrell obtained basic patents is known as the Cottrell process for separating one liquid suspended in another, There are many ways of putting this principle into practice with various shapes and sizes of electrodes and containers, and much experimental work has been done in determining the most effective frequency, voltage, and size of field applicable to various emulsions. One outstanding feature of the electric process is its lack of limitation. “All is grist that comes to the electric mill;” it is handling all types of emulsions, of all percentages, viscosities, and gravities. In fact, the ease of de-emulsification often increases with an increased water content up to 30 or 40 per cent, while larger percentages reduce slightly the gross daily capacity per treater. Re-treatment in field practice has never been found necessary, even on tank bottoms testing 95 per cent emulsion, which are treated successfully, reducing the water content to a fraction of 1 per cent. In California and the Gulf Coast fields i t has become the standard method of dehydration. Ninety-five per cent of the emulsion treated in California is handled by the electric process. Even where the crude oil is topped an electric dehydrator is often installed ahead of the topping plant. A record of eight years of field operation established the upkeep expense as not over $15 per treater per year. The total cost, including steam, electricity, royalty, labor, repairs, interest and depreciation, has been found to be from one to three cents per barrel of net oil. While a number of these electric plants are operated a t atmospheric temperatures, there is usually a certain critical temperature, varying somewhat with different emulsions, at which the plant shows its maximum capacity. The highest temperature used on extremely rebellious and viscous emulsions is 180” F. and the average temperature of all plants operating is 135” F. The lower gravity oils usually require a certain amount of heat before they can be handled or pumped satisfactorily. At this temperature the emulsion ordinarily can be broken up electrically, thereby saving not only a large amount of fuel but also the volatiles, which would be lost a t higher temperatures. In handling high gravity oils an enclosed-type treater operating under pressure retains in the oil practically all the lighter constituents
