INDUSTRIAL
AND
ENGINEERING
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C
ANALYTICAL E D I T I O N PUBLISHED
BY
THE
AMERICAN
CHEMICAL
SOCIETY
0
HARRISON
E.
HOWE,
EDITOR
Mineral Oil Deterioration System J. C. BALSBAUGH AND A. G . ASSAF Massachusetts Institute of Teobnobgy, Cambridge, Mass.
T .
HE application of mineral oils for various service appli-
However, in the authors’ laboratory aging tests have been made using oxygen or nitrogen (or hotb), with and without catalysts. The deterioration of an oil is accompanied by the liberation of volatile products, the addition of oxidation products to the oil, and changes in the physical and electrical properties. Since the chemical and physical changes which occur give a measure of the progress of the deterioration, the ideal procedure would be to follow accurately and completely all the changes which occur; hut this at present is neither possible nor practicable. Ordinarily a definite property or set of properties is measured as the deterioration progresses. The properties selected are dictated in many cases by limitations of the apparatus used, and t o a large extent by the field of application of the oil. In order that the limitations imposed by the apparatus may be eliminated as far as practicable, special attention has been given to the design of systems for deteriorating mineral oils by oxidation and heating. The
cations, such as for electrical insulation and for luhrication, depends upon an interpretation of the initial properties or characteristics of the oil in terms of the deterioration characteristics in service, Such interpretation depends upon f u n d s mental studies, appropriate deterioration tests, and service records, The general qualities of mineral oils for insulation, lubrication. and other uses can to some extent he determined by subjecting the oil to short-time aging tests, although these tests do not 2 fully represent long-time service con13 ditions. Provided the results can be properly interpreted, short-time tests 15 which last for a few days or weeks are to he preferred to service tests which may continue for years. Further, artificial deterioration under laboratory conditions, where there is more flexihilityand better controlof thevariables involved, gives fundamental information about the deterioration mechanism which is difficult t o obtain from other tests. The most common method of deteriorating insulating ails is to oxidize the ail either alone or in the presence of other materials, the oxidation being carried ont at an elevated temperature to increase its rate. A modified aging treatment is t o heat the oil in an inert atmosphere f a r m extended time, either done or in the presence of other substances. A combination of these treatments, whioh approximates conditions in practice, consists in oxidizing the oil until a definite quantity of oxygen has reacted and then continuing the deterioration by heating in the absence of oxygen. As catalysts, the materials added may be powdered or bulk metal oxides such as copper and lead oxides, soaps such as copper naphthenate or stearate, or pure metals such as copper (wire or cubes). Paper, which absorbs some of the oxidation prodnets and may
ments consist in subjecting Thcoil t o bcmbardment orexposinp it to ultraviolet
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ditionshf te&pern&re and voltage
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INDUSTRIAL AND ENGINEERING CHEMISTRY
An all-glass apparatus A closed system An adequate dispersion of the gas phase in the oil and an adequate circulation of the liquid phase A SvStem which nermits oxygen absomtion measure-
aa desired, ,
The ability to make electrical measurements on the sample in the deteriorating system A svstem which will nermit makine studies on small vo1um"es of oil, so as & make pracccahle work with straight hydrocarbons or special samples that may be taken from various stages of a refining process
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FIOURE 3,
DETERIORATION CELL
The quantity of oxygen absorbed in a unit weight of oil is considered to be the independent variable in an oxidation study, although the time during which the oil is subjected t o oxidation may be used as that variable. The latter quantity must be considered, but is not sufficient in itself, because the rate at which oxygen ir; absorbed by an oil varies with time for a given oil and the rate of absorption as afunction of time is greatly different for different oils.
Electrical Measuring Cells The electrical measuring cell (f) is shown schematically in Figure 1 and in assembled form in Figure 2. The cells are also shown as used in the deterioration cells for electrical measurements during a deterioration test in Figures 5 and 6 . These cells are utilized for making such measurements as conductivity, loss factor, and dielectric constant of the oil and an oilimpregnated paper sample at intervals during the deterioration.
DETERIOItATION CELL
MEASURING CELLS
The cell is of the three-electrode type for precise measurements and is of platinum-glass construction t o give a minimum electrode effect on the sample, and t o permit effective cleaning. The principal parts of the cell as indicated in Fjgure 1 axe: a guard section, tube 1 , 6 2 5 mm. (0.250 inch) in outside diameter by 0.175 mm. (0.007 inch) wall, sealed t o a No. 15 ground joint, 2. through a graded seal; a measuring section, tube 3, and guard section, tube 4, each 0.250 inch in outside diameter by 0.007 inch wall supported by glass seals 5 and 6 from tube 7, this tube being supported from the assembly supporting guard tube 1 by glass s e d 8; a high-voltage section, tube 9, 9.1 mm. (0.364 inch) in outside diameter by 0.007 inch wall supported by three glass pillars, 10 and 11, at each end from guard tubes 1and 4. Electrical connections external t o the cell are made with 20-mil platinum wire spot-welded t o the appropriate electrodes; guarded lead 12 with glass spmer 13 for connection to measurmg section 3 and supporting tube 7; high-voltage lead 14 sealed in ground joint at 15; guard connection ig made directly to guard supporting tube 1external to the cell with guard tubes 1 and 4 connected together by lead 16 within the cell. While different relative dimensions may be used in the construction of a cell of the type described, the cells normally used have been made with a measuring section length of 2.6 cm. (1 inch) and a 50-mil spacing, giving a vacuum capacitance of approximately 4.lpi.f. The length of the cell shown is determined principally by the sise of the deterioration cell in which it is used and the maintenance of the ground-glass joints external to the oven in which the deterioration cell is placed. The size of the cell may be decreased from that shown and described, and can be constructed so that the oil volume required for a measurement is principally that contained between the measuring electrodes. Thus, it may be adopted to measuring small volumes of oil, the present cell requiring only 3 00.
Deterioration Cells
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The deterioration cells for containing th, yl.u other material such as copper and paper, and the electrical yyAAArLu
August 15. 1941
ANALYTICAL EDITION
317
4, thus drawing gas from above the sample in chamber 1 through tubes 5 and 6 and then up through valve 3 and tube 7. and dis-
4: and then siccessivelv throu& tubes 9 a i d 10 contai&xe the
Gill take ulace even when the eozact &faces aye under oil.
vent ~Iass-to-slasscodtaetat the hottok of the plunger h o k k "~~~~ ~
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can be easilv increased or deore'aned. the rates eiven have been effective. In the cell shown in Figures 3 and 5, the contact materids such as paper and copper are introduced into the cell through tubes 2 and 5 with the oluneer removed from the cell. The mer is in the form of disks, ~proximetely0.5 cm. in dimet&,-md the copper in the form ofspirals 0.5 cm. in diameter and 2 to 3 cm. in length, using No. 36 copper wire. The cell of Fimre 4 has a mound flanee and cover d a t e which uermits use of ;mer disks ~ D P r o x i m a t bthe diameter of the I
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FIGURE6. DETERIORATION CELL WITH ELECTRICAL MEASURING CELLS AND PROVISION FOR WITHDRAWING SAMPLES
measuring cells (when electrical measurements are desired on the oil sample in the system during the test), are shown in Figures 3, 4, 5, and 6. The cell in Figure 4 is used only when the oxidation kinetics is desired, and the cell in F~~~~~7. oILFigure 5 when electrical measurements are to he obtained in addiDEGASSINGEQUIPtion. A cell of the type shown in MENT Figure 5 is mounted in an oven (Figure 8) with the degassing apparatus assembled for degassing an oil into the cell. The cell of Figure 6 has been used for larger volumes of oil samples, so as to peimit withdrawal of samples for chemical tests during the deterioration. This type of cell also has the electrical measuring cells placed in the main body of the sample instead of in connecting tubes as in the cell of Figure 5 . The cell of Figure 5 is shown schematically in Figure 3. The prinoipal parts are: a chamber, 1, of approximately 150-cc. volume for containing the sample and such contact materials as may he desired. a gas and liquid pump consisting of a plunger with "sealed in" iron core operating in tube 2 and ground-glass hall valves, 3 and 4, with ground seats; tubes 9 and 10 with ground joints 11 and 12 for containing the electrical measuring cells; tube 2 with ground joint 16 which is used for admission of the oil sample into the system and for connection with the automatic pressure regulating the oxygen feed system; support 13 serving as a stop far the reciprocating plunger operating in tube 2; and baffle 14 to prevent the contact materials included with the oil sample. such as comer and Dauer. from enterine tube 7 and
for a given volume of oil. the ground cover plate is 8eaied.to the h n g e by yater glass ap lied hetween the ground surfaces. In the cell in Figure 6 the aided materials me put into the cell through one of the ground joints supporting an electrical cell. In this System an oil sample may be removed from the cell through the oapillary tubing, stopcock, and ground joint shown, into a sampling tube mounted on the ground joint. The oil sample is forced into the tube by raising the gas pressure within the cell. The cell of either Figure 3 or 6 is designed to permit electrical measurements to he made on the electrical cells with the system under a vacuum before or after the oil is degassed into the deterioration cell. Following d e g a s s i n g into the svstem. t h oil may 6e brougk to the level of t h outlet tube fro1 tubes 9 and 10 cor t a i n i n g t h e elei t r i c a l cells, b operation of t h pump. After elei t r i o s 1 measure ments are made tlsystem is hrougk u p to 7 6 0 - m n pressure with t k gas used. Con necting tube 15 i Figure 3 equdiai the pressure ab01 the oil in tube with that of t h chamber containin the oil sample am thereby preven the oil from fillin tube 9 after gas admitted to t h system.
Degassing Equipment At the start iIf a test, the oil is admitted into t kie deterioration ce11 through the diL gassing equir ment. The purpose of degessing
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placement on the upward stroke opensvalve 3 and ^elos& valve
FIGURE 8. DEGASSING EQUIPMENT AND DETERIORITION CELL
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Automatic Gas Feed and Pressure-Maintaining Apparatus The maintenance of uniform conditions during the oxidation and the accurate determination of electrical and chemical data have required the use of an automatic system for feeding gas (oxygen or nitrogen) t o the deterioration cell as reaction with the oil occurs. This system is shown in assembled form in Figure 10. The component parts are: a 500-cc. waterjmketed buret for containing the oxygen or other gas, and using butyl phthalate as the disdscement medium: 8, hvdron bellows
FIGURE 9. DEGASSINGEQUIPMENT AND ELECTRICAL MEASURING CELL
FIGURE 10. AUTOMATIC OXYGEN FEEDAND PRESSUREMAINTAINING APPARATUS
other miking oontact with the mercury at a system pressure of 760 mm: and an automatic displacement mecha&m shown in part in Figure 11 for controlling the volumetric displacement of the system to maintain a pressure of 760 mm. in the deterioration cell. The operation of the system is BS fOllONS: When the system pressure decreases below 760 mm., a circuit is made between the two contact8 in the manometer. Closing of this circuit in conjunction with 8. vacuum tube control circuit and relay energizes the solenoid shown in Figure 11. This solenoid when eneraiaed dGws a wheel (with engaging pinj which is mounted on a steel tube and is normally held in a disengaged position by a spring, into contact with the star wheel shown in Fieure 11. The wheel and tube operate on a. chtinuously rotating shaft at slow speed and are driven from the shn,ft, t,hmunh
is ( a ) to remove dissolved gas and otht, .u.-u..u rlVYYYts in the oil sample so as to standardize initial conditions, (a) to filter the sample to remove any foreign particles, and (c) to permit a low pressure to be maintained in the deterioration cell during the admission of the oil, thereby thoroughly impregnating the paper in the cell. The degassing equipment is shown schematically in Figure 7 and assembled in position for degassing an oil sample into n deterioration cell in Figure 8.
suye of approximately 50 microns; a sintere&glass disk, 2. mounted between n male and female ground joint for filtering the ~~~
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of tube 8, a i d 8. jkcket fdrmed Gy tube 5 which permits tube 8 to he heated by steam applied through inlet 4 and drained out at 6 . The connection of vacuum pump is made through outlet 3, this arrangement preventing bhe pump from being fouled by Oil.
The oil sample is not heated before admission of the oil to a reduced pressure, and the method of heating the oil rtt reduced pressure prevents heating in excess of 100" C. The degassing equipment is also shown in Figure 9 in position for degassing an oil directly into an electric measuring cell (of the type previously describerl) for electrical measurements under vacuum. This procedure may be used for milking precise electrical measurements on the oil sample under carefully controlled conditions.
R.
elut,eh. The s t n r wheel
August 15, 1941
ANALYTICAL EDITION
is mounted on a threaded shaft which when rotated changes the displacement of the hydron bellows and accordingly the volume of butyl phthalate in the buret.
The control circuit is designed to give a time delay to prevent “chattering” of the mechanism due to system pressure changes produced by the solenoid pump. One notch on the star wheel corresponds to a change in the volumetric displacement in the system of 0.2 cc. The system is provided with manual control of the buiet volume by the crank shown in Figures 10 and 11, and provides outlets and controls for oven heating units, a thermoregulator, cooling water for the coils, and control for the solenoid operating the pump. The bystem as designed thus permits constant pressure conditions to be maintained in the deterioration system, and the rate a t which oxygen is consumed and total absorption as a function of time to be determined from buret readings.
Discussion The apparatus described has been used for studying mineral oil deterioration under a variety of conditions, such as continuous oxidation a t 760-mm. pressure, and limited oxidation with only a definite amount of oxygen admitted to the system, the system pressure being maintained with nitrogen ( 2 ) . The equipment described does not include provision for removal of the volatile oxidation products, although this may be effectively accomplished by connecting a n absorption
519
train in tube 6 (Figure a), thereby pumping the gas continuously through the absorption train. An electrical measuring cell, including an absorbent paper, may be placed in the gas line, tube 6, thereby permitting electrical measurements of the volatile products. Experience has indicated that the electrical measurements are of value not only for the specific application of mineral oils for electrical use but also for fundamental information concerning the mechanism of the deterioration.
-4cknowledgment The apparatus described in this paper has been developed in a program of research on mineral oil deterioration which until September I, 1939, was carried on under the sponsorship of the Utilities Coordinated Research, Inc., Association of Edison Illuminating Companies. Since that date it has been carried on in cooperation with a committee on insulating oils and cable saturants, Herman Halperin, chairman, representing the sponsors, The Engineering Foundation, and the American Institute of Electrical Engineers. Funds for this work are being contributed by a group of electric power companies, a group of oil companies, and a group of electrical manufacturing companies in addition to the sponsors.
Literature Cited (1) Balsbaugh and Howell, Rev. Sci. Instruments, 10,194 (1939). (2) Balsbaugh. Howell, and Assaf. ISD. ENG.CHEM.,32, 1497 (1940).
A New Laboratory Fractionating Column Head ‘I’ZENG-JIUEQ SGEiX, The Tung Li Oil TT orks, Chungking, China
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S C O S S T R U C T I S G and using a laboratory fractioiiatirig column for analytical purposes, a good column head is lust as imuortant as the column itself, if not more so. A ”perusal oP t,he brief reviews on laboratory fractionation ( 2 , 4, 7 ) reveals t’he l a r g e n u m b e r of types of columns ant1 heads in use. However, most of them are either very elaborate to construct or very expensive t o purchase.
The partial condensation type head of the well-known Peters column (5) is probably the simplest form with which the reflux ratio can be varieh at will, b u t n-ith i t t h e amount of reflux cnnnot be readily ascertained. The column of Cooper and Fasce ( 1 ) possesses the advantage that the amount of reflux can be d e t e r m i n e d by counting the number of liquid drops going back to the column. Its drawback is that, RS the area of the cooling s u r f a c e of
Water out
the partial condenser is fixed, the reflux ratio can be varied only by varying the rate of flow of the cooling medium. With liquids boiling above 100” C. the performance was found by the present author to be unsatisfactory. Furthermore, the thermometer reading of their column tends to be low at slow rate of distillation. The head designed by Simons (6) has proved very successful ( 3 ) , but its construction is rather elaborate.
A relatively simple column head has recently been built by the author and is shown in Figure 1. Its performance n-as found very satisfactory in actual use. It is a combination of the type of Peters and Baker and of Cooper and Fasce. The level of the cooling water in the partial condenser, C, can be adjusted by raising or lowering the outlet tube, 0, which is not in the same plane with the thermometer pocket, P. The reflux ratio can be estimated by counting the liquid drops at both tips A and T. It must be remembered that the drops at the two tips may not be of the same size and their relative value, if wanted, must be calibrated. The ground joint, J , enahles the head to be used with different columns.
Literature Cited M.,and Fasce, E. T., IND. Esc;. CHEM.,20, 420 (1928). ( 2 ) Dunstan, -1.E., et a[., editors, “Ycieuce of Petroleum”, Vol. 11. p. 1629, London, Oxford University Press, 1938. ( 3 ) Goldwasser, S.,and Taylor, H. S . , J . A4m.Chem. S O C . , 61, 1751 (1939). (4) Morton, A. A , . “Laboratory Technique in Organic Chemistry”, Chap. IV, Kew York, McGraw-Hill Book Co., 1938. (5) Peters, W.A., and Baker, T., IXD.ENG.CHEM.,18,G9 (1926). (6) Simons, J. H . , Ibid., -4nal. Ed., 10, 29 (1938). ( 7 ) Ward. C. C., U. 9. Bur. Mines, Tech. P a p r r 600 (1940).
(1) Cooper, C.
FIGUREI
