Determination of the Aniline Point of Dark
Petroleum Products ROBERT MATTESON, E. H. ZEITFUCHS, A N D K. R. ELDREDGE Standard Oil Company of California, Richmond, Calif.
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the box containing the complete apparatus. A photograph of the equipment is shown iu Figure 2. ELECTRICAL SYSTEM.A diagram of the electricd circuit is shown in Figure 3. The light from the lam , 2'8, controls the current flowing through the photocell, TI. &s current seta up a voltage across Rs which is applied to the grid of the vacuum tube, %, t o control the latecurrent through themeter, M. Any change in the amount ofradiation t o the photocell due to achange in the condition of the medium between the photocell and the lamp will be shown as a change in the reading of the meter. The initial reading of the meter is set by resistor Ra with resistor R. limiting the maximum bucking current. The sensitivity of the system is varied by resistor R I . Resistor R, limits the current in the lamp t o the maximum safe value t o obtain long life from the
HE aniline point (1) of a petroleum product is defined by the American Society for Testing Materids as the
minimum equilibrium solution temperature for equal volumes of d i n e and the petroleum product. The method of test (1) for determining the aniline point proposed by the A. S. T. M. depends upon the +sua1 observation of turbidity in the mixture, and the test is intended for examination of oils not darker than No. 8 A. S. T. M. color (1). The aniline points of darker oils must therefore be determined by other means. Methods for determining the aniline point of dark oils are described by Donn (E) and by van Wijk and Boelhouwer (4).
lamp.
of Operation ..1 ncnty millilitersMethod of tLc nniline-oil minurc nrc plwed
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.toppered smnplr rnnr,tinrr. '1l.e nropprr is fitted loosely, nnd flie mixture i. hrnred to >L mini ncll nhurr rlienunniunt eauilihrium solution temoeratur; The heated mixture 1s then shaken ~~~~~~~~
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experience enables the operator to determine t h e 5rooer amount of heating in 2 single operation.
FLASHLIGHT
CELL
FIG-
1. DIAGRM~ OF MECXANKCAL
EQUIPMENT
Donn's procedure consists in determining the temperr .e at which a break occurs in the viscosity-temperature c w e ; this tem erature is desi nated as the aniline point. The viscometer use$by Donn c o d not be used for very dark oils. The aniline point measurement of very dark oils was restricted to an approximate method in which the occurrence of turhidity was observed in the 50/50 volume per cent mixture under a microscope. Van Wijk and Boelhouwer (4)make use of the variation in transparency to infrared radiation of an equal volme mixture of oil and aniline. At the aniline point a masked change in the transparency is noted, owing to the appearance of a second liquid phase in the form of fine droplets. The purpose of the present paper is to describe a simplified type of apparatus employing infrared radiation for detecting the point a t which separation of the phases begns.
Description of Apparatus hlrciirr\lc*i. i : u m P n E w .
.4 diagram of tLc 3rmnpcmcnr of
tLeesseutrnl ~ ~ 3 ~ 1 s ~ i f i h e m ~ cequipment I I ~ n i ~ a Iisshoan in t'igun 1. T ~ siinmlr Q cnntaiuer ii a Pvrrx trsr tube. a~,uroximntclr25mm. outside diameter, with depressions as'd6wn t o form a "cell" 1 to 2 mm. thick and about 10 mm. in diameter. Light from the 1.1-volt lamp passes through the cell and falls upon the as-med photocell, which has maximum sensitivity at 7500 A. luhstitution of the photocell for the thermopile used hy van Wijk and Boelhouwer permits the use of an inexpensive micro.ammeter as the indicating instrument. The sample container is held in a Dewar flask and is stoppered with rubher stopper holding a mercury-in-glass thermometer of .suitable range. A light-tiht cap covers the whole assembly in
F I G ~2.E ANILINEPOINT INDICATOR
The heated sample is placed in the Dewar flask !st room temperature in such a position that the plane of the cell is normal to the incident radiation, the light-tight cap is placed in position, switches St and SS me closed, resistance RI is set to maximum sensitivity, aud Rn is adjusted to bring the needle of the microammeter to B reading of approximately 90 per cent full scale deflection. Where temperature-meter deflection curves 394
T3
R4
SI
Rl
OF ELECTRICAL CIRCUIT FIGURE 3. DIAGRAM
BI.
1.5-volt dry cell
M.
0-100 microampere meter, 3-inch face, 900 oiiilis
Bz. 2-45 volt B batteries Bs. 1-volt bias cell
Ri. 6-ohm variable resistor, sensitivity control
RI. 5000-ohm variable resistor, meter zero contra!
RI. 1500-ohm fixed resistor R4. 1.7-ohm fixed resistor Ra. 300-me ohm fixed resistor R E . 2-megofm fixed resistor SI. Single-pole single-throw toggle switch Sz. Single-pole single-throw toggle swiict. TI. RCA Type 868 photocell Tz. Type 1G4G vacuum tube TJ. Type 112 1.1-volt., 0.3-watt Pencell lamp, ~ I a z c l n
The absence of stirring also tends to give a value for the aniline point that will be somewhat higher than that determined by the visual method. The difference in the aniline point as determined by the above procedure and by the visual methods increases with the value for the aniline point. This makes i t necessary to establish a correction curve (Figure 5 ) by determining aniline points by the two procedures on a series of transparent samples covering a wide range of aniline points above room temperature. The reason for the rapid increase in the value of AT (infrared aniline point - visual aniline point) with aniline point is that the temperature-time curve follows
Where no record of the temperature-meter deflection curve is to be kept, the operator simply observes the point a t which the needle of the meter begins to move sharply. With the proper sensitivity setting and optimum film thickness, this point is always well defined. The time required for a determination is dependent upon the difference between the aniline point of the oil being tested and the surrounding temperature-approximately room temperature. For example, if a material having an aniline point only slightly above room temperature is heated to a high temperature, say 80" C., a t the beginning of the test, a half hour or more may be required for the solution to reach the aniline point. On the other hand, an oil having an aniline point above approximately 50" C. will reach its minimum equilibrium solution temperature in a few minutes, even if heated considerably above its aniline point. Average time for a test, including loading the sample container, heating, and cooling, is between 15 and 20 minutes.
Calibration By following the procedure outlined above, the temperature of the mixture drops a t the natural cooling rate. The thermometer bulb is placed about 5 mm. above the center of the cell. Under these conditions, the temperature indicated by the thermometer is somewhat higher than that in the cell, depending upon the rate a t which the temperature is falling.
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IO0 5
ANILINE POINT BY I N F R A RED RADIATION-'C.
FIGCRE 5. CORRECTION CURVEBOR INFRARED ANILINE POINTINDICATOR
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INDUSTRIAL AND ENGINEERING CHEMISTRY
396
Vol. 13, No. 6
Mixtures were found in a few cases, such as those described by van Wijk and Boelhouwer, wherein the aniline-oil mixture was more opaque above the solution temperature than after separation of the phases took place. The temperaturemeter deflection curves for these mixtures break sharply upward a t the aniline point in a direction opposite to that shown in Figures 4 and 6. The aniline point of an oil whose solution temperature with aniline is below room temperature is determined by blending the oil with a hydrocarbon diluent of higher aniline point. One such method (3) involves the use of a standard diluent such as a narrow boiling petroleum fraction of 60" C. (140" F.) aniline point and approximately 130 average molecular weight. A 50/50 per cent by volume mixture is made of the sample and the diluent. The aniline point of this blend is then determined. The aniline point of the sample is read from a reference curve showing the relation between the aniline points of oils and blends of these with the diluent. The reference curve is established by the visual method on a series of transparent oils covering a wide range of solution temperatures.
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45
40
50
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55
65
TEMPERATURE OF MIXTURE- "C.
FIGURE6. ANILINEPOINT
OF CRACKED TAR DETERMINED BY IXFRARED RADIATION
Acknowledgment an exponential law. The rate a t which the temperature of the liquid is falling is as follows:
Thanks are due to R. A. Krause for his valuable assistance in developing the electrical system.
de deg.
Temperature,
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C.
4.8
90 75 60 45
2.8 1.3 0.6
0 = temperature i = time
Literature Cited (1) 4 m . SOC.Testing Materials, "Standards on Petroieum Products
and Lubricants", Appendix 11, p. 14, September, 1940. (2) Donn, Leon, IND.ESG. CHEW., -4nal. Ed., 9, 202 (1937). (3) du Pont de Nemours & Co., E . I., Inc., Wilmington, Del., private
communication.
Results The apparatus and procedure described here have given satisfactory results on a wide variety of stocks, including straight-run residue, cracked tars, extracts from solventrefining operations, and black fuel oils. Figure 4 is the temperature-meter deflection curve for a transparent mixture of aniline and a blend of a highly paraffinic lubricating oil and a low aniline point extract. The point at which phase separation took place, as indicated by the meter, was 55.6" C. From Figure 5 the value for the temperature correction, AT2 is 1.1" C.; and the aniline point by the infrared method is 54.5" C. The value obtained by the visual method was 54.4" C. Comparison of the results obtained with transparent oils tested by both the visual and infrared methods indicates that when the correction froin Figure 5 is applied, the two methods check within 1O C. Application of the correction for cooling obtained from Figure 5 increases the accuracy of the present infrared method over that of van Wijk and Boelhouwer, who obtain agreement within 2" C. on tests of duplicate samples. The curve shown in Figure 6 was obtained on a black cracked tar. The aniline point after applying the correction, AT, is 51.7" C. In general, the form of the curves is erratic after phase separation has begun. The left side of Figures 4 and 6 clearly shows this. The erratic behavior is due to variations in the state of the dispersion of the separated aniline and to their effect on the amount of transmitted radiation. Secondary effects enter as other solubility phenomena appear. For example, in the case of the cracked tar--aniline solution, a point is reached where the transmission of radiation is greater than it was when the solution was above its separating temperature. This is probably due to the formation of large globules of aniline which transmit a wide band of radiation extending into the visible region.
(4) Van Wijk, W. R., and Boelhouwer, J. Tech., 24, 598 (1938).
IT.XI., J. Znst. PetroZeum
Thermoelectric Effects in Photometry J
J. K. BERRY Messrs. Courtnulds, Ltd., Coventry, England
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PHOTOMETER employing the barrier-layer type of cells for measuring light intensity can find many applications both in industry and other fields, particularly as ail aid to routine testing. Since most light sources have a variable intensity it is necessary to compensate for this, and it is usually done by a second photocell connected in opposition to the first across a suitable galvanometer. As pointed out by Lluller (3) the compensating device can be either optical or some form of resistance bridge. If the latter device is used it may be subject to considerable errors unless certain precautions are taken. Consider the circuit auggeatcd by Wilcos (4); a balance is obtained by varying resistors R1 and Rz (Figure 1). I n practically every case the metal of the sliding contact and that of the resistance wire will be different and will therefore be a potential source of a thermoelectric e. in. f. On varying the resistance, the friction of the contact arm on the wire causes a rise in temperature and the Seebeck effect a t once becomes considerable, the magnitude depending upon the metals of the resistance and speed of variation. For certain types of photometry this effect will probably be negligible, but for
