HIGH-TEMPERATURE VISCOSITIES OF000
LIQUID PETROLEUM FRACTIONS K. M. WATSON, JEROME L. WIEN, AND GEORGE B. MURPHY Universal Oil Products Company, Riverside, Ill. FIGURE1. HIGH-TEMPERATURE VISCOMETER to a preheating coil 10 feet long, also of l/s-inch tubing but of slightly larger inside diameter. The inlet end of the heating coil was connected to a Jerguson gage which, calibrated in cubic centimeters, served as a charging vessel. Both preheater and capillary coils were immersed in a bath set in a gas-fired furnace. The bath contained oil for temperatures up to 450' F. and a fused salt of approximately 50 per cent each by weight of sodium and potassium nitrates for temperatures above 450" F. The bath temperature was measured by a thermocouple connected to a recording potentiometer. The manometer connections from the end of the capillary coil were connected to the manometer as shown in Figure 1. The fluids in the manometer were the oil flowing in the tube and nitrogen gas above it.
S OPTIMUM design of petroleum refining equipment, calculations of heat transfer coefficients and pressure drops are of considerable importance. It is frequently necessary to know the viscosity of the oil a t temperatures ranging up to 1000" F. The literature contains very few data on liquid hydrocarbon viscosities above 300" F., and the proposed methods for extrapolating to obtain the values a t high temperatures appear uncertain. The purpose of the work here described was to determine the viscosities of various hydrocarbon materials a t high temperatures and develop a reliable method of general correlation. The viscosity determinations were made upon a series of liquid hydrocarbons ranging from the pure compounds, benzene and n-heptane, to lubricating oils and highly cracked compounds from commercial cracking units. The range of temperatures used was from 100" to 800" F. with pressures varying from atmospheric to 500 pounds per square inch.
The capillary tube method was used to determine the kinematic viscosity between 100" and 800"F. of a series of liquid hydrocarbons ranging from pure benzene and n-heptane to lubricating oils and products from commercial cracking units. The data can be satisfactorily expressed by the equation, log (log p / s 1.7 = a ( t 100) b, for temperatures above 210" F. On the basis of this equation a hightemperature viscosity chart was developed. A nomograph was developed permitting the estimation of the viscositytemperature curve of a liquid from laboratory inspection data. Pressures up to 500 pounds per square inch had little effect on the kinematic viscosity in the range of the determinations.
Apparatus and Procedure The viscosity measurements were based on Poiseuille's law stating that the pressure drop of a liquid passing in streamline flow through a capillary tube is proportional to the product of the absolute viscosity and rate of flow. In order to insure streamline flow conditions a t high temperatures and pressures where the densities are high and the viscosities low, it is necessary that a very long capillary of small diameter be used to permit measurable rates. Figure 1 shows the principal features of the apparatus:
+
It consisted chiefly of a coiled &foot length of steel tubing, inch outside diameter and approximately 0.054 inch inside diameter. To the ends of this coil were attached two tees which had connections leading to a differential manometer. The outlet end of the coil was fitted to a fine needle valve with a '/le-inch opening in its seat; the other end was joined by a union 605
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balance, there was evidence of a leak, and the run was discarded. The coil was emptied immediately to prevent any oil from coking or cracking. Before a different stock was run, the coil was cleaned by passing solvent naphtha, then motor benzene, and finally c. P. benzene through the coil, followed by nitrogen gas. Check runs were made at different rates of flow at the same temperature. At no time during any run was cracking indicated by gas at the outlet or vaporization in the tube which would have caused the manometer to be erratic. If there was cracking and the gas had been held in solution, it is assumed that the amount formed did not affect the measurements within the precision of the determination. Furthermore, the oil was in the coil such a short time that appreciable cracking at the temperatures employed was improbable. For temperatures between 100' and 210" F., and also as a check on the 200" F. determination of the high-temperature viscometer, the viscosities were determined in the laboratory by means of modified Ostwald pipets. After the apparatus was calibrated with pure liquids of known viscosities a t a variety of conditions of flow and temperature to verify the principle of the measurements, viscosity measurements were made on the stocks listed in Table I over the temperature ranges indicated. The detailed inspections of these stocks are shown in Table 11. In these runs the pressure was held at approximately 50 pounds per square inch greater than that estimated as necessary to prevent vaporization. A few runs were made on stocks 5 to 9; to determ'lne the effect of varying pressure.
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FIGVRE 2. VARIATION OF CALIRRATION CONSTANT WITH TEMPERATURE
A nitrogen cylinder equipped with a pressure regulator kept the desired pressure upon the charging vessel. An empty tank was inserted in the line to the nitrogen gas tank to take up the small pressure fluctuations from the regulator. The coil was calibrated with a liquid of known viscosity (chemically pure benzene) after which runs on the various stocks were made. After every five to eight runs the calibration of the coil was checked.
A typical run was conducted as follows: The bath was brought up to and held constant a t the desired temperature. A sample of oil to be run was filtered and charged into the Jerguson gage, and the desired pressure was put on the system. A small portion of oil was allowed to flow out of the manometer after which the manometer levels were adjusted at a suitable zero, with no oil flowing through the coil, by introducing compressed nitrogen to the top of the manometer. The run was started by opening the needle valve to give the desired differential pressure and observing the liquid level in the Jerguson gage and the time. The manometer was read every minute, and the reading kept constant by adjusting the needle valve. The time was recorded for every 5 cc. of oil, and a t least 30 cc. of oil were used in each run. The temperature of the room and pressure in t h e s y s t e m w e r e recorded, t h e latter being held constant by the pressure regulator. Rates of flow up to 2.0 cc. per minute of cold oil w e r e u s e d , maintaining differential manometer readings of from 4 to 10 inches. At high temperatures the pressure drop was kept low t o insure streamline flow. At none of the conditions investigated was there indication of deviation from streamline flow as evidenced by a change of appare n t v i s c o s i t y with change in rate. A f t e r the run the flow valve was closed, FIQURE 3.
PLOTOF LOG AL/S LOGt o F.
v8.
a n allowed e manometer was t o approach no flow equilibrium. If it did not
TABLE I. TEMPERATURE RANQEOF VISCOSITY MEASUREMENTS Stock
Temp. Range O F.
1. 300-400° F Midcontinent naphtha 2. 400-500" F:: Midcontinent kerosene 3. 500-600' F Midcontjnent gas oil 4. 600-700° F::Midcontinent gas oil 5. Pennsylvania lube oil, 8. A E. No. 10 6. Pennsylvania lube oil, S. A E. No. 50 7. Heat-exchanger condensate from Midcontinent topped crude 8. Recycle stock from Midcontinent topped crude 9. Combined feed from Midcontinent topped crude 10. Residuum from cracking Midcontinent gas oil 11. c. P. benzene (CeHe) 12. n-Heptane (n-C~Hle)
..
100-685 100-600 100-700 100-700 100-710 100-710 100-710 100-700 100-800 10 665 10g500 100-500
Discussion of Results The basic equation for calculating the viscosity is Poiseuille's law which, for liquids flowing through capillarytubes in streamline flow, is as follows: AP
where A P L
k LVP gd2
pressure drop through tube = length of tube d = inside diam. of tube V = linear velocity of liquid flowing through tube u = abs. viscositv of liauid g = acceleration "due to- gravity =
By considering a tube of definite length and inside diameter and rate of flow, the following equation is obtained to apply to the test apparatus:
where
y/s
=
kinematic viscosity, centistokes
C = calibration constant of tube
Ah = liquid differential of manometer, inches of fluid sc = do =
u =
flowing at room temp. sp. gr. of liquid flowing at room temp. density of gas (nitrogen) in manometer at room temp. and system pressure, grams/cc. rate of flow from charger a t room temp., cc./min.
In order to evaluate the calibration constant, C, of Equation 2, runs were made with liquids of known viscosity. Chemically pure benzene was most satisfactory. This calibration constant is a function of the coil's length and inside diameter and changes due to expansion of the coil with temperature..
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TABLE11. BOILING RANGEOF STOCKS (IN OF.) Stock9
1
2
3
4
11 8 47.2 750
11.8 40.4 750
11.8 35.3 750
11.8 30.4
296 319 329 340 34s 354 360
-
414 425 429 432 436 440 444
-
504 520 523 529 533 537 544
595 612 622 632 640 643 646
364 369 374 381
449 453 460 470
549 554 561 573
388 480 411 496 Table I describe8 the stocks.
585 589
Characterization factor K Gravity, O A. P , I. Pressure, mm. Initial B . P. 5% over 10% 20 30%
40% 50%
0
._
7
8
12.3 12.5 30.3 28.0 Vacuum Engler
11.2 19.5
10.7 22.2 750
276 737 747 760 765 765 767
735 762 770 812 830 857 880
396
-
390 494 565 612 650 680 697
-
650 662 672 685
777 790 802 830
755 795 827 887
713 738
872 910
940 977 1040 1055 (85%)
-
5
-
6
From the coefficient of expansion of the metal the ratio of length to the fourth power of the inside diameter was calculated for the different temperatures. The resulting relationship between calibration constant and temperature is plotted in Figure 2. The viscosity results obtained are plotted in Figure 3 with log kinematic viscosity vs, log temperature in O F . The numbers of the curves correspond to the numbers in Tables I and 11. The dotted portion of the lines were extrapolated for viscosity values to the estimated critical points (9). The data between 100" and 210" F. are laboratory determinations with the modified Ostwald pipets. Figure 3 shows that the lines in the range from 200" to 300" F. are continuous and the change in slope is uniform, indicating satisfactory agreement between the Ostwald and high-temperature viscometers. Curves 1, 2, 3, and 4 of Figure 3 represent narrow-boilingrange cuts from a Midcontinent crude. Herschel ( 7 ) pointed out that a series of cuts such as those plotted in Figure 3 give straight lines meeting a t a common point a t a relatively low temperature, These data indicate that this relationship is linear only over a relatively narrow range. The curves are not straight and show no indication of intersecting in the range investigated. A similar conclusion was reached by Fortsch and Wilson (4). Comparison of curve 8, a cracked stock, and curve 3, a n uncracked stock, shows that, although the two stocks have practically the same viscosity at low temperatures, the lines diverge at higher temperatures, curve 8 having a steeper slope. This effect shows that the cracked stock has a greater temperature coefficient of viscosity; it is more noticeable when a cracked residuum, curve 10, and a highly refined Pennsylvanih lube oil, curve 5, are compared. However, the difference in this slope is minimized a t temperatures above 210" F. where the lines tend to become more uniform. Several measurements were made a t pressures varying from 200 to 500 pounds per square inch a t 700" F. on stock 9. A similar series of measurements at different pressures were made on stock 5 a t 520" F. In both cases the effect of pressure on the kinematic viscosity was less than the probable error of the measurements. In general, it may be concluded that pressure, up to 500 pounds per square inch, has little effect on the kinematic viscosities of liquid hydrocarbons a t temperatures not too
915
...
458 485 505 525 547
573 603 638 700
9
10.8 10.2 19.6 5.4 Vacuum Engler 400 452 471 500 514 545 579
11
10
Sp. gr.
B. P . .
9.8 29.6 0.878 176
F.
12 12.5 75.5 0 6837 209
667 693 697 703 710 719 727
-
-
618 663 732 821
736 750 768 798
895 829
__ close to the critical. There is probably a considerable increase in absolute viscosity with increase in pressure a t high temperatures. However, this effect is compensated by the corresponding increase in density, leaving the kinematic viscosity little affected.
General Correlation For convenience in interpolation and accuracy of extrapolation it is desirable to develop a method of plotting to give straight-line relationships between temperature and viscosity. Numerous equations and empirical methods have been proposed for this purpose (1, 3 , 6 , 8 , s ) . However, none of these methods was entirely satisfactory when applied to the wide ranges of stocks and conditions here investigated. Figure 4 is such a n empirical chart; its ordinates are a function of the kinematic viscosity in centistokes and of Saybolt viscosity in seconds, and its abscissa is a function of temperature in " F. The scales were derived by first plotting the data by the method of Coats and Brown (2) for vapor pressure. A rectangular chart was derived from this plot by
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NO7-E.APPL/CABLE AT TEMPERAATURES BELOW 2/0'F FOR HFFAYY STOCKS NOT
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3 0.4
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FIGURE 5. HIGH-TEMPERATURE VISCOSITY NOMOGRAPH the method described by Watson and Wirth (11) in developing a vapor pressure nomograph. The resulting empirical functions are represented approximately by the following equation of the general form adopted by the A. S. T. M.: lOg(l0g p / s 1.7) = a log(t 100) b (3)
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The constants a and b are dependent upon the slope of the viscosity curve and its intercept, Figure 4 shows that, with this method of plotting, all the experimental curves are straight above 210" F. Straight-run stocks of normal width of boiling range and pure compounds are represented by straight lines throughout the range of temperature from 50" F. to the critical point. Light cracked stocks of normal boiling range, such as a recycle stock (curve S), are also straight below 210" F. Heavy cracked stocks, such as curves 9 and 10 (the former a combined feed and the latter a cracked residuum), deviate from a straight line. Curve 9 which is a cracked stock but of relatively wide boiling range, bends downward; curve 10, a cracked stock of narrow boiling range, bends upward. In general, the curves representing heavy stocks a t temperatures below 210" F. will vary from one extreme of curvature to the other, depending upon the width of boiling range. The line will be straight if just the right width of boiling range is encountered as shown by curve 7, a cracked stock of the same gravity as curve 9 but of a somewhat narrower boiling range. HA high-temperature viscosity nomograph (Figure 5 ) was constructed by making the scales the same as the ordinate and abscissa scales of Figure 4. Any straight line on Figure 4 is represented by a point on Figure 5. A series of oils
of the same type is represented by a number of points on the nomograph, and an index line is the locus of these points. The Universal Oil Products (U. 0. P.) characterization factor, K (9, IO), classifies the different types of oils as to paraffinicity varying in values of 12.5 for purely paraffinic stocks to 10.0 or less for highly cracked aromatic stocks. The index lines of Figure 5 are the loci of stocks of different K groups. To find the viscosity a t any temperature in the range of straight-line relationship from the nomograph, it is necessary to know only the characterization factor and the viscosity a t one temperature. Heavy stocks require the known viscosity to be a t any temperature above 210" F. If values of viscosity for heavy stocks are needed below 210" F., they should be determined in the laboratory to supplement the high-temperature data estimated from the nomograph. A correlation between U. 0. P. characterization factor, average boiling point, A. P. I. gravity, and viscosity a t 210" F. was recently presented by Watson, Nelson, and Murphy (IO). By imposing this relationship on the nomograph as an auxiliary chart, it is possible t o estimate the viscosity a t any temperature if only any two of the above physical properties are known. The nomograph and auxiliary chart are used in the following example: A residuum from cracking a Midcontinent gas oil has the following properties: Gravity, O A. P. I. A v . B. P., F.
5.4
730
Viscosity a t 210' F. Viscoaity at 122' F. Viscosity at 100° F.
5.7 28.0 72.6
MAY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
The characterization factor and the point representing this stock on the rectangular portion of Figure 5 may be located from either the viscosity a t 210" F. and the gravity, or from the gravity and boiling point. Two slightly different points, 1 and 2, result. For estimation of viscosities it is preferable t o use the index point based on a viscosity measurement. This fixes the characterization factor at 10.32 and the index point a t 3. The viscosity a t 900" F. is then estimated by projecting a line from 900 on the temperature scale through t h e index point to the viscosity scale where it intersects a t a value of 0.2 centistoke. From Figures 4 and 5 the viscosity of any liquid stock a t temperatures u p to the critical may be estimated from ordinary laboratory inspection data. Pressure up to 500 pounds per square inch has little effect on these relationships. A complete viscosity-temperature curve for a heavy stock requires combination of the high-temperature data estimated from Figure 5 with actual laboratory measurements a t temperatures below 210" F. The complete curve thus derived may or may not be a straight line below 210" F. when plotted
609
on Figure 4, depending on the width of boiling range and other factors such as wax content.
Literature Cited (1) Andrade, E. N. da C., Nature, 125, 309-10 (1930). (2) Coats, H . B . , Brown, G. G., Dept. Eng. Research Univ. Michigan, Circ. Series 2 ( D e c . , 1928). (3) Cragoe, C. S., Proc. World Petroleum Congress, London, 1933, 529. (4)Fortsch, A. P., and Wilson, R. E., IND.ENG.CHEM.,17, 291 (1925). (5) Generau, R. P . , Ibid,,22, 1382 (1930). (6) Hatschek, E., "Viscosity of Liquids," 1 s t ed., 1928. (7) Herschel, W. H., IRD.ENQ.CHEM.,14, 718-19 (1922). (8) Lederer, E. L.,Kolloid-Beihefte, 34, 270-338 (1931). (9) Watson, K. M., and Nelson, E. F., IND.ENG.CHEM.,25, 880-7 (1933). (10) Watson, K. M., Nelson, E. F.,Murphy, G. B.,Ibid., 27, 1460-4 (1935). (11) Watson, K. M . , and Wirth, C., IKD.ENQ.CREM.,Anal. Ed., 7, 72 (1935). RECEIVED December 4, 1935. Presented before the Division of Petroleum Chemistry a t the 90th Meeting of the American Chemical Society, San Fiancisco, Calif., August 19 t o 23, 1935.
Germicidal Properties of Phenolic Compounds CECIL G. DUNN Massachusetts Institute of Technology, Cambridge, Mass.
HE research presented in this paper was undertaken to determine the germicidal efficacy, under various conditions, of different solutions of sec-amyltricresol, o-hydroxy phenylmercuric chloride and a mixture, known as Mercresin, of the two chemicals. Information was also sought as to how solutions of these chemicals compared with some market mercurials and a phenol derivative in germicidal action. Experimental Procedure Food and Drug Administration methods ( 2 ) were followed. Preliminary work with mercurials showed that the apparent phenol coefficients obtained were often higher than the true ones, as the quantity of chemical carried from the medication tube to the broth subculture tube in the 4-mm. loopful required by the F. D. A. method was large enough to cause bacteriostasis. For this reason a second tube of sterile broth was always inoculated with four to seven 4-mm. loopfuls of material from the tube which had been inoculated directly from the medication tube. In a large part of the work a standard quantity of seven loopfuls was secondarily transferred. The secondary transfers were completed at once after each test in order to secure greater accuracy. Although the F. D. A. method requires results to be based on the 48-hour observation, incubations over longer periods of time were frequently made to ascertain what part bacteriostatic action played.
sec-Amyltricresol, o-Hydroxyphenylmercuric Chloride, and a Mixture of the T w o Test Organisms Staphylococcus aureus Rosenbach ( I ) (Government strain
No. 209) and Eberthella typhosa (Zopf) Weldin (Hopkins strain) were secured from the Food and Drug Administration a t Washington. Cultures of the same two organisms were also obtained from the Boston Biochemical Laboratory. The Health Department of Massachusetts a t Boston furnished a culture of a hemolytic streptococcus. Corynebacterium diphtheriae (Flugge) Lehmann and Neumann was received from the Harvard Medical School, and Sarcina ventriculi Goodsir from Brown University. Staphylococcus aureus Rosenbach, Escherichia coli (Migula) Castellani and Chalmers, Pseudomonas aeruginosa (Shroeter) Migula, Serratia p yoseptica (Fortineau) Bergey et all Proteus vulgaris Hauser, Staphylococcus citreus (Migula) Bergey et al., and Streptococcus Zactis (Lister) Lohnis were taken from the stock collection of the Department of Biology and Public Health a t the Massachusetts Institute of Technology.
sec-Amyltricresol (Pentacresol) sec-Amyltricresol was dissolved to the extent of 1 per cent in a 2 per cent soap solution (a potassium soap prepared from two parts of coconut oil and 2 parts of castor oil); and the germicidal efficacy of the soap solution of the chemical was determined, using first Staph. aureus (Government 209) as the test organism at 20" C. A phenol coefficient of 1 was ob-
