March, 1925
INDUSTRIAL AND ENGINEERING CHEMISTRY
291
Measurement of Absolute Viscosity of Light Distillates with the Saybolt Thermo-Viscometer’ By Arthur R. Fortsch and Robert E. Wilson STANDARD OIL COMPANY (INDIANA), WHITING, IND.
data had been published. N MAKING any fundaIn order to secure reliable data on the absoluteviscosities It therefore seemed highly of light petroleum fractions, such as gasoline, kerosene, mental study or correladesirable to determine the etc., for use in solving problems of design and performance tion of data on the flow calibration with reasonable in oil refineries, it seemed desirable to calibrate the Saybolt of fluids or the flow of heat accuracy. Since the instruinto fluids it is necessary to thermo-viscometer in absolute units. Although this inments have not been acknow with reasonable acstrument is very convenient and quite generally used to curately standardized-and curacy the absolute vismeasure the viscosity of light petroleum oils, there seems it would probably be difficosity of the fluid under conto be no published data as to the relation between the cult to standardize thems i d e r a t i o n . For all oils observed time of flow and the true viscosity of the oil. it was not considered necesh e a v i e r than very light By measuring both the absolute viscosity and the thersary to aim at any extreme lubricating oils the Saybolt mo-viscosity of a number of light petroleum fractions a degree of refinement. Standard viscometer or the satisfactory calibration curve applying to such oils was Saybolt Furol viscometer obtained and is presented herewith. This curve does not Experimental may be used together with apply with accuracy to liquids whose capillary rise is not At the outset the attempt accurate conversion charts very similar to that of the light hydrocarbons used in was made to calibrate the which give the absolute viscalibrating it. instrument by the use of cosities corresponding to the Means are suggested by which the operation of the several pure liquids whose various observed Saybolt Saybolt thermo-viscometer can be so changed as to give viscosities were given in the times. These instruments, reliable readings on all liquids regardless of the capillary literature. The results obhowever, are not satisfacrise. On the whole, however, the instrument is not well tained were quite discordtory for viscosity determinsuited for measuring absolute viscosities but is fairly ant, however, especially in ations on gas oil and lighter accurate for a limited class of oils of similar surface tenoils, or on the heavier oils at the case of water and carsion. bon tetrachloride. I n order temperatures much above 212’ F. that the calibration mieht be For very light oils the only device in general use in the oil as accurate as possible, it was deemed desirable to determine industry is the Saybolt thermo-viscometer, which is the rec- directly the absolute viscosities of a number of light liquids ognized instrument for measuring the viscosity of kerosene! and then compare them with the observed thermo-viscosities. gasoline, and similar light distillates. This instrument* To obtain the absolute viscosities, use was made of a modified consists of a long glass capillary which is immersed in the liquid type of the Ostwald viscometer, such as is described by t o be t e s t e d a n d B k ~ g h a m . ~This was placed in a bath held a t the same blown free of liquid temperature as that used in making the thermo-viscometer by means of a bulb readings. The density was also measured a t this temperaon the instrument. ture by using an accurate hydrometer. The liquids used were The number of sec- petroleum ether, acetone, cleaner’s naphtha, carbon tetrachloonds required for the ride, water, kerosene, and aniline. The data are given in oil to rise to a definite Table I. Two light oils were also used, their viscosities mark (about half an being determined by means of the Saybolt Universal visinch below the sur- cometer. face of the liquid) is According to theory, the relation between absolute vismultiplied by ten and, cosity and the observed time of flow in seconds should after using the ap- take the following form characteristic of all capillary tube proximate tempera- viscometers: ture correction tables, z-- -- A t - ; B is reported as net 3 & Saybolt thermo-viswhere Z = viscosity in absolute units s = density in grams per cc. cosity a t 60”F. t = time of flow in seconds In spite of the A and B are constants of the instrument rather extensive use of this instrument and It will be noted that if t is large the second term of the equaits convenience, the tion becomes negligible, and the plot of the logarithm of writers were not able Z/s versus the logarithm of the time of flow ought to give a to secure from either the maker or the Bureau of Standards any straight 45-degree line down to low viscosities,where B/t bedata as to the absolute viscosities corresponding to these read- gins to become appreciable and to cause some curvature in ings, nor did a survey of the literature indicate that any such the line. When the foregoing points were plotted in this manner, as * Presented before the Division of Petroleum Chemistry at the 68th in Figure 2, it was found that all the hydrocarbons, as well as Meeting of the American Chemical Society, Ithaca, N. Y., September 8 to 13, 1924. acetone and aniline, fell on a very satisfactory 45-degree line,
I
2 This instrument and its use are adequately described in “New and Revised Tag Manual for Inspectors of Petroleum,” p. 56.
a “Fluidity and Plasticity,” 1922, p. 76,
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I N D U S T R I A L AiVD ENGINEERING CHEMISTRY
Temperature
LIQUID
F. 72.6 70.0 70.0 71.4 t4.2 74.2 73.4
T a b l e I-Calibration Data for S a y b o l t T h e r m o - V i s c o m e t e r Saybolt Ostwald thermo viscometer time time' Viscosity" Viscosity Seconds Seconds Sp. gr. CP. Sp. gr.
Petroleum ether 8.5 544.2 .4cetone 8.3 814.6 Cleaner's naphtha 13.5 1131.2 Carbon tetrachloride 12.9 1736.7 Water 13.5 1670.1 Kerosene 37.0 :409.8 .4ni line 61.9 ,282.7 a Absolute viscosity was obtained from the observed time of efflux b y means of the equation: 2 = Cpl where, for the instrument used Z = viscosity in centipoises
- F,
C
p
c1 S 1
= = = = =
Vol. 17, KO. 3
0.00001104 50.54 grams per sq. cm. 11.5
density of viscous liquid a t temperature of experiment, in grams per cc. time of efflux in seconds
but that water and carbon tetrachloride showed marked deviations. This was to be expected on account of the large difference in surface tension of these liquids. The force which causes the liquid to rise in the capillary is the sum of the external head of liquid plus the surface tension force in the capillary. The value of the latter force can be compared directly with the liquid head if it is expressed in terms of "capillary rise," or the distance which the liquid would rise in this particular capillary above the level of the free liquid outside. A liquid which has a high capillary rise can thus be expected to rise more rapidly and give a lower thermo-viscometertime than a liquid of the same kinematic viscosity, but wibh a low capillary rise. T a b l e 11-Capillary Rise (Temperature approximately 70' F.) Capillary rise No. LIQUID Inches 1 Petroleum ether 1.66 2 Acetone 1.83 3 Carbon tetrachloride 1.05 4 Cleaner's naphtha 1.86 4.40 5 Water 2.04 6 Kerosene 2.30 7 Aniline 2.15 8 Straw oil
For comparative purposes the capillary rise of all the liquids used in this viscometer was therefore determined experimentally in the thermo-viscometer capillary a t approximately 70" F. The data are given in Table 11. It will be noted that on the whole the hydrocarbons are quite similar in capillary rise, although there is a slight increase as the VE A- UNCORRECTE hydrocarbon gets VE 6-CORRECTED heavier. Acetone and aniline also fit well into this series and give concordant results on the viscosity plot. Water, however, has a rise about twice that of any other liquid and would, therefore, be expected to give a time which is much too low, as has been shown in Curve A, Figure 2. Carbon tetrachloride, on the other hand, has about half the normal capillary rise and thus takes a much longer time than would be expected from its viscosity.
0.6627 0.7890 0.7425 1.600 0.9747 0.8179 1.0211
0.2949 0.3274 0.6234 0.9581 0.9248 1.8989 4.060
0.4450 0.4150 0.8396 0.5988 0.9488 2.3216 3.9670
Log I (Saybolt thermo)
0.929 0.919
1.130 1.111 1.130 1.568 1.792
Log viscosity Pp. - gr. 1 648
i 618
I 924 L.ii7
1.977 0 366 0 600
Notc-Washburn's equation4 for time of flow in vertical capillaries takes account of the surface tension. The equation with numerical values from approximate measurements upon the capillary tube of the thermo-viscometer is: - WA)Z 8 ( n - %a) ( h + A h ) + (77.4lr) 1 t = - - -8(n loge ( 1 - G2) YzDg rZDg 1 = time in seconds from an arbitrary initial % = viscosity of liquid = 0.009142 poises % A = viscosity of air = 0.000180 poises
time
-
1 = length of column of liquid in capillary a t time ( t ) = 29.95 c m . 1~ = total length of capillary 38.1 c m . r = radius of capillary = 0.01246 cm.
-
D = density of liquid 0.997grams per CC. R = acceleration due t o gravity = 980.1 cm./sec.r h = height of liquid above center of opening entrance of capillary = 20.15cm. 3 h = capillary rise = 11.6 cm.
Solving the equation for t gives 30.3 seconds, compared with an experimental value of 27.7 seconds. Considering that the measurements were only approximate and that the drainage error was not taken into account, this is a fair check.
The magnitude of the errors resulting from these differences in capillary rise will be realized from the fact that the actus1 liquid head just before the liquid crosses the final mark in the viscometer capillary is only 0.5 inch, while the head to be added to this due to capillary rise varies from 1 to 4.4 inches. For practical use in making conversions the lower portion of Figure 2 is replotted with direct coordinates in Figure 1. In this case again the line is straight except at low viscosities, where B/t becomes appreciable, but its slope is A , rather than 45 degrees. A slight modification of the present. procedure in the use of the viscometer would make i t fairly suitable for all classes of lighter liquids instead of oils alone, as a t present. As now used, the liquid level is adjusted to coincide with some mark on the viscometer tube regardless of the liquid used. If, instead of this, the level outside the viscometer is so adjusted that the maximum height to which the liquid rises in the capillary tube coincides with this mark, the variable capillary effect i s e l i m i n a t e d . By 2 PZTROUUM ETHER making this slight 3 CARION TRRACHLORIDE 4 CleANtR'5 MIIITHA change the remainder 5 DISTILLCD WATER of the present procedure may be followed 8 VERI UWT WOWCATout. As an illustration , the liquid level for water, instead of being a t the upper mark, would be 4.4 inches below it. Obviously, the times of fow will be longer in every instance, so that a new 4 Phys. (1021).
Rea.,
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March, 1924
INDUSTRIAL ,450 ESGIXEERISG CHE.1fISTRY
calibration curve is needed. Data for such a curve are given in Table I11 and the resulting curve is given in Figure 2 (Curve B). It will be noted that all the liquids check this line, regardless of their surface tension. Table III-Saybolt-Thermo Times vs. Kinematic Viscosities (Corrected for capillarity) t LIQVID Z/s Seconds log Z/s log 1 Acetone 0.4150 14.0 1.618 1.146 Petroleum ether 0.4450 14.9 1.648 1.173 0.5988 19.1 1,777 1.281 Carbon tetrachloride 1.398 0.8396 25.0 i ,924 Cleaner's naphtha Water 0.9115 27.7 i.960 1.442 Kerosene 2.322 71.3 0.366 1.853
Although the Saybolt thermo-viscometer is not an instrument for precise measurement of absolute viscosities, the modified method described, together with Curve B, gives a fair approximation and may be used as such on any light liquid. Howeyer, Figure 1 applies very well to the oils for which the
293
instrument was intended, since their capillary rise (Table 11) is approximately the same. It is based upon a procedure in almost universal use in the oil industry and is therefore put forth as a simple means of securing data for calculating pressure drop and heat transfer in the practical problems of an oil refinery. Another source of error in the presentviscometer is the drainage error. Ordinarily the operator presses the bulb for only 10 or 15 seconds to clean out the capillary before making a determination; if this time is increased to 2 or 3 minutes the reading in seconds is increased, especially in the case 6f fluids more viscous than kerosene, Apparently, 10 or 15 seconds is not sufficient time for all liquid to drain from the capillary. Fortunately, however, in the case of the lighter hydrocarbons, for which the instrument was designed, this error is comparatively small.
The Shimer Filter Tube' B y Eugene C. Bingham LAFAYETTZ COI,LBGB,EASTON, PA.
ELIEVISG that it will be of considerable service to chemists to have the Shimer filter tube2 made available in its improved form, the writer gives herein the specifications and details of the apparatus as it is now used in Dr. Shimer's laboratory. The apparatus shown in the figure consists of a Pyrex glass filter tube, 8,of 34 mm. outside diameter and 30 mm. inside diameter. The tube must have a uniform diameter, and for this reason the top of the tube should be ground off and not fire-polished. The stem of the tube, B , is 90 mm. long, of 10.5 mm. outqide and 9 mm. inside diameter. -4perforated glass, porcelain, or other resistant plate of 3 mm. thickness and 29 mm. in diameter is used. The perforations are numerous and should be not less than 2 mm. in diameter. The shoulder of the filter tube is made nearly flat, in order to afford a firm support for the plate. To use the tube, disks 30 mm. in diameter are cut from absorbent lint, such as is used in surgery, and one of these is placed on the supporting perforated plate. The tube is attached to a filter flask, by means of a rubber stopper, and into it is poured, under slight suction, a suspension of paper pulp made up to a creamy consistency. The excess of water is removed by suction, and when finely divided precipitates such as barium sulfate are to be filtered, the pulp is well rammed down by use of the stamper, C. For small gelatinous precipitates, and all others which never run through an ordinary filter, no stamping down is necessary. Bulky gelatinous precipitates must be filtered in the old way. The thickness of the layer of felted pulp will ordinarily be about 5 mm. When filtration and washing are completed, the handle of the stamper is run up through the stem as shown at D, and the contents of the tube are pushed cautiously upward until the filter felt just projects beyond the top of the filter tube. The felt, with its precipitate, can now be readily detached from the disk of absorbent lint and in most cases can be at once transferred in its moist state to a weighed crucible for ignition. The disk of absorbent lint can, of course, be used repeatedly.
B
Received October 8 1924, The first forms of the filter tube and detailed directions for its uoe were described by P W. Shimer. J . A m Chem. Soc , 27, 287 (1905), Chem. En&, 6, 197 (1907) I
The rod of the stamper is 210 mm. long and 8.5 mni. in diameter, and the rubber stamper is 27 mm. in its largest diameter. The end of the stamper rod must be ground off flat and true, so that the filter can be pushed out in a horizontal position, thus cleansing the sides of the tube of all adhering precipitate. Dr. Shimer has also long used successfully an alternative form of filter tube in which a perforated glass disk is made in one piece with a long glass tube. For most purposes, however, he prefers t h e f o r m herein described, since the other form is more fragile, The paper pulp can be prepared either by macerating ordinary washed p a p e r meFILTER TUBE chanically or by di30 I N S I D E DIAM gestion of unwashed 34 OUTSIDE D I A M paper for about 1 minute with pure hyFILTER M A T drochloric acid (speABSORBENT L l M T cific gravity 1.20) PERFORATED DISK slightly diluted with distilled water. The mass of paper, contained in a heavy glass or B a k e l i t e 9 HOLES vessel, must be vigor2 DlAM ously stirred with a wooden stirrer during SINSIDE DlAM the d is i n t e g r a t i n g process, and must t h e n a t once be strongly diluted with distilled water. Too long action of the strong acid must be avoided; otherwise the disintegration will
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