Viscosity of Hydrocarbon Solutions J
d
Methane-Ethane-Crystal Oil System' HE ability to predict the viscosity of hydrocarbon liquids as a function of pressure, B. H. SAGE AND W. N. LACEY temperature, and composition is of value California Institute of Technology, Pasadena, Calif. in the production and refining of petroleum. This study of the viscosity of the liquid phase of the methane-ethane-crystal oil system was made The viscosity of twenty-one liquid mixtures of methane, as part of a coordinated program of research ethane, and crystal oil was determined at pressures between directed toward such predictions. The work bubble-point pressure and 2500 pounds per square inch at was limited to a temperature of 100" F. and a temperature of 100' F. Information concerning the visto liquid phases containing less than 5 weight per cent methane and 10 weight per cent ethane. cosity of the liquid phase of these mixtures in the two-phase The viscosity of the liquid phase of twentyregion was also obtained. The results are presented in one mixtures in this range of composition was graphical and tabular form. determined in both the tmo-r)hase and the condensed liquid regions a t pressures as high as 2500 pounds per square inch. The method involved the measurement of the time for a steel The effect of pressure upon the viscosity of hydrocarbon ball to move down a closed, inclined, liquid-filled tube under the liquids has been studied by a number of investigators ( I , 4, 8, influence of gravity. The time of roll was ascertained by means IO) and appears to be of sufficient magnitude to be Torthy of of an electrically driven chronograph with an uncertainty of not consideration in engineering calculations. The effect of dismore than 0.15 per cent. The pressure existing within the viscometer was determined by means of a calibrated pressure balance solved gas upon the viscosity of hydrocarbon liquids has also with a sensitivity of 0.5 pound per square inch, and it is believed been reported (6, 9, 11, 12, 1.3). However, these results inthat the pressures within the apparatus were known with an unvolved the combined effect of the change in composition and certainty of not more than 2 pounds per square inch. At presthe change in pressure necessary to accomplish that change in sures below 50 pounds per square inch a mercury-in-glass manometer was employed. The temperature of the viscometer, which composition of the liquid phase. In the present work, howwas immersed in an oil bath, w&s ascertained by means of a ever, these effects have been separated and it is possible t o ,multilead copper-constantan thermocouple in conjunction with a ascertain individually the effect of changes in pressure and' in White potentiometer. An agitated ice bath was used as a refercomposition upon the viscosity of hydrocarbon liquids. ence temperature for one junction. The thermocouple was calibrated in place by direct com arison with a strain-free platinum resistance thermometer whicg had been standardized a short lMaterials time before by the National Bureau of Standards. The composition of the material under investigation was asA water-white oil refined from Pennsylvania crude stock certained by measuring known amounts of each of the components was used in this investigation. Its densitjr at 100" F. was into the apparatus. The crystal oil was added to the evacuated 51.47 cubic feet per pound (0.8244 gram per ml.), and the viscometer, and the amount was determined gravimetrically. viscosity-gravity factor (5) was 0.7979. This oil was the same The ethane was added by vaporization from a small weighing bomb, and the quantity ascertained by the change in weight of as was used in a n earlier investigation of viscosity from this the bomb. Liquid air was employed to recondense any ethane relaboratory ( 8 ) . It will be referred t o as crystal oil but is difmaining in the connecting tubing into the weighing bomb, thereby ferent in properties from the water-white oil used in a number avoiding the need for any correction on this account. The of earlier phase-equilibrium and viscosity studies from the amount of methane added was determined from the change in pressure in an isochoric, isothermal chamber due to the withauthors' laboratory. The ethane was obtained from the drawal of the gas into the apparatus. This reservoir wm caliCarbide and Carbon Chemicals Corporation, and a fractionabrated directly by a mercury-in-glass buret located within a tion analysis showed i t to contain 99.3 mole per cent ethane, constant-temperature air bath. It is believed that the weight of 0.3 mole per cent methane and noncondensable gases, and 0.4 each of the components was ascertained with an uncertainty of approximately 0.3 per cent. mole per cent heavier hydrocarbons. This material was not The viscometer was calibrated by measurement of the roll further purified except for a. partial condensation a t liquid time with fluids of known viscosity. The viscosity of these fluids inch of mercury. The air temperatures a t a pressure of was ascertained by means of a quartz modified Ostwald pipet methane was obtained from the Buttonwillow Field in Calia t atmospheric pressure, and it is believed that it was known within 0.5 per cent. Discussions of the parameters which must fornia; after the removal of carbon dioxide and water b y conbe considered in the calibration of instruments of this type have tact with potassium hydroxide and magnesium perchlorate been given by Flowers ( 2 ) and Hersey (3). They indicate that a at pressures in excess of 300 pounds per square inch, it is beknowledge of the density of the fluid is necessary in order to perlieved that the methane contained less than 0.1 mole per cent mit an evaluation of the viscosity from the measured roll time of the ball. In this instance the density of the liquid phase was of impurities. ascertained from the composition of the phase by a correlation of the partial volumetric behavior of hydrocarbons in the liquid Experimental Methods phase ( 7 ) . The apparatus employed in this investigation was deWithin the laminar regime the absolute viscosity of a fluid is a single-valued function of the rate of roll and the difference in scribed in connection with a study of the viscosity of the density between the fluid and the ball. However, at the more methane-propane-crystal oil system. The instrument was rapid rates of movement the flow around the ball is no longer similar in principle to that used b y Flowers ( 2 ) and Hersey strictly laminar, and it is necessary to make corrections for the (3): energy lost due t o turbulence ( I O ) . I n the present work nearly all of the measurements were made in the laminar regime, and in 1 Previous papers in this series appeared i n 1935 (page 9 3 4 ) . 1937 (page no case was the correction for the existence of turbulence more 8 8 8 ) , and 1938 (page 829). than 5 per cent of the measured viscosity.
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588
INDUSTRIAL AND ENGINEERING CHEMISTRY The effect of pressure upon the calibration of the i n s t r u m e n t was determined from a comparison of the indicated increase in viscosity with pressure of several organic liquids with that found by Bridgman ( 1 ) . T h i s comparison indicated t h a t t h e calibration of the instrument changed as much as 0.5 per cent. However, since t h i s was somewhat less than the e s t i m a t e d absolute uncertainty of measurement, no correction for the effect of pressure was made. I n measurem e n t s of t h i s nature i t is difficult to ascertain with accuracy the over-all unc e r t a i n t y of measurement. However, i t is believed that the instrument 'was sufficiently well c a l i b r a t e d and the independent v a r i a b l e s were controlled and determined with sufficient accuracy so that no uncertainties greater than 2 per cent are involved in t h e v a l u e s of v i s cosity recorded here.
500
VOL. 32, NO. 4
1500
1000
FRESSLRE
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PE?
2000 SO.
IN.
FIGURE 1. VISCOSITY OF BUBBLE-POINT LIQUID AND CONDENSED LIQUID FOR THE ETHANE-CRYSTAL OIL SYSTEM AT 100' F.
variation in the viscosity of ethane-crystal oil mixtures as a function of their bubble-point pressures. The curves sloping u p ward to the right for the individual mixtures depict the effect of pressure upon the viscosity of these mixtures in the condensed liquid region. In Figure 2 the ratio of the viscosity of the liquid to the viscosity of the liquid at bubble point is presented as a, function of the difference between the pressure and the bubble-point pressure of the mixture in question. In this case the liquids containing the larger amounts of ethane exhibit a smaller relative effect of pressure upon the viscosity. The viscosity of the mixtures investigated experimentally is recorded in Table I. Figufe 3 presents the variation in the viscosity of the ethane-crystal oil system with composition for several pressures. The effect of the presence of ethane is more pronounced at the lower concentrations of this material, which is in accord with the behavior found for a number of other hydrocarbon systems. The behavior of the methanecrystal oil system was investigated briefly, and the results obtained
Results T h e experimental measurem e n t s for t h e crystal oil are in excellent agreement with t h e values reported e a r l i e r f o r this material (8). The results of the experimental measu r e m e n t s upon the ethane-crystal oil system are presented in Figure 1. The lefthand curve represents the
1.30
>
1.20
1.10
P-Pb
FIGURE2. RATIOOF
LB.
PER
SQ.
IN.
THE VISCOSITYAT A GIVEN PRESVISCOSITY AT BUBBLE-POINT PRESSURE FOR MIXTURESOF ETHANEAND CRYSTALOIL AT 100' F.
SURE TO THE
APRIL, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
589
of these mixtures in the two-phase region. It must be remembered that, a t pressures below bubble point, the composition of the liquid phase does not correspond to the composition of the system as a whole.
IO0
80
80
>
60
i
60
>
40
40 20
20 WEIGHT
PER
CENT
ETPANII
FIGURE 3. EFFECTOF COMPOSITION UPON VISCOSITY FOR THE ETHANE-CRYSTAL OIL SYSTEM AT 100” F.
I
2
I
WEIGHT
PER
3
CENT
4
METHANE:
FIGURE5. EFFECT OF COMPOSITION UPON THE VISCOSITYOF BUBBLE-POINTLIQUID FOR THE METHANE-ETHANE-CRYSTAL OIL SYSTEM -4T 100 F. 35 W
The effect of methane upon the viscosity of bubble-point liquid for varying ratios of ethane and crystal oil is shown in Figure 5. Methane causes a much larger absolute decrease in the viscosity of the liquids which contain small amounts of ethane than it does in the case of those containing relatively large amounts of this material. I n general, the behavior of the methane-ethane-crystal oil system is similar to that found for the methane-propane-crystal oil system ( 8 ) ,
‘i! 0
a 3
I
30
> 25 0 U
‘c
Acknowledgment
PRESSURE
LB.
PER
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IN
F I G U R4.~ VISCOSITYOF BUBBLE-POINTLIQUID AND CONDENSED LIQUIDFOR MIXTURES OF METHANE, ETHANE, AND CRYSTAL OIL AT 100’ F.
This work represents a part of the activities of Research Project 37 of the American Petroleum Institute. The authors are indebted to this organization for financial support which has made the work possible. The Southern California Gas Company furnished the methane gas which was used. Lee T. Carmichael carried out the experimental measurements, and L. Fay Prescott assisted with the calculations.
Literature Cited were in excellent agreement with those previously reported (8) for this system. The effects of pressure and composition upon the viscosity of several ternary mixtures of methane, ethane, and crystal oil are given in Figure 4. All of the curves are for a constant ratio of ethane and crystal oil, with varying amounts of methane from one to another. The upper bubble-point curve represents the variation in the viscosity of the ethane-crystal oil system with its bubble-point pressure; the other bubblepoint curve shows the variation in the viscosity of the ternary mixtures with their bubble-point pressures. The viscosity of the liquid phase of the ternary mixtures investigated is recorded as a function of pressure in Table I. These results include information concerning the viscosity of the liquid phase
(1) (2) (3) (4) (5) (6) (7)
(8) (9) (10) (11) (12) (13)
Bridgman, Proc. Am. Acad. A r t s Sci., 61, 58 (1926). Flowers, Proc. Am. SOC.Testing Materials, 14, 565 (1914). Hersey, J . W a s h . Acad. Sci., 6, 525 (1916). Hersey and Shore, Mech. Eng., 50, 221 (1928). Hill and Coats, IND. EKQ.CHEM.,20, 641 (1928). Sage, IND. ENQ.CHEM.,Anal. Ed., 5, 261 (1933). Sage, Hicks, and Lacey, “Drilling and Production Practice, 1938”, p. 402, New York, Am. Petroleum Inst.. 1939. Sage, Inman, and Lacey, IXD. ERQ.CHEM.,29, S88 (1937). Sage and Lacey, “Drilling and Production Practice, 1935”, pp. 141-7, New York, Am. Petroleum Inst., 1936: Oil W e e k l y , 77, No. 10, 29 (1935); Oil Gas J . , 34, No. 1 (1935). Sage and Lacey, IKD. ENG.CHEM.,30, 829 (1938). Sage, Mendenhall, and Lacey, Am. Petroleum Inst., Production B u l l . 216, 45 (1935); Oil Weeklg, 80,No. 13, 30 (1936). Sage, Sherborne, and Lacey, Am. Petroleum Inst., Production BuEl. 216, 40 (1935); Oil W e e k l y , 80, No. 12, 36 (1936). Sage, Sherborne, and Lacey, IND. ENQ.CEEM..27, 954 (1935).
