JANUARY, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
of the irreversibility of the colloidal precipitate, the adsorbed salt is not released on cooling. The composition of the iron blue pigments, as shown in the data in Table 11, is dependent to a large extent on the composition and nature of the white paste. The ratio of external iron (the ferric cation) to the iron contained in the ferrocyanide complex decreases with an increasing ratio of sodium ferrocyanide to ferrous sulfate used in the preparation of the white paste. This relation is shown by the curves in Figure 2. The extent of the oxidation of the ferrous iron in the white paste increases with an increased reactant ratio. This relation may be the result of the fact that the particle size decreases, which presents a larger surface of precipitate with which the oxidizing agent makes contact. The extent of the oxidation of the ferrous ferrocyanide is definitely dependent upon the nature of the oxidizing agents reported, as indicated in Table 111. The excess of an oxidizing agent seemed t o have no effect on the product of the reaction. possible Of this investigation, it From the that iron blue (ferric ferrocyanide) pigments Of Consistently
91
similar qualities can be produced, if the concentrations of the sodium ferrocyanide and ferrous sulfate solutions used in the formation of the white paste are carefully controlled. The temperature in the formation of the white paste should be kept constant for consistent results in the production of the pigments.
Literature Cited (1) Davidson, D., and Welo, L. A., J. Phys. Chem., 32, 1191-6 (1928). (2) Grove, S. F., Drugs, Oils & Paints, 34, 399 (1919). (3) Itzkovich, P., and Shmulgan, I., Lalcokrasochnuyu 2nd. Za, NO. 3, 43-4 (1933). (4) Justin-Mueller, E., BUZZ. SOC. chim., 49, 1285-9 (1931). (5) Muller, E., J. prakt. Chem., 84, 353-69 (1911). (6) Muller, E., and Treadwell, W., Ibid., 80, 170-82 (1909). (7) Schmidt, P. F., and Rassow, B., Z . angew. Chem., 37, 333-4 (1924) (8) Stender, V. V., and Semenov, A. M., Chimie et industrie, 31, 647 (1934). (9) Woringer, P., Chem-Ztg., 36, 78 (1912). RECEIVED July 24. 1938. This paper is a dissertation from a thesis presenbed b y Elmer R. Ihne t o the Graduate School of Indiana University in partial fulfillment of the requirements for the Ph.D. degree in chemistry.
Surface Tension of Hydrocarbons DONALD L. IUTZ AND WILLIAM SALTMAN University of Michigan, Ann Arbor, Mich.
T
HE surface tensions of Data on surface tension of saturated plain glass window. The gage ethane, propane, and n-butane in the range was evacuated and Partially hydrocarbon liquids are filled with hydrocarbons so that important in of Oo to 45" c. are presented. These data the liquid level was at the processes (W), in heat transfer and in several other and those in the literature are by appropriate place. The Jerdata (I@, cases where petroleum i s means of a general curve for surface tension guson gage was suspended in a of normal paraffins as a function of reduced constant-temperature bath with handled and processed (21). a glass window, and the rise Little information has apA discussion of the of the meniscus in the capilpeared in the literature for the bility of using surface tension measurelary above the liquid level in the surface tension of hydrocarbon merits as criteria for critical gage was measured with a catheliquids i n equilibrium w i t h high-pressure vapors. Swart2 of petroleum hydrocarbons is included. tometer. investigated the surface tenThe tube used in the experiments was calibrated with dission of crude oils containing distilled water. The capillary rise a t seven different positions solved gases under pressure (11, 19). Considerable scattered data on the surface tension of various hydrocarbons have apfor the meniscus in the tube averaged 5.587 cm. in height, the average deviation being about 1 per cent. This average rise, peared, but no correlation or presentation in suitable form the density of water a t 26.1" C., the temperature of the calihas been given. The authors determined the surface tension of ethane, probration, and the surface tension of water of 71.80 dynes per pane, and butane in the range of 0" to 45" C. and a t equilibcm. a t this temperature gave a radius of 0.0263 em. for the capillary. rium vapor pressures. These data, along with those in the literature, were correlated to give the surface tension of the The computation of the surface tension of the hydrocarbon normal paraffin hydrocarbons from ethane through octane, liquids from the rise of the meniscus in the capillary above the level in the gage was made by the usual formula corrected from 0' C. through the critical temperature. The surface tensions for the normal paraffin hydrocarbons were plotted as for the liquid in the meniscus, the density of the vapors, and the rise of theliquid in the Jerguson gage around the capillary: a function of reduced temperature, giving a single curve. A discussion of the prediction of critical temperatures from surface tension data on hydrocarbon mixtures, using the reduced Y = '/%rg ( h ( d ~ dd (1) temperature-surface tension plot, is included. where h = height of meniscus, em. Experimental Data g = gravitational constant, 980.6 T = radius of tube, em. The surface tensions were measured by the capillary rise d L = density of liquid, grams/cc. method (6, 15, 16). A glass capillary tube approximately 0.5 dv = density of vapor, grams/cc. mm. in diameter was inserted in a Jerguson gage having a y = surface tension, dynesjcm.
+ 5)
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92
The rise in the meniscus on the outside of the capillary tube may be computed by assuming that the surface tension of the liquid on the inside of the capillary is the same as that on the outside of the capillary and on the inside of the Jerguson gage. Making this assumption and utilizing the same principle by which the surface tension formula is derived, it can be shown that the rise on the outside of the capillary equals the inside radius of the tube times the height of the meniscus divided by the inside radius of the Jerguson gage minus the outside radius of the capillary tube. The outside radius of the capillary tube was 0.397 cm. and the equivalent radius of the inside of the Jerguson gage was 1.124 cm. These values give a correction factor for the rise on the outside of the capillary tube of 0.0368, and this correction was applied t o formula 1. Equation 2 includes the corrections and was used in all computations for measurements in the Jerguson gage: y =
13.38 (h
+ 0.009) ( d -~ dv)
(2)
where h = observed reading
A few experiments using the capillary tube within the Jer-
VOL. 31, NO. 1
points being high as compared with data of Maass and coworkers was investigated, and no error or reason could be found. The correlation of surface tension data has often been made by utilizing Ramsay's and Shield's equations (5). A plot of surface tension times the two-thirds power of the molecular weight over density as a function of reduced temperature did not bring the data to a common curve. The success with which other properties of hydrocarbons were correlated with respect to the reduced condition suggested the plot of the surface tension us. reduced temperature, the reduced temperature being the absolute temperature of the surface tension measurements divided by the absolute critical temperature of the substance. Preliminary curves through data on Figure 1were used to obtain the surface tension as a function of reduced temperature for octane, heptane, and hexane. These data proved that these three normal paraffin hydrocarbons could be represented by one curve within 0.1 dyne per cm. Therefore, it was considered that the other hydrocarbons, if measured in the pure state, might equally well fall on the curve. A plot was made also of the logarithm of the molecular weight us. surface tension (lines of constant temperature) which showed that there were irregularities in the data for ethane, propane, and butane. Therefore the values of the pure compounds were taken from an average curve of surface tension as. reduced temperature (Figure 2) and plotted against temperature (Figure 1) and against the logarithm of molecular weight. These points gave smooth curves from ethane through octane on the latter plot, and it was concluded that the solid curves of Figure 1are the most probable values of surface tension. The data reported by Rittman and Egloff (17) for the fewer normal paraffin hydrocarbons below nonane are evidently of no value because they scatter with ratther large errors on the plot. When the data on CloH22through ClaHstare placed on the plot of molecular weight vs. surface tension, they show the values to be slightly higher than would be expected. The surface tension a t the reduced temperatures as computed
guson gage with distilled water proved that the corrections made in the formula were correct. The data and computations for ethane, propane, and butane are given in Table I. The ethane contained less than 3 per cent of impurities of ethylene and propane, and the critical temperature was observed to be close to 33.5" C. instead of the 32.1" C. for pure ethane. The propane and butane were the c. P. grade of natural products furnished through the courtesy of the Phillips Petroleum Company and are greater than 99 per cent of the desired compounds, with slight traces of close-boiling paraffin hydrocarbons. It was intended to run the ethane and propane both to the critical temperature, but only ethane reached the critical temperature. Because of the fact that a constant-volume apparatus was used, the true critical temperature could not have been reached unless the exact amount of hydrocarbons necessary to give the criticd density a t the critical temperatures had been placed in the system (80). Therefore, the reported 33.5" C. for the critical temperature TABLEI. SURFACE TENSIONS OF HYDROCARBONS of ethane is based upon the change in the height h+ of the meniscus from close to the top of the --Temp.h 0.009 dL d v dL - dv Y gage t o the bottom of the glass within 1"C. deDunes/ C. F. a K. Cm. Cm. G./cc. G./cc. G./cc. cm. TR gree rise in temperature, The fogging effect is based upon dropping the temperature a few Ethane. Critical Temperature, 306.6' K. 273.5 0.655 0.416 0.047 0.369 3.24 32.7 0.646 0.893 0.4 tenths of a degree. The closeness of the criti0.582 0.408 0.356 2 . 7 7 0 , 9 0 5 39.2 0.573 277.1 0.052 4.0 cal temperature is thus indicated. 0.479 0.332 2.12 0.394 50.2 0.470 0,925 283.2 0.062 10.1 0.345 0.304 0.378 60.8 0.336 289.1 0.074 1 . 4 0 0.944 16.0 The accuracy of the results may not be judged 0.284 0.289 0.366 0.280 0.082 1 . 1 0 0.955 6 6 . 7 292.4 19.3 0.212 0.348 73.4 0.203 0.966 296.1 0.095 0.253 0.72 23.0 directly by the accuracy of the measurements 0.103 0.318 0.203 0.28 0.094 0.979 27.0 300.1 0.115 80.6 made, owing to the possibility of slight conPropane. Critical Temperature, 369.9' K. tamination a t the surface. The accuracy of the 1,346 0 , 5 2 8 0.011 0.517 9.31 0.742 274.1 1.337 33.8 1.0 radius of the tube was within * 1 per cent. The 1.319 0.525 0 , 0 1 2 0.513 9.05 0.748 276.2 1.310 37.6 3.1 0.491 7 . 6 8 1.169 0.507 0.016 0.781 289.1 1.160 60.8 1 6 . 0 height of meniscus was measured to 0.01 cm., 0.490 7.62 1.163 0 , 5 0 7 0.017 0.782 289.3 1.154 61.2 16.2 0.490 1.142 0.507 0.017 7 . 4 9 0.784 289.8 1.133 62.1 16.7 using the average of three values as given in 0.477 7.22 1.130 0.497 0.020 0.801 296.2 1.121 23.1 73.6 Table I. For small values of y, the percentage 1.133 0.496 0,020 0.476 7 . 2 2 0.803 297.1 1.142 24.0 75.2 0.468 0.811 6.88 1,099 0.490 0.022 300.2 1,090 27.1 80.8 errors may be rather large. For values of y 0.461 6 . 6 3 0.821 1.076 0.485 0.024 3 0 3 , 6 1.067 30.5 86.9 0.460 0 . 1 5 0.823 0.024 0.484 304.1 0,990 0.999 31.0 87.8 above 10, the accuracy of the measurements is 0.452 6 . 2 1 0.834 1.026 0.478 0.026 1.017 308.1 95.0 35.0 about *3 per cent. However, a consideration 0.470 0,029 0.441 0.845 6.84 312.6 0,980 0.989 103.1 39.5 of these data along with those in the literature n-Butane. Critical Temperature, 426O K. is necessary before final judgment of absolute 15.4 0.646 1.934 0 , 5 9 8 0,002 0,596 1.925 275.2 35.8 2.1 1 5 . 1 0.652 0.593 1.906 0 , 5 9 5 0.002 1.897 278.1 41.0 5.0 accuracy may be given. 0.587 1 4 . 3 0.665 0.003 1.826 0.590 1.817 5 0 . 4 283.3 10.2
Correlation of Normal Paraffin Hydrocarbons The data of Table I and values in the literature (3, 7,!?,lb)are plotted on Figure 1. Discrepancies between the data of the literature and the authors on propane and butane may be observed. The reason for the authors' butane and propane
14.0 16.8 20.4 23.3 23.8 26.0 27.5 29.0 29.6 34.8 45.4
57.2 62.2 68.7 73.9 74.8 78.8 81.5 84.2 85.3 94.6 113.7
287.1 289.9 293.5 296.4 296.9 299.1 300.6 302.1 302.7 307.9 318.5
1.772 1.745 1.660 1.682 1 673 1:674 1.644 1.618 1.633 1.643 1.473
1.781 1.754 1.669 1.691 1.682 1.683 1.663 1.627 1.642 1.652 1.482
0.586 0.583 0.579 0.576 0.575 0,572 0.570 0.569 0.568
0.561 0.548
0.004 0,004 0.005 0,006
0.006 0.006 0.006 0,007 0.007 0.008
0.014
0.582 0.579 0.574 0,570 0.569 0.566 0.564 0.562 0,561 0.553 0.534
13.9 13.6 12.8 12.9 12.8 12.8 12.5 12.2 12.3 12.2 10.6
0.674 0.680 0.689 0.696 0.697 0.703 0.706 0.709 0.711 0.722 0.748
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INDUSTRIAL AND ENGINEERING CHEMISTRY
93
from extrapolated critical temperatures of normal paraffin hydrocarbons, extrapolating to 721O K. for C16Ha4, gives values higher than the general curve by only 0.3 dyne out of 27-29 dynes. The data on CzeHa, and C ~ H l z l(9) were also plotted on curves similar to Figure 2, using the extrapolated critical temperatures; the points fall 1.5 and 4.5 dynes per cm., respectively, below the general curve. However, both the CBHMand C ~ ~ H data M (8) fall close to the isomeric paraffin curve either by virtue of incorrect extrapolation of critical temperatures or a decrease in the surface tension with increased molecular weight on the reduced plot. The results on C M Hwould ~ ~ ~confirm the decrease for high molecular weight compounds or indicate a sharp shift to a constant critical temperature for molecular weights above about 600. The general curve of Figure 2 and the extrapolated critical temperatures of normal paraffin hydrocarbons were then used to give the extrapolated surface tensions of compounds with molecular weights of 140 to 300.
FIQVRE2. SURFACE TENSIONus. REDUCED TEMPERATURE
Other Hydrocarbons
FIGURE1. SURFACETENBIONOF NORMAL PARAFFINS
The isuineric paraffins fall about 1.1 to 1.3 dynes below the general normal paraffin curve of Figure 2. One curve represents the highly branched compounds, isobutane (S), isopentane (Q),2,2,3-trimethylbutane ( 7 ) , 2,2-dimethylpentane ( 7 ) , diisobutyl (9), etc., within 0.4 dyne and is included on Figure 2. The heptane data (7) show clearly that the isomeric compounds such as 2-methylhexane are only slightly below the normal paraffin curve, while the increasing branching lowers the values to the isomer curve for the compounds given. The data for the olefins of lower molecular weight (3, 16) are not in particularly good agreement on a reduced temperature plot. The propylene data near the critical temperature (63)and at low temperatures (16) fall on the normal paraffin curve; the ethylene data are 1.0 dyne lower, and the butylenes 0.5 dyne higher in the regions in which data are available (12 to 22 dynes per cm.)
.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
FIGURE 3. SURFACETENSION OF MISCELLANEOUS HYDROCARBONS
The acetylene data (12) are 3.0 dynes higher than the normal paraffin curve. The benzene data fall about 2 dynes higher than the toluene data on a reduced temperature plot; on a plot of surface tension us. temperature the curves cross each other as shown on Figure 3. Ethylbenzene and propylbenzene, using extrapolated critical temperature, check the toluene data on the reduced plot. A curve representing toluene on a reduced basis is included on Figure 2, as it appears to represent aromatics closer than benzene. Figure 3 was prepared to give the variation of surface tension with temperature for a few miscellaneous hydrocarbons other than the normal paraffins. When these data are placed on the reduced temperature plot, they follow the general curve or a curve displaced above or below the general curve a t high values of y and approaching it as the critical temperature is reached.
Surface Tension as a Criterion for Critical Temperature The excellent agreement of the surface tensions of normal paraffins when plotted as a function of reduced temperature suggested the possible use of such a plot for predicting the critical temperatures of the hydrocarbons. If a single curve would represent mixtures of paraffin hydrocarbons, the measurement of the surface tension a t a given temperature of such mixtures as mid-continent natural gasolines would establish the reduced temperature and hence the critical temperature from the temperature of the measurement. Similarly, the various base oils might be represented by a series of curves. The surface tension values a t a definite temperature were used in the form of parachors as means of identifying hydrocarbons (14, 21). The first consideration in substantiating the above proposal is the investigation of the behavior of the critical temperatures of mixtures as compared to the surface tension of the mixtures. The pentane-heptane critical temperatures (4)have additive properties on a liquid volume fraction basis, On a weight fraction basis the experimental critical temperatures are 5’ c. less than the additive values a t 50 per cent concentration. A few experiments a t room tem-
VOL. 31, NO. I
perature in the presence of air on the pentane-heptane system gave the pentane and heptane data of Figure 1. The data on mixtures were not entirely consistent, probably as a result of evaporation, but did give surface tensions about 0.2 dyne lower than the additive value a t 50 volume per cent and about 0.4 dyne less than the additive value a t 50 weight per cent. Within the accuracy of the data for pure compounds, the surface tension measurement would give the critical temperatures of this system. Data on a large number of solutions with two to five components show additive surface tensions on a weight basis to hold or give surface tensions slightly above the experimental values for similar substances (IS). These data are in the same direction as the critical temperatures of the ethaneheptane system (10) as well as the pentane-heptane system. The data (17) on the surface tension of cuts from Hemple distillations of gas oils, along with the surface tension of the blend, show the additive surface tensions to hold within the same order of deviations on both the volume and weight per cent bases. The critical temperatures of these fractions were estimated by the method of Watson and Nelson (82), and the surface tensions were then plotted on Figure 2 as a function of reduced temperature. The report on the critical temperatures of a gasoline and a naphtha did not include surface tension data of the materials (1). Using the molecular weights of the fractions to estimate the surface tensions from Figure 1, these points are also included on Figure 2. A survey of Figure 2 shows that the isomeric paraffin line is in good agreement with the estimated values for the gasoline, naphtha, and fractions. This curve is probably the best to use for paraffinic petroleum fractions. Further data are necessary to show the applicability of this method for correlating critical temperatures of petroleum fractions.
Literature Cited (1) Bahlke, W. H., and Kay, W. B., IND.ENG. CHEM.,24, 291 (1932). (2) Brown, G. G., and Souders, Mott, Ibid., 26,98 (1936). (3) Coffin, C. L., and Maass, O., J. Am. Chem. SOC., 50,1427 (1928). (4) Cummings, L. W. T., Stones, F. W., and Volante, M. A,, IKD. ENG.CHEM.,25, 728 (1933). (5) Daniels, Farrington, “Getman’s Outlines of Theoretical Chemistry,” 6th ed., p. 49,New York, John Wiley & Sons, 1937. (6) Dorsey, N. E., Bull. Natl. Research Council, No. 69,56 (1929). (7) Edgar, G.,and Calingaert, G., J. Am. Chem. SOC.,51, 1540 (1929). (8) Hunten, K.W., and Maass, O., Ibid., 51, 153 (1929). (9) International Critical Tables, Vol. IV, p. 452, New York, MoGraw-Hill Book Co., 1928. (10) Kay, W. B., IND.ENO.CHEM.,30,459 (1938). (11) Lacey, W. N., Am. Petroleum Inst. Bull. 210,16 (1932). (12) Maass, O.,and Wright, C. H., J. Am. Chem. SOC.,43, 1098 (1921). (13) Morgan, J. L. R., and Griggs, N. A.,Ibid., 39,2261 (1917). (14) Mumford, S. A , and Phillips, J. W. C., J . Chem. SOC.,132,2122 (1929). (15) Richards, T. W., an3 Carver, E. K., J. Am. Chem. Soc., 43, 827 (1921). (16) Richards, T.W., and Coombs, L. B., Ibid., 37, 1668 (1915). (17) Rittman, W. F., and Egloff, Gustav, J. IXD. ENQ.CHEM.,7,481 (1915). (18) Stroebe, G. W., Ph.D. thesis, Univ. Mich., 1938. (19) Swartz, C.A.,Phusics, 1, 245 (1931). (20) Tapp, J. S., Steacie, E. W. R., and Maass, O., Can. J . Research, 9,217 (1933). (21) Waterman, H. I., and Leendertse, J. J., J. Inst. Petroleum Tech., 24, 16 (1938). (22) Watson, K. M.,and Nelson, E. F., IND.ENQ. CHEM., 25,880 (1933). (23) Winkler, C.A,, and Maass, O.,Can. J . Research, 9,65 (1933). >-
I
RECEIVED August 15, 1938. Presented before the Division of Petroleum Chemistry a t the 96th Meeting of the American Chemical Society, Milwaukee. Wis., September 5 t o 9, 1938.
