Phase Equilibria in Hydrocarbon Systems VIII. Methane–Crystal Oil

INDUSTRIAL AND ENGINEERING CHEMISTRY

686

3SiO2. I n this forniula the term “U20” is used to represent exchangeable items, such as SarO, K20, CaO, or MgO, and the term “R203” is taken to represent either AI2O3or Fez03. With allowance for the loss of absorbed nitrogen in the ashing process, thereby creating a deficiency in the basic elements. this is unmistakably the formula for a zeolite. This view of the composition of the matrix in biological slimes is strengthened by the circumstance that the centrifuged or partly dried material is certainly gelatinous. I t would be most extraordinary for the elements in question to coexist in the alndge without forming a zeolite. The pertinent question as to x-hether tbe sludge does actually possess the physical properties of a zeolite has already been partly an.aered in the first paper of this series on tlie rate of clarification ( I O ) . Parson’s work on the equilibrium which obtains betn-een carbonaceous matters in sewage, as defined by the oxygen consumed test, and suspended sludge particles is very much in point. Evidence to the effect that the sludge will also adsorb ammonia readily from solution and that it can be repeatedly regenerated with sodium chloride in the same manner as the commercial zeolites will be given in the next paper of thiq series. Properly dried sludge should be a good source of zeolitic material for use in sewage purifica-

tion, with the possible advantage that carbonaceous matters may be removed, together with the nitrogenous compounds.

Literature Cited Alilaire, E., Compt. rend., 143, 176-8 (1908). B u c h a n a n , R . E., a n d F u l m e r , E. I., “Physiology a n d Biochemi s t r y of Bacteria,” p. 72, 1928. , 113-66 (1922). D i e n e r t , F., Rec. h y ~ .44, G u i l l e m i n , M., a n d L a r s o n , K. P., J. Infectious Diseaees, 31, 349-55 (1922). ( 5 ) Hillebrand, W. F., z‘.S. Geol. S u r v e y , Bull. 700 (1919). (6) K r a m e r , S. P., J . Gen. Physxol., 9,811-12 (1926). (7) R a h n , O., “Physiology of B a c t e r i a , ” p. 397, 1932. (8) Romcaiallo, A . , Riv. vitic. ital., 7, 307-14, 359-70 ( 1 8 5 3 ) ; cited by B u c h a n a n a n d F u l m e r ( 2 ) . (9) Schweinits, E. A. de, a n d D o r s e t , 31.,Centr. Bakt., Parasitenk., 2 3 , 993-5 (1898). (10) T h e r i a u l t , E. J., Pub. Health Repts., in press; see also 50, 143-4 (Feb. 1, 1935). (11) TI-agenhals, H. H . , T h e r i a u l t , E. J., and H o m n i o n , H. B., Pub. Health Bull. 132 (1923). (12) W a k s n i a n , 9. -4.., “Principles of Soil Microbiology,” p. 381, 1927. R E C E I V EMay D 2 , 1933. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 89th Meeting of the American Chemical Society, New York, N. Y . , April 22 to 26, 1936.

Phase Equilibria in Hydrocarbon Systems VIII.

Methane-Crystal Oil System N PART

I

111 of this series there was described the physical behavior of a twocomponent hydrocarbon system consisting of methane and propane and representing a simplified case of a [‘dry” natural gas and a very volatile oil. For comparison with these results, it is of interest to know how the equilibrium relations of pressure, volume, and temperature mould be altered by the substitution of a relatively nonvolatile, highmolecular-weight oil for the propane. With this point in view, a study was made of the system consisting of methane and crystal oil. The temperature range investigated was from 70” to 220’ F., and pressures m-ere varied from vapor pressure of crystal oil to 3000 pounds per square inch absolute. The mixtures used ranged systematically from pure crystal oil to a mixture containing over 50 mass per cent of methane. Measurements were made of the total volume of the system of known mass as a function of pressure, temperature, and composition.

VOL. 27, NO. 6

B. H. SAGE, H. S . BACKUS,

AND W. N. LACEY California Institute of Technology, Pasadena, Calif.

range of molecular weights, with the accompanying characteristics of low volatility, narrow boiling range, and moderately high viscosity. The sample used in this work was refined from a western, nonwaxy, asphalt crude oil. Its molecular weight, as determined by the freezing-point lowering

3Iaterials Crystal oil mas chosen for this and for subsequent studies to meet the requirements of a stable liquid hydrocarbon material which had high molecular weight combined with small 1 P a r t I appeared on pages 103-6, January, 1934; Part 11, pages 214-17 February, 1934; Part 111. pages 652-4, June, 1934; Part I V , pages 874-7, August, 1934; Part V, pages 1218-24, November, 1934: Part V I , pages 48-50, January, 1935; Part V I I , pages 162-5, February, 1935.

)

PRESSURE

LBS. P E R

2500

2000 SQ.

IN.

FIGURE1. REPRESENTATIVE EXPERIMENTAL CURVES

JUNE, 1935

INDUSTRIAL AKD ENGINEERING CHEMISTRY

687

TABLE I. AXALYSISOF CRYSTAL OIL B Y EXHAUSTIVE EXTRACTION WITH ANILISE Viscosity, Aniline, Temp. Gravity, Saybolt Viscosity Vol., of Recovery O A. P. I. Pour Universal Gravity Per Extn., Vol. at Point, Sec. a t Constant. Sample Cent F. Per Cdnt 60' F. e F. 210° F. VGC Crvatal oil before aniline extn." . ... 29.2 -30 40.8 0.S26f Extract 1 120 116 2.8; 25.0 .. 44.7 0.852 Extract 2 100 115 2.90 25.1 44.2 0.852 Extract 3 100 116 3.01. 25.7 .. 44.0 0,848 Extract 4 100 117 3.0;' 25.8 .. 42.9 0.848 Extract 5 100 145 4.88 26,s .. 42.2 0.844 Evtract 6 100 146 5.2ti 26.7 .. 41.3 0.844 Eutract 7 100 146 5.03 26.9 .. 42.0 0.842 Lxtract S i5 171 6.18 27.7 .. 41A 0.836 Extract 9 75 170 6.37 27.8 .. 43.0 0.833 Extract 10 171 6.42 28.0 .. 42.7 0.832 Extract 11 199 11.42 29.0 .. 43.0 0.824 Extract 12 75 200 13.83 29.5 .. 42.9 0.821 Extract 13 2; 201 12.12 30.1 .. 42.7 0.8164Extract 1 4 ta 200 9.6ti 30.7 .. 43.3 0.811 Raffinatc ... 32.1 - 5 44.2 0.800

.. .

..

..

z;

{b:!:!)

F. = 315'350. b Percentawe b y difference/' c Percentage from actual recovery of topped raffinate.

a

Flash/fire in

fied and could be removed. The impure methane gas thus produced was further cooled by the same methods until methane would liquefy a t a low pressure. The liquefaction was carried out a t low pressure for the purpose of removing nitrogen and other similar gaseous impurities. The liquid methane was heated to develop suitable pressure and allowed to vaporize into activated charcoal chambers a t 50 O 17.

3

'

I

1500

3

2

---

looo

I

that obtained by using methane obtained by other methods indicated a content of nitrogen and similar gases of less than 0.2 per cent.

Experimental Method and Accuracy o f Results The apparatus and experimental methods used have been previously described ( 1 , 3 ) . Known amounts of the two constituents were placed in the apparatus, called the "variable-volume cell," and brought to thermal and phase equilibrium by thermoetating a t the desired temperature while agitating the mixture in the cell by mechanical means. Upon attainment of equilibrium, the corresponding volume and pressure were determined. The volume was systematically varied by admission or removal of mercury under suitable I pressure. The satisfactory establishment of equilibrium in I the system was tested by making determinations with both I250 l50C I750 2000 2250 increasing and decreasing volumes. PRESSURE LBS. P E R SQ. IN. The experimental data are illustrated in Figure 1 which FIGURE 2. EXPERIYEIVTAL CURVES N E A R THE BUBBLE POINT shows representative isothermal volume-pressure curves for

i

INDUSTRIAL AND ENGINEERING CHEMISTRY

688

Temp.,

O F. 70.0

TABLE11. SPECIFIC VOLUMESOF MIXTURESOF METHANEASD CRYSTAL OIL

Abs. Pressure, ,Lb./Sq. In. 0

1.00 2.00 3.00 1532 544 1057 0.01827 0.01857 0.01870 0.01881 0.01823 0,01955 0.02614 0.03372 ..... . . . . . 0.02082 0.02525 ..... . . . . . 0.01933 0.02228 0.01817 0.01845 0.01877 0.02073 ..... . . . . . 0.01960 0.01813 0.01840 0.01862 0.01890 0

400 600 800

1000 1250 1500 1750 2000 2250 2500 2750 3000 100.0

.....

.....

0.01809

..... 0.01805 ..... 0.01801

400 800 1000 1250 1500 1750 2000 2250 2500 2750 3000 130.0 400 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000

400 600 800 1000 1250 1500 1750 2000 2250 2600 2750 3000

.....

.....

.....

..... 0.01867 ..... 0.01862

0.01835

0.01857 0.01873

0.01830

0.01852

..... .....

.....

0.01840 0.01835

0.01862

1604 0.01906 0 03651 0.02665 0.02334 0.02158 . . . . . 0.02027 0,01886 0.01936

0.01831

0.01856

0.01878 0.01899

0.01860 0.01846

..... .....

.....

.....

.....

.....

.....

..... 0 : Oiiis ..... 0.01851 .....

.....

.....

.....

.....

.....

.....

0.01872 0.01891

0,01822 0.01846 0.01867 0.01884 0 1674 587 1158 0.01873 0.01896 0.01914 0.01929 0.01869 0.02099 0.02870 0.03729 0.02283 0.02794 ..... . . . . . 0.02079 0.02439 0.01863 0,01889 0.01965 0.02244 ..... ..... ..... 0 02097 0.01858 0.01884 0.01909 0.01988

.....

..... ..... 0.01849 .....

0.01853

0.01844 0

160.0

.....

0.01826 0.01847 1111 567 0.01874 0.01892 0.02027 0.02742 0.02188 . . . . . 0.02018 0.01868 0.01926

0

600

..... ...I.

0.01878

..... 0.01873 .....

0.01869

.....

0.01924

.....

0.01916

.....

0.01889 0.01909 1200 0.01937 0.02997 0.02383 0.02155 0.02024

0.01880 0.01875

0 01901

0.01925

0.01949

0.01869

0.01896

0,01919

0.01941

..... .....

0.01885 I .

.....

.....

.....

612 0.01918 0.02171 0.01920

o.'oiioi ..... 0,01896 .....

1739 0.01954 0.03909 0.02944 0,02545 ..... 0.01912 0,02329 ..... . . . . . 0.02157 0.01906 0.01932 0.02043

0.01896 0.01893

...

.....

.....

.....

.....

.....

.....

.....

0.01890 0.01911 1241 634 0.01919 0.01943 0.01962 0.01914 0.02243 0.03025 0.01976 0.02484 ..... 0.02231 0.01907 0.01938 0.02084

o.oiQ33 1812 0.01978 0.04088 0.03084 0.02650 0.02415 ..... ..... . . . . . 0.02258 0.01901 0.01930 0.01957 0.02132 . . . . . 0.02011 0,01895 0.01926 0.01951 0.01974 0.01864 0

190.0 400 600

800

1000 1250 1500 1750 2000 2250 2500 2750 3000 220.0 400 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000

VOL. 27, NO. 6

..... ..... .....

.....

.....

.....

0.01889

..... ..... 0.01919 0.01884 0.01914 0 0.01943 0.01936 0.01933

655 0.01970 0.02315 0.02032

0.0192s

0.01962

0.01920

0.01954

.....

..... .....

0.01914

.....

0.01909

.....

0.01904

.....

.....

..... ..... 0.01942 .....

0.01949

0.01936

.....

0.01944

.....

.....

0.01966

.....

0.01958 1880 0.02003 0.04267 0.03224 0.02750 0.02500 . . . . . 0.02326 0.01984 0.02189 . . . . . 0.02063 0.01976 0.02000 0.01937 1287 0.01989 0.03253 0.02584 0.02307 0.02143

.....

.....

.....

.....

0.01968 0.01992 0.01961 0.01983

Mass Per Cent Methane as Follows: 4.00 6.00 10.0 1.50 1945 Ib./sq. in. abs., saturation pressure 0.01889cu. ft./lb.. . . saturation volume 0.04197 0.06091 0,09501 0.1343 0.03035 0.04232 0.06946 0.09795 0.02572 0.03280 0.05243 0.07296 0.02348 0.02934 0.04215 0,05850 0.02183 0.02663 0.03554 0,04820 0.02074 0.02481 0.03184 0.04230 0.01975 0 02350 0,02925 0 03818 0.01888 0.02247 0.02735 0.03481 . . . . . 0.02160 0.02587 0.03204 0.01880 0.02083 0.02489 0.03003 ...., 0.02052 0.02415 0.02859 0.01873 0.02018 0.02351 0.02767 2034 Ib./sq. in. abs., saturation pressure 0.01917cu. ft./lb., saturation volume 0.04423 0.06421 0.1006 0.1427 0.03212 0.04490 0.07142 0.1043 0.02706 0.03651 0.05569 0.07782 0.02467 0.03191 0.04646 0.06349 0.02284 0.02795 0.03876 0,05249 0.02151 0.02588 0.03441 0.04536 0.02035 0.02445 0.03086 0.03997 0.01935 0.02324 0.02870 0.03697 . . . . . 0.02225 0.02715 0.03402 0.01908 0.02150 0.02595 0.03185 0.02107 0.02511 0.03023 0.01900 0.02069 0.02448 0.02904 2137 Ib./sq. in. ab&, saturation pressure 0,01942cu. ft./lb.. saturation volume ~. 0.04650 0 06751 0 1061 0.1511 0.03389 0.04748 0 07568 0,1106 0.02841 0 03849 0 05895 0.08268 0.02570 0.03321 0 04922 0.06757 ~ . 0 .04107 ~ 0.02366 0 029.12 0.05585 0.02222 0.02697 0.03635 0.04818 0.02102 0.02532 0.03262 0.04249 0.01997 0.02401 0.03023 0.03914 0.02289 0.02844 0,03600 0.01935 0.02204 0.02705 0.03367 . . . . . 0.02148 0.02621 0.03188 0.01927 0,02121 0.02555 0,03051

.....

~

~

.

.

20.0

0.1707 0,1225 0.09230 0.07475 0.05142 0.06071 0.04873 0.04145 0.03807 0.03528 0.03292 0.03123

30.0 0.2270 0.1658 0.1225 0.09765 0.07907 0.06699 0.05734 0.05110 0.04618 0.04331 0.04019 0.03748

0.1818 0.1320 0.09868 0.07965 0.06503 0.05565 0.04483 0.04896

40.0

50.0

0.2744 0,3162 0,1910 0.2082 0.1408 0.1538 0.1114 0.1216 0.08872 0.0957 0.07403 0.07930 0.06384 0.06928 0.05722 0.06122 0.05115 (0.0482) (0.0457) (0.0428)

..... .....

..... .....

0.2425 0.1770 0.1313 0.1049 0.08496 0.07160 0.06177 0.05465 0.04064 0.04972 0.03766 0.04615 0.03506 0.04315 0.03316 0.04100

0.2932 0.2042 0.1515 0.1199 0.09577 0.08014 0.06909 0.06100 0.05522 (0.0518) (0.0489) (0.0459)

0.3377 0.2222 0.1651 0.1310 0.1035 0.08602 0.07497 0.06608

0.1929 0.1402 0.1051 0.08570 0.06935 0.05896 0.05220 0.04712 0.04322 0.04004 0.03722 0.03509

0.2579 0.1883 0.1402 0.1122 0.09084 0.07624 0.06620 0.05890 0.05340 0.04934 0.04602 0,04290

0.3120 0.2174 0.1619 0,1285 0,1028 0.08626 0.07434 0.06617 0.05973 (0.0555) (0.0524) (0.0489)

0.3592 0.2367 0.1763 0.1403 0.1107 0.09274 0.08066 0.07094

0.2040 0.2734 0.1996 0.1484 0.1114 0.1491 0.09103 0.1195 0.07367 0.09673 0.06263 0,08228 0.05520 0.07063 0.04995 0.06280 0.04580 0.05680 0.04243 0.05263 0.03955 0.04908 0.03703 0.04562

0.3307 0.2307 0.1722 0.1370 0.1099 0.09237 0.07959 0.07065 0.06380 (0.0591) (0.0557) (0.0522)

0.3807 0.2512 0.1876 0.1496 0.1191 0.09946 0.08635 0.07580

0.2151 0.1567 0.1178 0.09560 0,07799 0.06630 0,05867 0.05292 0.04837 0.04462 0.04153 0.03896

0.2888 0.2108 0.1579 0.1268 0.1026 0.08655 0.07506 0.06670 0.06073 0.05615 0.05204 0.04833

0.3495 0.2439 0.1826 0.1456 0.1169 0.09849 0.08484 0.07451 0.06743 (0.0628) (0.0589) (0.0553)

0.4022 0.2657 0.1988 0.1589 0.1269 0.1062 0.09204 0.08066

0.2262 0.1649 0.1242 0.1017 0.08231 0.06997 0.06190 0.05562 0.05095 0.04719 0.04389 0.04089

0.3043 0.2221 0.1668 0.1341 0.1085 0.09247 0.07949 0.07060 0 06405 0.05928 0.05501 0.05104

0.3883 0.2671 0.1930 0.1541 0.1240 0.1046 0.09090 0.07961 0.07150 (0.0664) (0.0623) (0.0585)

0.4237 0.2802 0.2101 0.1683 0.1347 0.1129 0.09773 0.08552

..... ..... ..... ....,

~~

.

I

.

2223 Ib./sq. in. abs., saturation pressure 0.01968cu. ft./lb , saturation volume 0.1596 0.04876 0.07081 0.1117 0.03566 0.05006 0.07995 0.1137 0.02976 0.04047 0.06221 0.08754 0.02681 0.03518 0.05198 0.07165 0.09471 0.03059 0,04338 0.05921 0.02317 0.02804 0.03828 0.05100 0.02173 0.02627 0.03425 0.04500 0.02037 0.02478 0.03161 0.04094 0.02356 0.02972 0.03798 0.01962 0.02265 0.02821 0.03548 . . . . . 0.02212 0.02722 0.03353 0.01953 0.02173 0.02643 0.03198 2334 Ib./sq. in. abs., saturation pressure 0,01991cu. ft./lb.. saturation volume 0.1680 0.05102 0.07411 0.1172 0.09240 0.03744 O.OZ264 0.08421 0.1233 0.03110 0.04245 0.06547 0,02792 0.03682 0.05475 0.07573 0.02556 0.03192 0.04568 0.06257 0.02396 0.02911 0.04022 0,05382 0.02267 0.02718 0.03595 0.04752 0.02148 0.02555 0.03307 0.04348 0.02033 0.02420 0.03101 0.03996 0.01987 0.02325 0.02938 0.03730 ..... 0.02268 0.02831 0.03517 0.01978 0.02225 0.02740 0.03346 2433 Ib./sq. in.abs., saturation presume 0.02015cu. ft./lb., saturation volume 0.08848 0,1764 0.05329 0.07741 0.1228 0.1296 0.03921 0.05522 0.03245 0.04443 0.06873 0.09726 0.02903 0.03845 0.05752 0.07981 0.02641 0.03324 0.04816 0.06593 0.02460 0.03019 0.04215 0.05664 0.02320 0.02798 0.03764 0.05003 0.02204 0.02632 0.03419 0.04540 0.02093 0.02485 0.03229 0.04194 0.02014 0.02386 0.03054 0.03912 . . . . . 0.02328 0.02943 0.03682 0.02004 0.02277 0.02845 0.03493

.....

a mixture containing 3.05 mass per cent methane. The break points in the isotherms indicate, the disappearance of the gas phase on increasing pressure (or appearance on decreasing pressure). This is often called the "bubble point," and at this state properties of the system as a whole are those of saturated liquid under the existing conditions. In order to show more in detail the behavior of the same mixture near the bubble point, an enlarged view of that portion of the diagram is shown in Figure 2.

.... .... .... ....

....

..... ..... .....

..... ..... ..... .....

The various measurements were made with sufficient precision and with adequate calibrations to insure accuracy of results within the following limits: pressure, 1 pound per square inch; temperature, 0.2' F.; methane and crystal oil quantities, 0.1 per cent of the mass used; and volume, 0.1 per cent. Some experimental points in Figure 2 show irregularities somewhat greater than would be consistent with these limits, but this is due to the difficulty of exact attainment of equi1ibriv.a very close to the bubble point.

IXDUSTRIAL AND ENGINEERING CHEMISTRY

JUNE, 1935

I

1

I

I

689

I 02

>

k

2

0.E

0

0 0.4 W

a v1

Oi

PRESSURE

LBS.

PER SQ.

IN.

GRAVITYOF THE SYSTEMAS A WHOLE FIGURE6. SPECIFIC AS A FUNCTION OF EQUILIBRIUM PRESSURE AT 160" F.

PRESSURE

LBS. P E R

SQ.

IN.

FIGURE5 . EFFECTOF THE PRESENCE OF GAS SPACE UPON THE VOLUME OF LIQUID PHASE

Experimental Results Since the experimental measurements were made a t odd values of pressure, a direct tabulation of them would be cumbersome and inconvenient to use. The direct experimental data have, therefore, been plotted on as large a scale as was consistent with their accuracy and the corresponding isotherms drawn. From these curves have been read values for suitable regular pressure values. The resulting data are contained in Tables I1 and 111. The values are reported upon a mass composition basis, although molal compositions would have many advantages for purposes of correlation with similar mixtures of other substances. However, the uncertainty in determination of the average molecular weight of crystal oil appears to be too great to warrant its use. I n order to aid in the visualization of the behavior of the system, several typical diagrams have been prepared from the tabulated data. The relation of equilibrium pressure to temperature is shown in Figure 3 for four mixtures a t their bubble points. These bubble-point pressure curves correspond to the vapor pressure curve of a pure substance except that in the latter case the bubble point and dew point coincide. Figure 4 shows the bubble point pressures as a function of the composition of the mixture for a series of temperatures.

I

I

I

30

40

I 10

20

MASS

PERCENT

J

METHANE

FIGURE7. SPECIFIC GRAVITY OF THE SYSTEM AS A WHOLEAS A FUNCTION OF COMPOSITION AT 160" F.

The more rapid increase of curvature of these saturated liquid lines a t higher pressures would be expected as the critical pressure of the system is approached. Under these conditions the equilibrium pressures differ from true bubble point pressures when there is an appreciable volume of gas phase present in equilibrium and there is a marked tendency for transfer of liquid constituents to the gas phase.

TABLEI 111. COMPOSITIONS AND SPECIFIC V o ~ n m sOF SATURATED LIQUIDMIXTURES OF METHANE AND CRYSTAL OIL Abs. Preasure, -70.0' Lb./Sa. In. C o m m . 0 200 400 600

800 1000 1250 1500 1750 2000 2250 2500 2750 3000

.. .. ..

(Compositions expressed a8 msds per cent methane, specific volumes as cubic feet per pound)

F.-

Volume

--lOO.Oo Comvn.

F.-Volume

r--13O.O0

Comvn. 0 0.34 0.75 1.02 1.36 1.72 2.17 2.65 3.15 3.69 4.26 4.88 (5.4)

F . 7

Volume

-160.0° Comm. 0 0.33 0.73 0.98 1.31 1.66 2.09 2.54 3.01 3.51 4.03 4.59 5.20 (5.8)

F . 7

Volume

-190.0° Comvn. 0 0.31 0.70 0.94 1.27 1.62 2.01 2.44 2.88 3.35 3.83 4.35 4.90 (5.5)

F . 7

Volume

-220.0° ComDn.

F.Volume 0.01943 0.01951 0.01959 0.01966 0.01975 0.019so 0.01987 0.01994 0.02001 0.02007 0.02012 0.02017 (0,0202) (0.0203)

690

INDUSTRIAL AND ENGINEERIXG CHEMISTRY

In order to determine the extent of the effect of the presence of gas phase at equilibrium in this system, measurements were made of the change in volume of the liquid phase due to solution of methane a t a series of increasing pressures in a constant-volume cell in the presence of gas phase a t all times. Similar measurements were made by Sage, Lacey, and Schaafsma ( 2 ) upon the methane-propane system. The apparatus and methods used have been described previously (1). A sample of crystal oil was placed in the equilibrium cell, filling approximately one-half of its volume. The liquid volume was measured with zero methane pressure and then a series of additions of methane was made, bringing the system to equilibrium each time and measuring the new volume of the liquid phase resulting. A series of such runs furnished the data for Figure 5. The solid-line curves show the relative volumes of the liquid phase a t various equilibrium pressures when a gas phase of approximately equal volume was present. The dashed-line curves show for comparison corresponding curves when only an infinitesimal volume of gas phase was present. The variation of the specific gravity of mixtures of methane and crystal oil of different compositions is shown in Figure 6 as a function of equilibrium pressure for a temperature of 160” F. These specific gravity values are referred to water a t maximum density for 1atmosphere pressure. The boundary curve marked “saturation” indicates the specific gravities of the saturated liquid a t bubble point. The region above

VOL. 27, NO. 6

this boundary line corresponds to the existence of only a liquid phase, while that below it charts the specific gravities of mixtures under such conditions that both liquid and gas phase coexist, except for the region near 100 mass per cent methane. In all cases the values shown are for the specific gravity of the mixture as a whole. Figure 7 presents similar specific gravity values a t 160”F. as a function of the composition of the mixture a t a series of equilibrium pressures. As before, the boundary curve separates the condensed liquid region from the two-phase region.

Acknowledgment This investigation was carried out under the auspices of the American Petroleum Institute as part of the nTork of its Research Project 37. The authors are also greatly indebted to U. B. Bray of the Union Oil Company, Los Angeles, Calif., for the analysis of the crystal oil used. John E. Sherborne assisted materially in the experimental measurements here reported.

Literature Cited (1) Sage, B. H., and Lacey, W. N., IND. ENQ.CHEW,26, 103 (1934). (2) Sage, B. H., Lacey, W. N., and Schaafsma, J. G., Am. Petroleum Inst., Production Bull. 212, 119-28 (1933). (3) Sage, B. H., Schaafsma, J. G., and Lacey, \V. N., IND. EXG. CHEM., 26, 1218 (1934). RECEIVED March 26. 1936.

Electrical Charges of Activated Carbons H. L. OLIN, J. D. LYKINS, ASD W . P. 3IUSRO University of Iowa, Iowa City, Iowa

HANEY and his co-workers (4) in an early paper on the adsorptive properties of activated carbons made a compre1iensiT-e presentation of the subject which will doubtless stand as authoritative for a long time to come. From this paper five postulates are quoted verbatim, based upon the results of their studies which sum up briefly their conception of the relations that exist between the electrical charge on the carbon particle and the effectiveness of the carbon as an adsorbent:

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1. The generalization that a given carbon will be most effective as an adsorbent if it carries on electrical charge opposite i n sign to that carried by the particle t o be adsorbed will be accepted. 2 . Active carbon may be neutral or may readily become positively or negatively charged b y the adsorption of hydrogen or hydroxyl ions from solution. 3. The carbon may be caused to assume the desired electrical charge prior to its introduction into any given solution or liquid. 4. The fact that a carbon is electrically charged does not influence i t s a d s o r p t i v e capacity when it happens t o be r e a c t i n g toward neutral particles. 5 . The differences in a d s o r p tive power caused merely b y

differencesin electrical charges on the carbon are not fundamental in estimating the intrinsic character of the carbon. In the main these postulates are generally accepted and are quoted here especially to bring up an apparent exception to postulate 5 in the light of results obtained in this laboratory. It should be noted however that Chaney ( 3 ) defines “electrical charge” as used in this sense as that imposed upon the carbon as a reqult of its equilibriuni with the electrolyte-

Evidence is presented to show that a definite relationship exists between the intrinsic adsorptive capacity of a carbon as determined by the conventional gas adsorption method and its speed of migration in the cataphoresis cell while suspended in an aqueous medium of high pH value-viz., 11.5 in the work described. The proof lies in the striking similarity between the curves obtained in plotting temperatures of activation against volumes of gas adsorbed and migration velocities, respectively. Results of studies on the cataphoretic behavior of carbons suspended in liquids of varying pH are shown graphically. In general, with shifting of pH the flow changes not only in velocity but in direction, so that roughly within the limits of pH 1 to 5 two isoelectric points are located.