HIGH-PRESSURE GASOLINE.4ND
ABSORPTIONPLANT O F THE DAXCICER OIL INC.,AT DANCIGER, TEXAS Operating pressure is 670 pounds per square inch KEROSENE
ASD
RE-
FINERIES,
Solubilitv of Methane in Benzene J
E. P. SCHOCH, -4. E. HOFFMANN, A. S. KASPERIK, J. H. LIGHTFOOT', AND F. D. MAYFIELD The University of Texas, Austin, Texas
A
inch. Frolich and co-workers CCURATE P-V-T-X data An apparatus is described for measuring (2) reported data a t 77" F. with for hydrocarbon mixtures P - V - T-X relations of hydrocarbon mixtures an accuracy limited to within . are needed for petroleum up to a pressure of 400 atmospheres. Spe5.0 per cent. Ipatieff and coengineering calculations. With cific volume and bubble-point data deterworkers (6) studied the solubility this in mind apparatus was mined at 100.27' F. are presented for eleven of methane in benzene but reconstructed in this laboratory ported no quantitative data. for the study of such mixtures mixtures of methane and benzene. The Further studies are in progress and was limited to the study mixtures ranged in concentration from 20 in this laboratory on the methof two-component systems in to 76 mole per cent methane corresponding ane-benzene system at higher which methane is the lighter to bubble-point pressures of 1500 to 5200 temperatures and also on the component. The methane-benpounds per square inch absolute. methane-cyclohexane and the zene system at 100.27" F. was m e t h a n e - n - he x a n e svstems. e x a m i n e d o v e r a n extended Benzene, cyclohexane, and n-hexane were chosen belause of pressure range, and the data obtained are presented in this their representation of typically aromatic, naphthenic, and paper. paraffinic hydrocarbons, respectively. The experimental data consisted of the determination of the total volumes of eleven mixtures of methane and benzene Apparatus of known composition a t 100.27" F. and total pressures u p to The assembled apparatus is shown in Figure 1 and consists of 6000 pounds per square inch absolute. Both the liquid two identical mercury displacement pumps, one injection cell, phase and liquid-vapor phase regions are studied. The one equilibrium bomb, one 6000 pound per square inch pressure solubility of the methane is obtained from the bubble-point gage with an oil-mercury contact cell and an oil pump, a constant temperature bath, and auxiliary motors and stirrin mechanisms. total pressure, temperature, and composition data. The mercury displacement pumps are essentially o f the same deOnly three other reports on the methane-benzene system sign as those described by Keyes (7) and by Beattie (1). The have been found in the literature. Sage, Webster, and highly polished piston is 1 inch (2.54 cm.) in diameter and 11 Lacey (12) presented data for two compositions a t three teminches (28 cm.) long, with a displacement of approximately 1.28 cc. per turn and a total displacement of approximately 90 cc. peratures and a maximum pressure of 3000 pounds per square Eight neoprene washers l/g inch (0.318 em.) thick and inch wide serve as packing. The pumps are equipped with a cyclom1 Present address, Humble Oil and Refining Company, Houston, Texas. 788
JUNE, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
eter and vernier arrangement by means of which the number of turns through which the piston moves can be determined t o 0.001 turn. The injection cell is a pressure bomb of approximately 85 cc. capacity with connections as shown in Figure 1; as this cell is used for constant-pressure injections only, no calibration is necessary. The construction of the equilibrium bomb is shown in Figure 2. The interior of this 75-cc. bomb is highly polished as is the steel electrical contact point introduced through the top. Laminated Bakelite is employed as a packing in the contactpoint packing gland. Two steel paddles mounted by means of glass bearings on the shaft of the contact point serve to mix the contents of the bomb as it is rocked back and forth. The bomb is continuously rocked through a 60" angle by a motordriven mechanism. Injections into the bomb are made through a special needle valve constructed in the base of the bomb. By employing a source of potential and a galvanometer, the position of the mercury at the contact point can be determined to 0.001 turn of the mercury pump. The pressure gage is of the Bourdon tube type with a 14-inch dial, calibrated and marked by hand in 10-pound intervals from 0 to 6000 pounds. The dial is equipped with a rotating zero arrangement for obtaining absolute pressures directly. An oilmercury contact cell and a small oil pump of the piston displacement type are employed in conjunction with the pressure gage in order to maintain the oil-mercury interface at a constant position and thus keep a constant quantity of mercury in the system. This oil-mercury contact cell is designed to accommodate two liquids and is equipped with an insulated steel contact point connected to a source of potential and a galvanometer just as in the case of the equilibrium bomb. With this arrangement the oil-mercury interface is maintained at the tip of the contact point. The pressure correction due to the change in the mercury level in the equilibrium bomb during the course of a pressurevolume determination is negligible. The change in mercury head upon lowering the level to the contact point is of such a magnitude that it does not affect the volume correction on the baseline P-V characteristic which is employed for specific volume calculations.
4_ c 'I
789
Each mercury pump piston was calibrated to obtain the displacement volume corresponding to each turn over its entire range. This was done by weighing the mercury ejected a t 1000 pounds per square inch absolute for every four pump turns through a small needle valve equipped with a fine delivery tip. These weighings and pump readings, together with the density (IO) and compressibility of mercury (9),enabled the volume calculations to be made.
FIGURE 2. EQEILIBRIUM BOMB
Because of the expansion of the steel and the compression of the mercury under application of pressure, a P-V characteristic of the equilibrium bomb, one mercury pump, oilmercury contact cell, and mercury sufficient to fill one mercury pump at zero turns had to be determined. This was done in the temperature bath, and all subsequent rolume measurements on the hydrocarbon mixtures were corrected by means of this characteristic. Care was taken to maintain exactly one pump full of mercury in this part of the system in all subsequent work in order to maintain the same base-line P-V characteristic. The temperature of the determinations was 100.2i" * 0.01" F. This temperature was measured by means of a Beckmann thermometer which had been set against a Sational Bureau of Standards calibrated platinum resistance thermometer used in conjunction with a calibrated Mueller bridge. This setting was further checked against a Bureau of Standards calibrated mercurial thermometer.
II 1 I FIGURE 1. ASSEMBLYOF APPARATUS .4. B.
C.
E . Oil-mercury contact cell Injection cell F. 6000-pound gage Equilibrium bomb G. Oil pump (Kumbers refer t o valves)
D. Mercury pumps
Flexible steel tubing ',/a inch 0. d. and l/,c inch i. d. is employed to connect the various units. These connections are made by mild steel conical ferrules with threaded followers. The valves employed are commercial needle valves which, although designed for operation at pressures up to 3000 pounds per square inch, have been found satisfactory for holding 6000 pounds per square inch on both the high- and low-pressure sides. The two mercury pumps, the injection cell, the equilibrium bomb, and the oilmercury contact cell are all immersed in a constant-temperature bath. These same units, together with the oil pump, are all rigidly mounted on a heavy steel framework equipped with vertical guides to facilitate raising the units out of the bath by means of a chain hoist.
Cali brati on The pressure gage was calibrated by means of eight sets of calibrations against a dead weight tester; four of these were under increasing and four under decreasing pressure conditions. The pressures are believed to be accurate t'o within 0.5 per cent.
Procedure For the experimental determinations, pump A in Figure 1 is used exclusively for injecting the samples of methane and benzene into the equilibrium bomb. Pump D is used exclusively for the determination of the P-TI characteristic of the hydrocarbon mixtures in the equilibrium bomb. Several runs are made on each system a t each temperature as a check against errors, each run consisting of one methane injection and one or more benzene injections; the P-V characteristic of the mixture within the equilibrium bomb is determined after each benzene injection.
INDUSTRIAL AND ENGINEERING CHEMISTRY
790
VOLUMESOF MIXTURESOF METHANEAND TABLEI. SPECIFIC
BEXZENE AT 100.27' F.
Abs. Pressure LbJsq.
Sp. Vol.
cu.
ft./lb. 19.46 Mole %, 4.72 Mass 7c Methane; Run 3 WL.
38.50 Mole 5 , 10.15 Mass % Methane; Run 3
3500 3300 3250 3200
0.02184 0.02189 0.02190 0.02192
46.85 Mole %, 15.31 Mass % Methane; Run 3 6000 0.02343 5500 0.02356 5200 0.02363 5000 0.02368 4500 0.02385 4350 0.02391 4300 0.02393 4250 0.02394 4200 0.02396 4150 0.02398 4100 0.02400 4050" 0.02406 4000' 0.02416 39500 0.02425 3900" 0.02435 3850" 0.02445 3800a 0.02465 (4080) 66.71 Mole %, 29.13 Mass yo Methane: Run 1
Abs. Sp. Vol. Pressure Lb./sq. Cu. in. ft./lb. 24.53 Mole % 6 25 &lass Methahe; gun 3
Abs. Pressure Lb,/sq.
36.42 Mole yo,10.51 .\lass 70 N e t h a n e ; Run 1 6000 0.02147 5500 0.02157 5200 0.02162 5000 0.02166 4500 0.02176 4000 0.02186 3500 0.02197 3400 0.02198 3350 0.02201 3300 0.02203 3250 0.02204 3200 0.02205 3150 0.02206 3100" 0.02210 3050° 0,02221 3000" 0.02231 2950" 0.02242 2900O 0.02252 (3113)
40.75 Mole %, 12.36 Mass 7' hlethane; Run 3
53.40 Mole %, 19.03 hfass yo Methane; Run 3 6000 0.02494 5500 0.02514 5200 0.02526 5000 0.02533 4850 0.02540 4800 0.02543 4750 0.02545 4700 0.02547 4650 0.02549 4600 0.02552 4550" 0.02556 4500" 0.02565 4450a 0.02575 44OOa 0.02584 4350" 0.02593 4300" 0.02603 (4566)
62.85 Mole % 9 26.76 Mass Methane; kun 2 6000 0.02763 5500 0.02793 5400 0.02798 5350 0.02801 5300 0.02804 5250 0.02806 5200 0.02809 5150 0.02812 5100 0.02816 5050° 0.02823 5000" 0.02831 4950° 0.02841 4900" 0.02850 4850" 0.02861 48OOa 0.02872 (5088)
Sp. Vol.
Cu.
ft./lb. 30.25 Mole 8.17 Mass yo Methane; Run 3 tn.
3800 3750 3700 36.50
r0,
0.02272 0.02274 0.02275 0.02277
then closed and mercury is carefully forced through valve 2 by mercury pump D until the line into the equilibrium bomb is just filled. After valve 2 is closed, mercury is carefully forced through valve 4 by pump A t o the desired level into the injection cell, and the injection cell is checked for high vacuum after valve 4 is closed. Valve 6 is closed and methane is introduced into the injection cell through the line below valve 6 a t a pressure of 1000 to 1500 pounds. Valves 1 and 4 are then opened, the methane is compressed to exactly 1500 pounds per square inch by pump A , and the pump reading is recorded. Pump A is then advanced the desired number of turns and valve 3 carefully opened until the pressure drops to about 1500 pounds. After valve 3 is closed, the pressure is carefully set a t exactly 1500 pounds by pump A and the pump reading recorded. The difference in the two readings together with the piston calibration gives the exact volume of methane introduced into the equilibrium bomb a t 1500 pounds per square inch and 100.27' F. From the methane compressibility data of Kvalnes and Gaddy (8) the mass of the methane is then calculated. Extreme care is taken in establishing the initial and final pump and pressure readings for all injections; although the pressure reading accuracy in general is reported to be within 0.5 per cent, it is believed that these injection pressures are accurate to within 0.25 per cent. Therefore it is believed that the methane injections are accurate to within 0.5 per cent. To determine the exact volume of the equilibrium bomb, valve 1 is closed, valve 2 is opened, and pump D advanced until the methane in the bomb is a t exactly 1500 pounds per square inch and the pump reading is recorded. The volume of the methane a t this reading is known from the injection data, and the volume from this reading down to the contact point is obtained by backing up on pump D until the mercury level is at the contact point. This gives the total volume of the cell down to the contact point as a basis for all future density calculations. The readings are corrected according to the P-V characteristic of the pump, bomb, and mercury.
z
s:
5000
Two-phase region. b Pressures in parentheses are bubble-point pressures.
'
1
/
\
? 4000,
W'
5 3 3000 W
Il
a
2
76.01 Mole c , 39.39 Mass % d t h a n e ; Run 3
VOL. 32, NO. 6
0 RUN 3
o
o
o
SA; d LACEY W~E r E R
~
I: 1000 m a l '0
FIGURE 3.
10
20
CHASGE IN
30
40 50 60 70 MOL PER CENT METHANE
I
0
BUBBLE-POINT PREsSURE WITH ,\TOLE METHANE-BENZENE SYSTEU AT 100.27' F.
P E R CENT hfETH.4KE IN THE
Before a run is started, both mercury pumps A and D are filled with mercury with the pistons backed out to zero turns. High-vacuum technique is always employed for these fillings. Then with valves 1, 2, 4,and 5 closed, the injection cell and the equilibrium bomb are carefully evacuated. Valve 3 is
For the benzene injections the same procedure is followed in filling the injection cell as is employed with the methane. The injections into the equilibrium bomb are made in the same way except that they are a t a pressure of 800 pounds per square inch. The mass of the benaene injected is calculated from the pump readings and piston calibration, together with the density and compressibility of benzene found in the literature (3). In order to drop the level of the mercury below the inlet from valve 3, the mercury level in the
INDUSTRIAL AND ENGINEERIIVG CHEMISTRY
JUNE, 1940
bomb is always set a t one turn below the con03600 tact point before injecting 03400 benzene. The accuracy of this - SAGE, WEBSTER a LACEY injection is be03200 lieved t o be within 0.4 per cent. After injecI! tion of a sample of methane and a sample of b e n z e n e , valves 3 and 1 are kept closed and mercury is sa i run into the ,02200 bomb by means of pump D unI ',\ til the methane . 0 2 0 0 0 ~ ~ has completely I dissolved in the I 1000 2000 3000 4000 5000 benzene and a PRESSURE, LBS PER SQ IN ABS p r e s s u r e of 6000 pounds is FIGURE 4. CHANGE IN SPECIFIC VOLUME WITH PRESSURE FOR THE METHANEbuilt up. After BENZENEMIXTURES AT 100.27" F. thermal equiMole per cent methane a8 follows: librium is at1. 76.01 S. 35.50 2. 66.71 9. 30.25 tained and the 3. 62.85 10. 28.53 ( f B ) 4. 53.40 11. 24.53 hysteresis a. 46.85 12. 19.46 effects of the G . 40.75 13. 18.01 (re) 7. 36.42 e x p a n s i o n of the steel have disappeared, the reading on pump D is recorded as well as the gage pressure. The pump is then backed off to give a lower pressure, and another set of equilibrium pressure and pump readings is recorded. These readings are continued until sufficient data are obtained in both the one- and twophase regions to establish the bubble point definitely. The mercury level is then backed down to the contact point, and the pressure and pump readings a t the contact point are recorded. Another sample of benzene is then injected and the process repeated. After a number of benzene injections the system is cleaned out, and the entire process repeated for a new run. The data presented here are the result of three runs. The method of detection of the bubble point for such mixtures was described previously by Sage, Backus: and Lacey (12). The method is simply that of plotting the P-V data obtained, a sharp break occurring in the plot a t the bubble point corresponding to the transition from the one-phase to the two-phase condition. The calculation of the specific volumes of the mixtures under the different pressures is evident, since the total mass and the total volumes of the mixtures are known under the different conditions. 038001
I
I
1
Purification of Methane and Benzene The starting material for the methane supply was the impure methane from the city domestic lines which was a p proximately 95 per cent methane. It was purified by passing successively through potassium pyrogallate solution, soda lime tubes, anhydrous magnesium perchlorate tubes, and a copper trap immersed in a solid carbon dioxide-acetone bath. The methane was then slowly condensed with liquid air into an evacuated still and afterwards distilled through a
791
Podbielniak column. Heart, cuts were condensed into an evacuated one-liter (one-quart) high-pressure bomb which was immersed in liquid air. When warmed up to room temperature, the resultant supply of methane had a pressure of about 1500 pounds per square inch. High-vacuum technique was employed throughout. For the benzene supply, c. P. benzene was refluxed with mercuric acetate for 24 hours to remove any thiophene. The sample was then distilled through a Widmer column, and the heart cut was refluxed with metallic sodium for 24 hours. The sample was then twice distilled through the Widmer column, and only heart cuts were taken. The specific gravity and index of refraction of the purified benzene were found to be 0.8786 a t 20°/4" C. and 1.5018 a t 20' C., respectively, as compared t o the values of 0.8788 (4) and 1.50144 (6) taken from the literature.
Results The results calculated from the experimental data are presented in Table I. All of the fundamental data of Table I are represented by Figures 3 and 4. Figure 3 shows the relation between bubble-point pressure and composition. The approach to the critical pressure for this temperature is evident in Figure 3 in the neighborhood of 5200 pounds per square inch. Figure 4 shows the relation between pressure and specific volumes for the various mixtures. The numbered lines are constant composition lines, and the long curved line represents the specific volume a t the bubble point. The area to the left and above this curve represents the two-phase region; the area to the right and below represents the one-phase region. The approach to the critical region is indicated again in Figure 4 in the higher pressure region. The data of Sage, Webster, and Lacey (12) are plotted in Figures 3 and 4 for comparison. Our bubble-point pressures agree with theirs to within 0.5 per cent, and the bubble-point specific volumes agree t o within 1 per cent. This agreement is considered satisfactory. The temperatures of the two sets of data differ slightly. The data of Frolich and co-workers (2) were not considered in this paper because their values were determined a t 77" F.
Acknowledgment The authors are indebted to Stuart E. Buckley of the Humble Oil and Refining Company for the suggestion of this problem as well as valuable assistance in its solution. They are also indebted to the Humble Oil and Refining Company for fellowship grants to J. H. Lightfoot and A. E. Hoffmann and to the Tau Beta Pi Association for a fellowship grant to A. S. Kasperik.
Literature Cited (1) Beattie, J. A., PTOC. Am. Acud. Arts Sci., 69, 389 (1934). (2) Frolich, P. K., Tauch, E. J., Hogan, J. J., and Peer, A. A,, ISD.ENQ.CHEM.,23, 548 (1931). (3) International Critical Tables, Vol. 111, pp. 29, 36, New York, McGraw-Hill Book Co., 1928. (4) Ibid., Vol. 111, p. 33 (1928). ( 5 ) Ibid., Vol. VII, p. 38 (1930). (6) Ipatieff, V. V., Jr., Levina, M. T., Stsiberovskaya, N. P., Teodorovich, A., and Diner, E. G., Sotsialist. Rekonstruktsiya i Nauka, No. 4, 175 (1936). (7) Keyes, F. G., Proc. Am. Acad. Arts Sci., 68, 505 (1933). (8) Kvalnes, H. M., and Gaddy, V. L., J. Am. Chem. SOC.,53, 394 (1931). (9) Landolt-Bornstein, Physikalisch-chemische Tabellen, 5th ed., Vol. I, p. 101, Berlin, Julius Springer, 1923. (10) Ibid., 1st Supplement, p. 12 (1927). (11) Sage, B. H., Backus, H. S., and Lacey, W. N., IXD. ENQ.CHEM., 27, 686 (1935). (12) Sage, B. H., Webster, D. C . , and Lacey, W. N., Ibid., 28, 1045 (1936).
