Solubilitv of Nitrogen and Oxygen in Liquid Sulfur Dioxide RALPH W. DORNTE AND C. VAUGHAN FERGUSON General Electric Company, Schenectady, N. Y.
I
The solubilities of nitrogen and oxygen in liquid sulfur dioxide have been determined for the temperature range -60" to -20" C. These gases are very soluble and have a positive temperature coefficient of solubility so that the gases are the more easily removed, the lower the temperature of the liquid. Evidence of the formation of sulfur trioxide from oxygen and liquid sulfur dioxide has been found in experiments at O O C . This reaction, however, was not catalyzed by water or steel.
N CONNECTION with a study of some reactions in liquid
sulfur dioxide, solubility data for nitrogen and oxygen in liquid sulfur were required. These data, however, were not available in the literature. Qualitative information was also desired on the extent of the reaction of oxygen with liquid sulfur dioxide at low temperatures. The following experiments were undertaken to obtain this information. The first static system, devised for the determination of the solubility of nitrogen in liquid sulfur dioxide, had a large free gas space which interfered with the establishment of equilibrium. A satisfactory static system (Figure 1) was finally designed so that only the partial pressure of the added gas was indicated on a differential mercury manometer. This construction eliminated the necessity of maintaining a constant temperature in the Dewar thermostat since the same pressure of sulfur dioxide is present on both sides of the differential manometer. The apparatus consisted of a gas buret, a differential manometer, and two 10-cc. bulbs connected as shown in Figure 1. The bulb on the measuring arm of the system was graduated so that the volume of liquid could be measured a t a known temperature. An unsilvered Dewar tube containing acetone served as thermostat; a constant temperature (*0.5" C.) was easily maintained by periodic additions of small pieces of solid carbon dioxide. The portion of system containing the graduated bulb had a volume of 116 cc. After the system was evacuated, exactly 1 cc. of liquid sulfur dioxide was condensed in each bulb by holding the thermostat a t -70" C. The stopcock connecting the two bulbs
SO,
ED
L J \
RENTIAL DIF MANOMETER
PUMP
BJ
G A S BURET
DEWAR
was closed, and a measured volume of gas was introduced into one side of the manometer from the buret. Equilibrium ' was readily attained in 10 or 15 minutes by agitating the liquid in the bulbs and by circulating the gas between the buret and bulb. The rather large pressure correction due to temperature differences on the system was determined in the absence of sulfur dioxide, and it was assumed to be the same in the presence of sulfur dioxide. This assumption is justified since this correction was independent of the total pressure. To ensure the absence of systematic errors which might arise from a nonuniform gas phase in the static system, the results were checked on a circulating system. The circulating system involved the differential manometer and required merely the addition of a circulating pump to one side of the static system. A sylphon circulating pump' caused the added gas to pass through a precooling coil in the thermostat and then to bubble through the liquid sulfur dioxide in the graduated bulb. All pressure readings were taken after the pump was momentarily stopped a t top dead center. With the pump in this position the volume of the system was 453 cc. The pressure correction due to temperature differences on the system was rather small in this case. Equilibrium between the added gas and liquid sulfur dioxide was established in 5 minutes by circulation.
FIGURE1. APPARATUS FOR SOLUBILITY EXPERIMENTS
1
112
Dornte, IND. ENQ.CHQM.,28, 26 (1936).
INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY. 1939
.
'C 0 -10 -20 -30 -40
1000
-50
-60
113
-70
100
~
"
;
"
4
@CIRCULATION E X P
@ CIRCULATION EXP. 2, I 340
360
380
400 420 I/T X I O 3 c K )
440
460
400
3.40
3.60
380
400
I/T
FIGURE2. SOLUBILITY OF NITROGEN IN LIQUIDSULFURDIOXIDE AS A FUNCTION OF TEMPERATURE
Results The preliminary results showed that Henry's law satisfactorily represented the experimental results for the temperature range -60" to -20" C. and for the pressure range 10 to 70 cm. of mercury. The Kuenen absorption coefficient, y , which is the volume of gas (cubic centimeters a t standard temperature and pressure) dissolved in 1 gram of the liquid a t the experimental temperature when the partial pressure of the gas is 1 atmosphere, has been calculated from the experimental data. The Kuenen absorption coefficients obtained from static and circulation experiments are recorded in Table I.
420
x io3 ('K)
440
460
480
FIGURE 3. SOLUBILITY OF OXYGENIN LIQUID SULFUR DIOXIDE AS A FUNCTION OF TEMPERATURE
From these equations the following values were calculated. These extrapolated values are probably as reliable as the experimental determined solubilities. The error in the absorption coefficients does not exceed * 10 per cent in the most unfavorable cbse. to
c,
-20 10 0 10 20 30
-
Nitrogen Oxygen Cc. (8.T.P.) at 1 atm./g. SOY 47 25 87 50 150 98 260 183 435 331 600 675
Positive temperature coefficients for the solubility of nitrogen and oxygen in liquid sulfur dioxide were not expected, OF GASESIN LIQUID SULFURDIOXIDE and special experiments also checked this result. The posiTABLE1. SOLUBILITY -NitrogenOxygen-tive temperature coefficient of solubility indicates that the y , static 7 , circulation Y , static 7 , circulation solution of these gases in liquid sulfur dioxide is an endothert o c. expt. expt. expt. expt. Cc. (8.T. P.)at 1 atm./g. SOz mic process which involves about 8,000 calories per mole for nitrogen and about 10,000 calories per mole for oxygen. ... 2.86 -60 These thermal values assume that the heat of dilution of a 6.35 -80 ... solution of nitrogen or oxygen in liquid sulfur dioxide is zero. 4.05 This assumption has no supporting evidence. -40 ... At the end of the oxygen experiments the sulfur dioxide was allowed to evaporate a t atmospheric pressure; the gradu27.2 -30 30.1 56.6 -20 ated bulb was washed with water, and washings were tested for sulfate. I n one experiment oxygen a t 20 cm. pressure was bubbled through 4.8 grams of liquid sulfur dioxide a t The results for nitrogen and oxygen are shown in Figures 0" C. for 4 hours; the total sulfur trioxide formed was about 2 and 3, respectively, where the logarithms of the absorption 1 mg., based on the amount of precipitated barium sulfate. coefficient are plotted against the reciprocals of the absolute Similar experiments with 1 per cent of water or 20 sq. cm. temperature. From these plots the following equations are of steel, or with both present in the liquid sulfur dioxide did derived for the temperature variation of Kuenen absorption not increase the formation of sulfur trioxide under the same coefficients: conditions. These experiments show that a very slow reaction of oxygen and liquid sulfur dioxide occurs a t 0" C. but 8 180 For Na: log y = 8.729 - Lthat the rate is not readily measured under these conditions. 4.58T
--
{El
For 02: log
y =
9.710
9,650 - 4.58T -
RECEIVED July 14, 1938.
