December, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Absorption of Carbon Dioxide and Ammonia from Gas Bubbles' By Paul G . Ledig B U R E A U O F STANDARDS, W A S H I N G T O N ,
I
D. C
N A N earlier paper2 a new method was described for study-
ing the rapid absorption of gases by solutions, particularly the absorption of carbon dioxide by sodium hydroxide solutions. The present report deals with a continuance of the work upon absorption, particularly the absorption of carbon dioxide by potassium hydroxide solutions, and of ammonia by water and ammonium hydroxide solutions. CARBON DIOXIDE ABSORPTION The study of potassium hydroxide solutions was made with the same apparatus used in the previous study of sodium
1231
rapidly absorbing potassium hydroxide solutions. A groundglass connection on the capillary tube made it possible to use heptane for this purpose without serious manipulative inconvenience. The potassium hydroxide solutions studied range from 0.5 to 13.0 N . The concentrated solution (13.0 N ) was carefully analyzed for hydroxide and carbonate content, and all the other solutions were made by carefully diluting it to the desired concentration. Samples taken from the diluted solutions after use in the apparatus were found to be more than sufficiently accurate in composition. From the photographic curves obtained, calculations were made for rate of absorption over the whole period from the beginning of absorption to the practical disappearance of the bubble. Fig. 3 shows a series of curves obtained by plotting the rate thus calculated against time, from the moment absorption begins. The initial points of the curves are also arranged in the order of the concentration of the solutions. Potassium hydroxide solutions absorb carbon dioxide more than twice as fast as sodium hydroxide solutions a t the lower concentrations (up to 3.5 N ) . (Fig. 4) Above this concentration the sodium hydroxide solutions show a decreasing rate with concentration, while the potassium hydroxide solutions show a slowly increasing rate to about 9 N . Above this
FIG. ~-DIAGRAMIMATIC S K E T C H OF A P P A R l T U S
hydroxide solutions. Fig. 1 gives a schematic representation of the method used, and Fig. 2 shows the apparatus in which the absorption takes place. A bubble formed under mercury rises into a stream of solution flowing downward and is there absorbed. The system is closed except for a narrow capillary tube open to the air, and as absorption takes place a OF column of liquid in the capillary moves a corresponding amount. A beam of light passing through the capillary and a slit in a light-tight drum produces a photographic shadowgraph of the moving liquid upon a strip of sensitive paper moving across the slit. An electrical tuningfork also makes time interval records on the edge of the paper. In this study of potassium hydroxide Mercury solutions, a bubbler tip which has sharper lip edges than the old form was used because it FIG SHA ABSORPTION APPARATUS gave more satisfactory reproducibility of bubble volume. Moreover, in spite of evidence previously obtained with sodium hydroxide solutions, it was found necessary to use a liquid of low viscosity and density in the capillary tube when working with the more 1 2
Published by permission of the Director, U. S Bureau of Standards. Ledis and Weaver, J . A m . Chem. SOC.,46, 660 (1924).
TUNING fORK F I G . 3-EFFECT
y/BPAT/ONS
O F CONCENTRATION UPON R A T E OF
ABSORPTION IN
KOH SOLUTIONS
concentration a very peculiar rapid rise in rate takes place as the concentration increases. An attempt has been made to link this rapid rise of rate with the known properties of the solutions-solubility of the carbonates, viscosity of the solution, and ionization of the hydroxide and carbonate solutions-but no quantitative relation has yet been found. The fact that the rate of absorption for sodium hydroxide solutions falls off as the concentration increases beyond 3 or 4 N can probably be explained by the low solubility of the carbonate and bicarbonate. In the experimental work on the 6.6 N solution minute crystals are actually visible at the surface of the small residual bubbles. AMMONIA ABSORPTION The absorption of ammonia in water was first tried with the apparatus described above, but it was immediately discovered that the gas in the tube leading to the bubbler tip
INDUSTRIAL A N D ENGINEEhYNQ CHEMISTRY
1232
expanded under the marked decrease in pressure as the ammonia was absorbed, and erroneous curves were produced. An apparatus was therefore devised which dowed the bubble to pass through a stopcock in the mercury
0
10
40
60
80
104
110
NO
I60
180
Vol. 16, No. 12
illary are approximately only one-half those secured by using the large capillary. Assuming that the results showing the highest rates were more nearly correct, a series of photographic curves was
200 220 240 260 280 so0 320 340 360 380 400
420
440
Tuoinq fork Infervats fsinqfe Yibrafions) F"3.4-Errrsm 0s CONCBA?Bh'ClON
oPDN RAT* 01) Aasoeprloir IN NilOA
So~vrloriis
column (Fig. 5), after which the stopcock could be closed made with use of the large capillary, as shown in Fig. 7. before absorption took place and all the pressure change The decreasing slope of the curves indicates the effect of inproduced would be bransmitted directly to the capillary creasing concentrat.ionupon the absorption. The oscillations tube. This proved satisfactory and was used in the work appearing o n t h e on ammonia. 16 photographic curves As in the case of the potassium hydroxide solutions, the a r e u n d o u b t e d l y concentrated solution of ammonium hydroxide was analyzed damped acoustic vibraand the lower concentrations were made by careful dilution tions of the liquid which of the stronger solution. Tlie dilutions were made by iutro- are set up as the bubducing a pipetful of solution into water in a separatory funnel, ble changes volume which was ako used for transferring the solutions to the ap- rapidly. paratus. The transfer was made by connecting the delivery The rate curves caltube of the separatory funnel, which had been bent into a U culated from these shape, with the drain curves are shown in cock of tho apparatus Fig. 8. The curves and foreingin the solu- probably do not give an tions by air pressure accurate picture of the Evaeir MLWC (cc/ applied through the true rates of absorp~ upper endof the funnel. tion during the ex- PIC. e--Epsa* OB C a ~ m . * aDNLWBIBB UPON APPARENT RATS os A B ~ O R ~ T ~ ~ N Ammonia is ab- tremely short period of sorbed very rapidly, time that absorption takes place (less than 0.01 second), and consequently the but the change in slope as the concentration of the ab inertia and viscosity of sorbing solution increases is appareritly proportional to the the liquid in the capillary tube ( h e p t a n e was used as in the work on potassium hydroxide, because of its low viscosity and density) have a marked effect upon the photographic curve produced. The capillary tube used in the work on carbon dioxide has an inside Fro 5 - A ~ p ~ n ~ r son o s T Z ~ BSIVDY os diameter of 0.7 mm.; A l a w o ~ mABSORPTION but this was thought to be too small for use with the very rauidlv absorbine ammonia solutions, and a new tube lkvidg an inside d c ameter of 1.5 mm. was prepared. The effect upon the ap-. ... . .. .. . -. . .. parent rate curve produced by this change in capillary diameter is shown in Fig. 6. The rates of absorption deter13 N 12.5 N 10 N 5 N Water Blank mined from a record obtained by the use of the small capFra. 7-Paorocnn~xrc Coavgs Oelrrmto wma A Y M O N ~ ~
I
December, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
pressure difference in the system caused by the absorption and indicates only the rate a t which this pressure difference causes the liquid to move in the capillary. The true rate of absorption must be considerably greater than the apparent rate shown by these curves, because the low pressures produced as absorption begins must seriously slow down the rate of absorption during the remaining period. However, a study of this series of curves and of the vapor pressure data on ammonia solutions brings out the interesting fact that the slope of the curves is proportional to the total gas pressure (1 atmosphere) minus the vapor pressure of ammonia above the solution.
1233
Comparative Absorption Rates for Various Gases By W. G . Whitman and D. S. Davis MASSACHUSETTS INSTITUTE
OF
TECHNOLOGY, C A M B R I D G E , MASS.
HE work described in this paper represents an experimental study of absorption through a free surface of liquid when the liquid is stirred.
T
To determine the relationships between absorption rates for different gases, four gases of widely varying solubilities were selected for investigation. These gases, oxygen, sulfur dioxide, ammonia, and hydrogen chloride, represent a range of about three hundred thousand fold in solubility under the conditions of the experiments. I n addition to the absorption runs, experiments on the rate of escape of sulfur dioxide from aqueous solutions by air were performed, including runs on the effect of rate of stirring and viscosity of solution. EXPERIMENTAL METHOD
BuabLE L&LUM€ F I G . 8--EFFEC’I
OF C O N C E N T R A T I O N U P O N
(CC)
The apparatus is shown diagrammatically in Fig. 1. The absorption chamber, A , is an 8-liter porcelain jar with side outlets for gas entrance and exit tubes, a and b, for a glass coil for cooling water, c, and for a tube for withdrawing liquor samples, d, and holding the liquor thermometer. A plate glass cover with rubber gasket is clamped over the jar, and the paddle stirrer, e, for gas and liquid passes through a stuffing box set in this plate. This stirrer is rotated a t 60 * 5 r. p. m. in all runs except when otherwise noted. For ammonia, sulfur dioxide, and oxygen the gas was bled from commercial cylinders, whereas the hydrogen chloride was generated by dropping sulfuric acid into concentrated hydrochloric acid solution. This gas stream, after passing through flowmeter B, mixes in chamber C with a stream of air which has passed through a pulsation chamber, D,and a flowmeter, E. The temperature of the mixed gas is taken a t a.
RATEO F ABSORPTION OF
AMMONIA
.......... DISCUSSION
Professor McAdams asked whether the higher rates with potassium hydroxide as compared with sodium hydroxide could not be explained by the lower solubility of sodium bicarbonate. Mr. Ledig stated that this might be the case, particularly as fine crystals were formed in certain of the experiments with sodium hydroxide. Mr. Wilson mentioned that carbon dioxide was very difficult to absorb from dilute gases, as he had observed in studying the absorption of various gases in gas mask research. The chairman asked whether the viscosity of the absorbing solution had been considered; furthermore, had the ammonia data been investigated with reference to the rate varying with the degree of unsaturation? Mr. Ledig replied that the data had been obtained very recently and had not yet been subjected to a thorough analysis. Milwaukee Tests Rubber P a v i n g A strip of rubber paving for test purposes has recently been laid on the approaches to the Sixth Street Viaduct, Milwaukee, Wis. The rubber blocks employed were similar to those laid some time ago on the Northern Avenue Bridge in Boston. Milwaukee is the fourth large city to test the rubber blocks, similar strips having been laid in Boston, St. Louis, and Chicago.
u
u I1I
FIG.1
The procedure in an absorption run was to determine by liquor analyses the rate of absorption in 4 liters of water when a steady stream of gas of constant composition was passed over the liquid. I n the cases of hydrogen chloride, ammonia, and sulfur dioxide, a 4-gram liquor sample was withdrawn a t intervals; for oxygen the sample was 250 cc. All samples were stoppered immediately after withdrawal. Hydrochloric acid solutions were analyzed with standard alkali and phenolphthalein, ammonia with standard acid and methyl orange, sulfur dioxide solutions with standard iodine and starch, and oxygen by the standard WinMer method. The procedure in runs to determine rate of escape of sulfur
