ADSORPTIOK O F hfIXTURES O F EASILY COXDENSABLE GASES* BY SIMON KLOSKY AND LEO P. L. WOO**
Extensive investigations have been undertaken on the adsorption of single gases in porous bodies such as charcoal, meerschaum] pumice, etc. Silica gels have been used by Patrick and others for the adsorption of sulfur dioxide,’ butane,* etc. Burggraff3 was the first who used titania gel for adsorption purposes. S’ery few attempts have been made to investigate the adsorption of mixed gases, The investigations of Joulin14Miss Homfray,6 Bergter16Hempel and Yater,’ and Lemon and Blodgetts were largely qualitative and were quantitative only when measuring the total volume adsorbed. Richardson and Woodhouseg were the first investigators who studied the adsorption of carbon dioxide and nitrous oxide by charcoal by the static method and analysed for the composition of the adsorbed gas a t different percentages. These two authors concluded from their experiments that “it seems possible to deduce the total amount of any mixture of carbon dioxide and nitrous oxide adsorbed by charcoal if the isotherms of the independent adsorption of the individual gases are known. The formula
in which Vsoz and VxrO represent the volumes of those gases separately adsorbed a t the total pressure of the mixture and a1 and a2 stand for the percentages of the respective gases in the mixture, holds within certain limits. On the other hand, there seems to be no possibility of calculating the volume of each of the component gases adsorbed in the charcoal from the volume of the gaseous mixture. I n other words the ratio of the amounts of the two gases adsorbed varies with the pressure whether we are dealing with them separately in contact with the charcoal or whether they are mixed.” I t was the purpose of this investigation to measure at ordinary temperature the adsorption of mixtures of easily condensable gases such as sulfur dioxide, methyl chloride, butane, etc., by titania gel which was first prepared by *Contribution from the Martin hlaloney Chemical Laboratory, of the Catholic University of America. **Extract from Research Work submitted as a Dissertation in partial fulfilment of the requirements for the Doctor’s degree, 1928. Patrick and McGavack: J. h m . Chem. SOC., 42,946 (1920). Patrick and Long: J. Phys. Chem., 29, 336 (1925). 3 Burggraff and Iilosky: J. Am. Chem. SOC., 50, 1045 (1928). Joulin: Ann. Chim. Phys., (4)37,472 (1912). Homfray: Z.physik. Chem., 74, 129 (1910). 6 Bergter: Ann. Physik, (4)37,472 (1912). Hempel and Yater: Z. Elektrochemie, 18, 724 (1912). E Lemon and Blodgett: Phys. Rev., (2) 14, 394 (1919). Richardson and Woodhouse: J. Am. Chem. SOC.,45,2638 (1923).
’
1388
SIMON KLOSKY AND LEO P. L. WOO
Klosky and Marzano,l in this laboratory and t o determine the amounts of adsorbed gases in the gel with the hope of establishing some relationship between them. Materials, Apparatus and Procedure Titania gel. The gel was prepared by Burggraff. The particles of the gel were 20-40 mesh size. It was activated a t 3o0°-3300 C before use. The weight of gel used for each single determination was 4-5 g m s . Two different samples of gel were used for the two systems. The gases were purchased in tanks from a commercial company. The sulfur dioxide, after being dried, was found 99.6-99YG adsorbable in NaOH solution. The butane was dried and purified according to the method employed by Patrick and Long. Kerosene was found suitable for adsorbing butane quantitatively. Methyl chloride was passed through NaOH solution and dried by calcium chloride. It was found 99.4-9970 adsorbable by glacial acetic acid.* Apparatus and procedure: All the determinations were made by a dynamic method similar to that used by Patrick and O ~ d y k e and , ~ described by Burggraff. The chief advantage of the dynamic method over the static one is that the former requires no exclusion of air and is more rapid although i t is not as accurate as the latter at lower pressures. The total pressure was always equal to the atmospheric pressure. The individual isotherms of each gas were determined by mixing with air. The composition of the mixtures was determined first by flowmeters and then checked by the analysis from the bottle. The analysis was carried out either by titration as in the case of sulfur dioxide or by adsorption as in the case of butane or methyl chloride. The flowmeters were calibrated with air and when the reading of the flowmeter, measuring the gas, was multiplied by the relative viscosity of the gas compared to air, the per cent by volume calculated from these readings agreed with the results of analysis within 1.5% in all cases. The time required for the equilibrium was from I to 2 . j hours depending upon the pressures used. I n every case a constant weight was obtained before changing the concentration of the gaseous mixtures. In the determination of independent isotherms one sample of gel was used for several different partial pressures. The partial pressures of the gas were changed from lower to higher in order to avoid the error due to the irreversibility of adsorption. Analysis of Gases As was mentioned above, the composition of each gas when mixed with air in the determination of individual isotherms was determined by analysis. The mixture of sulfur dioxide and air was analysed by the iodine method and also by adsorption in NaOH solution. Both methods checked closely. The mixture of butane and air and of methyl chloride were determined by absorption in kerosene and glacial acid respectively. 'Klosky and M a n a n o : J. Phys. Chem., 29, 1125 (1925). * Meighan: J. Ind. Eng. Chem., 11, 943 (1919.) Patrick and Opdyke: J. Phys. Chem., 29, 601 (1925).
ADSORPTION O F MIXTURES O F CONDENSABLE GASES
I389
The analysis of the mixtures of gases adsorbed in the gel presented great difficulties. It is impossible in the dynamic method to determine the composition of the adsorbed gases in the gel by knowing that of the unadsorbed gases, as in the case of the static method. The direct analysis of the adsorbed gases is necessary. After many trials it was found that the following method gave satisfactory results. The U-tube containing the gel, after constant weight was obtained, was connected to a separatory funnel in which a known volume of standardized NaOH solution was placed. The solution was carefully run into the gel and then the gel was washed into a beaker. It was found that the concentration of the KaOH solution should be above .5N; when .I- .35 N solutions were used, only about 66.6% of the sulfur dioxide could be obtained. The solution containing the gel was warmed for about three minutes and then the excess of the NaOH was titrated as soon as possible by a standard solution of nitric acid, using phenolphthalein as indicator. Warming was also necesWhen the weight of sary, otherwise the error became as high as 33.0%. the gases adsorbed and the amount of sulfur dioxide are known, the amount of the second component such as butane or methyl chloride can be readily calculated. Experimental Results Since Burggraff has already shown that the adsorption of sulfur dioxide by titania gel agrees very well with the equations of Freundlich, Patrick, and Polanyi, the adsorption of sulfur dioxide in this experiment was made a t only one temperature, while those of butane and CH&l were made a t different temperatures. I n Tables I-VI1 P = pressure in atmospheres x/m = grams of gas adsorbed per gram of gel Experimental Data TABLE I TABLE I1 Sulfur dioxide in gel KO. I Sulfur dioxide in gel No. 2 a t 35' C. a t 35' C. P(atm.)
x/m
. I22
0358 .0497 .0543 ,0632
'431 ,605 .995
P(atm.) ,
I94
.257
.478 ,766 I . 000
TABLE I11 Butane in gel KO.I a t oo C. P(atm.)
. I22
,401 ,610
x/m
'0346 ,0373 .0428 .0478 .OSIO
TABLE IV Butane in gel No. I a t 35' C.
x/m
P(atm.)
v'm
,0323
.IO0
,0562 ,0882 1065 1040 I340
,249
.or73 .0206
,332
'470 625 ,980
S I M O S KLOSKY AND LEO P.
I390
TABLE V CH3C1in gel No. a t 25%. P(atm.) ,182 ,427
,788 1.000
TABLE VI CHSCl in gel S o . a t 35OC.
2
x /m ,0369 ,0473 ,0683 ,0875
L.
WOO
TABLE VI1 CH3C1 in gel KO.2 at 45OC.
2
x/m
,203
,206
x/m 03 46 ,0324
P(atm.)
'
,570
,0440
.885
'790
,0519 ,0558
I . 000
,030; ,0398 ,0474 '0493
P(atm.) ,150
I 000
,486
I n the mixture of gases it was found most desirable to plot the number of mols against the partial pressures. I n Tables VIII-IX x1 and x2 represent the weight of gas adsorbed per gram of gel, the subscripts I and 2 indicate the first and second components of the gaseous mixture.
TABLE VI11 Sulfur dioxide-butane in titania gel Xo. I a t 35' C. 7c
so2
X
14.0
03 93 ,0445 ,0443
24.4
'0474
49.2
.os05
7 7 .o
.0j78 ,0625
0
11.1
100.0
'
(XI)
!sod
(x?)(C,Hiu)
.oooo .OIjj
. 0 2 70
,0228
.02 Ij
,0298 .03 60 ,0448 ,0625
,0145 ,0130
,0393
,0176
. 0000
TABLE IX Sulfur dioxide-methyl chloride in titania gel KO.2 at z j"C. 7c SO2
(xJ(S02)
(XP) (CHC1)
.os58
. 0000
.0jj8
13.5 23.1 29.6 42.3 64.0 79.2
,0585
,0193
,0392
,0600 ,0605
,0235
,0365
. 0 2j
,0590
,0298
.0292
,0578
'0374
,0204
,0545
, 0 4 0j
,0140
81.5
,0535
'
,0128
100.0
.05IO
0407 ,0510
.o
X
4
,0331
. 0000
Discussion of Results The data on the adsorption of single gases have been used to test the equations of Freundlich, Patrick, and Polanyi and found t o agree fairly well. The interesting qualitative discussion of Drucker' about the close relationship between viscosities and adsorption of mixtures of gases induced Drucker: Z. physik. Chem., 9 2 , 2 8 7 (1917).
ADSORPTION O F MIXTURES O F COSDEXSABLE GASES
1391
us to make an attempt to find some quantitative connections among them. It was found that the ratio of the molecular weights and viscosities of sulfur dioxide and butane is 1.80 which is almost exactly equal to the inverse ratio of the relative adsorption lowering of the two gases. I n Tables X-XI K and S’ represent respectively the number of mols of the first and second components of the gases adsorbed per gram of gel from the mixtures. The subscript zero represents the corresponding amounts adsorbed from the gas-air mixtures.
TABLE X Sulfur dioxide-butane, a t 3 jo C. F /C
Pi0
,000614 .000760 .000860 .000940
20
40
60 80
SO’ ,000305 ,000643 .oooj55 ,000625
Xo-S
s
S’
,000431 ,00054o ,000615 ,000718
,000165 ,000228 ,000256 .000350
N,‘-N’ N o ’ - ” ’ / h F
So‘
,298 ,290 ,286 .236
,522
1.7j
,509 .539 ,440
1.76
Average
so
,
so
I O
1.8j
1.86 1.81
TABLE XI Sulfur dioxide-methyl chloride, a t 3 5°C.
5
so
20
,000547
40 60 80
.000710
No’ .000620 .oooi;o .000900
.0007jj
.OOIOIO
,000643
s .000360 .0004jj ,000567 .000632
No-N No’-.U’ K@‘;s;/K@-Y --
so
”
No’
,342 .oo04~0 ,262 .000623 .201 ,000744 ,163 ,000275
Average I
These data are shown graphically in Figs.
,555 ,390 ,307 ,263
s
so
1.62 1.48 1.53 1.61 1.56
1-2.
The values of viscosities are taken from Landolt-Bornstein’s Tabellen a t since those a t 35’ C are not all available. We may also note that the ratio of viscosities does not vary appreciably with temperature, so no considerable error would occur when we use the ratio of viscosities a t 2 0 ’ C. for that a t 3 5 O C . The same procedure can be applied to the sulfur dioxidemethyl chloride system, where the average ratio is I . j3 as shown in Col. 8, Table XI. The inverse ratio of the molecular weights and viscosities of sulfur dioxide and methyl chloride is: 2o°C
If we use the equation
-
SO’
.-
SIMON KLOSKY AND LEO P. L. WOO
1392
to calculate the second component from the two independent isotherms and from the first component, a surprising agreement between the calculated and observed values is obtained as is shown in Table XII-XIII. Table XI1 NZ = butane
R
S(obs.)
N(ca1c.)
20
.00016s .ooozz8 .000256
.ooo16o
.000350
.000359
40 60 80
Average
TABLE XI11 NZ = methyl chloride
,000221
error 3.0 3.3
.000252
1.6 -2.5
N(obs.)
N(ca1c.)
,00027 5
.000296 ,000464 ,000626 ,000764
.o00470 .000623 .000744
2.6
Average
% error - 7. I 0.6
-0.5 - 2.8 2.8
FIG.I SOI-CIH~~
I n going over the data of Richardson and Woodhouse i t was unusually interesting to find that equation (I) again holds as well as could be expected. Their data were obtained from a static method. For the sake of comparison it was necessary to retabulate their results, that is, to plot volumes adsorbed against pressures. Curves were plotted on large scales according to Table XIV. The readings on Tables XV-XVII were obtained directly from the curves, and the agreement between the calculated and observed values are shown by the last columns of the three tables. The average per cent error is only 2.1-3.5.
ADSORPTION O F MIXTURES O F CONDENSABLE GASES
P (total) m /O
VI
49.2 50.8 73.9 26.1 23.4 76.6
29.2
mm.
1000
TABLE XIV P 2000 mm.
vz
VI
48.6
16.0
54.0 22.8
20.5
16.5
13.5
8.9 65.5 94.8
vz
81.8
72.5
84.2
v1
47.5
38.3
IO0
P 3000 mm.
VZ
40.7
53.1
I393
81.6 113.0
107.3
88.4 I21
.o
120.0
FIG.z SO,-cKJCI
TABLE XV When total P = 1000mm. % 20
V(ca1c.)
9.0
Vz(obs.)
9.5
40
25.7
27.5
60 80
47.2
48.0 69.4
70.5
Average
% error 5.0 6.0 1.5 -1.5 3.5
TABLE XVI When total P = 2 0 0 0 mm. %
V(Ca1c.)
Vz(obs.)
20
14.5 34.4 59.5 86.6
15.0 35.7 59.7 85.5
40 60 80
Average
% error 3.5 3.8 0 . 2
-1.0
2.1
I394
SIMON KLOSKY AND LEO P. L. WOO
TABLE XVII When the total P = 3000 mm. %
Vz (0bs.)
V(ca1c.)
20
14.2
15.0
40 60
39.1
40.3
65.1
80
92.4
66.0 91.8
Average
% error 5.5 3.0 1.2
-0.8 2.6
The ratio of molecular weights and viscosities of COZand KzO is almost exactly equal to I. Considering the fact that adsorption experiments are relatively difficult especially at low pressures, as it was stated by the authors themselves, “under the best conditions the amount of gas adsorbed by a given specimen of charcoal varies several cubic centimeters in duplicate determinations,” we feel that the agreement is remarkably close. So far as we know, the data of Richardson and Woodhouse are the only ones in the literature on adsorption of mixtures of gases by porous bodies which are extensive enough to be tested. Lorenz and Wiedbrauck’sl experiment on C02-CZHd mixtures does not furnish any data on the actual amount adsorbed, while Magnus and Ruth’s2 experiment on C02-HZ mixtures does not contain the individual adsorption isotherms. Hence these data cannot be used to test our equation. Again let us consider the experiments of Richardson and Woodhouse and ours: the methods, gases, adsorbents, temperatures and total pressures are entirely different, yet all of them can be represented by the simple equation. Hence, it is very probable that molecular weights and especially viscosities of the components play an important part in the complicated phenomena of adsorption of gases by, a t least, porous bodies.
It may be well to point out that the formula V (mix) =
Vial
+ Tr2a2 IO0
which has been used by Homfray, Richardson and Woodhouse, and others holds in our SOz-C4Hl0system. Let us change the form of the equation into
N (mix)
=
Nlal
+ NZaz IO0
where N indicates number of mols and the subscripts indicate the first and second components. The agreement is shown in Table XVIII. The equation does not hold even roughly in the case of the SO2-CHSC1 system. 1 2
Lorenz and Wiedbrauck: 2. anorg. allgem. Chem., 143,268 (1925). Magnus and Ruth: Z. anorg. allgem. Chem., 150,311 (1926).
ADSORPTION O F MIXTURES O F COSDENSABLE GASES
I395
TABLE XVIII 70
S (mix) (calc.)
X (mix) (obs.)
error
11.1
.0007 I I
,000739
3.9
14.0
.OOOj20
.000728
1.0
24.4 49.2 77.0
,000753
,000768
2.0
,000829
.000812
.000916
.000985
Average
-' 2 . 0 7.0 3.5
summary Adsorption isotherms of C4Hloa t o°C and 2 j°C, and CHICl a t z j°C, I) 35OC and 4j°C on titania gel have been determined and found to agree with the formulae of Freundlich, Patrick, and Polanyi. 2) The adsorption of mixtures of SO2 plus CH3C1, and SOz plus C4H10 by titania gel have also been measured. 3) A simple formula has been proposed which holds for all available data with an average deviation of approximately three per cent.
