SORPTION O F CHLORINE BY SILICA GEL
31
REFERESCES
(1) BRUSAUER, STEPHEN, A N D EMMETT, PAULH.: J . Am. Chem. SOC.57, 1754 (1935). (2) BRUNAUER, STEPHEN, A N D EMMETT, PAUL H.: J. Am. Chem. SOC.59, 2682 (1937). (3) EMIETT, PAUL H.,AID BRUSAUER, STEPHEN: J. Am. Chem. SOC.69, 1553 (1937). E. B.: J. Am. Chem. SOC.62, 2838 (1940). (4) KENRICK, (5) KISTLER,S. S.:J. Phys. Chem. 39,79 (1935). (6) KISTLER,S. S.,AND KEARBY, KENNETH K . : Acta Physicochim. U. R . S. S. 1,354 (1934). (7) WHITE,J. J.: Private communication.
T H E VAN DER WAALS SORPTIO?; OF CHLORINE BY SILICA GEL AT LOW TEMPERATCRES'I~ L. H. REYERSO?;
AXD
CYRUS BEMMELS3
School of Chemistry, Instzlute of Technology, Gnzverszty of Jfznnesota, Mznneapolzs, ilfznnesota Recezved August 11, 1041
Data for the sorption of chlorine, bromine, and iodine by silica gel have been presented in previous publications from this laboratory ( 2 , 3 , 4). The isotherms for the three halogens a t the same relative temperatures above their boiling points differed markedly from each other. The chlorine isotherm was concave toward the pressure axis, while that for bromine was slightly convex and that for iodine markedly convex. In their theoretical treatment of adsorption, Brunauer, Deming, Deming, and Teller (1) have shown that the isotherms of bromine and iodine are what they describe as Type I11 isotherms. By assuming that the heat of liquefaction of bromine, E,, is equal to the heat of sorption on the first layer E,, they were able to calculate isotherms for bromine which agreed remarkably with the experimental results from this laboratory. Similarly, by assuming that E , is greater than E, for iodine they obtained excellent agreement for the isotherms of iodine. The data for chlorine from this laboratory were not obtained a t sufficiently large relative vapor pressures to enable them to make similar calculations for chlorine. The sorptions of chlorine by silica gel were therefore measured a t much lower temperatures than before in order to fill this gap in the sorption literature. The experimental procedure was similar to that previously reported. The same type of McBain-Bakr sorption balance, consisting of a glass bucket suspended from a helical quartz spring, was used. The bucket contained about 1 Presented a t the Eighteenth Colloid Symposium, which was held a t Cornel1 University, Ithaca, Piew York, June 19-21, 1941. 2 This material is part of a thesis submitted by Cyrus Bemmels t o the G;aduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1941. 8 Eastman Kodak Company Fellow, 1940-41.
32
L. El. REYERSON AND CYRUS BEMMELS
0.1 g. of carefully purified silica gel. A reservoir ' liquid chlorine waa maintained in a large tube well below the balance, and the vapor pressure of the liquid was controlled by a cryostat the design of which has been described by Scott and Brickwedde ( 5 ) . The pressure of the vapor was measured by a quartz-spiral manometer of the Bodenstein type. The portion of the system above the cryostat was maintained at a temperature independent of the liquid reservoir by means of an air thermostat surrounding it. This had to be heavily insulated for the lower temperatures. An inner wall waa constructed inside of each of three sides of this air thermostat and in this space waa placed the solid carbon dioxide used to cool the thermostat to the desired temperature. Insulated and specially designed windows in the fourth side of the box permitted TABLE 1 Sorption of chlorine gas b y silica gel AT
m.2'c. f 0.3' Chlorinesorhed
~
Prwure
silica gel
mi~~imo~ur
0.0 40.0
?O:i ~
~
o.Oo0 0.159 0.392 0.700 1.031 1.256 0.707' 0.337:
AT 0 %
~
Pressure
per gram of
mm.
153.2 732.2 326.5 109.2
1
1
I
'1 ~
1
~
,
1
* 0.2' Chlorine sorbed per gram of silica gel
1
AT
-S.3'c.
& 0.5'
Chlorine mrbed
~
~~
m o:;
6.2 15.8 39.6 116.4 215.6 71.9 283.7 524.3 324,2 61.7 212.1
j
1 ~
I ~
1
1
0.133 0.229 0.379 0.801 1.274 0.589 1.624 0.507 1.147
~
mm.
millimlu
0.0 42.2 107.4 221.3 356.4
O.Oo0
726.1 426.6 583.7
' ~
152.7
0.913 1.685 2.930 4.214 6.328 7.225 4.946* 6.880 3.574; 2.216'
33
SORPTION OF CHLORINE BY SILICA GEL
system was sealed off from the pumps and the connection to one of the chlorine bulbs broken. Chlorine was allowed to diffuse slowly through the system and allowed to stay in contact with the gel for several hours. It was then frozen out
PRESSURE IN MM
FIG.1. Sorption of chlorine gas by silica gel; desorption points are solid D
Fro. 2. Sorption of chlorine gas by silica gel
and the system again evacuated, heated, and then sealed from the pumps. The second sample of chlorine was then diffused into the system and condensed in the bottom of the tube extending into the cryostat. Measurements were then made a t pressures up to about 1 atmosphere. Sorptions were determined a t
34
L.
n.
REYERSON AND CYRUS BEMMELS
30.2'C. f 0.3', 0.0'C. rt 0.2', and -25.3"C. f 0.5'; the results are given in table 1. Equilibria were reached in a reasonably short time and the sorptions were completely reversible. Figure 1 shows the sorption isotherms. The data of Reyerson and Wishart (4)obtained a t the lowest temperature of their work are plotted in this figure and the points are just slightly lower than the present results a t 30.4"C. This indicates a very small temperature coefficient for the sorption of chlorine in this temperature range. Rearrangement of the generalized adsorption equation of Brunauer et aZ. (1) shows that a plot of P / [ V ( P , - P ) ] against PIP0 should give a straight line. Here V is the volume sorbed, P is the pressure of the vapor sorbed, and P o is the vapor pressure of the liquid a t the isothermal temperature. Plotted data for chlorine are given in figure 2. A straight-line relation is found for the
PRESSURE IN MM
FIG.3. Sorption of chlorine gas by silica gel
lowest ternperaturc, while the straight-line relationship does not hold for the lower relative vapor pressures at the higher temperatures. From the slope of the line for the lowest temperature and the intercept the constants of the Brunauer expression were evaluated. The value of E, - E, was found to diminish slightly a t lower temperatures but was of the order of 1000 caloriw. Using these constants, theoretical isotherms were calculated by the method of Brunauer et al. These curves are given in figure 3. The theoretical curves are the solid lines, while the points are the experimental data. I t can be seen that the agreement is rather good. Thus the sorption of chlorine by silica gel fits into the Brunauer theory along with the data for bromine and iodine. SUMMARY
1. The sorption of chlorine by silica gel has been measured a t relatively low
temperatures. 2 . The results agree with the sorption theory of Brunauer and his coworkers.
SORPTION O F HYDROGEN HALIDES BY SILICA GEL
35
REFERENCES
(1) BRUNAUER, DEMING,DEMING, AND TELLER: J. Am. Chem. SOC.62, 1723 (1940). AND REYERSON: J. Phys. Chem. 39, 169 (1935). (2) CAMERON (3) REYERSON AND CAMERON: J. Phys. Chem. 39, 181 (1935). AND WISHART:J. Phys. Chem. 41, 943 (1937). (4) REYERSON Bur. Standards J. Research 6, 401 (1931). (5) SCOTTAND BRICKWEDDE:
T H E VAX DER WAALS SORPTION OF GASEOUS HYDROGEX CHLORIDE, HYDROGEN BROMIDE, AND HYDROGEN IODIDE BY SILICA GEL',' L. H. REYERSON
AND
CYRUS BEMMELSa
School of Chemistry, Institute of Technology, University of Minnesota, Minneapolis, Minnesota Received.August 14, 1941
In the previous paper by the authors (2), data were given for the sorption of chlorine a t relatively low temperatures. This work completed the studies on the sorption of chlorine, bromine, and iodine by silica gel from somewhere near their boiling points to temperatures about 100°C. above these points. Since the isotherms for each of these elements showed differences on silica gel, it seemed desirable to study their hydrogen compounds. These compounds are similar to inert gases in structure, so that they should show different isotherms than the elements themselves. The data here presented show this to be the case. The same experimental procedure was followed as was used in the low-temperature work on chlorine (2). Sorptions w$re measured a t the various temperatures and pressures indicated in the tables and figures. Equilibria were rather rapidly established. No hysteresis was observed in desorption determinations, indicating the complete reversibility of the sorptions. Tables 1, 2, and 3 give the experimental results and figures 1, 2, and 3 present the results graphically. The sorptions of these hydrogen compounds of the halogens on silica gel show regular behavior and are much alike. They also appear similar to those of chlorine. The isotherms were therefore compared at about 40°C. above the boiling points of the halogens and their halides. The results are shown in figure 4. The values for iodine mere those less than 2OOC. above the boiling point, because at this point the sorptions were very low, the points falling just above the pressure axis. The sorption of hydrogen iodide is almost the same as for chlorine, while the sorptions for hydrogen bromide and hydrogen chloride Presented a t the Eighteenth Colloid Symposium, which was held a t Cornel1 University, Ithaca, S e w York, June 19-21, 1941. * This material is part of a thesis submitted by Cyrus Bemmels to the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1941. a Eastman Kodak Company Fellow, 1940-41.
