THE SURFACE BEHAVIOR OF ZEOLITES V. R. DAMERELL AND R. CADLE Morley Chemical Laboratory, Western Reserve University, Cleveland, Ohio Received January 11, 1036
The authors wished to study the surface behavior of zeolites during dehydration by the method previously applied to aged hydrous alumina (2). Accordingly the water content of samples of scolecite and analcite of different average particle sizes was determined under the same conditions. The large particle samples (3 X l o 3 cm.2 apparent surface per gram) and small particle samples (5 X 103 cma2apparent surface per gram) were kept in weighing bottles in a desiccator at various temperatures and vapor pressures. A few of the many results obtained are given in table 1. As far as the authors could tell these were all equilibrium values, with the exception of sample g, since the water content-time curve had become level. These results become of special interest when applied to the equation derived earlier (1) c =
(WJW,'
- W S W l ' ) / ( W i + wgl - ws - wt')
w1and w 8represent water percentages contained by a pair of zeolite samples (large and small particles) at a given temperature and vapor pressure. wl' and w,'represent the percentages of water in the same two samples under different conditions. c will then be the calculated percentage of water in the zeolite when no water adsorption has taken place. Several values for c are given in table 2. Several interesting conclusions can be drawn from these results. The c values for scolecite are remarkable for their constancy. This fact, coupled with the data in table 1, leads to the conclusion that the water variation of this zeolite was due to a change in surface adsorbed water. The water content within the scolecite lattice did not change appreciably under the conditions of the experiment. The c values for analcite are also essentially constant. From the data in table 1 the change in water content at the higher vapor pressures was essentially due to a change in positively adsorbed surface water. But at the lower vapor pressure the water content of the small particle analcite sample is lower than that of the large particle sample. This fact, together with the calculated c values, clearly indicates that a surface dehydration took place. Water was lost from the surface portions of the zeolite lattice, 693
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V. R. DAMERELL A N D R. CADLE
forming a zone of skeleton lattice at the surface of the particles. As far as present experiments could show, this was an equilibrium condition. This case of surface dehydration is an example, on a larger scale, of what the authors believe happens during the dehydration of hydrates and related compounds. It seems likely that with such compounds a condition of surface dehydration may be a stable one, in which true equilibrium can be reached. This conception is discussed more completely in an earlier paper (2). TABLE 1 Water content of zeolites under various conditions PAIR
ZEOLITE
Scolecite. . . . . . . . . . . . . . . . . Scolecite. . . . . . . . . . . . . . . . . Scolecite. ................ Scolecite. ................ Analcite. ................. Analcite. ................. Analcite. ................. Analcite. .................
I
WATERPERCENTAGE
Large particle
a b c
16.09 16.15 15.78 15.56 9.388 9.491 9.214 9.135
d e
f g
h
1 ~
Small
BUBBTANCE IN DEBICCATOR
particle
16.34 16.44 15.90 15.58 9.402 9.512 9.143 9.056
-
CuSOa 5Hz0 Na2HP04.12H20 BaO BaO CuSO1.5Hz0 Na2HP04.12H20 PzO~,vacuum P~OS, vacuum
TEMPERATURE
C.
23 24 50 126 24 23 22 21
TABLE 2 Calculated water content f o r zeolites when n o adsorption takes place
-I
Scolecite ............... Scolecite. .............. Scolecite. .............. Scolecite.. .............
-I a,
C
b, c a, d b, d
-1-1
15.54 15.52 15.48 15.48
Analcite.. ......... Analcite ............ Analcite ............ Analcite ............
e, h f, h e, g
f, g
9.35 9.42 9.36 9.43
These results throw a somewhat different light upon the variation of the water content of zeolites, particularly at lower temperature. Such data as those of Tammann (3) may now be interpreted somewhat differently. REFERENCES (1) DAMERELL: J. Phys. Chem. 35, 1061 (1931). (2) DAMERELL, HOVORKA, AND WHITE:J. Phys. Chem. 36, 1255 (1932). (3) TAMMANN: Z. physik. Chem. 27, 323 (1898).
