June, 1952
HIGHTEMPERATURE EVACUATION STUDIES
Wettability tests showed that acetylated montniorillonite adsorbs organic liquids to a greater extent that H-montmorillonite. Hydrolysis of acetylated montmorillonite gives a product with wettability similar to the original H-montmorillonite. Acetylation of montmorillonite reduces its cation exchange capacity. Hydrolysis of acetylated montmorillonite restores the cation exchange capacity. hlontmorillonite acetylated with acetic anhydride gave a product containing 9.6y0 carbon compared to a trace of carbon in the original H-montmorillonite. The carbon content of this product was reduced to 1.5% by hydrolysis with Ba(0H)n.
The Nature of the OH Groups in Montmorillonite Martin and Kipping12found that the silicols were chlorinated by acetyl chloride but did not react with acetic anhydride. The acetylation of montmorillonite by both acetyl chloride and acetic anhydride indicates that the involved OH groups are more acidic than the OH groups of the silicols. The presence of OH groups in the montmorillonite structure can be explained by either the Edelrnanl3 structure or by the substitution of OH for 0 (12) G. Martin and F. S. Kipping, J. Chem. SOC.,96, 302 (1909). (13) C. H. Edelrnan and J. C. L. Favejee, Z. Xrzsl., 102, 417 (1940).
758
in the tetrahedral layer adjacent to the site of substitut.ion of A1 for Si as postulated by McConnell14 in his modification of the Hofmannls structure. This proximity of OH groups to the AI ions in the crystal lattices could well explain the acidic character of the OH groups in montmorillonite m a result of the strong electrostatic attraction between the A1 ions and the 0 ions of the OH groups. Water hydrolysis of montmorillonite, acetylated with aceticanhydride, released approximately 20% of the total acetyl groups and increased the cation exchange capacity of the derivative an equivalent amount. Since Hendricks16 found that 20% of the cation exchange capacity of montmorillonite resides on the edges of the platelike crystals, it would seem that the acetylated edges of the montmorillonite crystals are less stable toward water hydrolysis than the acetylated flat surfaces of the crystals. (14) D. hlcConnel1, Am. Mineral., 36, 166 (1950). (15) U. Hofmann, IC. Endell and D. Wilm, 2. Krial., EBB, 340 (1933). (16) 5. B. Hendricks, R. A. Nelson and L. T. Alexander, J. A m . Chem. Soc., 62, 1457 (1940).
SUliFXCE COMPLEXES ON CARBON BLACKS. I. HIGH TEMPERATURE: EVA4CUATIONSTUDIES BY R. B. A N D E R S O NAND ~ ~ P. H. EMMETT'~ Ueparfmenl of Chemical Engineering, The Johns Hopkins University, Baltimore 18, iIlarUlnnt1 Received October S, 1861
Surface compleses on four commercial carbon blacks have been studied by heating the blacks during evacuation a t temperatures as high as 12OOo0 and collecting and analyzing the evolved gases. Much of the watervapor and carbon diosidt The carbon monoxide and hydrogen are evolved primarily in the 600-900 and 900-1200 is given off at or below 600 regions, respectively. Surface area measurement,s show that the gas evolution from Spheron 6, Black Pearls 1, and Mogul could be account,ed for by postulating the esistence of a monomolecular layer of surface complexes. On the other hand, the gas from Lampblack T is several fold too great to be attributed to a single layer of surface complex and presumably arises from a layer several molecules thick.
.
It has been known for many years that oxygen complexes are formed on all types of carbon.2-6 These complexes can be removed a t considerably higher temperatures as oxides of carbon. Johnson7 showed that the oxygen complex on several commercial carbon blacks decomposed at an appreciable rate at temperatures above 400°, and at 955" was fairly completely removed in 30 minutes. To obtain more precise data on the oxygen complex of carbon blacks, several commercial blacks were evacuated at high temperature and the gases collected and analyzed. The results of these experiments together with calculations utilizing surface area measurements on the samples are reported in the present paper. (1) (a) Central Experiment Station, Bureau of Mines, Piltsburgh 13, Pennsylvania. (b) Mellon Institute, Pittsburgh 13, Pennsylvania. (2) R. B. Anderson and P. 11. T"inrnett,THrs .JOURNAL, 61, 1305 (1947). ( 3 ) R. hI. Barrer, J . Clirm. Yo?.. 1201 (19313). (4) 1. Imigiiiiiir. J . A m . C l ~ m S. U C . 37, , 1139 (1915). ( . 5 ) 11. TI. Lowry and C . A. IIlilett. iDid., 42, 1408 (1920). (0) T. 1'. E. Rheadand R. V. \Vheeler, J . Chem. Soc.. 103, 4G1, 1210 (1915); I'mr. Chem. Soc. ( L o n d o n ) ,29, 51, 193 (1913). (7) C. R. Johnson, I n d . Eng. Chem., 20, 904 (1938): 11, 1258 (1929).
Experimental The samples studied included threc carbon blacks, Spheron 6, Black Pearls 1, and Mogul. A sample of lampblack, Samuel Cabot's T black, was also included. These samples were furnished by Godfrey L. Cabot, Inc., and have been described in detail recently by Emmett and Cines.* The apparatus for high temperature evacuation has been described previously,2 and will be discussed only briefly here. The sample was placed in a platinum crucible within a quart: tube. The crucible was heated to temperatures of 900 with a resistance furnace and to 1200" with an induction furnace. The quartz tube was connect8edby a graded seal to the Pyrex tubing of the pumping system which included II Stimson mercury pump backed by an automat,ic Toepler pump. The evolved gases were fractionated into threc parts, volatile, respectively, in liquid nitrogen, Dry Ire and warm water. Each fraction was analyzed by the semimicro method of Taylor and Saunders.9 Actually, CO, COP,CHI, Hg,HzO and free NZwere determined. However, the volumes of methane were so small (0 to 0.3 cc.) that they were considered negligible. The evolved nitrogen was not listed in the table but is discussed below. The following procedure was used in the degassing experiments: The sample, which had been dried for a week or more over P z O ~was , pumped at room temperature to a vacuum of 10-6 inm. Then, a collection of the evolved gases ws: started while the sample was being heated rapidly to 300 . ( 8 ) P. H. Emmett end M. L. Cines, THIB JOURNAL, 61, 1329 11947). (9) H. A. Taylor and I
