756
R. B. ANDERSON AND P. H. EMMNTT
J'ol, 56
SURFACE COMPLEXES ON CARBON BLACKS. 11. THE ADSORPTION O F NHa, C 2 H 2 , C d H 1 0 , CH,NH, AND FVATER VAPOR BY R. B. ANDERSON'~ AND P. H. EMMETT'~ 1)eparl:nent of Chemical Engineering, The Johns Hopkins University, Baltimore 18, Maryland Received October 5 , 1961
'
For Spheron 6, Black Pearls 1, Mogul, and Lampblack T surface areas as calculated from nitrogen adsorption isotherms by the BET method, are in satisfactory agreement with those calculated by the BET method as modified by Anderson and Hall or by the method pro osed by Harkins and Jura, both for the original blacks and for the samples from which the complex had been removed \y degassing a t 1200' The adsorption of acetylene a t -78" and of butane a t 0" appeared to be purely physical in nature and yielded areas in satisfactory agreement with those obtained from the nitrogen isotherms a t -195". For Lampblack T, ammonia and methylamine isotherms gave apparent areas several fold greater than those obtained from nitrogen. The result presumably indicates the solution of ammonia and of methylamine in the large amount of oxygen complex known to be present in a layer several moleculefi thick on Lampblack T. For after-treated Lampblack and for a lampblack sample degassed a t 1200" the area obtained from the amyonia adsorption isotherms a t -46" were in satisfactory agreement wit,h those obtained from nitrogen adsorption a t - 195 . In confirmation of previous observations the water adsorption isotherms on the various carbon blacks were shifted in the direction of higher relative pressures for a given water sorption as the complex was removed from the surface by high temperature degassing.
.
In 1941 some experiments were undertaken in an attempt to find an adsorbate that would be preferentially adsorbed either by the portion of the surface of carbon black that was covered with oxygen complex, or by the portion that was free of complex. Such an adsorbate would help materially in determining rapidly the fraction of the surface of a carbon black free .of surface complex. Although the war terminated the research before such an adsorbate was found, a number of interesting experimental data were obtained that are here being reported. Specifically, adsorption isotherms for nitrogen, ammonia, acetylene and water vapor were determined on a series of carbon blacks both before and after the blacks were evacuated at high temperature to remove surface complexes; a few measurements were also made of the adsorption of methylamine and n-butane. Experimental Adsorpt,ion data for all of the gases and vapors csorpt water were obbined on a standard volumetric adsorption apparatus.2~3 A few of the water vapor isotherms were determined by this method, but the majority were deter~ usual types ,Of cold mined by a gravimetric m e t h ~ d . The baths were employed: liquid nitrogen for -195 , Dry Ice-acetone for -78", well-stirred chlorobenzene cooled by Dry Ice for -46", and wet ice for 0'. The source and purification of the adsorbates wcre as follows: prepurified nitrogen (Air Reduction) was condensed in a liquid nitrogen trap, and the middle portion distilled into a storage bulb. The remainder of the adsorbates were solids a t liquid nitrogen temperat,ures, and after condensation at - 195" were freed from volatile gases by repeatedly melting, freezing, and evacuating them or by repeated distillation from one trap to another in vacuum. The nbutane was a C.P. grade from the Ohio Chemical Co., and the ammonia was taken from a cylinder of anhydrous ammonia. Distilled water freed from air as described above was stored as liquid in a Pyrex bulb. Tvlet,hylamine was prepared by treating rerryst.alliacd methylamine hydrochloride with sodium hydrositk. solution, and drying t he resulting met,hylamine. Commercial wltling awtyl+m?was purified by passing it, t,hrough t8wo sc~ruhhr~rs containing saturated sodium bisulfite solution and through a soda lime tower. (1) Central Experiment Station, Bureau of Mines, Pittsburgh 13, Pennsylvania. (b) Mellon Institute, Pittsburgh 13, Pennsylvania. (2) P. H. Emmett, American Society for Testing hfaterials, Syinposiurn on New Methods for Particle Size Detertnlnation in the Subsieve Range, 1941, p. 95. (3) P . H. Emmett, Advances in Colloid Sui., 1, 1 (1942). (4) P. H. Emmett and R. B. .Inderson, J . Ani. Chem. SOC.,67, 1402 (1945).
hlosl of Ihc cartion black samples werc tho sainC aw those that, havc already been described by Eniinrtt, and Cines.s Thwc additional blacks usrd for some of the measurement,s were as follows: Spheron 4, a pelletized rubber grade channel black; a steam-activated black prepared by treating Spheron 4 with steam for two hours at 481'; and a sample of Shawinigan acetylene black. All samples were furnished by t8heGodfrey L. Cabot Co. Samples referred to as having been "degassed" were those that had been e!acuated in a n induction furnace a t tempcrat,ures up to 1200 They were believed to be fairly free of oxygen complexes after this t,reatmcnt,. By a suitsable t,echnique described in thc previous papcr,B it was possible to transfer the degassed samples to the adsorption apparatus without exposing them to air. Surface areas were calculatcd from adsorpt,ion isotherms by three methods: by the BET t,hcory for multilayer adsorption' (equation l), by the modification of t.his theory proposed by Anderson and Ha118.9 (equat,ion 2), and by the equation of Harkins and Jural0 (equations 3 and 4).
.
1 -- X V(1 - 2 ) - Tr,c
V(1
- 1)x +-(Cvmc
=- 1 (C - 1)r k s ) VmCk + logx = B - A / V 2 surface area = k'(A)'/2
p,c:
(1)
(2)
(3) (4)
I n all of these equations, V represents t,he volume of gas (S.T.P.) adsorbed; x, the relative pressure; C , a constant albz defined by the equation C = -- e ( E l - E [ , ) / R T , where a l , a h ax, b, and b? arc constant,s, E, is the "average heat of adsorpt,ion" i n thc first layer, and E L is the heat of liquefaction of the adsorbate; Vm,the volume of gas required to form R. monolayer on the surface of the adsorbent; A , the dope of t,h(! plot of log r against l / V 2 according to equation 3; and k' is a proportionality constant. Constant k is experimcnt.ally dntermined for each isotherm. Its significance has been discussed in previous publi~ations.8~~
Experimental Results T h e experimental da.tn are prescntctl in Figs. 1 to 8 ant1 in 'l'nl)les I to 111. Discussion For the determination of surface areas by equations l and 2, the cross-sectional molecular areas ( 5 ) P. H. Emmett and >I. Cines, THIUJOURNAL..61, 1329 (1947). (6) R . R . .Anderson and P. H. Emmett, ibid., 61, 1308 (1947). ( 7 ) S. Bninaiier, P. 11. Euirnett and E. Teller, J . Ani. Chem. Soc., 60, 309 (1938). ( 8 ) R. R. .inderson, i b i d . . 68, E86 (1946). (9) R . B. Anderson and W. IC. Hall, ibid., TO, 1727 (1948). (10) \V D. Harkins a,nd G . Jura. ibid.. 66, 1366 (19.44).
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757
SURFACE COMPLEXES ON CARBON BLACKS
Junle, 1952
TABLE I SURFACE AREAS OF CARBON BLACKS Temp.,
W.
- 195
Black Pearls 1 original Black Pearls 1 degassed
-195 - 78 - 46
GO.0
60.0
- 195 - 46 - 195
942.0 858.0
1015.0
0.51 .70
7G7,O 617.0
860.0 789.0
.60 .65
522.0 448.0 184.0 154.5 28.8 31.5 106.5 23.5 25.8 228.0 277.0
..40
-195 - 46 - 195 - 46 - 195 0 - 46 - 195 - 46 - 195 - 46
Rfogul degassed Lampldack T original Lampblack T degassed Lampblack T after-treated
0.67
131.8 130.9 118.2 128.4 118.0
- 46
Mogul original
m.l/g.
Moditied B E T (eq. 2) Surface area. n1.2/g. k
116.4 110.0 115.5 106.0 09.1
- 78 - 4G Spheron G deganad
BET (eq. 1) Surface area,
E
e
166.5 124.6 25.5 27.6 71.8 20.6 25.8 e e
(398.0
,645 .!IO
.67
. GS 1 .oo
127.4" 112.3' !)O.G"
110.8" 98.7'
.40
1080" 958" 940" 590" 929" 556" 176.6' 96.2' 25.8" 36.2d 85.9"
.80
20.9'
-45 .70 .80
.65 .65 1 .oo 0.30 .30
0.01-0,55 .22- .oo .o3- .75 .20- .75 .20- .95 .15- .GO . 16- .90 .lo- ,60 .25- .80 .I- .3 .08-
',
60
.l- . 8 .13- .40
.lo- .90 .15- .60 .18- . 7 .17- .95
e
350" 377c 143.9" 143.3' 598" 428"
.17- .65 ,14- .80 .16- .70 .15- .70 .18-.65 .15- .75
- 195 128.5 118.2 .70 - 46 134.7 155.6 .73 Spheron 4 - 195 510.0 .40 - 46 379.0 .53 steam-activated The value of H. and J. k' taken as 4.06. * The value of H. and J. k' taken as 5.04, the av. exptl. values compared with Spheron 4
. I
0
Harkins and J u r a (eq. 3) Surface area Linear 111.2/g. range
The value of H. and J. k' taken as 4.13,the av. exptl. values compared with NP. N,. 13.6. e Equation does not fit over an appreciable range.
TABLE I1 ADSORPTION OF WATERVAPOR AND AMMONIA AS A FUNCTION OF FRACTION O F SURFACE COVEREDBY OXYGEN COMPLEX Volatile content,
%F;agtle, % Surface covered at relative surface pressure of 0.4c areab H20 "a
The value of H. and J. IC' taken as
TABLE 111 VALUESOF C FROM EQUATIONS 1 AND 2
Black
Na NHa C~HI (-195:) (-46'). (-78:) inorlified modified modified BET BET B E T B E T B E T BET Treat- (eq. (eq. (eq. (eq. (eq. (eq. inent" 1) 2) 1) 2) 1) 2)
0 161 87 38 31 38 32 1,amphlack T 19.1 352 365 D' 5.5 83 67 8 8 32 2!1 Lamphlaclc T, after 0 Black Pearls 1 246 324 32 25 11.0 4.8 treated 90 133 n 176 214 23 '19 Spheron 6 5.5 67 135 4.2 Mogul 0 '... 382 , . 132 4.0 62 133 2.7 Spheron 4 361 132 13 D 0 49 2.2 11.5 155 Mogul Lampblack T 0 113 82 23 . . . Black Pearls 1 16.7 125 36 1.7 D 369 07 4 . . , Spheron 6,degassed 0.9 4.8 1.2 73 AT . . . 556 . . . . Spheron 4,steam
