1102
INDUSTRIAL AND ENGINEERING CHEMISTRY
so great that there appears t o be little possibility of these solvents entering seriously into our field of interest. The butyl acetate might be a possibility and, showing RS i t does its greatest selectivity below 20” C., might undcr special conditions prove to be the most. satisfactory solvent. I n interpreting the foregoing data it should be remembered that determinations of both oil and wax were made with only one of these constituents present in the solvent. Without doubt % mixture in which both a solvent of high selectivity and oil are present will have a greater solvent power for wax than will the pure solvent. Data of such a nature are,of course, essential to the proper development of a commercial extraction method. The securing of these data is
Vol. 21, No. 11
the next step which should be made toward the completion of this work. Literature Cited (1) Aktiebolaget Separator-Nobel, British Patent 276,658 (August 24, 1926). (2) Greenspar, U. S. Patent 1,562,425 (November 17, 1925). (3) Henderson and Ferris, IND. EYG.CHEM.,19, 2624 (1927). (4) Lane, U. s. Patent 1,706,120 (March 19. 1929). (5) Smith, Oil Gas J . , 26, No. 17, 146 (1928). (6) Sullivan, McGill. and French, IND. ENG.CARM.,19, 1042 (1927). (7) Truesdell, N u l . Petroleum N e w 20, No. 6, 22 (1928). (8)Wagner, U. S. Patent 1.669.151 (Msy 8, 1928). (9) Weber and Dunlap, N a f . Petroleum N e w s , 20, 383 (1928). (10) Wilson, Canadian Patent 269.444 (April 5, 1927). (11) Wyant and Marsh, Bur. Mines, Tech. Paper 368 (1925).
Adhesion Tension Values of Different Types of Carbon Black against Water and against B enzene”* F. E. Bartell and Carleton N. Smith UNIVERSITY
OF
MICHIGAN, ANN ARBOR,MICR.
Adhesion tension values have been determined for OMMERCIAL carbon not necessarily require the seven different types of carbon black against water and blacks from different presence of impurities, &s has sources exhibit widely against benzene. The carbons were subjected to heat often been maintained. On differentproperties. Numertreatment and evacuation. It was found that reliable t h e c o n t r a r y , it has been ous attempts have been made data could be obtained only when the carbon particles shown (6) that the presence to account for the diversity were SO large that compressed membranes of them had of “impurities” on the surin properties of such carbons. pore radii greater than (approximately) 2 x 10-8 cm. face tends rather to decrease The seemingly more plausible It has been shown beyond reasonable doubt that the adsorptive c a p a c i t y of theories attribute the diverdifferent commercial carbon blacks possess different carbon for other substances, sity to differences in (a) crysadhesion tension values against water and against inasmuch as the already adtal structure, (b) e f f e c t i v e benzene, and that heat treatment alters the adhesion s o r b e d impurity has used surface area, and ( c ) ‘Lac- tension of these carbons against different liquids. up part of the a.dsorption t i v i t y . ” The third factor surface. T h e conclusion is, however, largely dependent upon either or both of the seems justified that activity is largely a function of surface others. area. This view has been further substantiated by work in X-ray studies have contributed much to our information this laboratory on heat of wetting of carbon by binary liquid concerning crystal structure of the different modifications of mixtures (3). Recent unpublished work on adsorption by carbon. The diamond and graphite are generally accepted Bartell and hliller has shown that a direct relationship as being structurally distinctive forms. Opinions differ as exists between adhesion tension and adsorption when a to the structure of the so-called amorphous or microcrystalline given solid is used with different liquids. Adhesion tension form (IL), though much of the evidence points to a definite may be considered to represent the degree of wetting of a crystalline structure for it ( I ) . Microcrystalline carbon solid by a liquid (2, 4 ) . It is a measure of the change in free may, according to some investigators, appear in more than surface energy per unit area which occurs when a solid against one form-as, for example, alpha and beta modifications (7). air (or gas) interface is replaced by a solid against liquid Effective surface area of carbon depends not only upon interface. It is numerically equal to the difference between the degree of subdivision, which may be regulated by soot the surface tension of the solid, SI,and the interfacial tension deposition or by grinding and dispersion of massive carbon, solid against liquid, SI*,and may be expressed by the equation: but also upon the degree of surface roughening, as by pitting, A =s i - s12 etc., or upon the number and size of micropores which may Since the adhesion tension is a measure of the change of be present. The high “activity” of certain carbons has been attributed free surface energy per unit area which occurs when a solid (1) t o crystal structure, (2) to specific (effective) surface area, surface is wetted by a liquid, determination of adhesion and (3) to the presence of impurities. It has been found ( I S ) tension alone cannot serve to determine the fundamental that ash-free graphite adsorbs succinic acid but leaves methyl- difference between two carbons of different activity. If, however, adhesion tension values were obtained for ene blue untouched. Diamond powder adsorbs in the reverse order. Carbon black (methane soot) behaves like dia- a series of different carbons against several different liquids, mond, and activated anthracite like graphite. It thus one might have good evidence as to whether the difference appears that the precise crystal structure of a solid is im- in the adhesion tension values were due to differences in portant in determining its activity. The work of hliller crystal structure or to the presence of adsorbed impurities. ( I d ) has gone far t o prove that activation of carbon does In case the differences were due to crystal structure, a uniform difference in the adhesion tension values might be 1 Received Julv 29, 1929. expected for a given series of carbons against each of dif1 From a dissertation submitted b y Carleton N . Smith to the Graduate ferent liquids. If, on the other hand, the differences were School of the University of Michigan in par tidl fulfilment of the requirements due to adsorbed impurities, less of uniformity in the adlor the degree of doctor of philosophy, 1929.
C
INDUSl'RIAL A N D ENGINEERING CHEMISTRY
1104
carbons for the secood group uf adhesion tension measurements. They \vere heated at 450' C. for R half hour in the mume. This preliminary treatment was intended to remove most of the moisture and the more highly volatile compounds held on t,lie carbon surface. The carbon was transferred to a 2-liter clear quartz flask which was attached to a vacuum line. It was then evacuated down to 2 microns of pressure and heated a t 500" C . tinder vacuu~iifor 12 liours. (Figure 2) The flask was allowed to cad and the p s s u r e was then less than 0.1 micron. Oxygewfrec nitrogen w i s admitted until
Vol. 21, iio. 11
The pore radius decreases a~ the packing pressure is increased. This is to be expected, for a greater packing pressure will force the carbon particles more closely together and the interstices between the particles will become smaller. Low packing pressures did not hold the finer carbons firmly in place. A pressura of 79.6 to 159.2 kg. per sq. cm. for carbons F and G left them in the state of a loose powder, Higher packing pressures held them rigidly in place and reproducible adhesion tensions were obtained. These values were therefore taken as being truly represoiitative of the adhesion tensions for water and for benzene against the carbons. Nolc-The packins pre9suie gage ~ P calibrated P i n pounds per square The value8 rezisfeicd by it do not iepresriit the true pressure delivered by t h e hydraulic press on the packing pluoger. Tlle area of the Backing plunger end the ~ Y C cacct T which f h e mpporiiitg frame exerts on the plciiiger niust PISO be fakcn into account. BY niultiplyiny the gage value by the factor 0.07958, the delivered P ~ C S S I I T teading ~ in kilagrilrns pcc sfiwiie centimeter i s ohtiieed. Thur. z d ~ epr~s>uresoi 10110, 2000. 3000, 4000, and 6000 pounds per s q u i r c inch which W ~ : C acturily read io packing correspond t o deiivered prcssurri 01 79.6, 159.2, 238.7. 318.3.and ,477.5 kilograms per square centimeter, resi~ecdvely. These valuer ore recuidrd in t h e tables. inch.
I
I
Effect of High Temperature and Evacuation
-
.
A tliird group of experiments was carried out to determine the effect of higher temperatoi'e treatment together rvith longer evacuation upon the adlieaion tension values. Carbons A, C, and E were chosen for this work. They gave the liighest, the lowest, and an intermediate value, respectively, .__._ in the Ixeeedinrr experimente.
__ -.
. -.
.. .. . .
F i w r e 2 ~ ~ ~ F u r n sand c e V a c u u m Apparatus
Table III---Adhesion Tension Values of Different Carbon Blacks Heafed and Evacuated at 500" C.
atmosplicric pressure was reached. The carhiin wils ag;iiil highly evacuated and Iieatrd a t 500" C. E I I ~12 Iiours. The applied x-acutini should aid in the removal of nilsortied material and siiould t e d to eliminate surface rcat!tioiis that otherwise might i m u r at this temperature. It was nceesary to prepare sanrplcs of these carlions thoroi~gfily wetted with beriaeirr mid with water. This x"s done by adniitting tho= liquids tx, different s a n i p k while they were still under high vacuuin but after they had been allowed to cool to ruom temperature. In each case the liquid w:is directed onto t.he carbon tliniugli a capillary tube (about, 25 cm. long) which was insealed into tile vacuum line just &ve the yunrt.z flask. The seiiled tip of this tube was broken off under the surface of tlie liquid. The diameter of the capillary (approxirnately 0.5 mm.) was such that the liquid lras drawn i1it.o the fiask a t a satisfactory mte.
The treatment of the carbons was dlie s&me as that in tlie preceding group of experiments, except that they were heated at 1OOO0 C. (or periods of 24 and 96 hours. Table IV gives these adhesion tension T R ~ U C Stogether with those a t 5000 C. Table IV-Adhesion
Pressure of Packins
It was fouud necessary t o vary the pressure with whiclr the differeiit ciirboiis m r e pa~:ked into t l i e displncemcnt cells. lcor a coarse c;irlioir rciat.ively liiw pacliing pressures (70.6 kg. per sq. cm.) g a ~ ereproducilile adlirsi~~ri tension values; for a comparatively fine carbon prcssuri:s four or five times as great were necessary. Table I1 sho\i-s the coiistmcy of the rulues obt,:iined for ii coarse carbon nt l o w prcssuren aiid shows that hiehcr ., .uressures are iiecessarv for a finer carbon. Table 11-Adhesion Tenaion Valves of Carbon Rlacks nisPLncrMwT PRCSSURB
UENZBNIH-AIR
K g Per S P . m .
Grams per 30 em.
lilCIl PXI(5SURB
78.6 159.2 238.7 318.3
POYii
Rn~ms 10 - I ~ m .
"P PhCBlNr. -07
4870 5730 6500 7220
Ai:
Ijsnrs
13 1s 10.05 8.88 7.98
per rm.
NI;CI;SS*RY--CA,
