496
ROBERT S. HANSEN AND ROBERT D. HANSEN
VOl. 59
THE ADSORPTION OF HYDROCARBONS FROM METHANOL AND ETHANOL SOLUTIONS BY NON-POROUS CARBONS1p2 BY ROBERT S. HANSENAND ROBERTD. HANS EN^ Contribution No. 371 from the Institute for Atomic Research and Department of Chemistry, Iowa State College, Ames, Iowa Received Seplember d , 1064
Isotherms for the adsorption of octane, decane and dodecane from methanol solution by Graphon, Spheron-6 and DAG-1 have been determined at 25" over the range of hydrocarbon solubilities. Multimolecular adsorption of all of these hydrocarbons is demonstrable on Graphon and Spheron-6, and strongly indicated on DAG-1. Isotherms for the adsorption of decane and dodecane from ethanol by these same adsorbents have been determined over the entire concentration range. Primary dependence of adsorption on solute activity referred to pure li uid solute as standard state is again demonstrated. Surface excesses of hydrocarbon on Graphon markedly exceed those on Saeron-6 and DAG-1 a t given hydrocarbon activities, and the latter two adsorbents show adsorption inversion in the completely soluble systems.
Introduction In a recent study of the adsorption of aliphatic alcohols and acids from aqueous solution, Hansen and Craig3 found that adsorption tended to be independent of position in a homologous series if compared a t the same solute activity, and pointed out that this led t o a rational basis for Traube's rule. The present work represents an extension of this study to non-aqueous systems.
to m grams of adsorbent, AC is the solute concentration decrease due to adsorption in moles/liter) were converted to surface excesses I"dv of the Guggenheim and Adam convention by division by specific surface area of adsorbent.' Activities of the hydrocarbons in methanol solution were estimated from the Margules equation using constants calculated from solubilities, thus alao =
Experimental Preparation of adsorbents has been described previously. Surface areas as determined by nitro en adsorption were 114.0, 78.7 and 102.4 metersZ/g. for bpheron-6, Graphon and DAG-1, respectively. All alcohols and hydrocarbons used in the experiments were central fractions from distillation through a 30-plate vacuum jacketed Oldershaw column a t reflux ratio of 10: 1. Prior to distillation the ethanol was purified by the method of Lund and Bjerrum4 and the hydrocarbons were purified by extraction with concentrated sulfuric acid until the acid layer was colorless, washing with water and sodium carbonate solution, drying over sodium hydroxide pellets, and distillation from sodium. Starting materials and final boiling ranges corrected to 760 mm. were Methanol (General Chemical Co. Reagent 64.76- 64.86' grade) 78.62- 78.70' Ethanol (Commercial grade abs.) 125.88-126.00" Octane (Phillips Petroleum pure grade) Decane (Eastman Kodak Co. white label) 174.10-174.34' Dodecane (Eastman Kodak Co. practical 216.52-216.77' grade) Adsorption isotherms were determined according to the techniques described by Hansen, Fu and Bartells with modifications described by Hansen, Hansen and Craig6 and with the further modification that in most determinat,ions adsorption equilibration was carried out in Pyrex test-tubes which had been drawn out prior to addition of solution and sealed off subsequent to this addition. Solubilities were determined by interferometric comparison of saturated solutions prepared by equilibration for approximately 24 hour periods in a shaker at 25.0' with concentrated solutions of known composition.
Treatment of Data Experimental results in the form of quantities VAC/m (V is the number of ml. of solution added (1) W o r k was performed in the Ames Laboratory of the Atomic Energy Commission. (2) Based in part on a dissertation submitted by Robert Douglas Hansen in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Iowa State College, Ames, Iowa, July, 1953. (3) R. S. Hansen and R . P. Craig, THISJOURNAL, 58, 211 (1954). (4) H . Lund and J. Bjerrum, Ber., 64B,210 (1931). (5) R. S. Hansen, Y. Fu and 1". E. Bartell, THISJOURNAL, 63, 769 (1949). (6) R . 6 . Hansen, R . D. Hansen and R. P. Craig, ibid., 51, 215 (1953).
5(
1 0 ~ ~ c/ca)) 0 ~
CO
where p
=
1 -log 1 2x0
-
(1)
1 - xo -
xo
In these expressions a is the hydrocarbon activity based on pure liquid hydrocarbon as standard state, c is hydrocarbon concentration in moles per liter, and x is hydrocarbon mole fraction. ao, co and 5 0 are the values of these quantities for a saturated solution of hydrocarbon in methanol. This treatment amounts to assuming the hydrocarbonmethanol system to be a regular solution, and should be an improvement over an assumption that Henry's law is obeyed from zero to saturation concentration. Neither assumption is exact. Activity data for the systems ethanol-decane and ethanol-dodecane appear to be unavailable, nor does there appear to be a reasonable approximate method for estimating them.
Results Results for the adsorption of hydrocarbons from methane solution are presented graphically in Figs. 1-3, in which surface excess of hydrocarbon, I'z(v, are presented as functions of reduced hydrocarbon activity a l a . Results for the adsorption of hydrocarbons from ethanol are presented graphically in Figs. 4 and 5 , in which surface excesses of hydrocarbon, &(v), are presented as functions of hydrocarbon mole fraction, xz. All results were obtained a t 25.0 f 0.1'. Tabular experimental data are available on request (RSH). Solubilities of the following hydrocarbons in methanol at 25" were determined in the course of this work. Octane 19.25% by weight (1.282 moles/l.) Decane 10.25% by weight (0.5613 mole/l.) Dodecane 5.883% by weight (0.2696 mole/l.) (7) (a) E. A. Guggenheim and N. K. Adam, Proc. R o y . Soc. (Lond o n ) , A139, 218 (1933); (b) R. S. Hansen, THISJ O U R N A L , 55, 1195 (1951).
ADSORPTION OF HYDROCARBOW FROM METHANOL BY NON-POROUS CARBONS
Julie, 1955
497
I
71
W E
I n 3 W
9
-
2
2 C
P
I
0
I
0
01
02
03
04
a /a*.
05
06
07
08
09
10
x2
Fig. 1,-Adsorption of n-octane from methanol solution by non-porous carbons: oJGraphon; O, Spheron-6; 0 , DAG-1.
Fig. 4.-Adsor tion of n-decane from ethanol solution by non-porous cargons: 0 , Graphon; 0, Spheron-6; O JDAG-I.
I
6
7 5
6
N
N ’
3
4
a W
W
I n 3
I n 4
-1 W
w
0
0 = 3
1
2
?
t
2
0
0
P
1 0
I 0 0
I 0.1
I
I
I
I
0.2
0.3
0.4
I 0.5
I 0.6
I 0.7
I
I
0.6
0.9
1.C
ala.
Fig. 2.-Adsorption of n-decane from methanol solution by non-porous carbons: o1Graphon; 0 , Spheron-6; 0 , DAG-1.
ala,.
Fig. 3.-Adsorption
of n-dodecane from methanol solution bv non-porous carbons: 0, Graphon; 0,Spheron-6; 0, DAG-1.
Discussion Isotherms for the adsorption of octane, decane and dodecane from methanol are all of a definite sigmoid character, and are thus similar to isotherms in limited-solubility aqueous-fatty acid and aqueous-alcohol systems previously studied. 3 ~ 6 Surface excesses greater than 8.3 X moles/cm.2Jcorresponding to areas per hydrocarbon molecule less than 20 A.2, were obtained a t high reduced activities in all three solvent pairs with the adsorbents
~
0
I
I
01
02
_I
03
I 04
I_ 05
I
I
06
07
I
I
I
~
08
09
IO
~
X2
Fig. 5.-Adsorption of n-dodecane from ethanol solutions by non-porous carbons: 0,Graphon; 0 , Spheron-6; o, DAG-I.
Graphon and Spheron-6; such surface excesses are greater than can be accommodated in a unimolecular layer even in the most compact arrangement; and the multimolecular character of adsorption in these systems is therefore proved (points not show on graphs due to space limitation). I n view of the similarity of isotherms obtained with DAG-1 to those obtained with the other two adsorbents, multimolecular character of adsorption by DAG-l is to be presumed. Isotherms for the adsorption of the different hydrocarbons from methanol by a given carbon are remarkably similar functions of reduced activity; this result is again to be expected from the study of aqueous system^.^,^ Adsorption of octane from methanol by Graphon at reduced activities above 0.3 appears higher than would be expected from this rule; adsorption of octane by the other carbon adsorbents appears to be slightly higher than adsorption of the other hydrocarbons in the intermediate reduced activity range. At reduced activities less than 0.25 there is a definite progression of adsorption values a t a given reduced activity of the sort: dodecane > decane > octane, suggesting that a t least at low coverage the hydrocarbons may be adsorbed in a “lying down” configuration with resulting progression in adsorption energy. Areas per molecule in such a configuration are estimated to be 67,81 and 94 A.z for octane, decane and dode-
498
K. KASHIWAGI AND B. RABINOVITCH
cane, respectively; corresponding amounts of hydrocarbon required for complete unimolecular coverage are 2.48, 2.06 and 1.77 X 10-lo mole/cm.2, which values are rather close to the values a t the “shoulders” of the Graphon isotherms. Surface excesses in the slightly soluble hydrocarbon-methanol systems are fairly well represented for the adsorbents Graphon and Spheron-6 by functions of the sort b log-’/Z U O / U in the range 0.3 < u/ao < 0.9, and nearly as well by functions of the sort c log-‘/z uolu. This suggests that adsorption potentials in these systems are inversely proportional to the square or cube of the distance from the surface; such functions do not, however, represent adsorption of aliphatic acids and alcohols from aqueous solution by the same adsorbents. I n the completely miscible hydrocarbon-ethanol systems, surface excesses for a given carbon a t a given mole fraction are markedly higher for dodecane than for decane a t low hydrocarbon mole fractions, and slightly lower a t high mole fractions. Hydrocarbon adsorption from ethanol a t low mole fractions is probably a function of hydrocarbon activity very similar to that for adsorption of hydrocarbons from methanol by the same adsorbent. According to Ferguson, Freed and Morrisa the activity of heptane in ethanol, based on pure liquid heptane as standard state, is 0.897 a t mole fraction heptane of 0.337, and 0.609 a t mole fraction 0.092. The same activities should be reached by the higher (8) J. B. Ferguson, M. Freed and A. C. Morris, THISJOURNAL, 37,
a7 (1933).
VOl. 59
hydrocarbons a t lower mole fractions. The slightly greater adsorption of decane a t high activities could well be attributed to its smaller size. Comparing the different adsorbents, it is evident that surface excesses on Graphon are markedly greater than those on the other two adsorbents a t all concentrations. I n the slightly soluble systems surface excesses on DAG-1 and Spheron-6 are nearly the same a t low reduced activities, while surface excesses on Spheron-6 generally exceed those on DAG-1 a t high reduced activities. I n the completely miscible systems surface excesses on Graphon are .positive over the entire concentration range, while isotherms on DAG-1 and Spheron-6 show definite inversions. These results suggest existence of surface oxygen complexes on Spheron-6 and DAG-1; evidence for such complexes in the case of Spheron-6 has been presented by Anderson and Emmett. Qualitatively, such complexes would have the effect of reducing the area fraction in which hydrocarbon adsorption was preferential in the first layer, and decreasing the preference for hydrocarbon over alcohol in higher adsorbed layers; these effects are in accord with observation. Data on both slightly soluble and completely soluble systems suggest that the decrease in adsorption potential with distance is more rapid with DAG-1 than with Spheron-6, but that the adsorption potentials in the neighborhood of the first adsorption layer are nearly the same with these two adsorbents. (9) R. B. Anderson and P. H. Emmett, ibid., 66, 753, 756 (1952).
A SURFACE STUDY OF MYOSIN MONOLAYERS AND CERTAIN BIOLOGICALLY IMPORTANT SUBSTRATES. I. ADENOSINE TRIPHOSPHATE BY E(. KASHIWAGI’ AND B. RABINOVITCH Contribution from the Chemistry Department, Illinois Institute of Technotogy, Chicago, Ill. Received October 1.4, 1964
An actin-free myosin takes a finite and measurable time to spread on an aqueous KC1 solution at pH 5.4 and is dependent upon the area a t which it is allowed to spread. An expression derived to follow the kinetics of spreading leads to the suggestion that the forces retarding spreading might be due to ion-dipole interaction. The presence of adenosine triphosphate (ATP) in the substrate materially alters the rate of spreading and the equilibrium pressure obtained. The mechanism of spreading appears to be different under these circumstances, while the state of the equilibrium film obtained is easily explained on the basis of a physical binding of the ATP molecules to the protein in the surface. By reference to the titration curve of myosin in the presence of K + ions, the extent of binding of ATP is readily explained.
Few studies have been made on the physical or chemical interaction between a protein film spread at an air-water interface and biologically important substrates. Ridea12has summarized and discussed some of these, while more recently Geiduschek and Doty3 have worked in this way with antigen-antibody reactions and Munch-Petersen4 has worked on the myosin-adenosine triphosphate (ATP) reaction. The reason for this limited application of a potentially useful tool in protein chemistry prob(1) This publication is based upon a thesis submitted by I(.Kashiin partial fulfillment of the requirements for the degree of Master of Science at Illinois Institute of Technology, February, 1954. (2) E. K. Rideal, J. Chem. SOC.,423 (1945). (3) P. Geiduschek and P. M. Doty, J. Am. Chen. Soc., 74, 3110 ,( 1952). (4) A. Munch-Petersen, Nature, 162, 537 (1948). wagi
ably arises from the difficulty of obtaining a stable and reproducible protein That adenosene triphosphate (ATP) plays an important part in the mechanism of muscle contraction is well recognized. The function of ATP in muscle tissue appears t o be twofold, firstly to keep the muscle in a physically supple state and secondly to supply the substrate from which myosin, the main muscle protein, can extract the energy necessary for muscle contraction.8 The former of these functions probably arises from a physical interaction between the protein and its (5) J. 8. Mitchell, T r a n s . Faraday Sac., 88, 1129 (1937). (6) E. G.Cockbain and J. H. Schulman, ibid., 35, 1266 (1939). (7) J. H.P.Jonxis, Biochen. J., 88, 1743 (1939). (8) A. Saent-Gyorgyi, “Chemistry of Muscular Contraction,” Academic Press, Inc., New York, N. Y.,1951,Chapter VI.
