INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
July 1954
1481
TABLE IV. RANDOM COMPARISONS OF EXPERIMENTAL AND SMOOTHED VAPOR-LIQCID EQUILIBRIUW DATA Pressure Mm. ~ g
t
Temp., ’ F.
Naphthalene in Liquid, Mole % Exptl. Smoothed
Naphthalene in Vapor, Mole ??, Exptl. Smoothed
that such deviations are significant because of the size and character of the molecules (IO). The most significant observation to be made regarding the activity coefficient data is that the activity coefficients for octadecene show a positive deviation (greater than unity), while the activity coefficients for naphthalene show a negative deviation (less than unity) over most of the composition range a t all temperatures. Plots of the smoothed data, the solid lines in Figures 3 and 4, reveal fairly regular trends from 760 down to 200 mm. of mercury absolute. Octadecene tends to show less ideal behavior, while naphthalene tends to show more ideal behavior with decreasing pressure. Below 200 mm. of mercury absolute the effect of pressure on the smoothed activity coefficient data is slight and somewhat irregular. The indicated inaccuracies, which are inherent in the calculated activity coefficients based on eyperimental composition data and experimental vapor pressure data, make any conclusions regarding the behavior of this function for octadecene a t low pressures questionable. The temperature-composition diagrams and the liquid-vapor composition diagrams exhibit the usual behavior toward volatility with decreased pressure with no evidence of an azeotrope a t any pressure investigated. NOMENCLATURE
t
= equilibrium boiling point of mixture
t,
= equilibrium boiling point of naphthalene
equilibrium boiling point of octadecene mole per cent naphthalene in liquid phase mole per cent naphthalene in vapor phase vapor pressure of pure naphthalene, mm. of mercury absolute P5 = vapor pressure of pure octadecene, mm. of mercury absolute = ra = yo = P. = tb
Activity Coefficients
Isobaric
Av. Diff.. Mole
%
7,
Exptl.
7.5
Smoothed
Exptl.
Smoothed
PT
= total pressure on the system, mm. of mercury absolute
ya
= activity coefficient for naphthalene
75 = activity coefficient for octadecene
%Si
- refractive
index a t 81’ C. (sodium vapor light)
r~‘; = refractive index a t 25’ C. (sodium vapor light) LITERATURE CITED
Am. Soc. Testing Materials, Philadelphia, Pa., Committee D-2. “ASTM Standards on Petroleum Products and Lubricants,” p. 328, 1946.
Dodge, B. F., “Chemical Engineering Thermodynamics,” p. 555, New York, McGraw-Hill Book Co., 1944. Haynes, Stewart, Jr., and Van Winkle, M., IND.ENG.CHEM., 46, 334-7 (1954).
Hougen, 0. A., and Watson, K. M., “Chemical Process Principles,” Part 11, p. 656, Xew York, John Wiley & Sons, 1947.
International Critical Tables, Vol. 111, p. 226, New York. McGraw-Hill Book Co., 1933. Jones, C. H., Schoenborn, E. M., and Colburn, A. P., IND. ENG. CHEU.,35, 666 (1943). Jordan, B. T., and Van Winkle, M., Ibid., 43, 2908 (1951). Keistler, J. R., and Van Winkle, M., Ibid., 44, 623 (1952). Lange, A. L., ed.. “Handbook of Chemistry,” 6th ed., pp. 141617, Sandusky, Ohio, Handbook Publishers, Inc., 1946. Noyes, A. A., and Sherrill, R9. S., “Chemical Principles,” 2nd ed., pp. 259-65, New York, Maomillan Co., 1938. Rasmussen, R. R., and Van Winkle, M., IND.EKG.CHEX.,42, 2121 (1950).
Salceam, C., Compt. rend., 194, 863 (1932). Stull, D. R., IND.ENG.CHEM.,39, 517-40 (1947). Ward, S. H., and Van Winkle, M., Ibid., 46, 338-49 (1954). RECEIVED for
review September 25, 1953. ACCEPTEDFebruary 23, 1954. Abstracted from a thesis submitted in partial fulfillment of t h e requirements for the degree of master of science in chemical engineering, University of Texas.
Adsorption of Polar Organic Compounds on Steel NORMAN HACKERiMAN AND A. H. ROEBUCK’ Department of Chemistry, The University of Texas, Austin, Tex.
A
D E F I N I T E relationship has been shown (6) between the extent of adsorption of organic compounds on steel and their ability to inhibit acid dissolution. The experiments reported here were undertaken to gain a better understanding of this relationship and of the effect of various organic functional groups and structures on adsorption. Bowden and Moore (Z), using long-chain alkyl alcohols, esters, and fatty acids in benzene solutions with radioactive metal surfaces, showed that the adsorption forces were largely physical,
*
Present address, Argonne Xational Laboratory, Lemont, Ill.
For instance, no evidence was found of reaction of octadecyl alcohol with zinc, cadmium, platinum, or gold, although adsorption occurred. Stearic acid did not react with gold or platinum surfaces when adsorbed from benzene solutions, but did react with zinc, copper, and cadmium surfaces, as shown by the presence of soaps containing radioactive metals in the adsorbed layer of molecules. Sanders ( 1 7 ) concluded from his study of the orientation of ethyl stearate by electron diffraction methods that small amounts of stearic acid, formed by hydrolysis, were preferentially adsorbed on cadmium and zinc surfaces.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1482
0
5
IO
c
15
x io3
Figure 1. Sorption Isotherms of Octadeeanenitrile on Steel Powder at 30" C. Pickup per gram of metal us. molar concentration in benzene. c 0 Total adsorption Firm adsorption
Vol. 46, No. 7
rium with a thermostated benzene solution of an organic compound, and the amount of total adsorption measured gravimetrically. The powder wa8 then washed with benzene until no more sorbate could be removed. The amount of firmly adsorbed material remaining was also determined gravimetrically. The polar organic compounds used as sorbates were 1-alkane nitriles (octadecanenitrile, hexadecanenitrile, dodecanenitrile, decanenitrile, and octanenitrile), 1-alkane amides (octadecananiide, hexadecanamide. tetradecanamide, dodecanamide, decanamide, and octanamide), 1-alkane thiols (octadecanethiol, hexadecanethiol, tetradecanethiol, and dodecanethiol), 1,sdibutylthiourea, lJ3-diethylthiourea, cyclohexanecaproic acid, cyclohexanebutyric acid, cyclohexaneacetic acid, and 2-hydroxy4,6,6'-trimethylheptanoicacid. The melting points of the solid compounds, and the boiling points and refractive indices of the liquid compounds were determined as a check on their purity. Impure compounds mere either recrystallized or distilled until their physical properties checltcd closely those given in the literature. RESULTS A S D DISCUSSION
1.5
~
1.0
\
Y,
w
J
2 0.5 T 0 0
5
IO
cx Figure 2.
15
lo3
Sorption Isotherms of Octadecanainide on Steel Powder at 30" C.
Pickup per gram of metal US. molar concentration i n benzene, C. Concentration range limited by lesser solubility of these compounds 0 Total adsorption 0 Firm adsorption
Trillat and Brigonnet (18) measured the adsorption of oleic acid from lubrication oils onto steel ball bearings by changes in interfacial tension and obtained Langmuir-type isotherms. Hansen, Fu, and Bartell ( 7 ) obtained adsorption isotherms for 1-hexanoic acid, 1-pentanoic acid, 1-butanol, aniline, cyclohexanol, and phenol from aqueous solutions on graphite powders by interferometric measurements. They concluded that adsorption was multimolecular in all cases and found that it could be represented by the B.E.T. equation. They suggested this might be expected with any binary liquid, if the adsorbent \hiswork, as well as for those reported earlier (see Table I). Series of compounds included from earlier work are the 1-acids, 1-amines, and I-alcohols ( 3 ) . The adsorption data are given to t,wo significant figures. The data for the fractions of the surface covered are as precise as the reproducibility of the surface area measurements-i.e., 10%. The specific surface area of the steel as determined by adsorption of krypton a t - 195.8" C. mas 0.11 sq. meter per gram. Calculations made to determine the extent of surface covered assumed that a monolayer was completed before polylayer formation started, and that the molecular areas of the sorbate niolecules \yere the same as in a close-packed monolayer, as memured by the hydrophil balance ( 1 ) . I n Table I the first two columns of figures shox the amount of total and firm adsorption. The last three columns give the iract,iou of the sorbent surface covered by sorbate molecules. The first of these represents the maximum fraction covered by adsorption from the 0.015M solution, the next the fraction covered a t the break in the total adsorption isotherm, and the last gives t,he fraction of the surface covered at' the point the firm adsorption isotherm levels off. ADSORBABILITY AND REACTIVITY
The data shos a very definite relationship between firm adsorption and the reactivity of sorbate toward sorbent. Compounds with the greatest reactivity toward the sorbent shoned the greatest firm adsorption values, and had t'he most marked effects on the reactivity of the steel toward acid dissolution (3). Of the compounds studied, the acids and thiols were most chemically reactive toward the sorbent. The firm adsorpt,ion values for these compounds were the highest (see Table I). I n general, however, increasing activity of sorbate caused increased firm adsorption only t'o a degree; beyond this reaction occurred, resuking in lower values. The reactivit
