July 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
makes it possible to consider carrying out the process autogenously by using the by-product, carbon monoxide, as fuel for heating the reaction tube. This would not be the case if roaster gas were used directly as a source of sulfur dioxide because of the low calorific value of the by-product, gas, resulting from dilution by nitrogen. DISCUSSION L
+
One comprehensive experimental study of the SO2 C system has been reported in the literature. Rassow and Hoffman (12) caused carefully purified beech charcoal to react with dried sulfur dioxide a t temperatures ranging from 700" t o 1000° C. in 50" steps. As no mention was made of temperature gradients, it is assumed that the temperature was constant throughout the carbon charge. The maximum carbon disulfide yield was 357&, obtained a t temperatures of 850' t o 900" C. Large quantities of sulfur and carbonyl sulfide were obtained a t all temperatures. It is believed that the failure of Rassow and Hoffman to obtain high carbon disulfide yields was due to the uniformity of the temperature of the carbon bed. Similar results were obtained in the present investigation when the temperature of the coal column was uniform a t 900" and 1000" C. It seems that sulfur generated by the dissociation of carbonyl sulfide is more reactive toward coal than that obtained by other reactions. The discrepancy between the results of Rassow and Hoffman and those of the present investigation emphasizes the importance of considering the process in steps and carrying out each step under optimum temperature conditions. The size of the experimental equipment used in this investigation did not allow an accurate determination of the carbon efficiency of the process. The condition of the furnace residues indicated that high carbon efficiencies were possible. Quantitative data on this point must await the results of operations on a pilot plant scale. The type of carbon used in the process was important. When metallurgical coke was substituted for the anthracite coal, very little carbon disulfide was formed. The low chemical reactivity of metallurgical coke is well known. I n addition to having a greater initial reactivity than coke, the anthracite coal was con-
1233
tinually activated by the chemical reactions t h a t took place. It is practically4mpossible to activate graphitic carbon. The results of the experiments indicated that the reactions involved in Steps I and I11 took place a t high rates. The slowest step in the process seemed to be the dissociation of carbonyl sulfide. The rate of this reaction really depended upon the rate at which the energy necessary for dissociation could be supplied. For this reason, the efficiency of a furnace for making carbon disulfide will depend chiefly upon the length and temperature of the middle hot zone and the thermal conductivity of the materials of construction. ACKNOWLEDGMENT
The author gratefully acknowledges the indispensable assistance of D. L. Gamble, H. M. Cyr, and G. W. Bisbing. LITERATURE CITED (1) Bacon, R. F., and Boe, E. S., IND. ENG.CHEM.,37, 469-74 (1945). (2) Bell, R. T . , and Agruss, M. S., IND. ENG.CHEM.,ANAL.ED., 13, 297-9 (1941), Method 111. (3) Carter, B. M., U. S. Patent 2!141,740 (Dee. 27, 1938). (4) Doumani. T. F., Deery, R. F., and Bradley, W. E., IND.EKG. CHEM.,36,329-32 (1944). (5) Dow, H., and Strosacker, C. J., U. S. Patent 1,350,858 (Aug. 24, 1920). (6) Kelley, K. K., U. S. Bur. Mines, Bull. 384 (1935). (7) Ibid., Bull. 406 (1937). ENG.CHEM.,30,92-100 (1938). (8) Lepsoe, R., IND. (9) Ibid., 32, 910-18 (1940). (10) Lewis, G. N., and Lacey, W. N., J . Am. Chem. Soc., 37, 1976-83 (1915), (11) McElroy, K. P., U. S. Patent 1,369,825 (March 1, 1921). (12) Rassow, B., and Hoffman, K., J . p r a k t . Chem., 104, 207-40 (1922). (13) Stock, A., Siecke, W., and Pohland, E., Ber., 57B, 719-35 (1924). (14) Wagman, D. D., Kilpatrick, J. E., Taylor, W. J., Pitzer, K. S., and Rossini, F. D., J . Research Natl. Bur. S t a n d a r d s , 34,14361 (1945). ENG.CHEM.,38,906-12 (1946). (15) Walker, 8. W., IND. December 1, 1947. Presented before the Divpion of Industrial RECEIVED and Engineering Chemistry a t the 113th Meeting of the AMERICAN CHEMICAL SOCIETY, Chicago, Ill.
DIPHASE METAL CLEANERS Preferential Wetting by the Two Phases IRVING REICH AND FOSTER DEE SNELL Foster D. Snell, Inc., 29 W e s t 15th Street, New York 11, N . Y.
D
IPHASE metal cleaners, which involve the simultaneous contacting of the surface to be cleaned with a free unemulsified solvent phase and a n aqueous phase, present many aspects of theoretical interest. I n the course of a n investigation of such cleaners, a n attempt was made to explore the basic mechanism of their detergent action. Certain results obtained appear anomalous in the light of experience with textile cleaning by aqueous solutions of soap or synthetic detergents; however, they are explicable in the light of fundamental concepts. The diphase solvent cleaner (2, 4 ) used in these experiments had the following formula (in milliliters) : mineral spirits 56, triethanolamine 2, oleic acid 4,butyl Cellosolve 1, and pine oil 15. Pine oil and butyl Cellosolve were added to permit the formation of a homogeneous solution of triethanolamine oleate in the mineral spirits, and for other reasons. The interfacial contact angles of droplets of water on steel un-
der baths of solvent were measured as follows. The steel was grounded with a fine Alundum. paste, rinsed several times with distilled water, wiped dry with filter paper, and then placed in a glass cuvette containing mineral spirits. Droplets of water averaging about 1 mm. in diameter were placed on the steel surface under the mineral spirits through a capillary tube. Contact angles were determined by measuring heights and widths of droplets with a microscope having a micrometer eyepiece. The contact angle is specified by the formula, tan8/2
=
2H/D
where H i s the height and D the base width of the drop. Angles on glass were measured similarly. The glass consisted of microscope slides cleaned by rinsing with acetone, wiped with filter paper, rinsed under distilled water, and finally wiped dry. The materials were not specially purified; hence effects due t o
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 40, No. 7
As determined by interfacial contact angles, mineral spirits and water wet steel equally well. On glass, water showed preferential wetting. Oleic acid caused strong preferential wetting of steel by the solvent, while triethanolamine greatly increased the preferential wetting of glass by the aqueous phase. Triethanolamine and oleic acid together cause both effects simultaneously. Under the conditions there was an extensive hydrolysis of triethanolamine oleate, free oleic acid going to the solvent phase and free triethanolamine to the aqueous phase. The wetting phenomena described are explained as a result of this behavior. Diphase metal cleaners are used under conditions where free, unemulsified solvent as well as aqueous layer can contact soiled metal and thus permit removal of all types of soil. The fact that a surface active agent lowers interfacial tension between water and oil does not ensure that i t will increase the tendency of the aqueous phase to displace oil from a solid surface. As Adam
showed, interfacial tension between the solid and the liquid phases must also be considered. Distilled water proved effective in removing a mineral oil-umber soil from steel under controlled conditions. Solutions of neutral soap did not remove this soil unless alkali was added. This is explained as due to hydrolysis of the neutral soap, fatty acids eniering the soil and causing i t to become firmly attached to the metal. Alkali, by repressing the hydrolysis of neutral soap, avoids such fatty acid transfer. It would be expected that sulfonated agents would show the effect of hydrolysis less strongly and sulfated agents still less. This was found to be the case. The nonionic agents and cation active agents which were investigated did not show the effect. Approximately 0.29'0 of oleic acid had to be present in the oily part of the soil to increase the adhesion to steel markedly. Obviously, sorption onto the cleaned surface can greatly affect detergency.
traces of impurities cannot be ruled out. Aside from this, the variation of contact angles with slight changes in the condition of the surface upon which they are measured is notorious. N o claim is made for intrinsic accuracy of the angles measured, but they have been reproduced successfullv.
and a much smaller change in that direction on glass. Triethanolamine caused the water to preferentially wet the steel and also increased the preferential wetting of rrat,er on glass. The results of experiment D, homver, showed two opposite types of action for the same pair of liquid phases. Triethanolamine-oleic acid in combination caused the solvent phase to show strong preferential wetting for steel and caused the aqueous phase to show st,rong preferential wetting for glass. In essence, t,he angle on steel was the same as though no triethanolamine were present, and the angle on glass was as though no oleic acid were present,. Repetition of experiment D wit,hout pine oil or butyl Cellosolve gave substantially the same result. It seemed that the same chemical individual (triethanolamine oleate) was simultaneously causing preferential wett,ing of oil on one type of surface and preferential wetting of \vater on another. Iccordingly, 50 ml. of the diphase cleaner n-ere stirred with 1500 ml. of water for 5 minutes and heated to 70" C., and the unemulsified solvent phase which amounted to 30 ml. was separated. Upon centrifuging, an additional 5 ml. of solvent phase could be separated and was combined with the rest, leaving 15 ml. emulsified in t8heaqueous phase. dnalysis gave the following result,s (in grams) :
SYSTEMS .MEASURED
Interfacial angles were measured in the following four systems : Contact angleA. WATERox SOLIDUNDER ~ I I S E X ASPIRITS. L of water droplets on glass and steel were measured under mineral spirits. B. \FrA4TER O N SOLID UNDER OLEIC ACID-~'V~IKERAL SPIRITS A solution of 4 ml of oleic acid in 56 ml. of mineral SOLUTION. spirits was shaken with 480 ml. of water. Very little oleic acid entered the water phase. The two phases were separated, and contact angles of droplets of the aqueous phase on glass and steel were measured under the solvent phase. C. TRIETHANOLAMIXE-WATER SOLUTIOKUNDER MINERAL SPIRITS. A mixture of 2 ml. of triethanolamine plus 56 ml. of mineral spirits was shaken with 480 ml. of water. Substantially all of the triethanolamine entered the water phase. The two phases were separated, and contact angles of droplets of the aqueous phase on glass and steel were measured under the solvent phase D. AQUEOUSEMULSION PHASEUKDER SOLVENTPHASE OF DIPHASECLEAKER.A mixture of 60 ml. of diphase cleaner plus 480 ml. of water was stirred, vigorously for one minute a t 85 C., then allowed to cool to room temperature. The supernatant unemulsified solvent phase was separated from the aqueous emulsion phase. Contact angles of the aqueous emulsion phase on glass and steel were measured under the solvent phase. O
System B involved use of oleic acid without triethanolamine, system C involved use of triethanolamine without oleic acid, while system D involved both. Pine oil and butyl Cellosolve were present in system D, but experience showed t h a t they did not measurably affect the contact angle. The following angles were obtained: Experiment A
B
C
B
Ingredients besides Water a n d Mineral Spirits
.........*
Oleic acid Triethanolamine Triethanolamine, oleic acid, pine oil, butyl Cellosolve
Contact Angle of Aqueous Phase under Phase On steel On glass 88' 157-180O 56'
390 52;
