October 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
Because the intersection of plane A M N in Figure 21 and the quaternary solubility contour is the plait curve, this correlation makes i t possible t o determine the quaternary plait points from the two related ternary plait points and the solubility contour data.
4
(12)
LITERATURE CITED (1) Barbaudy, J., Rec. trav. chim., 45, 207 (1926). (2) Brancker, A. V., Hunter, T. G., and Nash, A. W., J. Phys. Chem.,44, 683 (1940). (3) Cruickshank, A. J. B . , Haertsch, N., and Hunter, T. G., IND. ENG. CHEM.,42, 2154 (1950). (4) Fieser, L. F., “Experiments in Organic Chemistry,” 2nd ed., p. 395, New York, D. C. Heath and Co., 1941. (5) Hand, D. B., J. Phys. Ckem., 34, 1961 (1930). (6) Hunter, T . G., IND. ENG. CHEM.,34, 963 (1942). (7) Lincoln, A. T., J. Phys. Chem., 4, 161 (1900). (8) Seidell, A,, “Solubilities of Organic Compounds,” p. 368, New York, D. Van Nostrand Co., 1941. (9) Ibid., p. 665. (10) . . Sherwood. T. K.. “Absorption and Extraction,” p. 242, New York, McGraw-Hill Book Co., 1937. (11) Shriner, R . L., “Quantitative Analysis of Organic Compounds,”
(13) (14) (15) (16) . . (17) (18) (19) (20)
2361
3rd ed., pp. 39-41, Bloomington, Ind., University of Indiana, 1944. Siggia, S., “Quantitative Organic Analysis via FunctionaI Groups,” p. 24, New York, John Wiley & Sons, 1949. Ibid., p. 85. Smith, J. C., IND.ENQ.CHEW,36, 68 (1944). Taylor, S. F., J. Phys. Chem., 1 , 461 (1897). Tresbal. R. E.. “Liauid Extraction.” P. 21. New York. McGrawHill Book Co.. 1651. Varteressian, K,‘ A., and Fenske, M. R., IND. ENQ. CHEM., 28.928 (1936). Washburnl-E. R., Beguin, A. E., and Beckord, 0. C., J. Am Chem. SOC.,61, 1694 (1939). Washburn, E. R., Hnizda,V.,and Vold, R., Ibid., 53,3237 (1931). Woodman, R. M., J. Phys. Chem., 30, 1283 (1926).
RECEIVED for review May 3, 1952. ACCEPTED June 24, 1953. Material supplementary to this article has been deposited as Document No. 4075 with the AD1 Auxiliary Publications Project, Photoduplication Service, Library of Congress, Waahington 25, D. C. A copy may be secured by citing the document number and by remitLing $2.50 for photoprints or $1.75 for 35-mm. microfilm. Advance payment is required. Make checka or money orders payable to Chief, Photoduplication Service, Library of Congress.
Influence of Hydrogen Sulfide on Flame Speed of Propane-Air Mixtures PHILIP F. KURZ Battelle Memorial I n s t i t u t e , Columbus, Ohio
T
HIS paper describes the influence of hydrogen sulfide, in additive amounts and also as a secondary fuel, on the flame
1
43
Inhibitors, on the contrary, retard ignition and reduce burning velocity. They are most useful in conditioning fuels for use in spark-ignition engines, Several effective inhibitors have been found. This paper describes the influence of hydrogen sulfide, an inhibitor, on the flame speeds of propane-air mixtures, as determined by measurements on Bunsen-type flames.
speeds of propane-air mixtures. The work reported was carried out as part of a larger program undertaken to develop an understanding of the mechanism by which additives influence combustion. An additive is defined arbitrarily as a substance which, when added to a hydrocarbon fuel in amounts not greater than 5 THEORY O F ADDITIVE ACTION volume %, significantly affects the burning characteristics of the The following working hypothesis is proposed, subject t o exhydrocarbon in air. When a substance is added to the primary perimental test, to explain the effect of fuel in amounts exceeding 5 but less than additives. In the initiation of hydrocar50 volume yo,it is considered a secondary fuel. bon combustion, hydrogen atoms are presumed to be produced in low concenAdditives may be classified as acceleratration from hydrocarbon molecules b y tors (promoters) or decelerators (inhibisome external influence, which may be of tors) according to their effect on ignition thermal, electrical, or actinic origin. lag and burning velocity. A good accelAtomic hydrogen then reacts with oxyerator would produce an increase in flame FLAME SHAPE gen to form OH radicals, which act aa speed and in flame stability, thereby postenergy carriers to promote the combusponing blowoff. Such additives would tion process. The hydroxyl radicals are be useful for improving the combustion regenerated in a chain reaction which of hydrocarbon fuels used in jet engines, may be rppresented as follows: where flame instability is a problem at 1, indicating inhibition in both instances. The reason for the howed curve being on opposite sides is given above.
cH28/c&
MODIFICATION OF SUMMATION EQUATION TO DESCRIBE BEHAVIOR O F PROPANE-HYDROGEN SULFIDE MIXTURES
As shown in Figui c 9, the summation Zc,/cz = 1 is not valid for propane-hydrogen sulfide mixtures. However, the curves for these mixtures appear to be symmetrical and approximately parabolic in nature. Accordingly, Equation 5 may be modified for lean mixtures as follows:
whence
(11)
Equation 10 is valid for rich mixtures containing up t n 3.0 volume % hydrogen sulfide, but does not hold for such mixtures Containing 5.6 to 6.0 volume % hydrogen sulfide. Figure 10 shows the relationship between Zc,/c*, - 1 (lean niixt,ures) or 1 - Zc,/c*, (rich mixtures) and the product, ( c c a ~ / c & ~( ~c H ) z ~ / c ~ , The ~ ) , relationships are linear and appear to converge. At the point of convergence, Equation 8 becomes
0.25 = A (0.5)" and is identical in value with Equation 11. Then,
(12)
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1953
2365
when Equation 7 may be written as 0 60
Similarly, Equation 10 may be written as follows:
Using Figure 10, values for n can be determined; these are given in Table 11.
TABLE 11. VALUESOF n
FOR LEANAND RICHPROPANEHYDROGEN SULFIDEMIXTURES
Flame Speed, Cm./Sec.
Condition of Value of n in Mixture Equations 14 and 15 Lean 20.1 0.78 Rioh 18.6 0.66a 21.0 Rich 0.57a 0 Valid only for rich ternary mixtures (propane-air-HzS) containing 3.0 volume % or less HIS.
Figure 11 shows the relationship between 1 - Zc,/c: and the product ( c c ~ H ~ / c & H ~(cHZs/c+,,s) ) for rich mixtures over the entire range of hydrogen sulfide input which was studied. As shown in Figure 10, the relationship is linear for rich mixtures containing up t o 3.0 volume % hydrogen sulfide and the lines for mixtures with flame speeds of 21.0 and 18.6 cm. per second converge at a point where 1 - Zc,/ct = 0.25 and where the product ( C C , ~ / C ~ ~ H J (cH~s/c&s)= 0.5. Rich mixtures containing 5.6 to 6.0 volume yo hydrogen sulfide do not follow the linear relationship, however. and the value of 1 - Zc,/c*, drops as the value of the product ( c c ~ H ~ / c ~ , ~ ) ( c ~is~ ~increased. / c ~ ~ ~ ) This is shown by the short dashed lines which slope downward to the right. When the flame speed is 21.0 cm. per second, the values for mixtures containing 5.6, 5.9, and 6.0 volume % are identical. When the flame speed is 18.6 cm. per second, the values for mixtures containing 5.6 and 5.9 volume % hydrogen sulfide are identical, and the value for the mixture containing 6.0 volume % hydrogen sulfide is slightly lower. The values which are nonlinear with respect t o Equation 15 appear t o be linearly related among themselves, as is shown by the solid line which slopes downward to the right. This indicates that, with large amounts of hydrogen sulfide present (in rich mixtures)-that is, 5.6 t o 6.0 volume %-there is less inhibition as the flame speed of the mixture decreases. This has been found true also with mixtures of other alkanes and hydrogen sulfide (Y), and will be discussed further in another article. PROPOSED MECHANISM FOR INHIBITING ACTION OF HYDROGEN SULFIDE i
The decrease in flame speed caused by the addition of hydrogen sulfide to hydrocarbon-air mixtures cannot be attributed to the lowering of the flame temperature. Calculations show t h a t the decrease in flame temperature resulting from the presence of 0.5 volume % hydrogen sulfide in a stoichiometric propane-airhydrogen sulfide mixture is less than 10' C. Accordingly, another explanation has been sought. According t o Fowler and Vaidya (4), the strongest feature of t h e flame spectrum of hydrogen sulfide is the band system of diatomic sulfur, E&. Also present in the spectrum are feeble emission bands of the free radical SO. Gaydon (6),in discussing the spectrum, suggests the following reactions for the formation of SZ and SO: HzS SO + HzO Sz (16)
+
s 2
+
+
0 2 +
2so
(17)
Figure 11. R e l a t i o n s h i p between 1 and
(F) ('E)
-Z2 C,*
CCnHa
Rich propane-hydrogen sulfide m i x t u r e s c o n t a i n ing up to 6.0 volume % hydrogen sulfide
The SI bands are intense, and, according t o Gaydon, are responsible for the violet color of hydrocarbon-air-hydrogen sulfide flames. Biinsley and Stephens (1) found that a deficiency of air-that is, rich mixtures-and low temperatures favor the formation of diatomic sulfur and suggest the equilibrium
+ '/zSz
2 s o % so*
(18)
However, there must be an appreciable concentration of diatomic sulfur in lean mixtures also, as these are distinctly violet in color. Gaydon reports a private communication from Crone (S), who observed strong SPbands in the flame of a hydrogen-oxygen mixture which contained traces of sulfur. Crone further suggests that the ease of excitation of the Sz bands in the hydrogen flame may be explained by the reaction Sz
+H +H
-+
+ Hz
S,*
(19)
Steacie (IO), in discussing this reaction, suggested t h a t t h e following two-body reactions, which produce the same end products as those shown in Equation 19, are more probable than the threebody collision shown above:
+H +H
Sz HS,
HS; +S ; + Hz +
(20) (21)
Equations 20 and 21 are the basis for a reasonable explanation of the large reduction in flame speeds which is observed when hydrogen sulfide is added to hydrocarbon-air mixtures. If it is assumed that hydrogen atoms play a considerable role in controlling flame speed of hydrocarbons, the effects of the reactions shown in Equations 20 and 21 would be t o lower the hydrogen atom concentration and, by this inhibiting action, t o cause a decrease in flame speed. I n reactions similar to that shown in Equation 20, diatomic sulfur could capture hydrocarbon fragments and regenerate hydrocarbons by a reaction of RCH,SZ with hydrogen atoms or with RCH2. Inasmuch as inhibition is observed, it is apparent t h a t these reactions must proceed more rapidly than do the reactions by which hydrogen atoms or hydrocarbon fragments are consumed in the normal combustion reactions of hydrocarbons burning with air. ACKNOWLEDGMENT
The author wishes t o express his thanks t o R . 8. Litton for his capable and faithful assistance in carrying out the experimental
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INDUSTRIAL AND ENGINEERING CHEMISTRY
work, and to J. F. Foster, supervisor of fuels research, and Fred Benington, assistant supervisor of fuels research, at Battelle, for their helpful interest and consideration. LITERATURE CITED (1) Brinsley, F., and Stephens, S., Nature, 157,622 (1948). (2) Coward, H. F., and Greenwald, H. P., Bur. Mines, Tech. P a p e r 427 (1928). (3) Crone, H. G., private communication to Gaydon mentioned in (6),pp. 91-2. (4) Fowler, A., and Vaidya, W.I f . , PTOC. Roll. SOC.( L o n d o n ) , 132A,
310 (1931). (5) Gaydon, A. G., “Spectroscopy and Combustion Theory,” pp. 88. 90-2, London, Chapman and Hall, 1948. (6) Kurz, P. F., “Stability Studies with Mixed Fuels. I. Hydro-
Vol. 45, No. 10
carbons, Hydrogen, Hydiogen Sulfide,” Battelle Tech. R e p t . 15036-3 to Wright Air Development Center, Contract AF 33 (038)-12656 (April 30, 1952). ( 7 ) Xurz, P. F., Battelle Memorial Institute, Columbus, Ohio, unpublished results. (8) Payman, W., J . Chem. SOC.,115, 1438-82 (1919). (9) Smith, F. A., and Pickering, S. F., Xatl. Bur. Standards J . Research, 17, 7-43 (July 1936). (10) Steacie, E. TV. R., personal discussion with P. F. Kurz a t Columbus, Ohio, 1950. RECEIVED for review May 15, 1953. ACCEPTED July 3 , 1953. Presented before t h e Division of Gas and Fuel Chemistry, AMERICAN CHEMICALSOCIETY,Pittsburgh, Pa., .4pril 1953. Work done under the sponsorship of the Flight Research Laboratory, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio.
Rate of Evaporation of Glycerol in High Vacuum D. J. TREVOY Research Laboratories, Eastman Kodak Co., Rochester, N . Y .
T
HE rate a t which molecules pass through an imaginary win-
dow in a uniformgas has been derived from the kinetic theory (8) and is given by
where r is the mass per unit area per unit time, p is the vapor pressure a t temperature 2‘, degrees absolute, ilf is the molecular weight, and R is the gas constant. For a liquid in contact with its equilibrium vapor, the maximum rate of two-way interchange of molecules a t the interface is also expressed by this relation. Langmuir ( 7 ) ,and later Knudsen (6),considered the evaporation process to proceed independently of the condensation process a t the interface. It follows that if the vapor is removed irreversibly as rapidly as it is produced, the maximum rate of evaporation into free space is also given by this equation. By experiment Knudsen found that the rate for liquid mercury was sometimes less than that predicted, and he introduced a n “evaporation coefficient” to absorb the discrepancy. Evaporation coefficients for a number of liquids were subsequently measured by Rideal ( I O ) , Alty arid Nicoll ( 2 ) , Alty ( I ) , Baranaev (3),Priiger (Q),and Wyllie ( I S ) . The results of these experiments suggest that nonpolar substances, such as carbon tetrachloride aud benzene, have evaporation coefficients near unity, while polar substances, such as water or ethyl alcohol, have much smaller coefficients (0.01 t o 0.04 for water). It is implied by these workers that each substance has an evaporation coefficient which is a characteristic physical property, and that the value of the coefficient for different substances may vary widely. Experiments in these laboratories, already described (5j, suggest that this may not be the case, but rather that fresh surfaces of all liquids evaporate a t the maximum theoretical rate. The fact that lower than optimum rates are often observed is an indication that the evaporating surface is not truly representative of the bulk material. Then an evaporation coefficient less than unity is not a basic characteristic of the substance but is determined by specific conditions at the surface. The emission characteristics of an old surface are consequently variable, and may depend on many factors, such as adsorption to the interface of soluble impurities from the liquid, orientation in the interface of polar molecules with or without subsequent adsorption of impurities from the liquid or vapor, and adsorption of impurities from the vapor. Alty (1) measured the evaporation of freshly formed drops of
water, the surface temperature being deduced from the surface tension which was measured simultaneously. The evaporation coefficient obtained was only 0.04. It is thought that the low value may perhaps be due to uncertainties in the surface temperature, or, as the drops were formed very slowly, there may have been sufficient time for the formation of inhibiting surface layers. In earlier experiments (5),di-Zethyl hexyl phthalate and di-2ethyl hexyl sebacate were evaporated from the constantly r e newed surface of a stream of liquid falling through an evacuated space. l i p to a vapor pressure of about 5 microns, the observed rate was exactly t h a t of the theoretical. The rate then fell off slightly as the vapoi pressure increased and Tas about 75% of optimum a t 100 microns. The 25% discrepancy in rate is believed due, not to an evaporation coefficient less than unity, but to a reduction in temperature a t the surface resulting from a steady-state thermal gradient in the fluid stream. Although these data support the thesis that the evaporation coefficient is unity for new, clean surfaces of all liquids, it seemed desirable to measure the coefficient for a liquid with very different propert’ies than those of the phthalate and sebacate esters. A search of the literature revcaled that in esperiments x-ith glycerol an abnormally low rate was obtained by Wyllie ( I S ) , an evaporation coefficient of 0.052 being reported a t 18” C., with a vapor pressure less than 0.1 micron. This fluid appeared suitable for falling-stream experiments, and vias particularly interesting because it is different in structure from the esters and is highly polar. The falling-stream technique was used in a tensimeter specially adapted to handling glycerol. METHOD
In principle, the apparatus was the same as that described earlier (6),but it differed in many details and is shown diagrammatically in Figure 1. Tubing a t least 18 mm. in outside diameter was used around the entire liquid path to minimize pressure drop. Two centrifugal impellers in series were needed to circulate the glycerol, and t h e temperature was controlled by a bimetallic thermoregulator which fitted snugly into a large thermowell in theleft arm. The glycerol wa8 distributed radially by flowing i t through a cylindrical wire screen, 11/3 turns of 30 mesh, just before it entered the jet tube, having an inside diameter of 1.27 om. and a length of 11.0 cm. The large jet tube was necessary t o obtain even a small stream a t
