INDUSTRIAL AND ENGINEERING CHEMISTRY
1116
Hulburt (7) presents an integrated expression for a first-order reaction on a cylindrical surface sparsely covered by the reactants and producbs. For a process in which the rate of diffusion of the reactant to the wall is very slow in comparison to the rate of reaction on the wall, his derivation reduces to: no
In - = 5.783
nl
D < t’ - In 0.692 R
(3)
where D, = diffusivity, sq. cm./sec. R = radius of cylinder, em. t’ = contact time = -
vr Q
Expressing the equation in the manner in TT-hich the data from this investigation were correlated:
Vol. 43, No, 5
Such a technique has been used to study the rate of decomposition of hydrazine in a silica vessel. I n silica vessels with surfaceto-volume ratios of 2.5 em.-’ or greater, the decomposition is completely heterogeneous over the temperature range 269 to 637” C. The rate of this heterogeneous reaction may be correlated by assuming it t o be directly proportional to the amount of hgdrazine in the gas phme. The reaction has been found to be very sensitive to the source and history of the silica surface, and, for this reason, the data presented should be used only as approximations of the magnitude of the decomposition reaction in any other system having silica surfaces. T h e hydrazine appears to decompose by two separate niodes of reaction, only one of which produces hydrogen. O
ACKNOW‘LEDGiMENT
The only temperature-dependent term is the diffusivity. Because the diffusivity varies with the absolute temperature to the 3/2 power (6), one would expect a variation of k of about 1.5 over the term range 600” to 800” K. The value of k for the unpacked reactor varied 29-fold over this same temperature interval, vihereas a 7-fold variation n-as obtained in the packed reactor. T h e temperature coefficients of the velocity constants obtained in this investigation are of such a magnitude that the reaction could not be diffusion-controlled. Actually, upon exact calculation, it was found that diffusion was exerting a modifying influence. However, the discrepancies caused by this effect were of the same magnitude as the spread of the data around the line drawn. MODE OF DECOMPOSITION
The hydrazine was found to decompose primarily to ammonia and nitrogen. The amount of hydrogen in the reaction products appeared to increase with temperature and was in the neighborhood of 6% of the hydrazine decomposing. T h e presence of this hydrogen could be explained by direct reaction of the hydrazine, or by decomposition of ammonia. The rate of ammonia decomposition has been studied in the packed reactor. This study showed the reaction to be much too slow to account for the hydrogen appearing in the reaction products. Therefore, it appears that the hydrazine undergoes two courses of reaction. This had been predicted by Bamford ( 2 ) . He proposed the following free radical mechanisms as a result of his studies of the decomposition on a quartz surface in the presence of nitric oxide.
The authors wish to express their appreciation to the Rand Corp. and to the Air blat6riel Command, United States Air Force, for their support of this research a t the Battelle bIemorial Institute and for their permission to publish the results. LITERATURE CITED
(1) Askey, P. J., J . Am. Chern. Soc., 52, 970 (1930). ( 2 ) Bamford, C. H., Trans. Faraday SOC.,35, 1239-46 (1939). (3) Bolles, W. L., Petroleum Refiner, 27, 120 (1948). (4) Brown, Cox, Venable, and Kearly, “Studies in the Preparation, Analysis, and Thermal Decomposition of Hydrazine, Methyl, and Ethyl Hydrazine,” Progress Report under ONR Pioject No. 349, University of Alabama, Xov. 1, 1948. ( 5 ) Hinshelwood and Burk, J . Chem. Soc., 127, 1105 (1925). (6) Hougen, 0. A., and Watson, X. hI., “Chemical Process Prinoiples, 111, Kinetics and Catalysis,” pp. 815, 988, New Y o l k , John Wiley B: Sons, 1947. (7) Hulburt, H. M., IND.EXG.CHEM.,37, 1063 (1945). (8) Krieger, F. J., private communication,Aug. 5, 1947. (9) Moffatt, M., Instruments, 22, 122 (1949). (10) Penneman, R.A , , and Audrieth, L. F., Anal. Chem., 20, 10.58 (1948). (11) Scott, Oliver, Gross, Ilubbard, and Huffman, J . a m . Chem. SOC., 71,2293 (1949). (12) Stephenson, C. C., and AIcbIahon, H. O., Ibid., 61, 437 (1939). (13) Sswarc, M., Proc. SOC.(London), 198, 267 (1949). (14) Wilhelm, R.H., Chem. Eng. Progress, 45, 208 (1949). RECEIVED October 20, 1950. Abstractcd from the 11.S. thesis of T. J . Hanratty t o the Department of Chemical Engineering, Ohio State L-niversity, Columbus, Ohio.
Direct Reinforcement of Natural Rubber Latex Mixes-Correction The following corrections should be made in the article on “Direct Reinforcement of Natural Rubber Latex Mixes” [Le Bras, Jean, and Piccini, Ivan, IND.ENG.CHEW, 43, 381 (1951)]: On page 383, second column, last line of table, 0.1 M should be used instead of 0.5 M . I n the third paragraph below this, the second sentence should read: “These resins, used in the proportion of 10 grams of preparation R1 t o 100 grams of 60% latex, gave the results indicated in Table 11.”
and
T h e accuracy of the data obtained in this investigation did not justify any attempt to correlate them by two separate rate equations, These inaccuracies resulted not only from temperature measurement and diffusion effects, but also from the apparent inconsistency of the reaction producing hydrogen and the apparent changes in surface conditions. CONCLUSIONS
It is possible to abtain rate data on a n extremely rapid and exothermic reaction by highly diluting the reactant with a n inert gas and passing the mixture rapidly through a hot zone.
..... Crystallization-Correction The authors of the review article on “Crystallization” [IND. ENG.CHEX..,43, 59 (1951)l regret that they erroneously gave credit to the Brush Development Co. for the illustration on “Successive Stages of Seed Growth into Final Capped Seed.” This photograph shows work of the Bell Laboratories and was originally published in the Bell Laboratories Record, Vol. 25, October 1947. C. S. GROVE,JR., AND J. B. GRAY
