November 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table IV. Effect of Purging on Activity of Coked Catalysts Precoking Time, Purge None Steani C None Nitrocend Steam None Nitrogen Steam None Nitrogen Steam
hIin.a 0
7
15 30
Activityb, Cc./Min. 67 67 45 55 63 35 43 58 28 37 60
2379
=‘-I
Coke, Final Rt.
%
0.04 0 : 16
0:is 0.26 0.25 0.46 0.41 0.43
+
a Precoking with cumene 3% styrene a t 800’ F. b Activity determined, .after purging, with purified cumene a t 800’ F. Activity without purging is instantaneous actlvity a t close of precoking run. C Purged with ateam f o r 30 minutes, then NZfor 30 minutes a t 800’ F., 200 cc./min. for each. Purged with nitrogen for 30 minutes at 800° F., 200 cc./min.
F I G U R E S = T I M E ON S T R E A M E A C H S Y M B O L = ONE CATALYST- IMPURITY C O V B I N A T I O N O - M I S C CATALYST-IMPURITY 6 0 M l N . RUNS
-
0.4
T h e inhibiting mechanism is t h a t of competition of the inhibitor and the cumene for adsorption on the active sites of the catalyst. The well-known inhibition of catalytic cracking by nitrogen compounds is analogous to the inhibition of cumene cracking by styrene or cumene hydroperoxide. The relative adsorption equilibrium constants of strongly adsorbed compounds can be calculated simply from measurements of their inhibiting effect on cumene cracking.
Figure 9.
0.8
I 2 1.6 C O K E ON CATALYST
2.0
2.4
2.0
(WT%)
Variation of carbon-hydrogen ratio i n coke
ACKNOWLEDGMENT
( 5 ) Laidler, K. J., “Catalysis,” vol. I, ed. by P. H. Emmett, Reinhold, New York, 1954. (6) Prater, C. D., Weisz, P. B., and Lago, R. M., to be published. (7) Shankland, R. V., and Schmitkons. G. E., American Petroleum Institute, Division of Refining, Symposium on Catalytic Cracking, 27th annual meeting, Chicago, Nov. 10, 1947. (8) Stright, P., and Danforth, J. D., J. P h y s . Chem., 57,448 (1953). Discussions Faraday Soc., No. 8 , 270 (1950). (9) Tamele, M.W., (10) Thomas, C. L.,U. S. Patent 2,352,236 (1944). (11) Weisi, P.B., and Prater, C. D., Advances in Catalysis,6 (1955).
The authors wish t o thank the management of Socony Mobil Laboratories, Socony Mobil Oil Go., Inc., for permission t o publ i ~ hthis paper.
RECEIVED for review April 16, 1954, ACCEPTED July 5, 1955. Divisions of Petroleum and Physical and Inorganic Chemistry, Symposium on Mechanisms of Homogeneous and Heterogeneous Hydrocai bon Reactions, 125th Meeting ACS, Kansas City, Mo., March-April 1954.
NOMENCLATURE
(A)
= concentration of unoccupied acid sites on catalyst, moles
per liter
(C) = concentration of cumene, moles per liter Co = mole fraction of cumene in charge ( C A ) = concentration of adsorbed cumene, moles per liter [d(C)/dt]o = cracking rate in absence of inhibitor [d(C)/dt], = cracking rate in presence of inhibitor = fraction of charge converted a t steady state
fk-
=
K,/K,
k1 kz
= rate constant for adsorption of cumene, sec.-l = rate constant for desorption of cumene, sec-1
ka kc
= rate constant for cracking of adsorbed cumene, sec.-l = rate constant for adsorption of inhibitor, set.-' = rate constant for desorption of inhibitor, sec.-l
kr ka k,
ks K,
= rate constant for polymerization of inhibitor, set.-' = rate constant for depolymerization of inhibitor, sec.-l = rate constant for hydrogen-exchange reaction, sea-1
constant for adsorption-desorption plus cracking of cumene = [kl/(k~ ka)] K, = equilibrium constant for adsorption - desorption of inhibitor = (k&) N = total concentration of acid sites on catalyst, moles per liter ( P ) = concentration of inhibitor, moles per liter P, = partial pressure of cumene, atmospheres PO = mole fraction of inhibitor in charge P, = partial pressure of inhibitor, atmospheres ( P A ) = concentration of adsorbed inhibitor, moles per liter Ro = rate of cumene cracking in absence of inhibitor, cc. of gas per minute = rate of cumene cracking in presence of inhibitor, cc. of R, gas per minute = equilibrium
+
LITERATURE CITED
Blanding, F. H., IND.ENQ.CHEM.,45, 1186-97 (1953). B. S., and Voge, H. H., Ibid., 37, 983 (1945). (3) Greensfelder, B. S., Vow, H. H., and Good, G. M., Ibid., 37, 1168 (1945). (4) Hansford, R.C., Advances in Catalysis, 4, 1-30 (1952). (1)
Editors’ Note INDUSTRIAL & ENGINEERING CHEMISTRY has through nearly half a century of publication prided itself on accuracy. Some of the very few corrections which we must issue are errors made by authors themselves, either of a typographical nature or, in rare instances, in experimental work itself. Others may be made in editing or in typesetting. A combination of circumstances-what we know not a t this time-has resulted in a comedy of errors in connection with t h e article “Burning Velocities--.4cetylene and Dideuteroacetylene in Air” [IND. ENG. CHEM.,43,2772-6 (1951)]. Heading of Table I of this article wa3 in error. T h e correction [IND. ENG.CHEM., 44, 603 (1952)], listed as kK’/kK‘, was also in error. T h e editors would like to t r y once more. Correct heading for the last column of Table I should be kK’/k’K.
Cost Estimate on Technical Grade Vinyl Stearate-Correction I n the article on “Cost, Estimate on Technical Grade ,Vinyl Stearate” [Redfield, C. S., Port, W. S., and Swern, Daniel, IND. ENG.CHEM.,47, 1707 (1955)], in Table I t h e price of t h e rotary vacuum dryer should be $19,470. Instead of the last item, “Pump, centrifugal,” t h e table should read:
(2) Greensfelder,
Pump, eentrifugal P u m p , positive delivery
Circulate hot water, 6 0 gal./ min. a t 50 lb./sq. inch Stainless steel
$560
470
