ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT dicated that the by-product slag produced in the fusion tests when phosphate matrix was incorporated in the charge was an effective fertilizer and should return a significant credit to the fusion process. It is recognized, however, that more extensive tests will have to be made to establish the agronomic value of this by-product. Estimates based on the exploratory studies, and not taking into consideration the processing that would be involved in purifying the sulfur-bearing gases for use in the manufacture of sulfuric acid, indicate that the cost of sulfuric acid from phosphogypsum by either process would be about 15% higher than the cost of acid from sulfur a t a plant a t Columbia, Tenn. With credit for by-product fertilizer slag, the cost of production by the fusion process would be 20 to 30% lower than the cost froni sulfur. The inveatment for a plant to manufacture sulfuric acid from phosphogypsum was estimated to be about twice that for a plant using elemental sulfur. Recovery of sulfuric acid from by-product phosphogypsum should be of increasing interest to industry in view of continuing increase in the cost of sulfuric acid and the increase in the production of concentrated superphosphate by the wet process, which is being spurred by the demand for high analysis fertilizers and the interest of the Atomic Energy Commission in the recovery of uranium from this process. I n view of the promising results of the exploratory studies, it is planned t o investigate the calcination and fusion processes further in pilot plant equipment to obtain data for more exact engineering and economic evaluations. If the results of this further work are promising, studies will be made of the purification of the
sulfur-bearing gas to make it suitable for product,ion of sulfuric acid. Acknowledgment
The work was conducted under the supervision of E. L. Stout. W. L. Darrow and H. M. McLeod, Jr., were in charge of certain phases of the work. Literature Cited
(1) Bedwell, M. L., Roy. Inst. Chem. (London) Lectures, Monographs, Repts., 3 (1952). (2) Frydlender, J. H., Rev.prod. chim., 29, 613-16 (1926). (3) Higson, G. I., Chem. Eng. News, 29, 4469-74 (1951). (4) Ilofman, H. O., and Mostowitsch, W., Trans. Am. Inst. Mining Met. Engrs., 39, 628-53 (1908). (5) Manning, John, FertiliseT Soc. (Enol.) Proc., 15 (1951). (6) Tennessee Valley Authority, Chem. Eng. Rept. 4, pp. 54-5, compiled by E. L. Stout, U. S. Government Printing Office,
Washington, D. C . (1950). (7) Ibid., 7, pp. 54-61, compiled by J. C. Brosheer and T. P. Hignett, U. S. Government Printing Office, Washington, D. C. (1953). (8) Vol’fkovioh, S. I., and Loginova, A. I., Wan?. Sei. I n s t . Fertilizers (U.S.S.R.), 101, 113-22 (1933). (9) Yates, L. D., and Getsinger, J. G., presented at the 120th MeetSOCIETY, Sew York, 1951. ing of the AMERICANCHEMICAL (10) Zelinskii, N. D., and Rakuzin, 31. A., Compt. rend. m a d . sci.
(U.R.S.S.), 1930A, 471-4.
RECEIVED for review April 15, 1953. A C C E P P E D December 3, 1953. Presented as part of the Symposium on Fertilizer Technology before the Division of Fertilizer and Soil Chemistry a t the 124th Meeting of the Q h i E R I C h x C H E M I C A L SOCIETY, Chicago, Ill.
Kinetics of Propylene and Ethylene Hydrogenation FLOW SYSTEM AND COPPER-MAGNESIA CATALYST M. V. SUSSMAN‘ AND CHARLES POTTER* Columbia Universify, New York, N. Y.
I
S P E S T I G S T I O N of the rate of hydrogenation of propylene to propane on a copper-magnesia catalyst is described in this paper. The chemical reaction and the catalyst studied are not commercially significant. However, the general reaction-the hydrogenation of olefinic matorials on heterogeneous metallic catalysts-is of considerable importance commercially. I n addition, the system chosen offers the following practical experimental operating advantages. The chemistry of the reaction is straightforward. Pyrolysis does not occur at the operating temperatures. There is only one possible forward reaction, and the corresponding reverse reaction is negligible at the temperature involved. The reaction is therefore completely described by the equation:
C3Hs
+ 112
+
C3Hs
and an expression for the reaction rate should be of minimum complexity. The copper-magnesia catalyst has been used previously in a study of ethylene hydrogenation, and details of its preparation 1 Present address, Dacron llanufaoturing Diviaion, E. I. d u Pont de Xiemours & Co., Kinston, N. C. * Present address, Amersil Co., Inc., Chestnut Ave., Hillside 5, N. J.
March 1954
are available ($5, 26). The use of an identical catalyst and similar operating conditions permits comparison of the results of the published ethylene study with the propylene hydrogenation data reported herein. The selection of propylene is also a step toward the attainment of a complete picture of the catalytic hydrogenation of the ethylene homologs, since, in addition to the ethylene study, butylene hydrogenation has been investigated under somewhat similar conditions (81). Investigations have been made on the catalytic hydrogenation of the lower molecular weight olefins during the past 50 years. GrasJi ( 7 ) and others ( 5 , 8, 12-15, 82) have studied the kinetics of ethylene hydrogenation on various types of reduced copper catalysts in static systems. hfaup more investigations of ethylene hydrogenation have been made on other catalysts such as nickel, platinum, and palladium (16). Pease (14, 15) investigated the adsorption and ethylene hydrogenation characteristics of copper catalyst. Taylor and Burns ( 1 8 ) measured adsorption of ethylene and hydrogen on various metallic catalysts. The nature of gas adsorption on metals was concluded to be different from that which occurs on activated carbon. Goldfeld and Kobozev (6) confirmed this latter observa-
INDUSTRIAL AND ENGINEERING CHEMISTRY
457
ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT tion in their study of the adsorption of ethylene and propylene on copper catalyst. Greenhalgh and Polanyi ( 8 ) studied hydrogen-dcutcriuni exchange during hydrogenation of ethylene over a copper catalyst and concluded that the hydrogen molecule dissociated into atoms prior to its combination with the unsaturate molecule. Similar conclusions w r e presented by Farkas and Parkas (5) and Twigg ( 2 2 ) , after analogous studies.
24/40
STD. TAPER JC4lrlT
SEALED THR
of unreduced catalyst), and p is the partial pressure of the coniponent gases (atmospheres). Equation 1 applies only to point conditions in a fixed catalyst bed or over a depth of bed wherein the concentration change is of a diffrrent,ial magnitude and Ivhcre chemical rate controls. Therefore, experimental rate data are obtained from measurcinent,a on a very shallow (differential) catalyst bed, which causiis less t,han 2% of reaction to occur. The average of the inlet and outlet' gas s h a m compositions and corresponding reaction rates obtained in such a differential catalyst bed are subst,ituted in each of the various rate cquat,ion&. The constants of the equations-via., a, b, c, and J-are then evaluated by the method of least squares. The suitability of any one reaction rate equation is deterniincd by the following criteria: 1. The calculated rate equation constants must be either zero or positive. This must be so if the constants are t,o have the theoretical significance assigned t o them in the derivation of tlic rate equation. 2. The rate equation should fit, the experimental data m-ithin the limits of experimental error. 3. The rate equation should be in agreement w t h the know1 adsorption characteristics of t'he catalyst. Experimental Technique includes GQS Purification and Catalyst Aging
WATER JACKET
U
>AS
Figure 1,
OUTLET
Catalytic Reactor
Propylenp hydrogenation has been inc rstgated by Kistiakowsky and his conoilrers (12, 13) and Emrnet and Graj ( 4 ) , using a copper and an iron catalyst, respectively, in a constant volume system. Toyama (BO) reported that propylene hp drogenates more slowly than ethylene on a nickel filament catal) st. Investigations of catalytic hydrogenation of low molecular weight olefins in flow systems are recent and fev. Tschernitz et al. (21) studied the hydrogenation of mixed butenes on a nickel catalyst. Kynkoop and TVilhelm (26) studied ethylene hydrogenation over a copper-magnesia catalj S+, prepaied in the same manner as the catalj st used in this stud). No record of a study of the kinetics oE ]~rop\.lenehydrogenntion in a flow system has been found. Differential Rate Data Are Fitted to Unintegrated Reaction Rote Equations
The theoretical basis and derivations of thc reaction rate equations used to correlate the data and determine the mechanisin for propylene hydrogenation are given in detail by IIougeii and Watson (10, 11). The general form of these equations is:
vihere the exponents, t, v, w,2. yl and z. depend on the reaction mechanism chosen for the derivation, a, b, c, and f are constants and functions of the adsorption equilibrium and reaction rate constants. r is the reaction rate (in gram-moles per hour per gram
458
Rea.ctor. The reactor used in this study is shown in Figure 1. I t is made of 20-mm. borosilicate glass tubing, in two parts, connected by a 24/40 ground-glass joint. The lower section contains a coarse glass grid for supporting the catalyst. ?i glass thermowell runs upward through the center of the section and through t,he center of the catalyst support grid. 9movable thermocouple is located in this thermowcll t,o measure vertical temperature gradients through the catalyst bed as ell as gas temperatuws abo.ve and below t'he bed. An additional bare thermocouple i;: sealed through the reactor wvall and rests directJy in the catalyst beJ. Gas flow through the reactor is from tshetop down. A Nichroine heating coil (25 gage X 10 feet) is wrapped 011 tlii. out,side of the lower section, and a 30-nim. glass wa.ter jacket surrounds it. The heating coil is used for reducing the catalyst in situ. Onw the catalyst has been reduced, the hea'ing coil is ,shut ofl! and water is run through the 30-mni. jacket t80maintain thii catalyst bed a t constani temperature. The upper section of tho reactor containe the feed gas inlet, and a thermowcll t,o moas x c gas temperatures. Ana!ysis. A Xodel aI/Kc-8 gas thernial conductivity cr.11 manufactured by the Gow-Mac Instrunlent Go. of S e w Jcr v a s used t o compare the hydrogen content of thc cyicriniental hydrogen, propylene, and propane mixtures bcforc i i r i t l aft'er pnssnge through the catalyst bed. A s long as the hydrogen content of the gas mixtures remains above 30%, the conductivit'y cell docs not, distinguish propane from propylene ( 2 4 , 2 6 ) . Gases. The propane and propylene used in this study were C.P. materials obtained from the Phillips Petrolcuin Co. of Beaumont, Tex. Spectrographic analysis of t,he gases was made by the vendor. The propylene contained 0.1 and 0 . 8 5 ethylene and propane, respectively, whereas the propane contained 0.2 and 0,5y0ethane and propylene, respect,ively. The gases were given a caustic wash t o remove all t'race of sulfur-bearing materials and were then dried by passage through an activated aluinina column. The admixed hydrocarbon impurit,ies were not removed, but their presence vias account'cd for in computing the analysis of the gas mixtures fed to thc rimtor. Elec.crolytic hyclrogeri ~ r a sobtained from the .iir Reduction Corp. of S e w York and contained oxygen and moisture as impurities. The oxygen was removed by catalytic hydrogenation in a glass colurnii containing palladized asbestos heated a t 250' C. Water vapor w,s then removed from the hydrogen in an activat'ed alumina column The alumina d r j h g columns v-cr(~ivound with Wichrome heating jackets so that they could be regenerated in place, should the aluinina become water saturated. Thc complete gas purification chain is shown in Figure 2 , which is a flow sheet for the entire experimental setup. The composition of the un-
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
1701, 46,No. 3
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT Reaction Rate Equation Is Derived for Vapor-Phase Propylene Hydrogenation
reacted gas mixture fed to the reactor was determined from the flow meter readings. Catalyst. 4 50-50 mole % copper-magnesia cat,alyst was chosen for this hydrogenation study because it has been used on a similar kinetic study of ethylene hydrogenation (25, 26') and, in addition, has generally desirahlo physical as well as catalyt'ic properties. The catalyst was prepared from highly purified, nickel-free copper, in accordance with thc method described by Wynkoop ( 2 5 ) ,using the reverse coprecipitation techniques of Taylor ( 1 7 ) . The catalyst is produced and stored as a copper oxide-inagnesium oxide pellet. Prior to its use for promoting hydrogenation, it is placed in the reactor and reduct:d in situ with hydrogen a t 250' C. After a suitable aging period, it achieves a reasonably constant level of activity. Procedure. Experimental technique consisted of passing mixtures of hydrogen, propylene, and propane of known composition through a catalyst bed approximately ' / p inch deep, containing approximately 1 gram of catalyst. The bed temperat'ure was held constant and the amount of conversion was measured. Before beginning experimental runs, a eample of unreduced oat,alyst was placed in the reactor and t8reatedwith hydrogen a t 250' C. for about 16 hours. The reduced catalyst was cooled and aged in a stream of hydrogen and propylene for the same period of lime until the catalyst had attained a constant activity level, as indicated by a constant thermal conductivity cell reading. To reduce the effects of any change in activity with time, all the runs at, any one given temperature were performed in the same day. I n addit,ion, the entire series of runs was performed within 3 days, on a single sample of catalyst. The catalyst sample was reduced and aged only once a t the beginning of the series and was not subjected to any further regenerat'ion during the course of the experiment. It was found that, better temperature control was obtained a t the beginning of a run if propane and propylene were introduced into the cat,alyst bed before the introduction of hydrogen. Bed t.emperature was maintained constant by water from a constant. temperature bath, which was pumped through the reactor cooling jacket a t a rate of about 5 gallons per minute. Jacket temperature was maintained about 5" C. below the catalyst bed temperatures. Reaction temperatures, pre, es, flow rates, and conductivity cell readings were recorded ai the system reached and maintained a steady state for at least
