Ind. Eng. C h e m . R e s . 1987,26,869-874 Dale, G. H.; McKay, D. L. Hydrocarbon Process. 1977, 56(9), 97. Donaldson, R. E.; Rice, T.; Murphy, J. R. Ind. Eng. Chem. 1961,53, 721. Duffy, B. J., Jr.; Hunt, H. M. Chem. Eng. Prog. 1952,48, 344. Erickson, H.; Keith, C. D. US Patent 3 234 119, 1966. Gossett, E. C. Pet. Refin. 1960, 39(6), 177. Grane, H. R.; Conner, J. E., Jr.; Masologites, G. P. Petrol. Refin. 1961, 40(5), 168. Habib, E. T., Jr.; Owen, H.; Snyder, P. W., Jr.; Streed, C. W.; Venuto, P. B. Ind. Eng. Chem. Prod. Res. Dev. 1977, 16, 291. Jaras, S. Appl. Catal. 1982, 2, 207. Johnson, M. M.; Tabler, D. C. US Patent 3 711 422, 1973. Magee, J. S.; Blazek, J. J. In Zeolite Chemistry and Catalysis; ACS Monograph 171; Rabo, J. A., Ed.; American Chemical Society: Washington, DC 1976; p 615. McIntosh, C. H. “Effect of Metal Oxides on Cracking Catalyst Activity and Selectivity,” Presented at the 126th National Meeting of the American Chemical Society, Sept 1954.
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Received f o r review August 8, 1986 Accepted December 22, 1986
Carbon Monoxide Hydrogenation Using Manganese Oxide Based Catalysts: Effect of Operating Conditions on Alkene Selectivity Richard G. Copperthwaite, Graham J. Hutchings,* Mark van der Riet, and Jeremy Woodhouse Department of Chemistry, University of the Witwatersrand, Johannesburg 2001, Republic of South Africa
A comparative study of non-alkali-promoted iron/ and cobalt/manganese oxide matrix catalysts for CO hydrogenation is reported. Iron/manganese oxide is less active than the cobalt/manganese oxide catalyst and also gives appreciably higher methane and decreased alkene yields. The alkene/alkane ratio is dependent on space time and conversion, and a t constant conversion/space time the effect of reaction pressure is also found to be significant. The results are explained in terms of primary alkene selectivity and subsequent secondary alkene hydrogenation. The high secondary hydrogenation activity of these catalysts is confirmed by using model ethene hydrogenation studies. In addition, a distinct but short-lived catalytic hydrogenation function for pure MnO is reported which is rationalized in terms of the defect structure of MnO. In recent years there has been considerable interest in the study of carbon monoxide hydrogenation catalysts that demonstrate high selectivities for the production of Cz-C4 alkenes. Particular interest has centered on catalysts exhibiting strong metal support interactions for metals supported on, or in solid solution with, a partially reducible oxide, e.g., MnO (Kugler, 1980). For a number of years it has been known that Fe/Mn oxide catalysts can give high alkene selectivity with low methane selectivity (Kolbel and Tillmetz, 1976; Bussemeier et al., 1976). These catalysts are known to contain ironjmanganese oxide solid solutions (Hutchings and Boeyens, 1986) and have been termed matrix catalysts (Schulz, 1985). Cornils et al. (1984) have shown that the yield of C2-C4alkenes with this type of catalyst is highly dependent on the reaction conditions. By modeling the reaction conditions, it was shown that increases in (a) conversion, (b) catalyst packing height, and (c) reactor tube diameter all decreased the C2-C4 selectivity. In addition, Schulz and Gokcebay (1984) have shown that for matrix catalysts of this type, variation in the CO/H2 ratio has little effect on the alkene selectivity. Barrault and co-workers (1983a,b: 1984; 1985) reported very high yields of C2-C4alkenes for low iron concentration matrix catalysts which were maintained for ca. 100 h; however, these results were obtained at atmospheric
* To whom correspondence
should be addressed.
pressure, and the catalyst activity was very low. The majority of published data on these matrix catalysts have been obtained at atmospheric pressure, and the activities quoted require considerable improvement if these catalysts are to have potential industrial interest. A typical procedure to secure such an improvement is to utilize an increased reaction pressure, but the effect of this parameter on alkene selectivity with these catalysts has received scant attention. We have recently reported (van der Riet et al., 1986) a stable cobalt/manganese oxide catalyst that demonstrates high alkene selectivity at elevated pressures. In this paper, we now wish to report our findings on the effect of reaction conditions on alkene selectivity of the manganese oxide matrix catalyst containing comparable amounts of iron and cobalt.
Experimental Section Catalyst Preparation. Coprecipitated cobalt/manganese catalyst (Co:Mn = 1:l by mass) and iron/manganese catalyst (Fe:Mn = 1:l by mass) were prepared by continuous coprecipitation at pH 8.3 and 70 OC by using the method of Maiti et al. (1983). The precipitate was collected by filtration, washed with distilled water, and dried at 110 OC and 10 kPa. Catalysts were pelleted, ground, and sieved to give particles (0.5-1.1%” diameter) which were calcined in air at 500 “C, 24 h, and then loaded into the reactor. Catalysts were reduced in situ in
0888-5885/ 87/ 2626-0869$01.50/ 0 0 1987 American Chemical Society
870 Ind. Eng. Chem. Res., Vol. 26, No. 5 , 1987 Table I. CO Hydrogenation Using Fe/MnO and Co/MnO Catalysts catalysta pressure, kPa GHSV, h-' temp, "C CO conversion, % hydrocarbon selectivity, % by mass
c1 C, c3 c4
c5+
total alcohols'
Co:Mn = 1:l
Fe:Mn = 1:l 600 275 220 6.0
600 280 250 19.0
350 555 300 5.6
600 555 300 33.4
850 555 300 36.2
350 86 300 27.4
600 269 300 57.1
850 351 300 71.3
350 232 190 1.6
600 264 190 38.6
850 285 190 42.9
350 100 190 23.7
850 352 190 44.3
600 250 220 43.0
4.4 5.1 6.3 13.1 64.0 7.1
6.3 6.8 8.5 9.5 42.4 2.8
10.3 8.5 9.5 7.5 64.3 0
13.0 9.8 12.4 11.0 53.8 0
14.4 10.8 15.0 12.8 47.0 0
27.5 19.9 21.9 11.9 18.8 0
18.2 12.9 20.1 14.5 33.6 0.7
15.9 11.9 18.8 13.1 37.8 2.5
2.8 2.7 5.6 3.6 85.2 0
11.5 10.0 21.5 12.9 43.8 0.3
7.0 7.1 17.9 10.0 58.0 0
5.9 3.9 7.0 4.8 77.9 0.5
10.5 9.3 22.8 13.1 43.2 1.1
8.5 6.9 19.8 10.0 46.9 7.9
Catalyst (2 g) stabilized a t each condition for 24 h prior to data collection. Initial stabilization period Fe/Mn = 60-80 h, Co/Mn = 100 h. bMeasured a t 101.3 kPa, 25 "C. Mainly C,-C5 primary alcohols, determined by analysis of aqueous liquid products.
l-k
Figure 1. Schematic representation of the experimental apparatus: (1)CO/H2 or ethene; (2) H,;(3) N,; (4) rotameter needle valve; (5) reactor with built-in preheater section; (6) electrically heated line; (7) condensation vessel, 20 "C; (8) back-pressure regulator range, 100-1500 kPa; (9) gas chromatograph. Only one reactor and gas feed/analysis system is shown. In the experimental work, six parallel reactors were used.
the reactor with hydrogen at 400 "C, gas hourly space velocity (GHSV) 200 h-', and 100 kPa. Catalyst Testing. CO hydrogenation was carried out by using a multi-fixed-bed laboratory reactor as shown schematically in Figure 1 which enabled the testing of catalysts under identical experimental conditions. The detailed design of the reactor (Korf and Espinoza, 1986) is shown in Figure 2. The reactors were made of 316 stainless steel with an internal diameter of 14 mm. The reactor consisted of three distinct sections: (i) a preheater filled with 1-mm stainless steel balls/ground glass balls that enabled thorough mixing and heating of the reactants, (ii) the reactor section containing 2 g of catalyst, and (iii) a postreactor wax trap filled with 5-mm glass beads. Preheated gas and catalyst temperatures were measured by using thermocouples located at position shown in Figure 2. For all data quoted in this paper, temperature control was better than i0.5 "C, and for all conditions no exotherms were observed in the catalyst bed. Premixed synthesis gas CO/H2 = 1 by volume (the CO/H2 ratio was fixed at unity for this study), C2H4/H2,or CO/CzH4/H2 mixtures were fed to the combined preheater/reactor at flow rates controlled by using rotameter needle valves, whilst pressure control was achieved by using a backpressure regulator located downstream of the reactor. Liquid products were condensed immediately after the reactor and analyzed by using off-line gas chromatography (30-m J+W DB-1 capillary column). Gas products were determined by on-line chromatography capable of analyzing for hydrocarbons (2-m, '/&. stainless steel Poropak Q and FID) and CO, COz, Hz, N2 (2-m, l/s-in. stainless steel Carbosphere and TCD). Alkene/alkane ratios for Cz and C3hydrocarbons could satisfactorily be obtained from the on-line analysis; the alkene/alkane ratio for C4 hydrocarbons was obtained by off-line gas chromatography
Figure 2. Reactor key: (1)thermocouple leads; (2) gas feed line; (3) solder seal; (4) '/&. Swagelok T-union; (5) Swagelok male NPT union; (6) M5 Allen-capped hardened steel bolts; (7) upper flange; (8) reactor body; (9) Helioflex HNlOO seal; (10) perforated top plate of the preheater; (11)perforated I/&. tube in preheater containing 4 x 1/16-in.thermocouples; (12) ground glass granules (1-2 ")/stainless steel (1 mm) balls; (13) preheater thermocouple; (14-16) catalyst chamber thermocouples; (17) bottom plate of preheater; (18) stainless steel grid to retain catalyst; (19) 1/4-in.Swagelok male NPT union.
(2-m, '/s-in. stainless steel Graphpac (+0.19% picric acid) and FID). For d data quoted, satisfactory mass balances, typically between 95-105% , were observed. Test experiments showed that blank thermal reactions in the absence of catalysts were negligible at and below 300 OC.
Results and Discussion Carbon Monoxide Hydrogenation. Carbon monoxide hydrogenation was tested using both the iron/manganese oxide and the cobalt/manganese oxide catalysts, and representative results are shown in Table I. A t comparable reaction conditions, the Fe/MnO catalyst was much less active than the Co/MnO catalyst, and hence to obtain data at equivalent conversions, the Co/MnO was investigated at 190 "C, whereas the Fe/MnO catalyst required a temperature of 300 "C. The catalysts also exhibited significant differences in the observed selectivities; in
Ind. Eng. Chem. Res., Vol. 26, No. 5, 1987 871 6r
20
U
5 L
-
51
12
(10’’
)
16 20 Space Time h
24
Figure 5. Alkene/alkane ratio vs. space time, Co/MnO catalyst, 190 O C : (A)350, (m) 600, ( 0 ) 850 Wa.
w 3
-
0
1
\
\ c
C
1 -=2
-
I t
2. 3
Od
10
5 (10’’
)
15
Space Time h
Figure 4. Alkene/alkane ratio vs. space time, Fe/MnO catalyst, 300 OC: (A)350, (El) 600, ( 0 ) 850 Wa.
1 -
particular, the Fe/MnO usually gave comparable amounts of C2, C3, and C4 hydrocarbons, whereas the Co/MnO catalyst produced low yields of C1 and C2 hydrocarbons together with a high C, selectivity. For the Co/MnO catalyst, the selectivity to total C3 hydrocarbons increased steadily with increasing conversion (Figure 3), whilst the CHI yield was usually
