3854
Ind. Eng. Chem. Res. 1996, 35, 3854-3860
CO-Catalyzed Conversion of H2S to H2 + S. 1. Reaction between CO and H2S Farhad Faraji, Imre Safarik, and Otto P. Strausz* Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Manuel E. Torres Hydrogen Research and Technology, Alberta Energy, 9945-108 Street, Edmonton, Alberta, Canada T5K 2G6
Erdal Yildirim Syncrude Canada Ltd., 9421-17 Avenue, Edmonton, Alberta, Canada T6N 1H4
The first step in the two-step CO-catalyzed conversion of H2S to H2 and sulfur, reactions 1 and 2, has been studied in order to establish the optimal experimental conditions for the reaction. Without a catalyst, H2S conversions of the order of only 1-2% could be achieved. NiS on alumina proved to be an efficient catalyst, and at 267 °C, H2S conversions reached 52% or 100% of the thermodynamic limit. Small amounts of CO2 and CS2 have also been detected among the products. In comparative experiments using CoS on alumina as the catalyst, up to 67% conversion, representing 100% of the thermodynamic equilibrium H2 yield, could be achieved at a substantially lower temperature, 177 °C. Furthermore, formation of CO2 and CS2 was found to be negligible ( [CO]/ [H2S] > 0.1) were determined at 200, 250, and 350 °C and at flow rates between 21 and 29 mL/min, corresponding to 25-30-s residence times. The effect of the catalyst, as can be seen from the data presented in Table 3, is spectacular: in less than half a minute, up to 84% H2S conversions, based on the thermodynamic equilibrium value, could be achieved. The highest H2 yields were obtained at 350 °C; the H2S conversions fell with decreasing temperature, but even at the lowest temperature, 200 °C, the reaction proceeded with measurable rate. At 350 °C, H2 and COS were formed in equal amounts as required by the reaction stoichiometry, but at lower temperatures, the [COS]/[H2] ratios exceeded unity, indicating the intervention of reaction 5. After having confirmed the high catalytic activity of NiS on alumina, detailed quantitative studies com-
Ind. Eng. Chem. Res., Vol. 35, No. 11, 1996 3857 Table 4. Nickel Sulfide Catalyzed H2S + CO h H2 + COS Reaction at T ) 253 °C and (PCO/PH2S)initial ) 0.81 as a Function of Residence Time % H2S conversion with respect to thermodynamic theoretical limit
exptl
residence time, s H2S/COS COS/H2 60 49.1 33.8 25.7 21.6
4.05 4.25 4.38 4.92 5.49
1.01 1.01 1.01 1.01 1.02
exptl 19.80 19.06 18.57 16.89 15.41
21.15 21.15 21.15 21.15 21.15
93.6 90.1 87.8 79.9 72.8
Table 5. Nickel Sulfide Catalyzed H2S + CO h H2 + COS Reaction at T ) 253 °C and (PCO/PH2S)initial ) 1.0 as a Function of Residence Time % H2S conversion
exptl
theoretical
with respect to thermodynamic limit
20.51 19.21 18.28 17.70 15.35 14.55 13.28 12.65 11.78
22.90 22.90 22.90 22.90 22.90 22.90 22.90 22.90 22.90
89.6 83.9 79.8 77.3 67.1 63.6 58.0 55.2 51.5
exptl
residence time, s H2S/COS COS/H2 49.1 33.8 28.4 23.5 15.4 13.5 10.8 9.8 9.0
3.88 4.21 4.47 4.65 5.51 5.87 6.53 6.91 7.49
1.01 1.01 1.01 1.01 0.99 1.01 0.99 1.00 1.02
Table 6. Nickel Sulfide Catalyzed H2S + CO h H2 + COS Reaction at a Residence Time of 60 s and (PCO/PH2S)initial ) 0.9 as a Function of Temperature % H2S conversion
% CO2
exptl
theoretical
with respect to thermodynamic limit
