Environ. Sci. Technol. 1999, 33, 2241-2246
Low Temperature Catalytic Oxidation of Hydrogen Sulfide in Sour Produced Wastewater Using Activated Carbon Catalysts AJAY K. DALAI,* A. MAJUMDAR, AND ERIC L. TOLLEFSON Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Canada T2N 1N4
A process is proposed for the removal of H2S from sour produced wastewater at lower temperatures ( 130 °C), 16.9 (T < 130 °C) 34.2 (125-200)
fixed
21.3 (8-24)
CFSTR
0.24
fixed fixed fluidized fixed fixed
Liquid-phase oxidation.
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Glossary CA CA 0 k n rA vo V XA
concentration of A at time t (µmol/L) initial concentration of A in the feed (µmol/L) specific reaction rate (µmol/L)0.74(1/min) order of the H2S oxidation reaction rate of the reaction (µmol/(L min)) volumetric flow rate of sour water (L/min) volume of the CFSTR (L) conversion of sulfide to sulfur and water
Literature Cited FIGURE 5. Temperature dependency of the reaction (eq 2) according to the Arrhenius equation. 1010 (µmol/L)0.76(1/min), respectively. These data are only valid for solutions being oxidized at pH values of 4.5. The rate equation obtained may be used in designing a pilot/ commercial CFSTR for one/multi stage liquid-phase oxidation of low concentrations of H2S. The apparent activation energy of the oxidation reaction is 21.3 kJ/mol, which is compared with values for gas-phase oxidation using activated carbon in Table 3. The value obtained in the present study is in close agreement with those obtained by other investigators. The difference in some values could be due to the types of activated carbon used as catalysts in various studies and the procedure used in its preparation (16) and/or due to the difference in the chemical nature of these porous materials (26). For example, active carbon obtained from sugar charcoal resulted in higher activation energy (37 kJ/mol) compared to that with carbon obtained from coconut shell (25.6 kJ/mol), showing that the former was more porous with low intraparticle diffusiosal resistances. The low calculated value for activation energy in the present case could indicate that there was, in most cases, a large influence of intraparticle diffusion on the observed rates. It may be noted that there was negligible effect of external diffusional resistances on the overall rate since this process was performed in a CFSTR with a high stirring rate. Similar low values of activation energies 23.6, 6.7-30, and 20.1 kJ/mol for the gas-phase H2S oxidation reaction on carbon catalyst had been observed by Ghosh and Tollefson (15), Sreeramamurthy and Menon (27), and Cariaso and Walker (28), respectively. These low values, despite high-temperature operations, could be due to the strong influence of external and intraparticle diffusional resistance on the overall rates of reaction. In all of these processes, the reactions are not surface-reaction controlled. The reactor pressure, due to liquid-phase reaction at low temperatures, may not influence the activation energy of the process. To exploit this process further, one could use two or more CFSTR reactors in series so as to achieve complete conversion of H2S in sour water.
Acknowledgments The authors wish to recognize the contributions made by Ms. Aimin Yang and Mr. Jian Liu for conducting some of the experiments toward the end of the project. The funding for the work was provided by the Canadian Gas Processors and Suppliers Association while the feed gas was supplied by Petrogas Processing Ltd., Balzac, Alberta. Both are gratefully acknowledged. 2246
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Received for review August 6, 1998. Revised manuscript received April 6, 1999. Accepted April 13, 1999. ES9808088
