A high-temperature experimental and modeling study of homogeneous gas-phase COS reactions applied to Claus plants

A high-temperature experimental and modeling study of the key reactions occ urring in (CO2 + H2S) and (CO + H2S) mixtures is reported. The experiments were conducted under dilute conditions (dilution >98%) in tubular flow reac tors over a temperature range of 800-1200 degrees C at pressures of 120-160 kPa. The corresponding gas residence time ranged from 0.5 to 2.0 s. The ex perimental results showed a negligible amount of COS formed from reactions of CO2 with H2S and with sulfur, contrary to popular belief. Hydrogen sulfi de decomposition into hydrogen and sulfur plays a critical role in the form ation of CO and COS and can be described by the simple rate expression: (- r(H2S)) = k(1)C(H2S)C(M), where C-M is the molar concentration of the colli sional molecule (N-2) and the rate constant k(1) = 1.68 +/- 0.86 x 10(11) e xp [(-28940 +/- 840 K)/T] m(3)/(kmols). Further, the reaction of CO with H2 S was found to be rapid and equilibrium COS conversions were attained in le ss than 700 ms at temperatures greater than 1000 degrees C. The COS forming reaction between CO and H2S could be represented by the rate expression (r (COS)) = k(3)C(CO)C(H2S)(0.5), where the rate constant k(3) = 1.59 +/- 0.86 x 10(5) exp[(-13340 +/- 930 K)/T] (m(3)/kmol)(0.5)/s. In a (CO2 + H2S) mix ture, the hydrogen produced from H2S decomposition reacts with CO2 to form CO. Finally, the rate of CO formation could be described by the following r ate expression: (r(CO)) = k(4)C(CO2)C(H2)(0.5), where k(4) = 3.95 +/- 0.35 x 10(10) exp[(-31220 +/- 180 K)/T] (m(3)/kmol)(0.5)/s. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.