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

Abstract

A high-temperature experimental and modeling study of the key reactions occurring in (CO 2+H 2S) and (CO+H 2S) mixtures is reported. The experiments were conducted under dilute conditions (dilution >98%) in tubular flow reactors over a temperature range of 800–1200°C at pressures of 120–160 kPa. The corresponding gas residence time ranged from 0.5 to 2.0 s. The experimental results showed a negligible amount of COS formed from reactions of CO 2 with H 2S and with sulfur, contrary to popular belief. Hydrogen sulfide decomposition into hydrogen and sulfur plays a critical role in the formation of CO and COS and can be described by the simple rate expression: (−r H 2S )=k 1C H 2S C M , where C M is the molar concentration of the collisional molecule (N 2) and the rate constant k 1=1.68±0.86×10 11 exp[(−28940±840 K)/T] m 3/(kmol s). Further, the reaction of CO with H 2S was found to be rapid and equilibrium COS conversions were attained in less than 700 ms at temperatures greater than 1000°C. The COS forming reaction between CO and H 2S could be represented by the rate expression (r COS )=k 3C CO C 0.5 H 2S , where the rate constant k 3=1.59±0.86×10 5 exp[(−13340±930 K)/T] (m 3/kmol) 0.5/s. In a (CO 2+H 2S) mixture, the hydrogen produced from H 2S decomposition reacts with CO 2 to form CO. Finally, the rate of CO formation could be described by the following rate expression: (r CO )=k 4C CO 2 C 0.5 H 2 , where k 4=3.95±0.35×10 10 exp[(−31220±180 K)/T] (m 3/kmol) 0.5/s.