Fluidised bed reactor studies of H2S decomposition over supported bimetallic Ru catalysts

H2S is produced in large quantities in the coal, petroleum and mineral processing industries. The decomposition of H2S to recover both salable sulphur and H-2 which may be recycled for further re-use in upstream hydrodesulphurisation (HDS) units is important in the context of zero-pollutant discharge. Several transition bimetallic sulphide catalysts (with Ru as a constant ingredient) were evaluated in a fluidised bed reactor operated at 160 kPa and 883-1003 K. The Ru-Mo pair emerged as the "best" catalyst for H-2 production. The activity of the catalysts was well correlated with the same electronic and metal sulphur bond properties, A-character, seen for HDS reactions. The Ru-Mo catalyst exhibited a first order kinetics in H2S partial pressure with an activation energy of 69.7 kJ mol(-1). Due to thermodynamic limitations Ha yields are low. This study shows that H2S conversions in a fluidised bed reactor may be higher than those obtained from a fixed bed configuration operating under same flow conditions. Indeed, conversions in the fluidised bed reactor were higher than equilibrium values near minimum bubbling conditions at all the temperatures examined. However, as the flow rate increased beyond this point, conversion dropped significantly probably due to the onset of slugging. This improved conversion was attributed to the "membranous effect" in the fluidised bed since reaction occurs primarily in the emulsion phase and the migration rate of the relatively low molecular weight H-2 product from the catalyst-containing emulsion phase to the solid-free bubble phase helped to shift the reversible reaction in favour of hydrogen. (C) 1999 Elsevier Science B.V. All rights reserved.