New directions for COS hydrolysis: Low temperature alumina catalysts

Abstract

Carbonyl sulphide hydrolysis using two alumina catalysts (surface areas 150 m2g- 1 and 300m2g- 1) has been studied. Previous studies have focused upon concentration ranges for the reactant ([COS] typically > 1000 ppm) and temperatures (typically > 100 °C) that are much higher than those encountered commercially. In the study presented here, the concentration of carbonyl sulphide is 150 ppm, reactor pressure (125 – 187 kPa) and temperatures in the range of 30 – 250 °C. At the higher temperature (250 °C) the data collected are in agreement with previous studies and the reaction follows Langmuir Hinshelwood kinetics with the surface hydrolysis of a thiocarbonate being the rate determining step. Data obtained at lower temperature (30 – 60 °C) indicates that the rate of COS hydrolysis decreases monotonically with increasing [H2O]. These data are consistent with Langmuir Hinshelwood kinetics where the products are not adsorbed and either (a) the adsorption of COS is rate determining or (b) the surface reaction of adsorbed COS and an intermediate derived from H2O is rate determining. The current experimental data cannot differentiate between these possibilities. Using present test conditions it is apparent that the surface area of the alumina catalyst is an important design parameter, a feature not observed in previous high temperature studies.