Determination of rate constants for the reaction between diglycolamine and carbonyl sulphide

Abstract

The kinetics of the reaction between carbonyl sulphide (COS) and aqueous 2-(2-aminoethoxy) ethanol (diglycolamine or DGA) were investigated over a temperature range of 307 to 322 K and pressure range of 345–414 kPa. A gas-liquid contactor was designed to simulate a single tray in an absorption column. The contactor was operated isothermally with both the gas and liquid feeds continuous, the liquid being perfectly mixed. In the contactor, the gas was sparged through the aqueous DGA solution using a fritted plate and the froth spilled over a weir where the gas disengaged from the amine solution. Good material balance closure verified that the reactor could be used to obtain absorption rate data. The carbonyl sulphide and other components in the amine solution were analysed with a gas chromatographic (GC) technique developed as a part of this work. The GC analysis could be performed in less than 10 min and comparison of the results from the GC technique with material balance closure showed excellent agreement. The experimental data were correlated by assuming the reaction to be kinetically controlled. The observed reaction rates were significantly larger than those for the COS/H2O system. Therefore, it was concluded that DGA had a catalytic effect on the COS hydrolysis reaction. The analysis indicated that the reaction followed a second-order rate equation: first-order in COS and first-order in DGA. Justification for assuming kinetic control of the absorption was demonstrated by doubling and tripling the stirring speed which produced no significant change in the absorption rate (mol s−1). Another series of tests were carried out which showed that the absorption rate (mol s−1) was proportional to the reactor volume. In addition, the activation energy was out of the range of ordinary mass transfer control.