On the Formation of COS from H2S and CO2 in the Presence of Zeolite/Salt Compounds

A gaseous mixture of hydrogen sulphide and carbon dioxide (20% H 2 S, 80% CO 2 ) was brought into contact at 25°C with NaY and NaX zeolites in an as-synthesized form as well as after modification by the inclusion of salts (NaCl, NaBr) in the small cages of the aluminosilicate framework and ion exchange with aqueous CaCl 2 solution. At small contact times (5 h), the degree of conversion of H 2 S according to the reaction H 2 S + CO 2 → COS + H 2 O by the various samples was found to follow the sequence NaY/NaCl ≈ NaY/NaBr ≈ NaX/NaCl(CaCl 2 ) < NaY « NaX/NaCl ≈ NaX. Long-term runs with NaY and NaY/NaBr revealed that the latter zeolite retained a very low level of H 2 S conversion for contact times as long as 250 h. It is concluded that such low H 2 S conversion requires the absence of low-coordinated sodium cations in the supercages or their replacement by calcium ions, and blocking of the β-cages with salt anions.