To develop a new method to recover
elemental sulfur from the desulfurization process, a study on the
sulfur evolution mechanism during the reduction of SO2 with
CO over carbon was carried out. Thermodynamic equilibrium calculations
showed that the elemental sulfur, as well as CO2, is the
primary product of SO2 reduction with a CO/SO2 ratio of 2. Carbonyl sulfide (COS), instead of elemental sulfur,
became the primary S-containing product with a CO/SO2 ratio
of 3. Moreover, it decomposed to CO and elemental sulfur at temperatures
above 500 °C. Experimental results showed that during the CO–SO2 reaction over carbon materials, COS was formed as a byproduct
in the gaseous phase and elemental sulfur was generated following
a COS intermediate mechanism. In the solid phase, SO2 reacted
with the carbon surface to form oxidized S-containing compounds and
these compounds were reduced by CO. COS did not reduce the oxidized
S-containing compounds but combined with the carbon matrix to form
reductive compounds. The abundant pore structure of the carbon surface
was beneficial for SO2 reduction, as it enhanced the generation
of oxidized S-containing compounds. Moreover, high Fe2O3 content improved the reactivity due to the formation of metallic
sulfides.