Sulfur Evolution Reaction during Reduction of SO2 with CO over Carbon Materials

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 degrees 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.