Effects of O₂ on Characteristics of Sulfur Added to Petroleum Coke through Reaction with SO₂

Alberta oil-sands petroleum coke is an abundant byproduct of the upgrading of bitumen. The current study aims to improve the current understanding of sulfur added to the surface of petroleum coke through reaction with sulfur dioxide (SO 2 ) and how this is affected by a large excess of oxygen (O 2 ). Particular focus is given to the distribution and speciation of sulfur within the coke particles, as well as its thermal stability. Petroleum coke was activated in SO 2 with and without O 2 in a packed bed reactor at 600−800 °C. The activated cokes were characterized with electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Cross-sectional analysis with EPMA of activated coke particles revealed that sulfur-rich coke particles (i.e., SIAC) could be produced with and without O 2 . Under low SO 2 (3%), high O 2 (18%) conditions, however, O 2 competitively reacted with coke at 600 °C, and SO 2 only reacted to form a sulfur-rich layer after O 2 had been depleted. Analysis with XPS suggested that the sulfur-rich layer of the coke particles was made up of thiophene from the coke plus carbon−sulfur surface complexes, mainly heterocyclic sulfide and disulfide, while the presence of aliphatic sulfide, thiolactone, and thiol could not be ruled out. TGA and DSC analyses confirmed that sulfur added to activated coke via reaction with SO 2 was not elemental in nature. In both N 2 and air, sulfur added via high-temperature reaction with SO 2 is more thermally stable than that of a commercial SIAC sulfurized at lower temperatures. This may have beneficial implications if these SO 2 activated cokes were to be used to capture mercury, since they could be thermally regenerated with minimal loss of active sulfur surface sites while the captured mercury is collected, avoiding the costly and potentially problematic landfill disposal of Hg-containing activated carbon.