Sulfur speciation in fluid coke and its activation products using K-edge X-ray absorption near edge structure spectroscopy

Abstract

Fluid coke is a by-product of bitumen upgrading process and a stockpiled industrial waste produced in large quantities in Alberta, Canada (overall 10,000 tonnes per day). It has been used as a raw material for manufacturing sulfur-impregnated activated carbon (SIAC). Properties of sulfur in the SIAC are critical to the effectiveness of SIAC in adsorbing mercury at ppb levels. K-edge X-ray absorption near edge structure (XANES) spectroscopy was employed to characterize sulfur in two fluid coke samples and their activation products. It was found that about 90% of sulfur in two coke samples is of organic nature, with over 50% of sulfur in the form of thiophene and the rest 40% being organic sulfide. About 10% of sulfur is in the form of oxides, i.e. sulfate. To simulate the coke samples and validate the analytical technique, a mixture of pure sulfur compounds and graphite was prepared and examined with XANES; the results showed good agreement between the actual and measured sulfur contents in specific forms. XANES results were found to be consistent with X-ray photoelectron spectroscopy (XPS) results. The two techniques are complementary to each other; XANES is capable of distinguishing sulfur species at low oxidation states whereas XPS is able to separate some sulfur species with higher oxidation state. The activation process with KOH and SO2 affected the chemistry of sulfur in fluid coke. XANES surface analysis identified disulfide, sulfide, sulfonate, and sulfate in SIACs and found no thiophene, suggesting a complete removal of thiophene from carbon surface by KOH.