Mechanistic Study of the Carbothermal Reduction of Sulfur Dioxide with Oil Sand Fluid Coke

Abstract

Carbothermal reduction is a reducing reaction involving carbonaceous materials at high temperatures. Oil sand fluid coke is a high-carbon byproduct of the thermal cracking of oil sand bitumen via a process called fluid coking. To lay a foundation for the development of a process that removes and converts sulfur dioxide into elemental sulfur, the kinetics of the carbothermal reduction of SO2 by coke at 700−950 °C was investigated using a packed-bed reactor. Analysis using the shrinking core model revealed that the overall process is controlled jointly by surface chemical reaction and diffusion in a product ash layer. The existence of the layer was confirmed by SEM examination of a cross section of spent coke particles. The activation energy of the overall reaction was found to be 154 kJ/mol, which is in a good agreement with literature values. The sulfur balance was analyzed with data obtained using a total sulfur analyzer and a gas chromatograph. SEM-EDS analysis indicated that the ash layer was low in sulfur. At the ash−coke interface, however, an accumulation of sulfur was found that was attributed to C−S complexes. The chemical states of sulfur in the spent coke were determined using an X-ray photoelectron spectrometer. The sulfur in the raw coke was likely dominated by its thiophenic forms, whereas the sulfur in the ash layer was likely sulfite.