Catalysis and absorption behaviors of the shelled-hollow CaO-MgO microspheres on product distributions and desulfurization during waste tire fast pyrolysis

Fast pyrolysis is an efficient technology in recycling waste tires (WT). However, relatively more sulfur was found in pyrolysis volatiles during WT fast pyrolysis process than slow pyrolysis, which had negative impacts on the subsequent utilization of pyrolytic products. The short volatile residence time in fast pyrolysis also caused the higher content of heavy hydrocarbon fractions in fast pyrolysis oil, reducing its added value. To improve these deficiencies, shelled-hollow CaO-MgO microsphere materials with improved textural properties were synthesized. Ca-enriched materials presented a better sulfur fixation effect compared with Mg-enriched materials. The solid-state sulfur reached up to 69.39 wt.% by the assistance of Ca₈₅Mg₁₅, and in turn significantly inhibited the formation of oil-S and gas-S. Meanwhile, CaO and MgO jointly catalyzed the aromatization of volatiles with a peak content of 74.56% when using Ca₁₀Mg₉₀. Furthermore, it is worth noting that sulfur was primarily fixed into the solid by reacting metal oxides with sulfur to form sulfide by Ca-enriched materials, while sulfur was trapped in the solid via aromatization reactions in terms of sulfur-containing organic compounds with Mg-enriched materials. These findings could provide insights for guiding the industries to minimize sulfureous volatile formation and improve the oil quality in WTs pyrolysis.