Sulfur in tire-derived oils and modified catalysts for sulfur reduction

Abstract

A number of contaminating sulfur compounds of about 1.4-1.5 wt% in tire-derived oils are a problem of not only the oil properties but also environmental regulations. This reason leads to the development of strategies for simultaneous cracking process of tire together with sulfur content reduction. The combination of catalytic pyrolysis of waste tire and desulfurization are required in order to obtain light oil with the lowest sulfur levels by using cracking and desulfurizing catalysts. The high sulfur levels in the oil products can be diminished by using a rhodium catalyst because it was found to has both cracking and desulfurization ability. In this work, Rh supported on different zeoilites (KL, HY, and HBETA) were investigated for the influences of the supports. Moreover, regenerated commercial sulfide NiMoS/AL₂O₃ and fresh CoMoS/Al₂O₃ catalysts were also used as a catalyst for the pyrolysis of waste tire since they contain both acid and metal sulfide functions that could potentially benefit cracking and sulfur removal simultaneously. It was found that 0.25 wt% Rh/HBETA increased gas yield, especially the cooking gas with the lowest of liquid product, and resulted in the transformation of sulfur in oil to H₂S gas and the remaining 0.75 wt% of sulfur in pyrolysis oil. It also was observed that the introduction of Rh led to remarkable formation of mono-aromatics. The commercial hydrodesulfurization catalysts had less cracking activity than 0.25 wt% Rh/HBETA, so they gave less gas yield but high selectivity to light alkane gas product. The quality oil reached the lowest sulfur in oil (0.55 wt%) by using CoMoS/Al₂O₃ catalyst. However, the sulfur species found the most in this study were benzothiophene derivatives.