Effect of Waste Tires and Waste Tire Components on Hydrocracking and Heteroatom Removal Reactions Using Model Systems

Abstract

The effect of waste tires and waste tire components, such as styrene butadiene rubber (SBR), carbon black, and solid residues from waste tire liquefaction, on hydrocracking reactions that occur in coal and waste tire coliquefaction was evaluated using the model compound 4-(1-naphythylmethyl)bibenzyl (NMBB). The reactions were performed thermally and catalytically using slurry phase catalyst precursors including molybdenum naphthenate, iron naphthenate, and other iron precursors. The reaction conditions were 400 °C for 30 min with a H2 pressure of 8.7 MPa introduced at ambient temperature. Carbon black was active for hydrocracking NMBB and selective for cleaving the naphthyl−methylene bond and resulted in 79.1 ± 2.7% hydrocracking while the waste tires themselves, SBR, and untreated solid waste tire residues were not active, yielding between 11.3 ± 2.2 and 32.5 ± 3.1% hydrocracking. However, when the residue from the liquefaction of waste tires was heat-treated and then reacted with NMBB, the treated residue showed substantial activity for promoting hydrocracking. The amount of activity was dependent upon the composition of the residue. The heat-treated carbon black-rich residue yielded 52.9 ± 1.7% hydrocracking while the mineral-rich residue yielded 99.7 ± 2.1%. Higher activity was obtained when the residues were reacted in the presence of molybdenum naphthenate and excess sulfur. In addition, the effect of carbon black and heat-treated residues from waste tires reacted individually and in conjunction with molybdenum naphthenate was examined for heteroatom removal and hydrogenation of dibenzothiophene and 5-methyl-8-(1-methylethyl)dibenzothiopen-4-ol (MMDH). Carbon black and the heat-treated residues, particularly in conjunction with molybdenum naphthenate and excess sulfur, promoted these reactions. The substituted MMDH was more reactive and responsive to catalytic promotion by these agents than was its unsubstituted analogue, dibenzothiophene.