2009 Volume 52 Issue 6 Pages 341-350
Hydroconversion of methylcyclohexane was conducted over various noble metal-loaded catalysts at 493 K and atmospheric pressure. On the bases of the proposed reaction route and the rate of reaction over Ir/H-β zeolite, which was the best catalyst examined, we concluded that the low yield of the desired dimethylpentanes (18%) and high yield of undesired methylhexanes (25%) were due to two reasons: (1) formation of ethylcyclopentane with high selectivity at low conversions and (2) higher ring-opening rate of ethylcyclopentane (a precursor of methylhexanes) than that of dimethylcyclopentanes (a precursor of dimethylpentanes). In order to improve the yield of dimethylpentanes, two catalysts for ring contraction from methylcyclohexane to ethyl- or dimethyl-cyclopentanes (Pt-H4SiW12O40/SiO2 or Pt/H-β) and for ring opening of the produced cyclopentanes (Ir/Al2O3) were used either in one reactor as a physical mixture or in two separate reactors connected in series. When the physical mixture (Pt-H4SiW12O40/SiO2 and Ir/Al2O3) was used, there was only a slight increase in the dimethylpentanes yield (20%) with a large amount of undesired products, such as monobranched heptanes and cracked products. In contrast, when two consecutive reactors packed with Ir/H-β and Ir/Al2O3 were used, the yield of dimethylpentanes increased to 30%, which was nearly two times of that of methylhexanes, at a 65% conversion of methylcyclohexane, while the yield of undesired methylhexanes was about 15%.
