Ring contraction and selective ring opening of naphthenic molecules for octane number improvement

Different catalytic strategies have been evaluated to maximize the production of non-aromatic compounds with high octane number, starting from naphthenic molecules, which are typically obtained from the saturation of aromatics. The research octane number (RON), the motor octane number (MON), and the specific volume of the product mixtures were evaluated in each case. The product distribution obtained on acidic and Pt-containing zeolites was investigated in the temperature range 533-563 K in the presence of hydrogen at a total pressure of 2 MPa. It was found that skeletal isomerization (ring contraction) was the primary reaction in both HY and Pt/HY catalysts. The presence of Pt was found to enhance the stability of the catalyst, but also greatly altered the distribution of RC products, enhancing 1,1-dimethylcyclopentane. This enhancement can be explained in terms of a higher rate of hydride transfer caused by the presence of the metal. Evaluation of the octane numbers of the product indicated that a mixture of RC products results in rather high RON, but the MON and specific volume were about the same as that of the feed. To improve MON and specific volume an Ir/SiO2 catalyst with high hydrogenolysis activity was added to realize the ring opening (RO). The combination of RC and RO was tested on physical mixtures and segregated beds of WHY and Ir/SiO2 catalysts in order to optimize the production of the iso-alkanes with highest octane number. It was found that with segregated catalyst beds, a better control of the selective breaking of C-C bonds of RC isomers can be achieved, which optimizes octane number and specific volume. (C) 2007 Elsevier B.V. All rights reserved.