Interplay of Metal-Acid Balance and Methylcyclohexane Admixture Effect on n-Octane Hydroconversion over Pt/HUSY

Abstract

Hydroconversion feeds are mixtures comprising alkanes and cycloalkanes, for which the binary impact on the respective reaction pathways, is still not completely understood. Methylcyclohexane admixture on n-octane hydroconversion over Pt/HUSY catalysts has been investigated using the pure compounds and their equimolar mixtures in a wide range of operating conditions. The hydroconversion behavior on catalysts with various Pt loading was examined to investigate the role of the active sites. No impact of methylcyclohexane admixture to n-octane was observed over catalysts which ensured ideal hydrocracking (0.5 and 0.1 wt%Pt). In contrast, methylcyclohexane addition decreased the octane isomer yield at iso-conversion over 0.07 wt%Pt/HYUSY. A lower metal loading of 0.04 wt%Pt led to a pronounced decrease in n-octane conversion in the mixture. The methylcyclohexane conversion was not affected by n-octane addition regardless of the metal-acid balance. The negative admixture impact on the n-octane conversion and isomers yield, combined with the absence of any impact on the methylcyclohexane behavior, was attributed to preferred cycloalkane adsorption on metal sites, resulting in a reduced metal site availability for alkanes. A cycloalkane admixture to an alkane in hydrocracking can, hence, induce a regime shift from ideal to nonideal hydrocracking. Consequently, bifunctional catalysts developed purely for alkane hydroconversion may prove not to be optimal for realistic feeds, including cycloalkanes.