Reaction Pathways of 1-Cyclohexyloctane in Admixture with Dodecane on Pt/H–ZSM-22 Zeolite in Three-Phase Hydroconversion

Abstract

Isomerization and hydrocracking of a mixture of 1-cyclohexyloctane and dodecane were performed on Pt/H-ZSM-22 in a three-phase Robinson Mahoney reactor with complete internal mixing (T=523–543 K, P=7–8 MPa, H2/HC=5). The reaction products from 1-cyclohexyloctane were analyzed in detail and compared with those obtained in the absence of dodecane in a fixed-bed vapor-phase reactor (T=460 K, P=0.45 MPa, H2/HC=450). In the presence of dodecane, the main reaction pathway involved contraction of the six-membered ring to a five-membered ring with concomitant elongation of the octyl chain by one carbon. Subsequently, the nonyl chain underwent methyl branching at carbon positions far from the ring. Methyl branching rearrangements of the cyclohexane ring of 1-cyclohexyloctane were suppressed in the presence of dodecane. In the reaction product fraction of heptylmethylcyclohexanes, all cis–trans and positional isomers were formed except the 1,1′-heptylmethylcyclohexane isomer. The isomer distributions were explained with pore mouth and key–lock catalysis. Pt/H-ZSM-22 did not favor the paring reaction. The distribution of cracked products, and especially the abundant formation of alkylcyclopentanes, was in agreement with cracking through β-scission in the chain rather than by ring dealkylation typical of the paring reaction. Ring opening in 1-cyclohexyloctane and its isomers is a less important side reaction.