Coke Formation during Thermal Decomposition of Methylcyclohexane by Alkyl Substituted C₅ Ring Hydrocarbons under Supercritical Conditions

Abstract

In this study, a mechanism for coke formation of methylcyclohexane (MCH) was investigated by sampling products in a batch type reactor during thermal decomposition. Alkyl substituted C5 ring hydrocarbons, which have a 5-member ring structure with alkyl groups as side chains, were the major products of thermal decomposition of MCH before coke formation (below 465 °C). The composition of alkyl substituted C5 ring hydrocarbons gradually increased without any decrease during the reactions before coke formation. The composition of alkyl substituted C5 ring hydrocarbons decreased after considerable increase, when coke formation occurred as 0.084 g coke/ml MCH for 10 h at 465 °C. Coke was formed via an increase in polycyclic aromatic hydrocarbons (PAHs). Based on this result, it was hypothesized that the abundance of alkyl substituted C5 ring hydrocarbons caused the formation of PAHs and coke. To identify the role of alkyl substituted C5 ring hydrocarbons on coke formation, thermal decomposition of MCH with 1,2,3,4-tetrahydroquinoline (THQ) was performed. THQ was used as the hydrogen donor, which inhibited coke formation. When coke formation was completely inhibited with 5.0 wt % THQ at 465 °C, the composition of all alkyl substituted C5 ring hydrocarbons decreased compared to the experiment without THQ. In addition, PAHs were not completely formed throughout the reaction. These results demonstrated that an abundance of alkyl substituted C5 ring hydrocarbons caused the formation of PAHs, which were precursors for coke under supercritical conditions.