Role of a phenolic pool in the conversion of m-cresol to aromatics over HY and HZSM-5 zeolites

• m-Cresol is irreversibly trapped by HZSM-5 and HY zeolites in the 400–600 °C range.
• At high temperatures, trapping is less while production of aromatics increases.
• Condensed products on the surface lead to the formation of a phenolic pool.
• The benzene/toluene ratio in the products increases with temperature.
• Changes in selectivity are not due to secondary reactions of toluene to benzene.

The conversion of m-cresol over two acidic zeolites has been studied on a micro-pulse reaction system in the temperature range of 400–600 °C. The zeolites were HZSM-5 and HY and had the same Si/Al ratio of 40. At 400 °C both zeolites were found to be highly efficient in trapping irreversibly the phenolic reactant. As the temperature increased, the extent of phenolic trapping was lower, resulting in a reduced amount of carbonaceous deposits, while the coke became more graphitic. While m-cresol only produced isomerization and transalkylation vapor phenolic products, the vast majority of the amount of injected m-cresol resulted in condensed products on the surface that lead to the formation of a phenolic pool. Therefore, the aromatic hydrocarbons that dominate the reactor output originate from the cracking of the surface pool. At low reaction temperature, toluene is the major pool cracking product, but at higher temperatures the selectivity to benzene increases. Independent measurements of toluene and xylene conversion, under the same conditions, indicate that these changes in selectivity are not due to secondary reactions of toluene to benzene, but rather a change in the cracking pattern of the surface pool.

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