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

Abstract

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 o C. The zeolites were HZSM-5 and HY and had the same Si/Al ratio of 40. At 400 o 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 isomers 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.

Hydride transfer between a phenolic surface pool and reactant paraffins in the catalytic cracking of m-cresol/hexanes mixtures over an HY zeolite

“…In a previous study, we demonstrated that hydride transfer from tetralin was able to reduce coke formation and catalyst deactivation during the conversion of anisole on acidic zeolites [20]. The coke from the reaction of phenolic compounds over zeolites is either phenolic oligomers (i.e phenolic pool) from condensation reaction or polyaromatic (or graphitic) coke from further cracking of the phenolic pool [16].…”

“…Moreover, they tend to accelerate deactivation due to enhanced coke formation and strong adsorption on acid sites of the zeolites [14][15][16][17]. Therefore, to get a full assessment of the pros and cons of the co-processing strategy a detailed investigation of the behavior of these phenolic compounds in zeolites and their influence in the deactivation of hydrocarbons cracking catalysts is necessary.…”

Novel Micro-Mesoporous Composite ZSM-5 Catalyst for Aromatics Production by Catalytic Fast Pyrolysis of Lignin Residues

“…According to the hydrocarbon pool mechanism, in the case of poplar CFP, the major intermediates were polymethylbenzene carbocation. Further, in the case of pure lignin CFP, there was a phenolic pool rather than hydrocarbon pool, of which the intermediates were larger [17,32]. This necessitated higher requirements for the mass transfer and diffusion capacity of the catalyst.…”

Recent research progress on bio‐oil conversion into bio‐fuels and raw chemicals: a review

“…The porous structure and acidity (acid strength and number of acid sites) of zeolites play an important role in coke formation. Larger pore sizes are beneficial to enhance the accessibility of oxygenates to active sites, although large molecules are trapped, thus leading to the formation of carbonaceous deposits and fast deactivation . In general, zeolite catalysts with higher acidity are more effective in promoting bio‐oil catalytic cracking reactions.…”