Activation of n-pentane while prolonging HZSM-5 catalyst lifetime during its combined reaction with methanol or dimethyl ether

This work explores the synergies during combined reactions of n-pentane (nC(5)) with oxygenates (methanol or dimethyl ether, OX). The experimental runs have been carried out in a packed bed reactor at 500 degrees C, using a high silica HZSM-5 zeolite-based catalyst with different oxygenate-to-n-pentane (OX/nC(5)) ratios in the feed. A sig-nificant enhancement of the n-pentane conversion occurs for low OX/nC(5) ratios in the feed (0.1-0.25), especially when using dimethyl ether (DME). In addition, the presence of n-pentane reduces the rate of catalyst deactivation by coking during the conversion of oxygenates. These results have been explained on the grounds of a mecha-nistic interaction between the reactants: (1) the fast formation of methoxy and olefin intermediates from oxy-genates, particularly from DME, could explain the promotion of n-pentane cracking, by facilitating the activation of the alkane by hydrogen transfer reactions; (2) the attenuation of deactivation during the conversion of oxy-genates could be related to a lower extent of the arene cycle in the dual-cycle mechanism (limiting the poly-methylbenzene formation). The analyses of used catalysts by means of temperature-programmed oxidation and confocal fluorescence microscopy have pointed out the higher reactivity of DME than that of methanol also for yielding coke structures.

Automated summary

This study investigates the synergies between oxygenates (especially dimethyl ether) and n-pentane at low OX/nC(5) ratios, enhancing n-pentane conversion while reducing catalyst coking rate. The analysis of used catalysts reveals that dimethyl ether exhibits higher reactivity than methanol in forming coke structures.