Structure-reactivity relationship for aromatics transalkylation and isomerization process with TNU-9, MCM-22 and ZSM-5 zeolites, and their industrial implications

Abstract

TNU-9 is a medium pore zeolite with a complex tridimensional channel system. Its catalytic properties have been studied in some reactions that involve the BTX fraction, such as benzene and toluene alkylation with methanol, ethanol or isopropanol. These reactions use in practice medium pore zeolites such as ZSM-5 (MFI) or MCM-22 (MWW), and the selectivities obtained with TNU-9 are compared and analyzed from the point of view of the zeolite structure and pore topology, as well as from its possible industrial application. For benzene alkylation to give ethylbenzene (EB), TNU-9 is an active and selective catalyst with selectivities to EB much higher than ZSM-5 and close to those of the industrially relevant MCM-22. However, olefin oligomerization within the pores of TNU-9 occurs in a larger extension than with MCM-22, leading not only to some lower selectivity, but also to a faster catalyst deactivation. In the case of cumene formation, again the selectivity of TNU-9 to the desired product is higher than ZSM-5 but lower than MCM-22, owing to the formation of larger amounts of n-propylbenzene in the former as a result of its pore topology. Nevertheless, TNU-9 may be worth to be studied further for the disproportionation of toluene to give xylenes. In this case, its comparison with ZSM-5 appears of interest. By studying the alkylation of toluene with alcohols of different chain length, i.e. methanol, ethanol and isopropanol, it has been found that TNU-9 has an antagonistic behaviour, closer to ZSM-5 or MCM-22 depending on the activity or selectivity parameters considered that could be explained by its complex topology, formed by 10-ring tortuous channels with crosses as in ZSM-5, and large cavities as in MCM-22.