Enhanced performance of glycerol to aromatics over Sn-containing HZSM-5 zeolites

Abstract

The green production of aromatics from glycerol, a by-product of biodiesel manufacturing, is a potential alternative to the conventional production of aromatics through fossil fuel-based technology. In the present work the one-step catalytic conversion of glycerol to aromatics has been conducted over pure HZSM-5 and several metal species (Zn, Mo, Sn, Ni and Ag) modified HZSM-5 catalysts. Both the roles of metal species and HZSM-5 supports played during the GTA (glycerol to aromatics) procedure as well as the whole GTA catalytic process were investigated in this article. There are two main routes existing in zeolite upgrading of glycerol to aromatics, one by aldol condensation of glycerol dehydration products, in which oxygen in the glycerol is removed in the form of H₂O, whereas the other by oligomerization of olefins originated from the decarbonylation of glycerin dewatered products, in which oxygen in the feedstock is removed in the form of CO or CO₂. Among all the catalysts tested, 2.34 wt% Sn/HZSM-5, which exhibits 21.1 wt% in BTX aromatics yield and 10 h catalyst lifetime compared to the bare HZSM-5 (13.9 wt% of BTX aromatics and 5.5 h catalyst lifetime) and our previously reported optimum base-treated HZSM-5 catalyst (25.2 carbon yields%, i.e. 16.7 wt% of BTX aromatics), has demonstrated to be a potential candidate in the catalytic upgrading of glycerol. The incorporated Sn cations may preferentially accelerate the competitive decarbonylation steps (i.e., acetone → butene), and thus, facilitated the generation of xylene aromatics. Furthermore, the incorporated Sn cations could heal the framework defects in the HZSM-5 crystals and promote the transfer rate of coke precursors, greatly lessening the occurrence of the subsequent coking reactions during the whole GTA process.