Catalytic hydrocracking reactions of tetralin biomass tar model compound to benzene, toluene and xylenes (BTX) over metal-modified ZSM-5 in ambient pressure reactor
Andrii Kostyniuk, David Bajec, Blaž Likozar
Abstract
The tetralin hydrocracking process into benzene, toluene, and xylenes (BTX) was investigated over metal-modified (Ga, Nb, Ni, NiMo, Sn, W, Zr or H3[P(W3O10)4])/ZSM-5 zeolite catalysts without sulfidation procedures, mechanism was analyzed, and compared with a pristine microporous material in a packed bed reactor under applied atmospheric pressure (p). This experimental study presents an investigation of the metal-promoted ZSM-5 for the BTX production under the ambient p for the first continuously-operated time. It is demonstrated that metal-wise there are no significant improvements in the formation of BTX. The yield of 43.1 mol% towards BTX over the parent HZSM-5 (SiO2/Al2O3 = 30) at 420 °C after 4 h on time on stream (TOS) was achieved, while methane, ethylene, ethane, propylene and propane were main gas products. The outstanding functional performance of HZSM-5 was mainly ascribed to structure, its high dealkylation and a measured large amount of the solid surface area in tandem with the porosity, protonating total Brønsted (BAS)/Lewis (LAS) acidity and BAS/LAS ratio. However, BTX dropped drastically with increasing TOS due to coke. It was found that HZSM-5 was the most affected within studied reaction conditions, but could be easily regenerated with preserving realistic catalytic chemistry. The pathway of cracking was proposed. Simultaneously, the 5wt%Zr/ZSM-5 catalyst possessed the highest selectivity (SBTX = 24.2 mol%; TOS = 25 h; 370 °C) due to the low diffusion thermomigration of the Zr species into framework compared to parent zeolite under the same reaction conditions after a long TOS. Influence of metal loading on the activity of ZSM-5 zeolite was systematically studied and the complex relationship between physicochemical properties and catalytic activity of bifunctional catalysts was observed. All these findings shed light, on how the incorporation of different metals affects BTX selectivity.