Synergistic shape selectivity of H-Beta and H-ZSM-5 for Xylene-rich BTX production by hydrocracking of heavy-aromatic compounds

Abstract

Catalytic hydroconversion of C10+ heavy aromatics (C10+ Aro) from an aromatic complex was studied to produce benzene, toluene, and xylenes (BTX), rich in xylenes. Two catalytic schemes, direct hydrocracking (HDC) and hydrotreating (HDT) followed by HDC, were explored. The Mo2C/γ-Al2O3 catalyst exhibits excellent selectivity for mono-aromatics and catalytic stability in the HDT of C10+ Aro. HDC catalysts containing BZ (H-Beta/H-ZSM-5 = 9/1 weight ratio) exhibited a significantly enhanced yield of BTX but significantly reduced the formation of alkylbenzenes (other than BTX) and heavy aromatic residues compared to the HDC catalyst without H-ZSM-5. H-ZSM-5 with smaller pore size and higher Brönsted acidity than H-Beta promoted dealkylation of alkylbenzenes into BTX while limiting heavy residue formation. HDC of HDT-C10+ Aro over NiMo/BZ catalyst resulted in BTX and BTX + C9 Aro yields as high as 47.7 and 61.1 wt%, respectively, which were significantly higher than those obtained from direct HDC of C10+ Aro (44.4 and 53.8 wt%). Unlike model tetralin HDC, the BTX distribution was in the order X > T > B from the HDC of HDTC10+ Aro. Transalkylation reactions between benzene/toluene and tetramethylbenzenes (in C10+ Aro) have been suggested as possible mechanisms for the formation of xylene-rich BTX.