Effect of ZSM-5 on the aromatization performance in cracking catalyst

Cracking of FCC naphtha has been investigated on the model catalysts containing ZSM-5 (Si/Al-2 = 50, 500), Zn-ZSM-5 (Si/Al-2 = 50) and USY The presence of ZSM-5 and USY causes a tremendous decrease in olefins of gasoline fraction, leading to an enrichment of the aromatics in liquid product. It is evidently that aromatics are generated from lower olefins. The property of lower silica-to-alumina ratio of ZSM-5 and Zn modification enhance the aromatization process for higher cracking reactivity and dehydrogenation. The result of evaluation in confined fluid bed apparatus (CFBA) with the mixture of VGO and VTB as feed further confirms the aromatics generation in cracking reaction stimulated by ZSM-5 additive over base catalysts with different hydrogen transfer activity. Based on these results, relations between scission and aromatization in FCC catalyst containing ZSM-5 zeolite could be proposed. The suggested reaction path could better explain the reasons that effectiveness of ZSM-5 additive to lighter olefins is more profound in base catalyst of low hydrogen transfer activity and why so many researchers had not observed the aromatics generation motivated by ZSM-5 additive in catalytic cracking reaction. (C) 2004 Elsevier B.V. All rights reserved.