Hydrogen transfer reaction in butene catalytic cracking over ZSM-5

Hydrogen transfer reaction (HTR) is the pivotal side reaction in the catalytic cracking process of low carbon olefins. The intricate reaction pathways and product diversity of HTR directly impact the selective formation of ethylene and propylene. Therefore, elucidating the key HTR in various reaction pathways and defining the hydrogen transfer index (HTI) as a criterion lay a scientific foundation for precisely regulating HTR during olefin catalytic cracking process. Herein, the influence of the acid strength of ZSM-5 zeolites on the HTR degree was analyzed in butene catalytic cracking. Results showed that isobutane was the predominant component of HTR products, mainly derived from HTR during the dimerization-cracking of pentene (butene primary cracking product). Subsequent pentene catalytic cracking experiments validated this conclusion. Thus, the HTI in butene or pentene cracking process was defined as follows: for butene cracking process, HTI = S_i–C4H10/S_C5H10; for pentene cracking process, HTI = S_i–C4H10/S_C4H8. The HTI accurately reflected the extent of HTR with respect to the acid properties of the catalysts. Moreover, the reaction network of butene catalytic cracking process was optimized, providing a comprehensive explanation for the intriguing phenomenon of decreasing butene conversion with increasing reaction temperature when the acid strength of ZSM-5 was weak. Finally, a high-performance butene catalytic cracking catalyst, De-TS-1-0.25%P, was developed, exhibiting high olefin selectivity (92.33 %) and outstanding stability (307 h) in the conversion of butene.