Cracking of Mixed C4s to Propylene and Ethylene Over Modified ZSM-5 Catalysts

Catalytic cracking of mixed C4s to propylene and ethylene was investigated over ZSM-5 with different acidity, crystallite size, modification technique and various feed composition in a continuous fixed-bed reactor. It was found that the acidity of zeolites plays important role in the catalytic activity and stability. In high acidity ZSM-5 catalysts, the high activity but low stability were obtained. Deactivation is ascribed to a consecutive reaction of hydrogen transfer and oligomerization. While, the ZSM-5 with low acidity exhibits good stability. Moreover, the crystallite size of zeolite was markedly influenced the stability of catalysts. The high stability of zeolite could be gained on smaller (< 0.5 micrometer) crystallite size. Modification of ZSM-5 possessed low Si/Al ratio by alkaline and alkaline earth ion exchange was remarkable decreased the conversion of mixed C4s. While, platinum impregnated provide a higher activity, as compared to the parent ZSM-5. In the reaction using olefin-rich as feed, it was found a higher conversion over acid catalyst, as compared to that of higher paraffinic hydrocarbons. Moreover, the suppression of hydrogen transfer by reduction acid site and reaction temperature, can enhance the ethylene and propylene selectivity. After the catalyst was regenerated by air, it was found that the higher activity was obtained, as compared to the fresh one, owing to the formation of Lewis acid site.

Keywords: Catalytic cracking, ZSM-5 catalyst, C4 Hydrocarbons

Corresponding author: E-mail: kstawan@kmitl.ac.th