Elucidating the structure-performance relationship of typical commercial zeolites in catalytic cracking of low-density polyethylene

Abstract

Zeolite exhibits excellent catalytic performance in the catalytic cracking of polyolefins, but the reaction results are often controversial due to the differences in the lab-scale synthesized zeolites and the types of reactors selected. In this work, in order to eliminate the differences of catalysts synthesized by individual researchers, we studied the catalytic performance of four typical commercial zeolites (HZSM-5, Hβ, HY and SAPO-11) in the cracking of low-density polyethylene (LDPE) by self-designed batch reactor. By comparing the reaction performance of four zeolites under the same condition and correlating with the pore structure and acidity of the zeolites, it was found that the acid strength of zeolites was positively correlated with the cracking conversion. HZSM-5 and Hβ zeolites with high acid strength achieved a LDPE conversion of above 94%. Large micropore is beneficial to the formation of isomerized products, but promotes the formation of coke precursors, resulting in serious coking. By analyzing the product distribution over different zeolites, it was observed that Hβ achieved the highest yield of gasoline components. HZSM-5 and HY exhibited high yields of aromatization products. The high aromatization activity of HZSM-5 was attributed to its strong acidity which enhanced the hydrogen transfer process, while HY possesses high concentrations of both Brönsted and Lewis acid sites, and the synergistic effect of these two acid sites promotes the aromatization process.