Investigation into the shape selectivity of zeolites for conversion of polyolefin plastic pyrolysis oil model compound

Abstract

The relationship between the structure of zeolites and their performance in 1-octene conversion, a model compound in polyolefin plastic pyrolysis oil, has been elucidated. Zeolite topology determines reaction pathways being possible to direct the reaction to the formation of light olefins or aromatics. Small pore zeolites (≤ 6.1 Å), facilitate octene-cracking reactions. For example, MOR produces 98% of small olefins (54% C5). Large pore size zeolites catalyze aromatizations to BTX, also producing paraffins and hydrogen. Zeolites with pore sizes around 6.1 Å produce BTX with reduced coke formation. Thus, MFI produces 32% of C2-C5 olefins, 27% paraffins, and 23% of BTX. The olefins, paraffins, and BTX are found in an alkylation/dealkylation equilibrium conditioned by the catalyst's pore size: the larger the pore size, the longer and more branched the products are. In addition, 1-octene isomers are dominant products at low contact times (∼0.045 s) and BTX at long contact times (∼4.5 s).