In situ analysis of volatiles obtained from the catalytic cracking of polyethylene

The effects of the solid-acid-catalyst pore size and acidity on polyethylen e catalytic cracking were examined with a comparison of the temperature-dep endent volatile-product-slate changes when the polymer was cracked with HZS M-5 and HY zeolites and the protonated form of MCM-41. Volatile-product dis tributions depended on the catalyst acidity and pore size. With HZSM-5, par affins were detected initially, and olefins were produced at somewhat highe r temperatures. Aromatics were formed at temperatures 30-40 degreesC higher than those required for olefin production. Small olefins (C-3-C-5) were th e most abundant products when HZSM-5 and MCM-41 catalysts were employed for cracking polyethylene. In contrast, cracking with HY produced primarily pa raffin volatile products (C-4-C-8). HY pores were large enough and the acid sites were strong enough to promote disproportionation reactions, which le d to the formation of volatile paraffins. Compared with the other catalysts , HZSM-5 with its smaller pores inhibited residue formation and facilitated the production of small alkyl aromatics. Volatile-product variations could be rationalized by a consideration of the combined effects of catalyst aci dity and pore size on carbenium ion reaction pathways. (C) 2001 John Wiley & Sons, Inc.