Catalytic cracking of a polyolefin mixture over different acid solid catalysts

Catalytic cracking of a polyolefin mixture consisting of polypropylene and both low- and high-density polyethylene has been studied at 400 degrees C o ver a variety of acid solids as catalysts,The highest activities were obtai ned over HMCM-41, n-HZSM-5 zeolite, with nanometer crystal size, and HBeta zeolite. The high surface area and large pores present in HMCM-41 are respo nsible for the high conversions obtained with this catalyst. Likewise, in t he case of n-HZSM-5, the presence of a high external surface area enhances its cracking activity, because the zeolite external acid sites are not ster ically hindered for the conversion of the bulky polyolefin molecules. Signi ficant differences are observed in the product distribution: n-HZSM-5 shows the highest selectivity toward C-1-C-4 gaseous hydrocarbons (50 wt %), HBe ta leads mainly to liquid hydrocarbons in the range C-5-C-12 (60 Wt %), whe reas HMCM-41 yields both C-5-C-12 (54 wt % and C-13-C-30 (32 wt %) fraction s. A certain loss of activity of these catalysts has been observed after on e cycle of regeneration. For HMCM-41, this phenomenon is caused by both dea lumination and particle aggregation that take place during the regeneration treatment.