Thermal and catalytic cracking of polyethylene under mild conditions

Thermal and catalytic cracking of both high and low-density polyethylene (HDPE and LDPE, respectively) under mild conditions have been investigated in order to study the properties of the solid waxy product so obtained. The catalysts employed were n-HZSM-5 and HY zeolites, amorphous silica-alumina, activated carbon, Pd charcoal powder and mesoporous aluminosilicate materials (MCM-41), with and without impregnated Pd. The best results achieved in the LDPE degradation with regard to stability and homogeneity of the waxy product were obtained using MCM-41 as catalyst. The high BET surface area, uniform mesoporosity and medium acid strength of this catalyst promotes the polymer cracking according to a random scission mechanism, as well as, the development of hydrogen transfer reactions which reduce the olefinic character of the solid product. On the other hand, the product obtained from HDPE has a higher homogeneity than that coming from LDPE, leading to a waxy product with better quality for potential applications. (C) 2001 Elsevier Science B.V. All rights reserved.