The effect of pore shape on the catalytic performance of zeolites in the liquid-phase degradation of HDPE

The liquid-phase catalytic degradation of HDPE was studied on BEA, FAU, MWW, MOR and MFI zeolites with different pores to illustrate the effect of pore shape on their catalytic activities. High conversions of HDPE were obtained on BEA and MFI zeolites, because bent pores retarded catalytic deactivation due to carbon deposit suppressing the formation of longer molecules. On the other hand, rapid blocking of linear pores even by a small amount of carbon deposit decreased the activity of MOR zeolite. Large pores of FAU zeolite connected through supercages enhanced mass transfer, resulting in a high yield of liquid product. The slow diffusion of cracked products in MWW zeolite due to its repeated larger spaces, brought about further cracking, enhancing the yield of small hydrocarbons. The pore shape of the zeolites was important in determining activity and product selectivity in the degradation of polymers by influencing the diffusion rate of cracked products and suppressing the formation of large molecules. (C) 2002 Elsevier Science Ltd. All rights reserved.