Catalytic degradation of low density polyethylene over ZSM-11 zeolites: Catalyst deactivation study

MARÍA S. RENZINI; LILIANA B. PIERELLA

Ixtapa-Zihuatanejo, Guerrero, Mexico

Congreso; Mexican Congress on Chemical Reaction Engineering; 2008

Chemical recycling is an important technique to convert these wastes into gas and liquid hydrocarbons; moreover, the addition of catalysts improves the thermal process because it permits more valuable products to be obtained than in thermal processes at low temperatures and at lower reaction time. Several catalysts have been used to catalyses the cracking, but zeolites and mesoporous materials are the most important because it permits more valuable products to the obtained than in thermal processes. The more important disadvantage of these catalysts is the formation of heavy by-products which form a deposit on the surface (coke) and cause the gradual deactivation of the catalyst and also affect the activity and selectivity for the desired products. Furthermore, it is important that a catalyst retains its activity and selectivity for the longest time possible. Depending on the process, the catalyst life cycle may vary from a few seconds, as in fluid catalytic cracking, to several years, as in, for instance, ammonia synthesis. Catalyst deactivation scientifically presents many challenges. The carbonaceous compounds deposited in the zeolite cause an important decrease of the active sites and eventually pore blockage. If the coke molecules are trapped in the pore system, an important reduction of the pore size is produced and consequently, a decrease in the extension of bimolecular reactions can be observed. In this work, consecutive low density polyethylene (LDPE) cracking experiments over Zn-ZSM-11 and H-ZSM-11, were carried out in order to study the catalyst deactivation and possible coke location, using different techniques such as thermal analysis, X-ray diffraction and FTIR of the fresh and coked zeolites.