Evolution of the deactivation mode and nature of coke of HZSM-5 and USY zeolites in the catalytic cracking of low-density polyethylene during successive cracking runs

The coke deposited in the HZSM-5 zeolite at higher coke levels causes a more important pore blockage than the coke deposited in the HZSM-5 zeolite at low coke content. On the other hand, it would appear that there is an important deactivation mode change in the USY coked zeolites during the cracking runs and when the coke level in the catalyst increases an important pore blockage is observed. In the HZSM-5 zeolite, it seems that the formation of insoluble coke during the several polymer cracking runs, as well as the possible location in the external surface could be responsible for the important pore blockage observed in this zeolite. In the USY coked zeolites, the study of the nature of the soluble coke suggests that the pyrene compounds and their evolution to insoluble coke could probably be responsible for the important pore blockage observed after the second cracking run.

The influence of successive cracking runs on the deactivation mode and nature of coke of HZSM-5 and USY zeolites during the catalytic cracking of LDPE has been studied. The comparison between the behaviour of both zeolites indicates that the evolution of the nitrogen adsorption capacity during the different cracking runs is more marked in the USY coked zeolites than in the HZSM-5 coked samples. The chemical analysis of the coke obtained in each case has been used to explain the different deactivation phenomena. Figure optionsDownload as PowerPoint slide