Plastic catalytic degradation study of the role of external catalytic surface, catalytic reusability and temperature effects.

Technological advancements over the last century have lead large and continuous growth in the output of plastic materials. This exponential growth has created public concern over the environmental impact caused by the polymeric waste produced. These have acted as driving forces for a lot of current research aimed at the development of plastic recycle processes. As a result, the conversion of plastic waste to useful products is gaining increasing attention. The aim of this work was to study aspects of polymer catalytic degradation using zeolite based catalysts. More specifically the study focused on identifying the role of the external catalytic surface on overall polymer decomposition reactions, the reusability of the catalysts as well as temperature and acidity effects. The first stage of this investigation aimed to explore the premise behind the assumption that polymer catalytic degradation takes place initially on the external catalytic surface by selectively poisoning the external sites of a zeolite catalyst (ZSM-5). Degradation results in a semi-batch reactor as well as thermogravimetric analysis demonstrated that the activity of poisoned catalyst samples was indeed lower than that of fresh catalyst. The next stage of the study involved an investigation of the extent of catalytic reusability of four zeolite catalysts - HZSM-5, USY and two commercial cracking catalysts containing 20 % and 40 % USY respectively. While the performance of US-Y showed deterioration with each cycle, ZSM-5 and both commercial cracking catalysts retained consistent levels of activity that enabled full polymer conversion in each cycle. Finally, the temperature effect on catalytic reactions was studied as well as the effect of catalyst acidity. While temperature effects were not conclusive regarding selectivity towards gas or liquid products prompting the suggestion of further work using a continuous flow reactor system, the formation of liquid products showed a maximum with the acidity content.