(305f) Zeolite Catalysts for Low-Density Polyethylene Cracking

Almost half of the global polymer production stands for polyolefins, and low-density polyethylene (LDPE) takes a significant portion [1]. As only a small number of consumed polymers are recycled, finding a mature technology for recycling is of utmost importance. Traditional polymer recycling methods require high process temperature which limits product selectivity [2]. Therefore, in this research, the recycling of LDPE into valuable gases at low temperatures using solid-acid zeolite catalysts via a catalytic cracking process is investigated.

Low-temperature catalytic cracking of LDPE was studied using various lab-made and commercial zeolite catalysts. Among the catalysts explored, ZSM-5 was selected as the base catalyst due to its high Bronsted acidity and simple synthesis procedure. Our results indicate a correlation between LDPE conversion to hydrocarbon gases and the external surface area of the zeolite catalyst. Higher external surface areas facilitate increased LDPE conversion due to enhanced accessibility of polymer to the active sites of catalyst. However, introducing transition metals onto the extra-framework of H-ZSM-5 zeolite did not yield increased LDPE conversion. On the contrary, it led to decreased LDPE conversion to hydrocarbon gases, likely due to the replacement of active sites by metal ions. Moreover, we investigated the effect of water within the zeolite catalyst on LDPE catalytic cracking. Interestingly, the presence of water resulted in higher LDPE conversion to products, attributed to reduced carbon deposition on the catalyst.

Obtained results contribute to improving our comprehension of LDPE recycling processes and catalyst design for effective plastic conversion into valuable products at lower temperature regimes.

[1] Geyer, R.; Jambeck, J.; Law, K. L. Production, use, and fate of all plastics ever made. Science Advances 2017, 3 (7), e1700782.

[2] Hopewell, J.; Dvorak, R.; Kosior, E. Plastics recycling: challenges and opportunities. Philosophical Transactions of the Royal Society B: Biological Sciences 2009, 364, 2115-2126.