Improving the Circularity of Medical Plastics by Chemical Upcycling: A Study on Zeolite and Zirconia Catalysts

Abstract

Global policy and opinions are evolving in response to the increasing environmental damage caused by the expansion of landfill sites, and the lack of circularity in polymer waste management. To address this challenge, initially waste bound polymers, can be repurposed for chemical recycling, supporting the development of a more circular polymer economy. Hydrocracking of polymers is a process, that offers significant potential for a selective recovery of valuable chemicals, using bifunctional catalysts. It operates under milder conditions than the more commonly used pyrolysis process, resulting in reduced energy consumption and enhanced product quality. This study aimed at converting medical polymers through hydrocracking, which has seen a surge in use due to the COVID-19 pandemic, where polypropylene will be converted into hydrocarbons gas and liquid, mostly liquified petroleum gas (LPG) (C3-C4) and naphtha (C5-C12). Reactions were carried out in a 300 mL batch reactor, within a temperature range of 300-330 °C and a pressure of 20 barg. Hydrocracking catalysts used, where the support materials included zeolite USY, zeolite Beta, sulphated zirconia, tungstated zirconia, with an active metal loading containing platinum, where catalyst where modified to increase activity and stability during hydrocracking. The initial study started with a catalyst screening, where virgin polypropylene was used to evaluate the catalysts' cracking performance, coke formation resistance, and reusability. Subsequently, the study was extended to medical polymers that included facemasks and clinical gowns. The novelty of this research can be seen in deploying various hydrocracking catalysts to deconstruct medial polymers that can be used as feedstock for the chemical industry. The USY zeolite catalyst was the superior catalyst, typically achieving the best performance based on polymer conversion, the high selectivity of LPG and naphtha, and high reusability across virgin and medical polymers. For medical polymers, USY zeolite successfully showed the ability to deconstruct both heavy and light medical polymers, achieving conversion of 97-100%, LPG and naphtha selectivity of 96-98% and reusability up to 9 cycles. Overall, this research highlights the effectiveness of the USY zeolite catalyst for recovering valuable chemicals from medical polymer waste, paving the way for improved sustainability in the management of medical waste