Chemical Recycling of Polyolefins via Pyrolysis and Hydrothermal Conversion

Abstract

Chemical recycling technologies hold significant potential to enhance the circularity of plastic materials, but further developments are clearly needed to make these techniques technically as well as economically feasible at larger scale. In this PhD thesis, we aimed to generate new knowledge that may contribute to improving these chemical recycling processes and guide the design of suitable catalyst materials to increase product yields. We demonstrate that pore size plays a critical role in polymer conversion during catalytic pyrolysis. Without sufficient infiltration, polymers cannot access the active sites located within the pores of a catalyst material, leaving much of the catalytic potential unused. This insight provides a valuable basis for the rational design of new catalyst materials for polymer conversion. In the second part of the PhD thesis, we highlight the importance of reaction parameters in hydrothermal polyolefin conversion and compare the process with pyrolysis. For the non-catalytic hydrothermal process, high temperatures and long reaction times were shown to be necessary to achieve full conversion and produce valuable products. However, by applying common solid catalyst materials, the product scope and reactivity was significantly affected, underscoring the potential of catalysis to improve the feasibility of hydrothermal conversion in future applications.