Catalytic Solvent-based Recycling of Plastic Waste

Plastic waste management is one of the most pressing challenges of the 21st century, with global production exceeding 380 million tons annually. The ubiquity of plastics in everyday life-spanning packaging, construction materials, and a variety of consumer products-has led to a continuous surge in plastic waste. Despite efforts to mitigate this issue through traditional recycling methods, only a small fraction of plastic waste is effectively recycled. The majority of waste is either incinerated or sent to landfills, contributing to pollution, resource depletion, and greenhouse gas emissions. The development of chemical recycling technologies presents a promising alternative by transforming plastic waste into feedstocks for producing new plastics or other industrial chemicals. This so-called closed-loop recycling could provide a path toward a circular plastic economy, addressing the vast quantities of plastic waste. This PhD research aims to develop new technology for the catalytic conversion of plastic waste, as well as separative solvent-based recycling. The first focus is on multilayer packaging waste, where selective solvent-based dissolution of its polyurethane (PUR) adhesive enables the sustainable separation of different plastics, such as polypropylene (PP) and polyamide (PA), from the multilayer material. The second focus is on the recycling of chlorinated plastics, specifically polyvinyl chloride (PVC), which is commonly used in the construction sector. Although mechanical recycling technologies for PVC exist, they are limited due to the presence of toxic legacy additives like phthalates and lead-based stabilizers. To address this, two catalytic systems were developed for chemical PVC conversion using a novel tandem dehydrochlorination-hydrogenation reaction. In the first system, a tetrabutylphosphonium ionic liquid combined with a homogeneous Rh-complex enables fast dechlorination (~80%) of virgin PVC, producing a polyethylene (PE)-like product. In the second system, a combination of ZnCl2 and Ru proved to be an effective dual catalytic system for post-consumer PVC waste, achieving complete dechlorination. Crucially, the use of methyl cyclohexane carboxylate as a novel solvent for PVC was identified as essential for achieving excellent reactivity. Overall, the technologies developed in this research offer a pathway for recycling challenging plastic waste streams, potentially transforming plastic waste management.