Oneesha Panditha Gunawardene - CoC Seminar and Panel Presentation

Abstract: Due to rapid industrialization and urban development worldwide, the use of plastics has increased significantly across various sectors, including packaging, healthcare, construction, and consumer goods, owing to their low cost, durability, and ease of processing. Soft plastics, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), flexible polyvinyl chloride (PVC), and thermoplastic elastomers (TPEs), are widely used for bags, films, and packaging due to their flexibility, strength, and barrier properties. Predominantly single-use, they can persist in the environment for up to 400 years, leading to substantial waste accumulation. Poorly managed soft plastics often end up in landfills or oceans, posing threats to ecosystems, wildlife, and human health through microplastic exposure and emissions, while also contributing to climate change. To mitigate plastic waste accumulation, various waste management methods are employed, including mechanical recycling, chemical recycling, biological degradation, incineration, and landfilling.
Soft plastic packaging is rarely found separately in landfills or waste streams due to contamination with hard plastics (e.g., polyethylene terephthalate (PET), polystyrene (PS), PP, HDPE, LDPE), food residues, paper, wood, and multilayer packaging. Given this complexity, among various plastic waste management strategies, pyrolysis, classified under chemical recycling, offers high tolerance to contaminants, reducing the need for pre-sorting. It thermally decomposes feedstocks in an inert atmosphere into solid, liquid, and gaseous products. The yield and quality of these products depend on parameters such as feedstock composition, temperature, heating rate, vapour residence time, reactor design, and, critically, catalyst selection. Thermal and catalytic degradation of waste plastics represent two distinct pyrolysis pathways within the broader framework of chemical recycling. From a kinetic and thermodynamic perspective, catalysts play a pivotal role not only in accelerating reaction rates but also in steering product selectivity, optimizing conditions, and reducing energy demand.
Researchers have investigated various solid catalysts, including zeolites, mesoporous aluminosilicates, bimetallics, silica, fly ash, clays, red mud, metal oxides, activated carbon, and alkaline earth compounds. Among them, solid acid catalysts with moderate Si/Al ratios and micro-mesoporous structures effectively enhance pyrolysis oil yield and quality by increasing monoaromatic content, shortening hydrocarbon chains, and eliminating oxygenates, polyaromatics, and heteroatoms thereby enabling high-value applications such as fuels, olefinic and aromatic chemical feedstocks, solvents, and precursors for plastics and resins. Despite extensive studies, the existing literature lacks a comprehensive evaluation of how variations in feedstock composition, pyrolysis temperature, and heating rate influence the yield and quality of pyrolysis products derived from mixed soft plastic waste streams contaminated with hard plastics, food residues, and paper. Furthermore, limited understanding exists regarding how the surface chemistry and textural properties of low-cost catalysts such as pond ash, cenospheres, and kaolin clay affect product yields and quality under such complex feedstock conditions.
Therefore, this investigation aims to assess the influence of pyrolysis temperature and heating rate on pyrolysis product distribution from a representative mixed soft plastic waste stream contaminated with hard plastics, food residues, and paper, under fixed residence and vapour residence times. It further evaluates the catalytic performance of pond ash and cenospheres (by-products of coal-fired power plants) and kaolin clay (a naturally occurring aluminosilicate), which are solid acid catalysts with distinct physical and chemical characteristics. The catalytic performance will be examined by varying catalyst loading and calcination temperature to optimize oil yield and quality. The study also explores the influence of additional common contaminants present in waste streams. Finally, a feasibility assessment will be conducted to determine the suitability of the resulting pyrolysis oil for plastic production and high-value chemical recovery, thereby strengthening the case for catalytic pyrolysis as a viable strategy for managing complex, contaminated plastic waste streams.