This doctoral thesis investigates the chemical recycling of plastic waste through pyrolysis by integrating reactor and catalyst engineering. It focuses on three major polymers, polystyrene (PS), polyethylene (PE), and polypropylene (PP), which account for more than 50% of global plastic production. The objective is to improve the selective conversion of these polymers into monomers and higher value products. Regarding PS pyrolysis, the main challenge lies in controlling the design and operational characteristics of the reactor in order to preserve styrene and limit secondary reactions. Short gas residence times and enhanced heat transfer are critical factors. For this purpose, a vortex reactor was evaluated at pilot scale. This reactor is characterized by high tangential gas velocities and intensified heat and mass transfer. The results showed significant suppression of secondary reactions, achieving styrene yields of 86 wt.% at 600 °C and 88 wt.% at 700 °C. These values surpass those obtained in conventional reactors, such as stirred-tank and fluidized-bed reactors, where back-mixing and long vapor residence times promote by-product formation. This study represents the first pilot-scale demonstration of a vortex reactor operating continuously and consistently exceeding the threshold of 85 wt.% styrene recovery. With respect to polyolefins, the main challenge concerns the upgrading of pyrolysis oil while simultaneously minimizing coke formation. The study was conducted using model compounds, namely 1-decene and 1,9-decadiene, which represent key components of PE and PP-derived pyrolysis oils. HZSM-5 catalysts were employed to enhance light olefin production. Through controlled steam treatment, the density of Brønsted acid sites was reduced, limiting excessive cracking and aromatization. The results showed that catalyst performance primarily depends on the severity of the steam treatment. Reaction pathway analysis revealed that 1-decene mainly leads to the formation of light olefins, whereas 1,9-decadiene follows cyclization and β-scission pathways, resulting in increased coke formation. These findings identify dienes as major coke precursors and suggest two strategies: feedstock pretreatment for diene management and catalyst design with tailored acidity. Based on the results of this work, an integrated strategy for intensifying plastic pyrolysis can be proposed. Vortex reactors improve monomer recovery in PS pyrolysis, while acidity-tuned zeolite catalysts, combined with appropriate feedstock pretreatment, enhance light olefin production with reduced coke formation. In conclusion, this doctoral thesis, through pilot-scale experiments using the innovative vortex reactor, mechanistic understanding of pyrolysis, and modeling support, contributes to the technological maturity and industrial application of chemical recycling.
Bahman Goshayeshi (Thu,) studied this question.