The recovery of high-value chemicals, such as naphtha, aromatics, and monomers, from plastic waste via, e.g., pyrolysis comes along with significant challenges due to the complex composition of the resulting oil phase. The variability in feedstock streams leads to fluctuations in both the composition and quantity of pyrolysis oil, affecting downstream processing due to the presence of olefins, heteroatoms, and inorganic compounds, which can cause corrosion, fouling, and catalyst poisoning in subsequent downstream processing. It is therefore usually necessary to treat, or upgrade, such pyrolysis oils. Key processing steps typically include distillation and hydrotreatment of pyrolysis oils, but, although both being well-known and established industrial processes on their own, the optimized combination of both in the context of pyrolysis oil upgrading is whether trivial nor a priori known: The sequence of distillation and hydrotreatment significantly impacts hydrogen and energy consumption, product and by-product yields, and overall efficiency of the entire downstream processes. As an example for the complexity of the process design, a distillation performed first may reduce hydrogen demand in later process steps, whereas hydrotreating first could yield a higher fraction of usable chemicals due to the controlled breakdown of long-chain hydrocarbons. However, the latter route may require higher energy input for subsequent distillation due to increased boiling points of alkanes over alkenes, or vice versa, in case of a comprehensive shift in the chain length distribution towards smaller hydrocarbons. Thus, to enable the reintegration of high-value chemicals from pyrolysis oils into the chemical industry, a systematic and holistic approach to downstream process development is necessary. Such a holistic approach must consider several key questions:
#1 What is the optimum sequence of distillation, hydrotreatment, and unit operations in general in terms of minimized energy and hydrogen consumption while maximizing high-value chemical yields?
#2 How can byproducts from pyrolysis and downstream processing be effectively utilized in the chemical industry?
#3 How can such (downstream) processes be fully integrated into circular production system models?
To address these questions, a systematic evaluation of process configurations is conducted to determine the most efficient downstream sequence. For that, various separation and conversion techniques are analyzed to aiming at the recovery of even gaseous products, and different oil fractions such as monomers and naphtha cuts, and solid residues. Potential applications in petrochemical feedstocks and alternative processing routes are explored regarding material circularity. This includes computational modeling and experimental validation to compare hydrogen demand, energy input, and overall product yield. Based on that, within the framework of a systemic model a holistic method for closing material loops by recovering complex waste streams – based on the chemical recycling of plastics as an example – is developed, including process optimization strategies, approaches for by-product utilization, and assessing economic and environmental impacts of entire process configurations.