(393e) Early-Stage Screening of Reaction Pathways for Innovation Toward a Sustainable and Circular Chemical Industry

The chemical industry is facing mounting societal pressure to reduce its environmental impact, particularly with regard to climate change and plastic pollution. To address this challenge, many companies have pledged to become carbon neutral within a few decades. Transforming the life cycle of chemical products from the current linear or open-loop system to a circular or closed-loop system is essential for meeting these pledges. However, developing such a system requires a systematic approach that takes into account the economic feasibility and sustainability of emerging technologies. In this study, we propose a method for developing circular economy systems that are carbon-neutral, economically feasible, and environmentally sustainable. To develop an extensive network of current and emerging reaction pathways in the circular chemistry of a specified product, we use reaction databases such as Reaxys, machine learning-based tools such as ASKCOS, and scientific literature.

Our preliminary study focused on methanol as the target material to establish our methodology for developing the reaction network. Using the retrosynthetic method, we explored various reactions and chemicals that could be used to synthesize methanol, considering both raw materials and end-of-life chemicals. We compared these raw materials and end-of-life chemicals with the intermediate chemicals identified in our retrosynthetic analysis, and we identified possible reaction pathways between the screened chemicals with high chemical similarities. We collected information from a reaction database to further expand our understanding of the possible reaction pathways. With this information, we developed a more comprehensive reaction network than those found in the existing literature, which enabled us to synthesize methanol.

We establish a step-wise approach for evaluating many potential pathways from this reaction network and eliminating less promising options. Our approach relies on process syntheses and design methods, such as hierarchical design, reaction and process network flux analysis, and multi-objective optimization. We screen the reaction network with economic and environmental criteria to eliminate reaction pathways. This is done with increasing knowledge, starting with stoichiometry information, yield information, reactor information, etc. At each stage of the hierarchy, we consider each pathway's environmental impact by considering the life cycle impact. We illustrate the characteristics of our framework by using it to identify carbon-neutral, low-cost, and high-circularity pathways for methanol and polyethylene terephthalate (PET). The framework also identifies potential bottlenecks in meeting the specified objectives. At each stage of the hierarchy, we consider each pathway's environmental impact by considering the life cycle impact.

We have divided our analysis into two scopes: Scope 1, which focuses on reaction network design, and Scope 2, which extends from Scope 1 to include life cycle design. In the case of methanol production, we found that recycling CO₂ could contribute to low-cost and carbon-neutral production. However, when the yield of the CO₂ recycling reaction is low, the environmental and economic performance deteriorates. In the results of Scope 2, we found that supplying the energy required for the reaction greatly impacts the environment and economic feasibility. Therefore, we conclude that energy system improvement and reaction efficiency improvement should be carried out together to build a sustainable system.

This study provides insights that may guide future research and innovation toward practical carbon-neutral solutions, particularly in the area of recycling used plastics. While many efforts have been made to develop innovative alternatives using experimental work and molecular dynamic simulation, these methodologies can be time-consuming and difficult to screen all technologies and conditions. However, this study contributes to the design of experiments by providing a systematic approach to reaction selection and condition setting. The findings of this study offer a method for developing circular economy systems that are environmentally sustainable, economically feasible, and carbon-neutral. By utilizing emerging technologies and existing databases, viable pathways can be identified to reduce the chemical industry's environmental impact and support the transition toward a more circular economy.