Toward sustainable circular economies: A computational framework for assessment and design

Numerous directives and strategies in recent times aim to establish a Circular Economy (CE) for retaining the value of consumer discarded products within the technosphere, thereby implicitly reducing the burden on the ecosphere. Many opportunities to recycle, down-cycle or up-cycle products have also been identified for enabling greater circularity. However, to obtain a Sustainable Circular Economy (SCE) there is a need to holistically assess and design entire value chains of the product while considering various alternatives that may be available at each stage of its circular network. Systematic methods are also needed to determine the environmental, economic, and social implications of various value chain pathways and quantify their trade-offs with circularity from the perspective of multiple stakeholders. We propose a systematic and rigorous computational framework to analyze existing circular systems and develop new designs. This framework combines the computational approach of life cycle assessment with optimization-based approaches for process synthesis and network representation. Life-cycle networks are modified to contain multiple alternatives along the value chain and permit circular flows between modules. Four basic types of nodes are identified such that any SCE network may be represented as their combination. The additional degrees of freedom generated in such a superstructure network are determined by using principles of allocation and displacement, material-energy balances and physico-chemical governing equations of modules, thereby permitting integration of fundamental models with data-based LCA methods. Typical cases that may arise in potential circular value chains are formulated and solved to highlight the wide applicability of the framework. Both analysis and synthesis methods are proposed to evaluate candidate pathways within the superstructure network. Application of this framework to illustrative examples highlights its use for systematic design of circular value chains to meet SCE goals by quantifying the trade-offs between objectives. Such a framework is needed to develop general software to study the scope of innovation at different stages of the value chain, and contribute toward optimal closing of the cycles of different materials. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This article discusses the importance of establishing a Circular Economy and proposes a systematic computational framework for analyzing and designing circular systems. By combining the computational approach of life cycle assessment with optimization-based process synthesis methods, it allows for a comprehensive assessment and design of product circular value chains.