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Chemical recycling; Plastic waste; Sustainable polymer manufacturing; Circular economy; environmental impact; Economic feasibility

Introduction

Plastic pollution has emerged as one of the most pressing environmental challenges of our time, with vast quantities of plastic waste accumulating in landfills, oceans, and ecosystems worldwide. Traditional approaches to plastic waste management, such as landfilling and incineration, are inadequate and often exacerbate environmental degradation and resource depletion [1]. In contrast, the concept of a circular economy offers a transformative framework for mitigating plastic pollution and promoting sustainability by closing the loop on material flows through recycling and reuse. Chemical recycling, also known as advanced recycling or feedstock recycling, represents a promising strategy for breaking down plastic waste into its molecular building blocks, which can then be used to produce new polymers [2,3]. Unlike mechanical recycling, which involves melting and reshaping plastic waste into secondary products, chemical recycling processes can convert a wider range of plastic types, including mixed or contaminated plastics, into high-quality feedstock for polymer manufacturing. However, the technical, economic, and environmental feasibility of chemical recycling technologies vary widely, necessitating a critical evaluation of their strengths, limitations, and potential implications for sustainable polymer production [4,5]. Plastic pollution has surged to the forefront of global environmental concerns, catalyzing a paradigm shift in how we approach plastic waste management and polymer manufacturing [6,7]. With conventional linear models of production and consumption proving unsustainable, there is a growing imperative to transition towards circular economy principles, where materials are kept in use for as long as possible through recycling and reuse. In this context, chemical recycling technologies have garnered significant attention as a potential solution for transforming plastic waste into high-quality feedstock for sustainable polymer manufacturing. Chemical recycling, also referred to as advanced recycling or feedstock recycling, represents a diverse array of technologies designed to break down plastic waste into its constituent monomers or other valuable chemical intermediates [8,9]. Unlike mechanical recycling, which involves melting and reshaping plastic waste into secondary products, chemical recycling offers the possibility of converting a broader range of plastic types, including mixed or contaminated plastics, into feedstock suitable for polymer production. While the concept of chemical recycling holds promise in theory, its practical implementation poses numerous technical, economic, and environmental challenges that warrant critical appraisal [10].

Types of chemical recycling technologies

Chemical recycling encompasses a diverse array of technologies, each with its unique mechanisms, inputs, and outputs. Broadly categorized, chemical recycling methods can be classified into thermal, catalytic, and biochemical processes. Thermal processes, such as pyrolysis and gasification, involve the decomposition of plastic waste at elevated temperatures in the absence of oxygen, yielding gaseous, liquid, and solid products that can be further processed into feedstock or fuels. Catalytic processes leverage catalysts to facilitate the breakdown of plastic molecules into valuable chemical intermediates, while biochemical processes employ enzymes or microorganisms to biodegrade plastics into biodegradable compounds.

Technical feasibility and process efficiency

The technical feasibility of chemical recycling technologies depends on several factors, including feedstock composition, process conditions, reactor design, and product quality. Pyrolysis, for instance, has emerged as a prominent thermal recycling method capable of processing diverse plastic feedstocks, including mixed or contaminated plastics, into pyrolysis oil, gas, and char. However, challenges such as reactor fouling, product contamination, and energy requirements hinder the scalability and efficiency of pyrolysis processes. Catalytic depolymerization offers advantages in terms of product selectivity and energy efficiency but faces challenges related to catalyst deactivation, feedstock variability, and reactor design optimization.

Environmental implications and sustainability assessment

The environmental sustainability of chemical recycling technologies hinges on their ability to mitigate plastic pollution, reduce greenhouse gas emissions, conserve resources, and minimize environmental impacts throughout the lifecycle. While chemical recycling holds promise as a means of diverting plastic waste from landfills and incinerators, its environmental benefits are contingent on factors such as feedstock availability, energy intensity, emissions profile, and waste management practices. Life cycle assessment (LCA) studies play a crucial role in evaluating the environmental impacts of chemical recycling processes and comparing them with conventional waste management strategies to inform decision-making and policy development.

Economic viability and market dynamics

The economic viability of chemical recycling technologies depends on various factors, including capital investment, operational costs, feedstock prices, product yields, market demand, and regulatory incentives. While some chemical recycling processes have achieved commercialization and market adoption, others face challenges related to cost competitiveness, scale-up constraints, and market penetration. Economic feasibility assessments, including techno-economic analysis (TEA) and cost-benefit analysis (CBA), are essential tools for evaluating the economic potential of chemical recycling technologies and identifying strategies to enhance their competitiveness and attractiveness to investors and stakeholders.

Scalability and integration into circular economy models

The scalability of chemical recycling technologies is critical for their widespread adoption and integration into circular economy models that prioritize resource efficiency, waste minimization, and sustainable consumption and production patterns. Challenges such as infrastructure development, supply chain logistics, regulatory compliance, and public acceptance can impede the scale-up and deployment of chemical recycling facilities. Collaboration among industry stakeholders, policymakers, researchers, and civil society is essential for overcoming barriers to scalability and realizing the full potential of chemical recycling in advancing the transition towards a circular economy for plastics.

Conclusion

Chemical recycling technologies hold significant promise as a critical component of the transition towards sustainable polymer manufacturing and circular economy practices. Throughout this appraisal, we have examined various aspects of chemical recycling, including its technical feasibility, environmental implications, economic viability, and scalability, with the aim of providing a comprehensive understanding of its potential role in addressing plastic pollution and promoting resource efficiency. Our analysis revealed that chemical recycling encompasses a diverse array of technologies, each with its unique mechanisms, inputs, and outputs. Thermal, catalytic, and biochemical processes offer distinct advantages and face different challenges in terms of feedstock compatibility, process efficiency, and product quality. While thermal processes such as pyrolysis demonstrate versatility in processing various plastic feedstocks, catalytic processes offer higher selectivity and energy efficiency, and biochemical processes show promise for biodegradable plastics.

Acknowledgment

The completion of this critical appraisal would not have been possible without the support, guidance, and contributions of several individuals and organizations that we gratefully acknowledge. First and foremost, we extend our deepest appreciation to the researchers, scientists, and engineers whose groundbreaking work in the field of chemical recycling has paved the way for sustainable polymer manufacturing. Their dedication to advancing knowledge and innovation has been instrumental in shaping this review. We also express our gratitude to the academic institutions, research centers, and funding agencies that have provided resources, facilities, and financial support for this research endeavor. Their commitment to scientific inquiry and knowledge dissemination has been invaluable in facilitating our exploration of chemical recycling technologies.

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