This study presents a comprehensive process, economic, environmental, and socioeconomic analysis of the enzymatic recycling of poly(ethylene terephthalate), which is the most widely used synthetic polyester. The analyses predict that PET deconstruction using enzymes can achieve cost parity with terephthalic acid manufacturing as well as substantial reductions in both supply chain energy use and greenhouse gas emissions relative to virgin polyester manufacturing. This study also highlights key research areas for further impactful development of biocatalysis-enabled plastics recycling.
This study develops an approach to incentivize both higher extents of waste plastics reclamation and use of bio-based chemicals. In particular, reclaimed plastics (polyethylene terephthalate) and chemicals derivable from renewable resources are combined to create high-performance, long-lifetime composite materials with properties that exceed those of standard petroleum-based materials and that exhibit higher selling prices than reclaimed plastic. Analysis predicts that this approach results in reductions in energy input and greenhouse gas emissions relative to standard composites manufacturing today.
Over 400 million metric tons of plastic waste are generated globally each year, resulting in pollution and lost resources. Recycling strategies can recapture this wasted material, but there is a lack of quantitative and transparent data on the capabilities and impacts of these processes. Here, we develop a data set of material quality, material retention, circularity, contamination tolerance, minimum selling price, greenhouse gas emissions, energy use, land use, toxicity, waste generation, and water use metrics for closed-loop polymer recycling technologies, including mechanical recycling and solvent-based dissolution of polyethylene, polyethylene terephthalate (PET), and polypropylene, as well as enzymatic hydrolysis, glycolysis, and vapor methanolysis of PET. Mechanical recycling and PET glycolysis display the best economic (9%−73% lower than competing technologies) and environmental (7%−88% lower) performances, while dissolution, enzymatic hydrolysis, and methanolysis provide the best recyclate material qualities (2%−27% higher). We identify electricity, steam, and organic solvents as top process contributors to these metrics and apply sensitivity and multicriteria decision analyses to highlight key future research areas. The estimates derived in this work provide a quantitative baseline for comparing and improving recycling technologies, can help reclaimers identify optimal end-of-life routes for given waste streams, and serve as a framework for assessing future innovations.
PREFACEThis is one report in a series that explores the costs, benefits, and other impacts of state renewable portfolio standards (RPS), both retrospectively and prospectively. The terminology applied in this series does not align precisely with the traditional concepts of costs and benefits, but rather is a function of how RPS programs have often been evaluated in practice. In particular, this analysis series evaluates RPS programs in terms of the following:• RPS compliance costs represent the incremental cost of meeting RPS compliance obligations, from the perspective of the utility or other load-serving entity, compared to the costs that would have been borne in the absence of the RPS. RPS compliance costs may be negative, if the renewable electricity used for RPS compliance is less expensive to the utility than the alternatives.• Benefits, as analyzed in this report series, consist specifically of environmental benefits that accrue to society at large, rather than to individual utilities. In theory, such benefits may be negative, representing net environmental costs, if the renewable electricity used for RPS compliance leads to more harmful environmental impacts than it avoids.• Other impacts, in the form of resource transfers from one market participant or segment to another, are also evaluated. These other impacts may also entail net costs or benefits to society at large, but our analyses focus only on the gross impacts, not the net cost or benefit. This report, the second in the series, analyzes historical benefits and impacts of all state RPS policies, in aggregate, employing a consistent and well-vetted set of methods and data sets. The analysis focuses on three specific benefits: greenhouse gas emissions, air pollution, and water use. It also analyzes three other impacts: gross job additions, wholesale electricity market price suppression, and natural gas price suppression. These are an important subset, but by no means a comprehensive set, of all possible effects associated with RPS policies. These benefits and impacts are also subject to many uncertainties, which are described and, to the extent possible, quantified within the report.The present report is intended to help policymakers, RPS administrators, and other decision-makers gauge the potential significance of a number of key benefits and impacts from state RPS programs. By noting limitations, caveats, and uncertainties in these results, the report also seeks to highlight important methodological considerations to evaluating RPS benefits and impacts. This report does not, however, provide a complete picture, and comparable information on both the costs and benefits, as well as other impacts, are ultimately needed to inform decision-making. To that end, a third report in this series is planned for the coming year to evaluate the future costs, benefits, and other impacts of state RPS policies, under both current policies and possible revisions. A prior study ) and subsequent update in this report series found that RPS compliance costs over the 2...
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