The increasing amount of plastic waste generation has become an important concern for the chemical industry and government agencies due to high disposal and environmental leakage rates. Chemical recycling is a promising technology due to the potential reduction of pollutant emissions and the establishment of a circular economy through the production of monomers and fuels. However, there is scarce information on industrial scale processes of this technology and their energetic, economic, and environmental performance. Therefore, the present process modeling study presents a novel multiproduct pyrolysis-based refinery for the conversion of 500 tonnes/day of waste high-density polyethylene (HDPE). The products obtained from the modeled refinery were chemical grade ethylene and propylene, an aromatics mixture, and low-and high-molecular weight hydrocarbon mixtures (MWHCs). Part 1 of this study focuses on the energetic and economic evaluation of the refinery and the potential effects of heat integration. The energy efficiency was 68% and 73% for the base case and the heat integrated refinery, respectively. The net present values (NPVs) were 367 and 383 million U.S. dollars (MM USD), for the base case and the heat integrated process, respectively. These results suggest energetic and economic sustainability of the design and its promising application on an industrial scale.

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Today, polyurethanes are effectively not recycled and are made principally from nonrenewable, fossil-fuel-derived resources. This study provides the first high-resolution material flow analysis of polyurethane flows through the U.S. economy, tracking back to fossil fuels and covering polyurethane-relevant raw materials, trade, production, manufacturing, uses, historical stocks, and waste management. According to our analysis, in 2016, 2900 thousand tonnes (kt) of polyurethane were produced in the United States and 920 kt were imported for consumption, 2000 kt entered the postconsumer waste streams, and 390 kt were recycled and returned to the market in the form of carpet underlayment. The domestic production of polyurethane consumed 1100 kt of crude oil and 1100 kt of natural gas. With the developed polyurethane flow map, we point out the limitation of the existing mechanical recycling methods and identify that glycolysis, a chemical recycling method, can be used to recycle the main components of postconsumer polyurethane waste. We also explore how targeting biobased pathways could influence the supply chain and downstream markets of polyurethane and reduce the consumption of fossil fuels and the exposure to toxic precursors in polyurethane production.

Thermal degradation of plastics is a promising technology for addressing the waste management issues of landfill disposal, while obtaining useful products. Primary thermal degradation of polymers usually yields a large quantity of high molecular weight compounds with a limited applicability, making necessary a secondary degradation to improve the product quality. In this study, pyrolysis vapors from waste high density polyethylene (HDPE) were subjected to secondary degradation by varying the temperature and vapor residence time (VRT) in the reaction zone of a new two-stage micropyrolysis reactor (TSMR) attached to a commercial micropyrolysis unit. Temperature and VRT variations showed a strong effect on the product distribution, with low temperature (625 °C) and short VRT (1.4 s) producing a wide range of gases and liquid products and with high temperature (675 °C) and long VRT (5.6 s) producing mostly hydrocarbon gases and mono- and polyaromatics. The results showed a good agreement with previously reported product distributions for larger-scale pyrolysis reactors and were well explained by known degradation mechanisms.

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