New Research Evaluates Impact of Plastic Waste Chemical Recycling

Detailed Framework of Recycling Process

In a new paper, “Consequential Life Cycle Assessment and Optimization of High-Density Polyethylene Plastic Waste Chemical Recycling,” published in the journal ACS Sustainable Chemistry & Engineering, Fengqi You, Roxanne E., and Michael J. Zak, professor in energy systems engineering and doctoral student Xiang Zhao detail a framework incorporating several mathematical models and methodologies that factor everything from chemical recycling equipment, processes and energy sources, to environmental effects and the market for end products.

The framework is the first comprehensive analysis of its kind that quantifies the life-cycle environmental impacts of plastic waste chemical recycling, such as climate change and human toxicity.

Superstructure Optimization for Minimizing Cost

You’s framework can quantify the environmental consequences of market dynamics that typical life-cycle sustainability assessments would overlook. It’s also the first to combine superstructure optimization – a computational technique for searching over a large combinatorial space of technology pathways for minimizing cost – with life-cycle analysis, market information and economic equilibrium.

In one scenario, to maximize economic outcomes while minimizing environmental impacts, life-cycle optimization produced a more than 14 percent decrease in greenhouse gas emissions and a more than 60 percent reduction of photochemical air pollution when compared with the attributional life-cycle assessment approach typically used in environmental assessment studies.

Varied Technology as per Chemicals

While the analysis gives industry experts and policy makers a general pathway for advancing chemical recycling and a circular economy for plastics, a myriad of choices and variables along the technological path must be considered.

For instance, if the market demand for basic chemicals like ethylene and propylene is strong enough, the framework recommends a specific type of chemical separation technology, while if butane or isobutene are desired, another type of technology is optimal.

It’s a chemical process and there are so many possibilities,” You said. “If we want to invest in chemical recycling, what technology would we use? That really depends on the composition of our waste, the variants of polyethylene plastic, and it depends on current market prices for end products like fuels and hydrocarbons.

The framework found that producing butene onsite as opposed to having it supplied can reduce photochemical air pollution from recycling plants by nearly 20 percent, while onsite use of natural gas increases more than 37 percent of potentially harmful ionizing radiation.

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