Research guides future of plastic waste chemical recycling

Date:
September 20, 2021
Source:
Cornell University
Summary:
New research aims to ease the process of chemical recycling --
an emerging industry that could turn waste products back into
natural resources by physically breaking plastic down into the
smaller molecules it was originally produced from.



FULL STORY ==========================================================================
New research from Cornell University aims to ease the process of chemical recycling -- an emerging industry that could turn waste products back
into natural resources by physically breaking plastic down into the
smaller molecules it was originally produced from.


==========================================================================
In a new paper, "Consequential Life Cycle Assessment and Optimization of
High- Density Polyethylene Plastic Waste Chemical Recycling," published
in the Sept.

13 issue of the journal ACS Sustainable Chemistry & Engineering,
Fengqi You, the 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.

Billions of tons of plastic have been produced since the 1950s, yet
most of it -- 91%, according to one often cited study -- has not been
recycled. While growing landfills and contaminated natural areas are
among the concerns, the failure to reduce and reuse plastic is also seen
by some as a missed economic opportunity.

That's why the emerging industry of chemical recycling is capturing the attention of the waste industry and researchers like You, who is helping
to identify optimal technologies for chemical recycling and providing
a roadmap for the future of the industry.

Not only does chemical recycling create a 'circular economy,' in which a
waste product can be turned back into a natural resource, but it opens the
door for plastics such as high-density polyethylene -- used to produce
items such as rigid bottles, toys, underground pipes, and mail package envelopes -- to be recycled more commonly.



========================================================================== 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.

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

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 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." Environmental consequences of chemical recycling depend on variables such as supplier
process of chemical feedstocks and products. For instance, the framework
found that producing butene onsite as opposed to having it supplied can
reduce photochemical air pollution from recycling plants by nearly 20%,
while onsite use of natural gas increases more than 37% of potentially
harmful ionizing radiation.

"There's always something we can twist and adjust in the technology and process, and that's the tricky part," said You, who added that as new
chemical recycling techniques emerge and markets change, consequential life-cycle optimization will remain a powerful tool for guiding the
emerging industry.

The research was supported in part by the National Science Foundation.

========================================================================== Story Source: Materials provided by Cornell_University. Original written
by Syl Kacapyr, courtesy of the Cornell Chronicle. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Xiang Zhao, Fengqi You. Consequential Life Cycle Assessment and
Optimization of High-Density Polyethylene Plastic Waste Chemical
Recycling. ACS Sustainable Chemistry & Engineering, 2021; 9 (36):
12167 DOI: 10.1021/acssuschemeng.1c03587 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210920173135.htm

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