The Critical Role of Process Analysis in Chemical Recycling and Upcycling of Waste Plastics

Abstract

There is an urgent need for new technologies to enable circularity for synthetic polymers, spurred by the accumulation of waste plastics in landfills and the environment and the contributions of plastics manufacturing to climate change. Chemical recycling is a promising means to convert waste plastics into molecular intermediates that can be remanufactured into new products. Given the growing interest in the development of new chemical recycling approaches, it is critical to evaluate the economics, energy use, greenhouse gas emissions, and other life cycle inventory metrics for emerging processes, relative to the incumbent, linear manufacturing practices employed today. Here we offer specific definitions for classes of chemical recycling and upcycling and describe general process concepts for the chemical recycling of mixed plastics waste. We present a framework for techno-economic analysis and life cycle assessment for both closed- and open-loop chemical recycling. Rigorous application of these process analysis tools will be required to enable impactful solutions for the plastics waste problem. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Expanding Plastics Recycling Technologies: Chemical Aspects, Technology Status and Challenges

“…14,[680][681] There are many reviews in the literature summarizing recent progress in chemical plastics recycling, as well as several which focus solely on PET. 17,298,[681][682][683][684][685][686][687][688][689][690][691][692] Chemical recycling of PET is an area of intense focus in the literature, and a comprehensive review of every report in this field is thus not attempted here. This section summarizes each strategy for PET depolymerization, with a focus on important and practical advances and their potential for industrial application.…”

Life cycle assessment of enzymatic poly(ethylene terephthalate) recycling

“…Normalized life cycle impacts for the entire rPET system -including production of the original PET feedstock -over multiple lifetimes were calculated according to a system expansion approach. 29 First, the number of product lifetimes (L) that can be obtained from rPET were calculated with Eq. 1:…”

“…Normalized life cycle impacts for the entire rPET system – including production of the original PET feedstock – over multiple lifetimes were calculated according to a system expansion approach. 29 First, the number of product lifetimes ( L ) that can be obtained from rPET were calculated with eqn (1):where: a = mass yield of the enzymatic process (including rTPA and rEG yields), b = mass yield of pre-enzymatic steps including PET collection, sorting, and flaking, c = mass ratio of rTPA and rEG contained in 1 kg of secondary rPET, and n = number of recycling cycles. For the base case, a = 0.677 (incorporates 95% mechanical pre-treatment yield, 90% depolymerization of PET to rTPA and rEG, 90% rTPA recovery, and 50% rEG recovery), b = 0.837 (90% sorting yield and 93% bale-to-flake yield), and c = 0.879 (assumes 100% of TPA for rPET repolymerization comes from rTPA, but that only 56% of EG comes from rEG due to its lower yield in the enzymatic process), for a total of L = 2.81.…”

Expanding Plastics Recycling Technologies: Chemical Aspects, Technology Status and Challenges

“…14,[661][662] There are many reviews in the literature summarizing recent progress in chemical plastics recycling, as well as several which focus solely on PET. 17,280,[662][663][664][665][666][667][668][669][670][671][672][673] Chemical recycling of PET is an area of intense focus in the literature, and a comprehensive review of every report in this field is thus not attempted here. This section summarizes each strategy for PET depolymerization, with a focus on important and practical advances and their potential for industrial application.…”