Solvent-free chemoenzymatic degradation of plastics

News

Published: 2Oct2020

Invention 2020-014

Solvent-free chemoenzymatic degradation of plastics

 

Efficient closed-loop recycling of PET.

Mild, waste-free process using renewable biocatalysts.

Eliminating the environmental burden of petroleum-based plastics.

 

Abstract

Worldwide, less than 9% of all plastic is recycled and approximately 75% finds its way into the environment, imperilling both marine and terrestrial ecosystems. One of the most widely used plastics is poly(ethylene terephthalate) or PET, with about 50 M tons produced globally each year. While PET is considered recyclable, its recycling is typically limited to re-use in lower-grade products (e.g. from bottles to carpets), which is not recycling but downcycling. Our technology allows for the true recycling of PET plastics, with minimal cost and energy requirements.

 

Benefit

Our invention is based on the unexpected discovery that enzymes promote the degradation of PET plastics more efficiently in damp-solid reaction mixtures than in the ‘gold-standard’ buffered solution. Our method proceeds without any harsh reagent, solvent, or high temperature/pressure. In contrast to other processes, enzymatic activity under our conditions is independent of the percent crystallinity of PET, allowing the depolymerization of untreated high crystallinity PET (e.g. plastic bottles). By minimizing the total volume of the reaction mixture, our method greatly facilitates handling and mixing, curtails waste, and avoids solubility issues.

PET is an excellent material for packaging and other applications; it is non-gas-permeable, transparent, non-toxic, robust, and keeps food fresh. Our method of true recycling would allow us to keep using this material without the environmental cost of waste. The drawbacks of moving away from PET are steep as 1) we already have good methods for sorting PET out of waste, 2) the introducion of biodegradable new plastics contaminatethe plastics waste stream with more and more different types of plastics, that can lead to sorting difficulties at recycling plants, and 3) The «biodegradable» packaging created is often biodegradable only under very specific conditions.

 

Market Application

PET is considered easily recyclable, however the existing open-loop recycling methods are restricted to products made of virgin pet (e.g. clear plastic packaging), as the material is degraded in the recycling process. The resulting lower-grade PET, generally used in non-recycled materials (textiles, carpets), thus simply postpones the disposal of PET, instead of eliminating the production of waste. In order to reduce the consumption of non-renewable resources to make virgin PET, we need efficient methods to move back up on the materials ladder and produce higher grade PET, which is only possible with true recycling, e.g. full depolymerization to monomers and re-polymerization. The true recycling of PET into food-grade products is challenging, as current methods use high temperatures and/or pressures, with corrosive strong bases or acids, and generate the desired terephthalic acid monomer along with several by-products. Our invention, in contrast, completely avoids these harsh conditions by using renewable selective biocatalysts at ambient temperature and atmospheric pressure, requiring solely a minimal amount of clean water to proceed. By minimizing the total volume of the mixture, this technology greatly facilitates handling and mixing, curtails waste associated with processing, and avoids solubility issues. This is an unprecedented breakthrough for the true recycling of plastics.

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