Recycled ethylene glycol (rEG); AI is rewriting the recycling story of waste plastics.

Under the dual drive of the 'dual carbon' goals and plastic pollution management, chemical recycling of waste plastics is no longer an unfamiliar concept. However, when we shift our focus from macro policies and production figures to a key small molecule—ethylene glycol (EG), a deeper, more technically rich track quietly unfolds. Recycled ethylene glycol (rEG), this 'molecular bridge' connecting waste polyester with high-end recycling, is becoming a crucial player in the green transformation of the chemical industry.

1. What is recycled ethylene glycol?

Before talking about 'recycling,' let's get to know the main character—ethylene glycol (EG).

Ethylene glycol (C₂H₆O₂, abbreviated EG) is one of the largest basic chemical raw materials globally. At room temperature, it's a colorless, transparent, hygroscopic liquid that can mix with water and alcohol solvents in any proportion.

l Global annual consumption exceeds 30 million tons, with China's annual consumption surpassing 20 million tons. Historically, the country depended almost 70% on imports, and currently domestic recycled ethylene glycol capacity still accounts for only a very small portion of total EG supply, leaving ample room for growth.

l Over 75% of downstream consumption is for synthesizing PET polyester (bottle chips, polyester fiber, films), while the rest is used in antifreeze, polyurethane, coatings, pharmaceuticals, and solvents.

l Traditional production routes include petroleum-based ethylene oxide hydration and coal-based syngas oxalate methods, both heavily reliant on fossil fuels and generating high carbon emissions and energy consumption. They are classified as high-energy-consuming coal chemical products controlled by the National Development and Reform Commission.

Recycled ethylene glycol (rEG): produced from solid waste such as discarded PET bottles, used polyester fabrics, polyester films, and polyester offcuts through chemical depolymerization and refined purification, rEG is a circular recycled chemical raw material. Essentially, it breaks down waste polyester macromolecules into original monomers, achieving a 'waste plastic → monomer → new polyester' closed-loop cycle.

After purification and refining, rEG can meet the polyester-grade premium standards of the national standard GB/T 4649-2018 'Industrial Ethylene Glycol':

1. Ethylene glycol content ≥ 99.9%

2. Diethylene glycol content ≤ 0.050%

3. Moisture content ≤ 0.08%

4. Color (platinum-cobalt) ≤ No. 5

Once impurities and purity meet standards, rEG can be completely equivalent to virgin ethylene glycol and used in high-value applications such as food-grade packaging and high-end fiber spinning.

2. Why is recycled ethylene glycol so important?

Outstanding environmental value. Every year, tens of millions of tons of waste PET are produced worldwide. Traditional disposal methods like landfill and incineration not only take up a lot of land but also release greenhouse gases and microplastic pollutants, increasing the ecological burden. Chemical recycling technology for recycled ethylene glycol turns waste polyester into standardized chemical raw materials, reducing plastic waste from the source and significantly lowering the environmental impact of waste disposal at the end of the lifecycle.

Significant resource saving. Traditional production of ethylene glycol heavily relies on fossil resources such as petroleum and natural gas. Compared with conventional processes, recycling routes can greatly reduce water and energy consumption. Life-cycle assessments show that recycled PET uses 59% less energy and generates about 32% fewer greenhouse gas emissions than virgin PET. In today’s world of increasingly tight resources, this is highly meaningful.

Policy and market dual drivers. Worldwide, legislation on minimum recycled content requirements is accelerating. The EU’s Packaging and Packaging Waste Regulation (PPWR) sets clear mandatory requirements for the proportion of recycled material in packaging, and brands’ demand for sustainable materials continues to rise. According to industry market research, the market for recycled PET bottle ethylene glycol is expected to grow from $2.2 billion in 2026 to $5 billion in 2036, with a compound annual growth rate of 8.6%. Polyester fiber production leads the end-use market with a 41.8% share, while textile and apparel is the fastest-growing application area.

3. Three main technical routes for recycled ethylene glycol

Currently, there are three parallel technical paths for recovering rEG from waste PET:

Route 1: Chemical glycolysis

This is currently the most industrially mature route. After purification, BHET can either be directly polymerized into recycled PET or further hydrolyzed into TPA and EG in a hydrolysis route for monomer recovery.

- Research published in ACS Engineering Au in 2023 shows that using a niobium-based sulfonated catalyst can achieve 100% PET conversion and 85% BHET yield at 195°C in 220 minutes.

- BHET can then be stepwise recovered into terephthalic acid (TPA) and EG via hydrolysis or methanolysis, or directly repolymerized into recycled PET.

Advantages: Relatively mild conditions and controllable catalyst costs. Challenge: Product purification (removing dyes, comonomers, and other impurities) is the key bottleneck for industrial cost reduction.

 Ethylene glycol hydrolysis 

Pathway 2: Methanolysis

PET is depolymerized into dimethyl terephthalate (DMT) and EG using methanol under high temperature and pressure. DMT can be separated by distillation, and EG is purified through rectification.

Advantages: The technology is relatively mature, and some international companies have already commercialized it. Challenges: High equipment investment and high energy consumption.

Methanol alcoholysis 

Pathway 3: Enzymatic Hydrolysis

In recent years, this has become the "hottest" technology route. Specific PET hydrolases (like LCC, IsPETase, and their engineered variants) can directly break PET into TPA and EG monomers in aqueous environments at 50–70°C.

- A 2024 review in *Applied Microbiology and Biotechnology* summarized current PET enzyme improvement directions. PET hydrolase engineering has shifted from traditional thermal stability optimization to flexible regulation of the substrate-binding groove—moderate flexibility can actually enhance the degradation efficiency of crystalline PET.

- Internationally, some companies have already built pilot plants for enzymatic recycling based on engineered LCC, achieving a closed-loop cycle from waste PET bottles to new bottles.

Advantages: Room temperature and pressure, almost "green chemistry," very high product purity. Challenges: Production cost of enzymes, and degradation efficiency for highly crystalline PET (like textile fibers) still needs improvement.

4. How Can AI Empower Breakthroughs in Recycled Ethylene Glycol?

Each of the above technical routes faces the same type of problem: how to simultaneously optimize the efficiency, selectivity, and cost of catalysts/enzymes?

Take the enzymatic route as an example: naturally discovered PET hydrolases (like IsPETase from *Ideonella sakaiensis*) are reasonably active at room temperature but lack thermal stability; on the other hand, thermophilic enzymes (like LCC) are more stable at high temperatures (the glass transition temperature of the amorphous regions of PET is about 67–70°C), yet their hydrolysis rate for crystalline substrates is still not ideal. This requires "fine-tuning" combinatorial mutations at dozens or even hundreds of amino acid sites—traditional directed evolution and rational design just can't keep up with the experimental throughput.

This is the field that AI-driven protein design really shines. 

 MatwingsVenus™（晓鹜™）

Taking MatwingsVenus™ (XiaoWu™) platform of Shanghai Matwings Technology Co., Ltd. as an example: the platform integrates large-scale protein sequence-structure-function data and uses deep neural network models to efficiently search the amino acid sequence space. It can complete mutation scanning and combination optimization in a few days—a process that would take traditional methods months or even years. Combined with wet lab closed-loop validation, it can accurately converge on engineered enzyme variants that are both highly active and highly stable.

What does this mean? — In rEG production, taking published engineering cases as a reference, AI-assisted optimized PET hydrolases can increase the hydrolysis activity on crystalline PET by several times while maintaining thermal stability. This means that under industrial conditions, higher conversion rates and shorter reaction cycles are possible, reducing the enzyme cost per unit of rEG and allowing tolerance to a wider range of pH and temperature fluctuations, thereby significantly lowering the overall cost of industrial operation.

AI protein design is turning the 'impossible' into 'mass-producible.'

5. Outlook: The Next Boom in the Circular Economy

As AI greatly lowers the R&D barrier for enzymatic routes, the industrialization of regenerated ethylene glycol (rEG) is being accelerated. rEG is not just a chemical product but also represents a shift in industry thinking—from the linear 'extract-use-dispose' model to a circular 'recover-regenerate-reuse' model.

With continuous breakthroughs in chemical recycling and enzyme-based technologies, and significant improvements in R&D efficiency brought by intelligent tools like AI, rEG is transitioning from a 'policy-driven eco-friendly choice' to an 'economically driven business choice.' As global demand for virgin ethylene glycol continues to grow, rEG, as a low-carbon alternative feedstock, is expected to continue increasing its market share. It is predicted that the global ethylene glycol market will grow from about $50.2 billion in 2025 to $81.72 billion in 2032, with rEG steadily increasing its proportion of this expanding market.

For chemical companies, brands, and investors, rEG represents not only an emerging market but also a ticket to a sustainable future. Companies that integrate cutting-edge technologies like AI into green chemical R&D early on will undoubtedly gain a first-mover advantage in this transformation.