May 2022

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Circular Economy: Innovative recycling, driving circularity while decarbonizing the petrochemical industry

Plastic pollution’s environmental challenges, as well as new government legislation, are having a significant impact on the plastics industry.

Plastic pollution’s environmental challenges, as well as new government legislation, are having a significant impact on the plastics industry. Polymer manufacturers are being urged to experiment and implement alternative production processes—such as bio-based plastics and recycling—to decarbonize their products.

The complexity associated with the development of alternative production processes is amplified by the fact that there are a variety of polymers, and the formulations generated by adding additives differ depending on how they are used.

Let us first focus on recycling thermoplastics. Thermoplastic waste can be either mechanically or chemically recycled. Presently, chemical recycling only accounts for about 1% of recycled plastics. However, that proportion is expected to rise sharply, especially given that this approach enables the production of polymers that can be reused in a true circular closed loop, even for the most demanding applications, such as food or pharmaceutical plastic grades.

This field of chemically recycling plastics is where the authors’ company has applied its long-standing expertise [chemicals and chemical engineering, catalysis (homogeneous and heterogeneous), analysis, process engineering and modeling, pilot and demonstration design, and scaleup to industrial units] to develop innovative process technologies.

Chemical recycling opens new opportunities to bridge the gap between the need for additional plastics recycling capacity and the need for high-quality recycled plastics products. For example, chemical recycling addresses more difficult waste plastics feedstock that cannot be valorized through mechanical recycling, while fully meeting quality requirements and regulatory objectives. Chemical recycling prevents routing all plastics waste to a mechanical recycling process. It also enables the following:

  • Valorizes mixed plastics streams in a closed-loop complex, where sorting and separation stages, and regeneration processes required for recycling are too complex.
  • Valorizes plastic polluted during the various stages of its life (from its manufacturing to its arrival at the recycling plant), including contamination from the different sorting steps or contamination from contact with other materials during its use.
  • Removes all intentionally added contaminants to allow for a true closed recycling loop of plastic wastes (e.g., pigments, dyes, forbidden additives).
  • Creates an infinite closed recycling loop of plastics vs. mechanical recycling, where recycling may be limited to a certain number of cycles. Those cycles’ limitations are due to the temperature effects associated with the various stages of the recycling process, ultimately causing degradation of the recycled raw material and preventing upcycling (e.g., recycling of waste textile into food grade packaging such as bottles).

Chemical recycling (also referred to as advanced recycling) encompasses different processing technologies. Depolymerization and conversion processes can be used to modify the chemical structure of the polymer and purify the resulting product to enable the production of new raw polymers. Dissolution processes are also being developed to recover additive-free polymer chains. Some argue that dissolution is an extension of mechanical recycling, as the chemical structure of the polymer remains unchanged. However, that process relies heavily on chemical stages and is often grouped with chemical recycling.

Depending on the type of polymer waste, some chemical recycling routes are more appropriate than others. For example, waste polyethylene terephthalate that cannot be mechanically recycled will be recycled through a depolymerization process and is not suitable to conversion or dissolution processes.

The already proven and robust pyrolysis pathway

The following will focus on the conversion process, with a special focus on mixed plastic pyrolysis and its associated purification and decontamination steps. This is a key building block to a sustainable polyolefin chemical recycling value chain.

Pyrolysis of mixed plastic waste is considered the novel route to accomplish a true closed-loop recycling process of polyolefins, adhering to quality requirements and regulatory objectives. However, this route relies on the ability to properly purify the pyrolysis oil for reprocessing it in an existing petrochemical plant. That purification step is not a trivial refining process, as pyrolysis oil usually combines multiple contaminants and unstable molecules that—if not removed and stabilized—would jeopardize the operation of a petrochemical plant’s steam cracker.

Repsol and the authors’ company have joined their efforts to unlock the recovery of plastic waste that would otherwise remain in landfills or be incinerated. The consortium has developed and commercialized a proprietary pyrolysis purification processa to solve the challenges of purification and decontamination of pyrolysis oils. This process technology removes impurities such as silicon, chlorine, diolefins and other metals from the produced plastics pyrolysis oils, allowing the direct and undiluted feed to the steam cracker. Proper and reliable purification is paramount, as contaminants could not only jeopardize the operation of petrochemical steam cracker furnaces, but can also leak and concentrate in downstream units, ultimately ending up in polymers produced.

The successful commercialization of the purification technology would not have been possible without the development of new analysis methods by IFP Energies nouvelles to properly assess the different qualities of pyrolysis oil. Pyrolysis oil products concentrate a large proportion of multiple contaminants, making it difficult to analyze through conventional analysis methods.

As pyrolysis oil qualities vary substantially, the proprietary purification processa has a unique flexibility (vs. conventional hydroprocessing refining units) to cope with quality changes, enabling it to continually guarantee production of on-specification products suitable for direct undiluted processing in a naphtha steam cracker. In addition to processing the full range of pyrolysis oil, the proprietary purification processa can also embed a cracking option that will convert heavier products back to virgin-equivalent recycled naphtha, maximizing the closed-loop production of circular polymers.

Through its collaboration agreement with Plastic Energy, the authors’ company is also able to license patented, industrially proven advanced recycling technology, which uses a thermal anaerobic conversion pyrolysis processb.

With thermal anaerobic conversion pyrolysis processb and proprietary purification processa, which are commercial technologies, the pyrolysis pathway for plastics recycling can play an important role in mitigating the environmental impact of plastic waste. It also unleashes the full potential of converting any polyolefin plastic waste into food-grade quality.

At the onset of plastic recycling projects, the authors’ company’s experts support project developers on questions related to waste feedstocks characterization, technology performance, costs and potential financing strategies, taking full advantage of the unique expertise the company has built and developed with partners in the field of chemical recycling. HP

NOTES

  a Axens’ Rewind™ Mix technology

  b Plastic Energy’s thermal anaerobic conversion pyrolysis process

The Authors

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