PlastXnow explains  Chemical Recycling: New Approaches for Plastic Waste 

Plastic waste poses major challenges for industry and society. Chemical recycling makes it possible to convert complex or contaminated plastic streams back into high-quality raw materials. 

Modern life would be unthinkable without plastics. They form the foundation of numerous value chains—from packaging and automotive applications to high-tech and specialty chemicals. 

Consequently, the challenge of returning these materials to the petrochemical feedstock base at the end of their life cycle is significant. According to recent surveys, less than 40 percent is recycled in Germany. This also means that the majority is still being incinerated.

Chemical recycling returns hard-to-recycle plastic waste back into the cycle 

Various mechanical methods have since been developed plastic recycling methods and sorting processes for plastic waste have been developed, though some of them face technological limitations. These include waste that is too heavily contaminated or very complex plastics. Furthermore, not all potential markets are accessible in terms of applications; for example, products that come into contact with food and medical devices.

This is exactly where chemical plastic recycling comes into play. This article explains the most important processes, their advantages, and their role in a sustainable circular economy. 

What is chemical recycling?

Chemical recycling (also known as material recycling) is an umbrella term for processes in which plastic waste is not simply shredded and remelted, as is the case with mechanical recycling. Instead, it is broken down into its basic building blocks (monomers). These can then be used to produce new plastics, raw materials, or chemicals.

What procedures are available?

In recent years, the term “chemical recycling” has been discussed primarily in connection with packaging waste. In most cases, this referred to the process of pyrolysis. However, the term also encompasses other recycling technologies that, in some cases, differ significantly from pyrolysis in technical terms.

An overview of various plastic recycling processes. Source: nova-institute.eu, at www.renewable-carbon.eu/graphics

In addition to pyrolysis, which has already been mentioned, the main processes include both solvolysis and gasification. We will briefly explain these in the following section:

• In pyrolysis, plastic is thermally decomposed at high temperatures in the absence of oxygen. This process produces oils, gases, and solid residues (coke/ash), which can be reused as raw materials. Pyrolysis is primarily in Germany the currently dominant technology. 
• Solvolysis breaks down plastics using a solvent, converting them back into their monomers or basic chemicals. Unlike pyrolysis, this process relies not only on heat but also on chemical reactions, often at moderate temperatures.
• In gasification (gasification), plastics are converted into synthesis gas (syngas) at very high temperatures using a controlled amount of oxygen. Unlike pyrolysis, for example, this process uses a small amount of oxygen or water vapor to ensure that the material does not burn but instead turns into a gas. Gasification is still largely in the pilot stage and currently plays hardly any role.

In addition, there are a number of special processes, particularly in the field of PET (polyethylene terephthalate), a plastic commonly used in packaging and bottles:

Advantages of Chemical Recycling

Chemical recycling offers several potential benefits. This is especially true in cases where mechanical recycling reaches its limits.

• Recycling of heavily contaminated or mixed plastic waste: Much plastic waste (including composite materials, mixed films, and contaminated packaging) can be recycled mechanically only to a very limited extent, if at all. Chemical plastic recycling can nevertheless make use of such material streams.
• Production of “as-new” raw materials: The plastics are broken down into monomers or chemical raw materials that are nearly identical to fossil-based feedstocks. This enables the production of virgin-quality products, even for demanding applications.
• Closed-loop recycling for plastics: Materials that would otherwise be incinerated can be reintroduced into the chemical value chain. This conserves resources and can reduce the demand for petroleum in the long term.
• Potential for CO₂ savings: Depending on the process and energy source, chemical recycling can improve the carbon footprint, especially when renewable energy is used or when it replaces incineration (which produces fossil fuel emissions).

Disadvantages of Chemical Recycling

In addition to its advantages, chemical recycling also has significant disadvantages and challenges that are currently the subject of intense debate. Most processes (pyrolysis, gasification, solvolysis) require high temperatures and thus a great deal of energy. 

Critics criticize above all the enormous amounts of energy required. Pyrolysis takes place at over 400 degrees Celsius, and gasification at over 1,200 degrees. By comparison, mechanical recycling requires only 200 degrees. The energy consumption is three to four times higher than that of mechanical processes. 

Another drawback is the low level of industrial maturity to date. Many plants are still in the pilot or demonstration phases. This is also due to the fact that some of these plants are highly complex, and their construction and operation involve significant costs.

Critics also point out that these processes are sometimes presented as a solution for “all plastic waste.” However, chemical recycling is only practical for certain material streams. Furthermore, there are doubts about whether the materials are actually being recycled.

For which plastics are these processes suitable?

Chemical recycling is particularly suitable for plastic waste that is difficult or impossible to recycle mechanically. In principle, many plastics can be chemically recycled, but their suitability depends heavily on the process and the degree of contamination.

It is particularly well-suited for recycling mixed plastic waste, such as mixed films, composites, and mixed plastics from household waste. There are also applications for waste made of polycarbonate (see video), polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyamides.

Like any recycling innovation, chemical processes also have their limitations. Waste made of polyvinyl chloride (PVC) or polyurethane (PUR) can only be processed to a limited extent using these methods. High-performance plastics that are particularly stable (such as PTFE) and materials containing a high proportion of additives pose a special challenge.

Applications & Industries

Chemical recycling is particularly useful for industries and applications that require high-quality recycled material or generate plastic waste that is difficult to recycle:

Real-World Example: Extracting Valuable Materials from Diaper Waste

Disposable baby diapers are one of the clearest examples of the linear economy: They are typically used once and then incinerated or landfilled, even though they contain valuable nonwoven fabrics and polyolefin-based films. 

In response, Woosh, a Belgium-based brand of reusable diapers, Borouge International, a global leader in polyolefin solutions, and BlueAlp, a leading company in the field of chemical recycling with a commercially operated facility in Ostend, Belgium, have joined forces. Together, they have demonstrated that plastics from used baby diapers can be recovered and chemically recycled into raw material for new polymers. 

The Future of (Chemical) Recycling

Plastics recycling is essential to sustainability efforts—particularly in the circular economy for plastics. Industry and policymakers are already largely in agreement on this: the key technology for this is mechanical recycling. 

Chemical recycling, however, can serve as a useful complement. Until then, there are significant hurdles to overcome. Both the technologies themselves and their economic viability must be further optimized. In addition, approaches that deviate from the proportional approach are needed mass balance approaches that deviate from the proportional approach.

In closing: Good to know

Chemical recycling has been around for decades. As early as the 1970s, Professors Hansjörg Sinn and Walter Kaminsky were conducting research on fluidized-bed pyrolysis at the University of Hamburg. In the “Hamburg process” they developed, plastic is decomposed in a fluidized-bed reactor at temperatures between 300 °C and 900 °C in the absence of oxygen.