Supercritical CO2: From coffee decaffeination to PVC recycling

We need more polymer recycling and a genuine circular economy. As an executive board member of a polymer processing company, this is crystal clear to me. Achieving this would be more valuable for sustainability and climate protection than all the debates about renunciation.

At the same time, it is still a difficult path to take. The technical hurdles are real, as are the economic challenges. In this article, I would like to use the example of polyvinyl chloride, or PVC, to highlight both the problems and a particularly clear solution, thereby objectifying the debate on plastics and sustainability.

Because one thing is certain: progress is not achieved through bans and renunciation, but through innovation. 

PVC is actually a prime example of recycling potential. In theory, the polymer can be remelted any number of times and, in practice, up to 10 times, and processed into new products. But there is a problem—additives.

To give PVC its properties, we mix numerous additives into the plastic: plasticizers for flexibility, UV stabilizers for weather resistance, flame retardants for safety, and heat stabilizers, without which PVC could not be processed at all. These additives make PVC an extremely versatile, durable, and safe material for everyday use.

However, they become an obstacle when it comes to recycling.

Each application requires specific additive mixtures: a window frame needs different stabilizers than a medical tube, and flooring needs different plasticizers than roofing membrane.

Legacy additives—substances that were previously approved but are now considered harmful—are particularly problematic. One example is lead-based heat stabilizers, which are now a recycling problem.

Until now, it has been virtually impossible to remove these additives from PVC. Mixed or contaminated waste often had to be thermally recycled, i.e., incinerated.

The inspiration for a solution to the additive problem comes from a completely different industry: the food industry.

Since the 1970s, supercritical carbon dioxide has been used there to gently extract caffeine from coffee beans.

The principle is fascinatingly simple: under high pressure and elevated temperature, CO2 transforms into a supercritical state. In this state, its properties change dramatically – it becomes a highly selective solvent that can dissolve specific substances without damaging the basic structure.

What works for coffee beans also works for polymers. Supercritical CO2 can precisely extract liquid plasticizers and other liquid additives from the PVC matrix without attacking the polymer itself.

This turns a proven food technology into a game changer for the circular economy. Even though the technology still has its limitations when it comes to solid additives such as heavy metal stabilizers or color pigments, this is a huge step forward. However, parallel projects are underway to develop special solvent mixtures that can extract the other additives in addition to the plasticizer.

Recent studies confirm that the extraction of plasticizers from PVC using supercritical CO₂ is extremely effective. Under laboratory and pilot conditions, more than 98 percent of the plasticizers can be removed at pressures of 100 to 500 bar and temperatures between 75 and 110 °C. The resulting PVC achieves a purity of over 99.5 percent and retains its material structure completely.

The technology is still under development, but the potential for the circular economy is enormous.

The process is no more complex than decaffeinating coffee – the reactor vessels are even similar to those used in the food industry.

What sounds convincing in theory is already being put into practice at RENOLIT. To this end, we are working with an external partner that specializes in optimizing CO2 extraction processes.

The next step is a pilot plant that can handle larger quantities of PVC waste. There, the extraction process will be further optimized and prepared for industrial scale. 

What can be achieved with the CO2 extraction process is more than just recycling—it would be a completely closed cycle. The purified PVC with less than 0.1 percent additive content could, for example, be further processed into technical films. In this way, problematic waste could be turned back into high-quality products.

The extracted plasticizers and additives would not necessarily have to be destroyed either. They could be chemically broken down into their raw materials or converted into harmless substances, which could then be returned to the material cycle. Nothing would be lost.

The key point is that the entire process uses CO₂, which is completely removed after extraction by simple pressure relief. There are no chemical residues, no solvents, and no waste. The use of supercritical CO₂ in such processes does not contribute to global warming, but is a closed process. The CO₂ is reused and is not lost.

A process that is as clean as decaffeinating coffee.

In this way, a problematic waste product could be turned back into a harmless raw material using a proven process. Circular economy as it should be.

Coffee decaffeination demonstrates the way forward: proven technologies can solve recycling problems that seemed unsolvable for years. Supercritical CO2 turns PVC waste back into a valuable raw material. Not all technical hurdles have been overcome yet, especially with solid additives. But we are on the right track. Innovative processes such as these need targeted support now – both from companies such as RENOLIT and from industry and politics. After all, the best sustainability strategy is one that transforms challenges into recyclable materials.