Dissolution – The “Physical Recycling” Method

Dissolution or purification is an option for recycling polymers without altering their chemical structure while ensuring energy efficiency. Nevertheless, solvents may be an environmental concern.

Dissolution, or purification, processes stand apart from other molecular recycling methods because they do not break the plastic polymer bonds.

You can also read: Rethinking the System: We Need Molecular Recycling

Purification Process

Because it is non-chemical, this process is often referred to as “physical recycling.” Purification uses solvents to extract colors and additives from single-polymer feedstock or mixed plastics, resulting in virgin-like polymers. These processes maintain the integrity of the material, ensuring a plastic-to-plastic outcome. Additionally, purification is part of molecular recycling technologies, but this specific method does not break the polymeric structure.

Applications and Advantages

Dissolution-based recycling is highly effective in managing plastic product waste. It efficiently converts plastic waste into new chemicals, optimizing sustainable supply chains for chemical companies. Moreover, it offers significant advantages, such as reduced energy consumption, by operating at lower temperatures. This method increases reliability by ensuring consistent recycled materials quality and effectively handling mixed plastic streams within a single process. Additionally, it minimizes the impact of contaminants present in end-of-life products on the recycling process.

Companies’ Innovative Approach

Dissolution-based recycling is an emerging field, and a few companies are at the forefront of applying or developing similar solvent-based recycling methods.

• PureCycle‘s process integrates well-established operation units, with extraction and filtration central to the method. These straightforward concepts enable the production of ultra-pure recycled plastic, a first in the industry.
• Ioniqa Technologies, based in the Netherlands, has developed a chemical recycling process that involves the use of solvents to break down PET waste into its monomers.
• Carbios, the French company, focuses on enzymatic recycling but also explores advanced methods that include the depolymerization of plastics through the use of solvents.
• Jeplan, the Japanese company, is involved in the recycling of polyester using their chemical recycling technology. Their process involves dissolving polyester fibers using solvents to separate and purify the material, allowing it to be reused in new products.

Breakthroughs in Research to Avoid Harsh Chemicals

Researchers at the Joint BioEnergy Institute (JBEI) have developed a technology that reuses synthetic plastics while reducing energy requirements and avoiding harsh chemicals. This process, which is halogen-free, uses biocompatible solvents like amines produced by actinobacteria. Under mild conditions and at room temperature, the synthetic plastics undergo dissolution and depolymerization, breaking down the long-chain polymer molecules into monomeric units. This approach prevents the degradation of material quality, which is often seen in traditional recycling methods. It also creates opportunities to repurpose these monomers into new, high-quality plastic products.

Experimental Findings

Experimental results are promising, showing up to 95% depolymerization of PET in ethylenediamine at room temperature. PET also demonstrated solubility in other solvents, achieving a 92% isolated yield of the water-soluble product N,N-bis(2-aminopropyl)terephthalamide in 1,3-propanediamine at room temperature. The addition of JBEI solvents extended water solubility to a wide range of synthetic plastics, including those commonly used in consumer products and packaging materials, such as PUR, PC, PS, PP, LDPE, and HDPE. For instance, PC was fully soluble in ethylenediamine, while PUR showed limited solubility. Plastics with a C-C backbone, like PP, PS, and PE, exhibited limited solubility in ethylenediamine at room temperature.

Sustainability of Solvent-Based Recycling

Some solvents used in dissolution processes can be toxic or hazardous to human health and the environment. Handling, storage, and disposal of these solvents require stringent safety measures to prevent environmental contamination. If not appropriately managed, toxic solvents can lead to air and water pollution, posing risks to ecosystems and human health.Therefore, developing safer, environmentally friendly solvents is crucial, as demonstrated by research efforts like those at the Joint BioEnergy Institute, which focuses on implementing solvents without harmful chemicals.