What differences exist between the chemical recycling process and the one with supercritical water

The now fairly consolidated statement that mechanical recycling alone has become insufficient and not completely efficient in the management of plastic waste is a sufficiently realistic thesis.

Net of interventions upstream in the supply chain, which suggest reducing consumption, reusing, repairing and improving the useful life of objects , the issue of managing the plastic waste that is produced every year around the world would require new technologies, new political and entrepreneurial foresight, to develop, combined with mechanical recycling, other forms of recycling such as chemical recycling and supercritical water recycling.

What is supercritical water

Supercritical water is a state of matter in which the pressure and temperature are so high that the distinctions between liquid and gas become blurred. In this state, water exhibits unique properties and is used in various industries, such as extracting chemicals and cleaning materials.

How supercritical water is produced

To produce supercritical water, it is necessary to reach a temperature above 374 degrees and a pressure of at least 22.1 MPa, which corresponds to approximately 218 atmospheres. These extreme conditions can be achieved using special equipment called high-pressure reactors.

Typically, the process involves heating water to a temperature above its critical point and applying sufficiently high pressure.

How supercritical water is used in plastic waste recycling

Supercritical water is used in the recycling of plastic waste through a process known as supercritical hydrotreatment. With this method, supercritical water is used to degrade and remove contaminants from plastic waste.

The process involves several stages:

Pre-treatment

Plastic waste is prepared, removing any gross contaminants and separating the plastic materials based on the type they belong to, where possible.

Exposure to supercritical water

The prepared waste is then exposed to supercritical water under specific temperature and pressure conditions. In this environment, water can penetrate the molecular structure of plastics, making it easier to remove contaminants.

Depolymerization

Supercritical water can contribute to the depolymerization of plastics, breaking long polymer chains into simpler components or monomers.

Product recovery

Products obtained from depolymerization, such as monomers or oils, can be recovered for reuse in the production of new materials.

What are the final products made after the recycling process with supercritical water

The process of recycling plastic waste with supercritical water can generate different end products, depending on the composition of the treated waste and the specific conditions of the process. Let's see some of the final products:

Monomers

The long polymer chains of plastics can be fragmented during the process, producing monomers. These can be used to synthesize new polymers and plastic materials.

Oils

Depolymerization can also generate oils or light hydrocarbons, which can be used as raw materials in various industrial sectors.

Gas

The process may release gases, such as carbon dioxide, depending on treatment conditions. The recovery and use of these gases can contribute to the sustainability of the process.

Recycled solid materials

After treatment, it is possible to obtain recycled solid materials that can be used in various applications. These materials can be incorporated into manufacturing processes to create new products.

The main objective of recycling with supercritical water is to minimize plastic waste, recover useful resources and reduce the environmental impact associated with plastic waste. The versatility of the process allows it to adapt to different types of plastic, thus contributing to more sustainable waste management.

What process differences exist in the recycling of plastic waste between chemical recycling and supercritical water recycling

Chemical recycling and supercritical water recycling are two distinct approaches to treating plastic waste, with significant differences in the processes. Let's see some:

Chemical recycling

This recycling system involves chemical processes to break down the polymer chains of plastics, turning them into monomers or oils, often requiring the use of harsh chemicals and high temperatures or pressures.

Recycling with supercritical water

This system uses supercritical water to treat plastic waste, penetrating its structure and facilitating depolymerization.

To do this it is necessary to reach high temperatures and pressures, but without the use of aggressive chemicals as in traditional approaches. The process can generate monomers, oils and other useful materials, while minimizing toxic residues.

Key differences between the chemical and supercritical water processes

Chemical recycling uses harsh chemical reagents, while supercritical water uses the unique properties of water in a supercritical state to degrade plastics.

In fact, supercritical water can be more environmentally friendly from a chemical point of view, as it reduces dependence on toxic or dangerous substances.

Both processes aim to recover monomers or oils for the production of new materials, but the exact details of the process and the products obtained can vary.

Both approaches contribute to sustainable plastic waste management efforts, but the choice between the two depends on the specific needs, types of plastic and environmental objectives of a given recycling process.

What economic advantages exist between chemical recycling and supercritical water recycling

The economic benefits between chemical and supercritical water recycling can vary based on several factors, including market conditions, raw materials involved and production scale. However, there are some general considerations:

Chemical management costs

Chemical recycling may require the use of expensive or particularly reactive chemicals, increasing management and safety costs.

Energy consumption

In chemical recycling, processes can require significant amounts of energy, affecting overall operating costs.

While in supercritical water recycling, although the process requires high temperatures and pressures, recycling can be more energy efficient compared to traditional chemical processes.

Residues and environmental management

In chemical recycling, some chemical processes can be used that can generate unwanted by-products or toxic residues, increasing environmental management costs.

By using supercritical water, the process is cleaner and less toxic, reducing costs associated with environmental management and regulatory compliance.

Adaptability to types of plastic

With chemical recycling there is greater process adaptability to a wider range of plastic types, while the use of supercritical water could be more selective or effective for certain types of plastic.

Automatic translation. We apologize for any inaccuracies. Original article in Italian