Not so difficult after all: microwaves target PET

demeto microwave depolymerisation process

Contaminated and composite plastics in the waste stream – such as food trays, opaque bottles and textiles containing polyester – are currently in the ‘difficult’ or even ‘impossible’ to recycle category. Much of this material ends up in landfill or incineration after being discarded, which removes it from the materials cycle for ever.

But what if these unwanted plastics could be broken down back into their component ‘build­ing blocks’ – known as monomers – for use again by manufacturers? This is essentially what those involved in the Demeto research project are working to prove at industrial scale.

The chemical recycling project is funded by the EU’s Framework programme for research and innovation, Horizon 2020. A consortium of experts which represent the entire value chain of polyethylene terephthalate (PET) recy­cling are involved in the process, including major European PET manufacturer Neo group and global fashion chain H&M.

There are 13 partners working with the inventors of the depolymerisation technology and downstream process that form the Demeto consortium. Each perform specific specialist tasks:

3V Tech – provider of process solutions and process equipment. Capable of supporting full R&D-to-industrialisation projects.

ACTOR – specialist in the modelling, design and implementation of advanced controllers for the process industry to assure that they reach the upper limits of attainable performance.

Technical University of Denmark (DTU) – includes a department focused on the engineering of advanced chemical and biochemical processes.

European Outdoor Group – association that represent the common interests of the European outdoor industry.

EuPC – EU-level trade association, based in Brussels, representing European plastics converting companies.

Fricke and Mallah – German supplier of microwave ovens for industry and research.

GR3N – inventor and owner of the depolymerisation technology and its patent, the scientific core of Demeto.

H&M – Swedish multinational clothing retailer, the world’s second largest.

Neo group – one of the biggest manufacturers of PET granules in Europe, located in Lithuania. It makes and sells more than 308,000 tonnes a year, or 12% of European production.

PETCIA – a mechanical recycler of PET that produces rPET flakes from post-consumer PET bottle waste collected from Spanish municipalities.

Processi Innovativi – owned by Kinetics Technology, which provides process services for the chemical, petrochemical, oil, gas and energy industries.

Recuprenda – European organisation focused on the innovative recovery of textile and footwear waste, as well as the connection of value chains in circular business models.

SUPSI – offers applied research in the fields of wired and wireless telecoms, security and in the design of high-frequency sensors and electronic systems.

Synesis – a non-profit technology transfer organisation that supports start-ups and SMEs in bringing innovative solutions to the market.

Switzerland-based Maurizio Crippa, inven­tor of the technology and founder of Gr3n, a company he set up to develop the technology, tells MRW that it all started after he came across the problem of hard-to-recycle plastic trays, made of a blend of polyethylene (PE) and PET.

“People said to me there is a problem because we can’t recycle this material,” he says. “Then I thought, well, we can depolymerise PET to pro­duce the monomers and then separate PET from the PE.” Crippa, who was working in a university at the time, bought a PET bottle from a vending machine, cut it up, and went to his lab. His microwave reactor was being used by someone else, so he went to the lab of his friend Matteo Parravicini and asked if he could use his reactor.

“After half an hour, he came into the lab and saw me cutting up this bottle and asked what I was doing,” he recalls. After Crippa explained, Parravicini agreed it was a good idea, and that was how it all began. The two started working together, set up Gr3n, patented and developed the idea, and brought on-board a chief financial officer.

The essence of the Demeto process is the chemical depolymerisation of PET at industrial scale using microwave-based process intensifi­cation. The technology would be able to pro­vide an indefinite life for PET by taking it back to its component elements: ethylene glycol (EG) and terephthalic acid (PTA) without degrading the materials. They can then be used again and again, as if they were virgin material.

This means the technology has the ability to close the loop and keep the materials in use if they can be captured, put through the chemical recycling process and then made into new products, repeatedly.

The use of microwave radiation as a physical catalyst means the process reduces the reaction time and the complexity of the purification steps needed for PTA, as well as enabling a con­tinuous rather than batch processing system, which increases efficiency.

In terms of the big picture, the vision is to eliminate the global issue of plastics waste by offering plastic producers and waste recyclers a profitable way to treat the waste through chemical recycling. Currently, PET-based waste streams are treated mainly using mechanical processes. This recovers the plastic solid waste for reuse but, because of the degradation and heterogeneity of this waste stream, only sin­gle-polymer plastics can be processed, while the more complex and contaminated waste is excluded.

When dealing with mechanically recycled products, quality is a key issue because this is essential to being able to reuse the material.

Crippa explains that Demeto’s solution would be able to deal with the dirty and con­taminated material that the current mechani­cal recycling systems cannot, and so the technologies are compatible rather than com­petitive with each other.

If the project proves that the technology and downstream processes work at industrial scale, it offers a truly revolutionary prospect for man­ufacturers, recyclers and waste management companies.

For manufacturers, it would be a new source of material comparable to virgin plastic, com­petitive on price but with green credentials. For waste management firms and recyclers, it would offer a new outlet and income for what is currently an unwanted waste stream. More broadly, it would also reduce the resource bur­den of the plastics manufacturing sector and improve the environmental footprint of PET.

Crippa says the reactor is running and work­ing, and all the necessary tests are being con­ducted: “The second step of the project is the development of a whole plant containing an entire reactive unit – which means more than one reactor working in parallel – and then developing the entire downstream of the pro­duced material.”

Project aims

Technical objective: Build a full and industrial-grade pilot plant of the depolymerisation process, with a Gr3n reactive unit at its core, while optimising the purification steps.

Strategic objective: Exploit the mature market of the packaging waste, while preparing the technology for transfer to the huge and unexplored polyester/textile value chain.

Environmental objective: Enable a fully circular economic approach to reduce the environmental footprint of PET production and usage by more than 50%.

History of development

Ahead of the current Demeto project, Gr3n was involved in a European project called Symbioptima, which was focused on developing beneficial flows (such as of waste, recycled materials and by-products) that could result in greater resource efficiency and less adverse environmental impact.

This first project enabled ‘proof of concept’ of the technology and received positive feedback, leading to the application for further funding for the Demeto project, to take the process and technology to an industrial scale.

Both projects were co-funded by the European Commission.

The reactor and downstream process are patented. Crippa explains that what makes the downstream process unique is that it takes care not just of the purification of the monomers but also the main by-product of the reaction, which is sodium chloride (salt). This is important because, due to its approach – which couples its purification plant with an electrolyser – the chlor-alkali plant transforms the sodium chlo­ride into sodium hydroxide and hydrochloric acid, which are the chemicals needed for the reaction and the downstream process.

“The point is that the plant is self-sustaining,” he says. “It doesn’t have chemicals going back and forth. The chemicals are produced from the main by-product, so it is really green chem­istry. What we need is energy and water.”

At the moment, the test reactor is producing 10kg/hour of product – the monomers – which are being sent to the Technical University of Denmark in Lyngby, for measurement. By the beginning of 2020, a 1,000 tonnes a year Demeto plant in Switzerland should be produc­ing monomers for manufacturers to use.

Monomers from the test plant have been sent to consortium partner Neo group, based in Lithuania, which is a major producer of polyester in Europe. Crippa says: “To be honest, they were shocked when they received the first sample – in a good way. They couldn’t [believe] that it came from coloured bottles.

“Our process has the great ability of purifica­tion…despite [the fact that] we have a huge variability of feedstock: coloured bottles, contaminated bottles, opaque bottles, plastic trays or textiles.”

Due to the kind of chemical reaction used, the process is able to produce monomers of the same quality in a steady manner, despite con­tamination, which makes it a robust system.

“Our process has the great ability of purification… despite [the fact that] we have a huge variability of feedstock: coloured bottles, contaminated bottles, opaque bottles, plastic trays or textiles.”

“The kind of intermediary we produce after the reaction [EG and PTA] is easy to purify,” Crippa explains. “In other [types of] depolymerisation, the purification ability is very lim­ited. Our competitors have to select the feedstock while we start from dirty, contami­nated feedstock. Being able to purify so well gives us the possibility to work with the most contaminated or degraded material.”

Regarding textiles, tests have been con­ducted which show that the process can still produce the same quality monomers regardless of contamination from other fibres, meaning it could treat blended fabrics.

Crippa says: “We tested coloured bottles, opaque bottles containing titanium dioxide, then I contaminated the material with cotton, with paper, and there was no problem. Cotton and paper do not react and are filtered after the reaction. We also contaminated with polyole­fins such as PE and polypropylene (PP) – they came out of our reactor with no problem. Then we contaminated with 20% nylon, 20% rayon viscose and 20% spandex – they are all removed without problem.”

He explains that the microwave radiation technology used reduces the reaction time from two to three hours to just 10 minutes.

“We don’t use the microwave to warm up the mixture but we take advantage of the catalytic effect of the microwave,” he says. “To my knowl­edge, this [technology] is not used very often in industry to produce a reaction.”

Commissioning of the plant is planned for the end of 2019/beginning 2020, with almost the whole of 2020 dedicated to testing different materials in the plant: bottles, textiles and other polyester materials. Crippa says that, in general, there are four types of input material that could be treated: colourless bottles, coloured bottles, opaque and difficult-to-recy­cle material, and textiles.

At present, colourless bottles are generally recycled into new textiles, with a small amount going into bottle-to-bottle recycling plants.

“The coloured bottles go into other kinds of fabrics – for example, car seat belts which are typically black. Then we have the opaque bot­tles such as the white ones containing titanium dioxide typically used for milk [in continental Europe], or coupled materials such as PE/PET, PP/PET . These materials are not useful for any recycling and are burned.

“Finally, textiles [containing polyester] which, sooner or later, goes to incineration.”

Crippa’s vision is that the mechanical recy­cling of bottles should continue, but we should turn to chemical recycling for the plastics that would otherwise go to landfill or incineration.

He explains that with current mechanical recycling technology for clear PET bottles, aside from a yellowing that starts to occur if you increase the recycled content above certain thresholds, there is a reduction in the intrinsic viscosity of the polymer.

“Every time you warm up a polymer, espe­cially polyester, you have a ‘random cleavage’ of the polymer chains. This is caused by the presence of water and heat in the polymer and reduces its intrinsic viscosity,” he explains. “The polymer then has lower mechanical properties so you cannot use it for certain applications.

“For example, if you want to blow a bottle with 100% colourless recycled PET, because its intrinsic viscosity is lower, you need to produce a bottle with a thicker wall. When you do it with virgin polyester you have a thinner wall.

“By increasing the recycled content in the polymer, you affect the mechanical properties. But random cleavage is not a problem for us because we cleave the polymer at the end of its life. We completely cut the monomers and recover them, so it is fine. That is why I don’t see us as a competitor of the existing value chain – we are compatible. We open the possi­bility to increase the recycling rate of the cur­rent bottle stream, for example.”

In terms of the economics, Crippa says the cost of its monomers is competitive with the cost of monomers from oil because the pro­cess is very efficient. “Of course, the cost of the feedstock has an impact on the final cost of the monomers. If we work with colourless bottles the price of the feedstock is too high, but if we work with coloured bottles, it is fine. If we are working with textiles it is much better because nobody can process textiles,” he adds.

“I don’t see us as a competitor of the existing value chain – we are compatible. We open the possibility to increase the recycling rate of the current bottle stream, for example.”

Textile recycling is an area where he sees a lot of potential for the technology, particularly in light of the EU circular economy package targets, which decree that, by 2025, member states need to have separate recycling collec­tions for textiles. There will need to be recycling systems in place to treat all the material that is collected, much of which will be clothing containing blended fabrics such as polyester.

Asked if he is concerned about any potential shift away from plastics, and Crippa responds that, while he understands the current consumer concerns around plastics, he believes the material plays an essential role in reducing food waste, keeping food fresher for longer and improving food safety. He adds that the only real way to measure the environmental impact is via life cycle assessments, and points to studies which have found that the impact of food wasted is greater than the impact of the packaging used to protect it.

His vision is to gain more value from the plastics in use that we lose for ever to landfill and incineration at the end of their life: “Mechanical recycling is limited. Chemical recycling is appearing and it will integrate with mechanical recycling. With the help of con­sumers, we can make a better value chain.”