We go beyond to develop recycling solutions

Evonik is researching a technique for recycling the flexible polyurethane foam from used mattresses. The innovative hydrolysis process breaks down the recyclable material into its basic chemical building blocks, from which new products can be manufactured

In Europe alone, people dispose of around 40 million mattresses every year. If they were stacked on top of each other, they would create a mountain of waste around 8,000 kilometers high. Currently, only 17 percent of mattresses are recycled—but this is accompanied by a loss of product quality. Moreover, half of the discarded mattresses end up in landfills and one third are incinerated. Evonik has developed a process to produce flexible polyurethane (PU) foam for the circular economy.

EVONIK DEVELOPS HYDROLYSIS PROCESS FOR CHEMICAL PU RECYCLING

The 40 million discarded mattresses contain an estimated 300,000 tons of flexible PU foam. With the right technology, the foam can be transferred to the circular economy as a usable recyclable material. Evonik came up with the idea of breaking the polyurethane back down into its basic chemical building blocks in order to produce new mattresses from them. Flexible foam manufacturers will therefore not have to rely solely on petroleum-based raw materials to manufacture new products in the future. Evonik has developed a new hydrolysis process that enables the polyols contained in flexible PU foams to be completely recovered. What has so far proved successful in the laboratory is to be realized on an industrial scale in the long term.

PU RECYCLING AS A CROSS-UNIT INNOVATION PROJECT

This is the job of Annegret Terheiden. Several years ago, Terheiden, who has a PhD in chemistry, teamed up with colleagues at Evonik’s strategic research unit and business incubator Creavis to initiate this recycling project. “Our core competence lies in the development of additives that make it possible to give PU flexible foams the desired properties. Our Comfort & Insulation business unit is the global market leader in this area,” she says. “With the combined expertise of Creavis, process engineering and our business unit, we can also implement innovation projects in other areas, such as PU recycling.” 

Terheiden is working on the project together with Michael Ferenz. Ferenz and his colleagues use an especially developed catalytic system to split the polyurethane. The catalyst ensures that the chemical bonds are broken quickly and efficiently and that the reaction can take place within an acceptable period of time.

THE LENGTHY ROAD TO ACHIEVING PU RECYCLING

At the end of the process, there remains a liquid mixture containing pure polyol and an amine (TDA). The latter can be converted to the isocyanate TDI in a subsequent reaction. The substances required for the production of polyurethane are recovered in a further purification step. In order for the molecules to be suitable for foaming again, they first have to be cleanly separated from one another. “We can do that now, but it took a long time to get there,” says Ferenz.

Once the process had been developed, Evonik’s process engineering experts went into action. Particle engineers clarified how mattresses can be shredded better, while fluid process engineers looked for a solution to separate the liquid mixture into its components quickly and cleanly. Digitizers, measurement and control technicians, environmental technicians, and safety technicians also continuously improved the process.

RECYCLATES WITH AN EXCELLENT LIFE CYCLE ASSESSMENT AND A PROMISING PRODUCT QUALITY

Even at the current stage of development, industrial partners are enthusiastic about the recycled products. Among the partners is the British flexible foam manufacturer The Vita Group, which has been working closely with Evonik since 2021. In addition to the very promising product quality, the outstanding life cycle assessment of the recyclates is a unique selling point of the process, according to the company’s managers. 

To close the material loop in the PU industry, Evonik has also been working since 2023 with the Remondis Group, a leading global recycling company. In order to ensure that the foam from used mattresses is also available for recycling processes in the long term, the partners are currently working together to develop suitable logistics, sorting and pre-treatment concepts. 

The development of value chains is causing Evonik to break new ground. “Forward-looking chemical recycling requires both upstream and downstream cooperation with partners in order to close the material cycle and maximize efficiency. Finding optimized processes for collaboration is still uncharted territory for the entire industry,” says Bettina Gerharz-Kalte, Head of the New Growth Area Circularity at Creavis. “The pioneering work that we are doing as a key enabler for circularity in this polyurethane recycling project will ultimately also benefit other projects in the circular economy and thus Evonik’s customers.”

EVONIK COLLECTS VALUABLE DATA ON PU RECYCLING

The recycling project resembles a huge mosaic that is being worked on in parallel at several locations. The big picture comes together at a pilot plant in Hanau, where the process for recovering raw materials from old mattresses is currently being further optimized. This is the responsibility of process engineer Andree Blesgen. “We’re scaling up the recycling process here at the Hanau site and collecting valuable data,” he says. “It will help us to set up a demonstration plant in the next step and use it to show that our process also works on a larger scale.” 

At the end of 2022, Evonik commissioned the part of the plant in which the mattress foams are broken down into their individual components. The second part of the pilot plant was built at the same time. Since 2023, this facility has separated the individual components from each other and continuously improved their quality. “Our aim now is to operate both sub-plants together in order to close the internal recycling loop,” says Blesgen. In the next step, corresponding quantities of foam could be recycled on a small industrial scale.

“The experience gained in this project also opens up new business opportunities for our additives business,” says Bettina Gerharz-Kalte. “We are learning a lot about the ‘design for recycling’ of mattresses and therefore the development of customized additives for an optimal recycling process.”