A NEW LIFE FOR MATTRESSES

The processes that had been commercialized until then did not allow PU to be completely broken down back into polyol and isocyanate. Instead of individual molecules, the processes create mixtures of short-chain oligomers, which lead to far poorer foam properties than the original ingredients. A maximum of 20 percent of fossil polyol can be replaced with this process in the manufacture of new mattresses; otherwise the product properties will suffer. Terheiden wants to achieve a better result. The research work began back in early 2019, and Creavis was involved in this work from the very start. It is responsible for exploring business ideas for Evonik in new areas and markets. Thus, Terdeiden can concentrate on the chemistry and the application of the end product.

As a “flexible foamer,” as chemists in this field call themselves, she knows that European Union regulation requires a recycling solution for PU foams. The “Directive (EU) 2019/904 of the European Parliament and of the Council on the reduction of the impact of certain plastic products on the environment”—also known as the “Plastic Directive” for short—stipulates that by 2025 many plastic products must consist of a quarter of recycled material. Manufacturers must also present a plan for recycling their products at the end of their useful life. “PU is not yet regarded as strictly as single-use plastic,” says Terheiden. “But it’s not a question of whether that will happen, but when.”

In her office on Goldschmidtstraße, Terheiden puts on a white lab coat and makes her way to Michael Ferenz’s lab. Ferenz, who is an experimental chemist, joined the recycling project a year ago and has been responsible for the experiments in the laboratory in Essen since last summer. Behind a raised pane of safety glass is a shiny silver head-high apparatus: a hydrolysis reactor with a capacity of five liters. “In there I separate the PU foams with the help of additives,” says Ferenz.

The list of ingredients is constantly being optimized. “First we used finely ground PU ‘snow’,” says Ferenz. “However, this has a very low bulk density, which made it significantly more difficult to fill the reactor. So we are now working on other dosage forms.”

After loading, Ferenz sets the parameters for the experimental setup. The reactor has a laptop wired to it. This laptop depicts colorful curves from the last experiment and enables Ferenz to command and control everything. The temperature in the housing is shown in red, the temperature in the reactor in orange, and the pressure in blue. The last curve shows the stirrer rpm. It ensures that all reactants are mixed well.

If you ask Ferenz what exactly happens in this pressure cooker, you will get a quick refresher on chemistry. After clicking on his pen and getting out a notepad, he writes down the key to recycling success. It was discovered during research and employs hydrolysis, one of the fundamental reactions in organic chemistry, by using a catalyst. “We don’t yet know exactly how it works,” Ferenz admits. “The working hypothesis is that the catalysts bring our reactants together better.”

Ferenz and his colleagues use a catalytic system to split the polyurethane. By using a catalyst, the reaction can proceed under milder conditions. The catalyst ensures that the necessary chemical bonds are broken quickly and efficiently and that the reaction can take place within an acceptable period of time.

Ferenz shows what the result looks like in a small bottle. It contains what remains after the successful hydrolysis of PU foam: a deep brown liquid containing pure polyol and an amine (TDA). The latter can be converted into the isocyanate (TDI) in a subsequent reaction, resulting in precisely those substances that are required for the production of polyurethane. In order for the molecules to be suitable for foaming again, they have to be cleanly separated from one another.

“It took us a long time to get this far,” says Ferenz. Countless experimental setups provided useless parameters. Lots of catalysts and additives proved to be unsuitable. It was basically the normal life of a researcher. However, the proof of concept has now been achieved: a completely closed circuit without the addition of fresh polyol.

That was the starting signal for many experts at Evonik, especially in process engineering. Particle technicians are clarifying how mattresses can be shredded better, fluid process technicians are looking for a solution to separate the dark brown liquid into its components more quickly and cleanly, digitizers, measurement and control technicians, environmental technicians, and safety technicians are all solving problems relating to the process.

The result is still not completely perfect. Although the foams made from the recycled molecules behave flawlessly, they are brownish in color. Polyol derived from fossil sources is colorless, unlike its recycled chemical twin.

Despite these challenges, partners from industry are already very impressed by the process—for example the British flexible foam manufacturer The Vita Group, which produces high-quality mattresses and works closely with Evonik. “We have trialled Evonik’s recycled polyols in several of our flexible foam formulations and the outcome has been very positive,” says Vita CEO Ian W. Robb.

The company considers itself a pioneer in the environmentally friendly production of mattresses. The outstanding environmental balance of the recycling project is therefore a decisive factor for Robb. “We see it as our responsibility to be at the vanguard of the development of eco-friendly technology (within our industry),” he says.

How hydrolysis can be used to recycle PU foam

“This partnership represents a key milestone on our journey to achieving a circular economy.” At Evonik, the recycling project now resembles a huge mosaic that is being worked on in parallel at several locations. Business lines beyond Comfort & Insulation’s foam experts support the project. For example, colleagues from the Crosslinkers unit made their facilities available at the Marl Chemical Park.

However, the big picture should be visible in Hanau in a few months. A pilot plant is being built there in which the components of polyurethane are to be obtained in larger quantities. The plant is the responsibility of process engineering project manager Andree Blesgen, who joined the project in 2020. Instead of five liters, as in the previous reactors, the new plant should produce a multiple of that amount.

“We hope to go into operation in 2022 and to advance into the tonnage range with the new plant,” says Blesgen. That would be extremely rapid progress. “From patent research to the miniplant in three years—that’s ­really quick,” says Blesgen. One of the reasons for this is the enthusiasm within the company for the project. “It’s great fun to do something that is so environmentally beneficial. This generated an incredible amount of team effort,” he says. The project is even paying off for Blesgen, 45, at home. “When I used to talk about my job, my children were only moderately interested. However, they find it really exciting that I’m now helping to make mattresses recyclable,” he says.

Read on the same topic: The plastic cycle, Plastic recycling: Facts and figures

Photos: Henning Ross (6), Dave Kowal

Illustration: Oriana Fenwick / Kombinatrotweiss on the basis of an original photograph by Hamid Sadeghi

Infographic: Maximilian Nertinger