Environmentally friendly recycling process developed for "Teflon"

Objective: pilot plant for the industrial recycling of fluoropolymers

Varietal PTFE granules. © Chair of Materials Processing / University of Bayreuth
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Bayreuth researchers, in collaboration with an industrial partner, have succeeded in developing a new process for the recycling of high-performance plastics. The method is economically efficient and without ecological risks. The construction of a pilot plant would open the way to the industrial recycling of so-called fluoropolymers, say the scientists.

Fluoropolymers are high performance plastics that are used in a variety of products worldwide. In particular, the polytetrafluoroethylene (PTFE), world-famous under the legally protected brand name "Teflon", is an indispensable material in many industrial sectors. It is characterized by a high resistance to heat and chemicals, almost nothing sticks to it.

Not only frying pans, but also numerous seals and bearings - for example in motor vehicles - are coated with PTFE. The textile industry also uses PTFE as a material for breathable membranes in functional textiles, and in electrical engineering PTFE is an important material for cable insulation.

Recycling instead of burning

But what happens to PTFE-containing industrial waste and used products? There is no industrial recycling of fluoropolymers worldwide. This problem is getting more and more explosive. This is because combustion, which is still common today, releases highly toxic, environmentally harmful vapors which also damage the incinerators. And a landfill of contaminated sites will be banned in the future due to European Union legislation.

Waste containing persistent organic pollutants - such as fluoropolymers - must be recovered or disposed of in such a way that the pollutants are destroyed or irreversibly converted into non-hazardous substances. display

Economically efficient and without ecological risks

In solving this problem, a research project at the University of Bayreuth has achieved a decisive breakthrough. Three partners have been involved: the Institute for Materials Processing, the research institute InVerTec and Dyneon, which today is one of the world's leading producers of PTFE and has a high interest in recycling.

In close collaboration, the scientists developed an economically efficient and ecologically safe process that decomposes the fluoropolymers into recyclable components. The method is characterized by the fact that the large PTFE molecules are decomposed to a very high percentage into smaller molecules, so-called monomers. These building blocks are molecules of gases, in particular of tetrafluoroethylene and hexafluoropropene.

Almost complete material cycle

Up to 93 percent of these gases, which make up the PTFE, can be recovered through the tried-and-tested method of the Bayreuth-based high-tech laboratories, in such a way that no harmful effects from this process can occur The employees involved go out.

The gases can now be returned to the PTFE producer under environmentally safe conditions and used again for the industrial production of PTFE. As a result, the fluoropolymers are almost completely returned to the material cycle. Together with the Dyneon company, Bayreuth engineering scientists have already developed a concept for how this recycling can be realized on an industrial scale.

From recycling concept to pilot plant

The decomposition of PTFE into its components is a process known in the research as depolymerization. The process developed for this purpose in Bayreuth is a so-called fluidized bed process. Of central importance are very short-term heating of the fluoropolymers and a pyrolysis triggered thereby. Microwaves are used as energy source.

Together, the project partners investigated which technology is particularly suitable for implementing the process on an industrial scale. The evaluation included a variety of economic, environmental and technical criteria. The result: The process, which leads to the decomposition of the fluoropolymers, can be implemented all in all especially advantageously with a stirred kettle technology.

Solution for an urgent disposal problem?

Based on these findings, the Department of Materials Development and Dyneon are currently working on the concept of a pilot plant for this process.

"The construction of this pilot plant would open the way to industrial recycling of fluoropolymers, thereby solving an urgent disposal problem, " explains Professor Monika Willert-Porada. The scientific and technological know-how for this we have worked out. Now all project partners want the necessary financial resources to be made available for the construction of the pilot plant. "

(idw - University of Bayreuth, 12.08.2010 - DLO)