New electrochemical processes transform environmental toxins into valuable raw materials

Halogenated chemicals are indispensable in countless everyday products - from pesticides and flame retardants in electronics to medical contrast agents. However, their chemical stability, which makes them so valuable for applications, becomes an ecological curse: they accumulate in ecosystems and do not return to the recycling cycle.

Fluorinated compounds such as PFAS and chlorinated pesticides such as lindane in particular resist natural degradation for decades and pollute the environment and health. A perspective article published today in CellPress by Prof. Siegfried R. Waldvogel and Dr Sebastian Beil points to a way out.

Resources in waste: global deposits as a source of raw materials

Gigantic quantities of halogenated pollutants are stored worldwide, which could serve as future sources of raw materials. These include lindane residues from pesticide production, with an estimated volume of four to seven million tonnes, which were produced as waste isomers during the manufacture of the insecticide.

Equally relevant are PVC waste from the construction industry, of which around 60 million tonnes are produced annually, and brominated flame retardants in plastics, which account for up to 33 per cent by weight. Even seemingly minor contaminants such as iodinated contrast agents in hospital wastewater or industrial gases such as sulphur hexafluoride from electrical equipment become relevant resources when their global distribution is considered.

These 'waste deposits' contain valuable halogens, in particular chlorine, bromine and iodine, which are difficult to recover using conventional methods. Prof. Siegfried Waldvogel sees electrochemistry as a solution in his research: 'Electrochemistry offers an energy-efficient strategy for transforming global pollutant problems into sustainable value chains.'

Electrochemistry as a key technology

Waldvogel's team uses electric current to specifically separate halogens from pollutants and make them available for new syntheses. The approach combines several advantages: the reactions take place under mild conditions at room temperature, avoid toxic additives and can be powered by renewable electricity, which significantly improves the carbon footprint.

Concrete successes underscore the potential. For example, lindane waste serves as a source of chlorine for the production of new dichlorine compounds - a process that simultaneously releases benzene as a usable by-product. In the case of PVC waste, electrochemical dechlorination not only enables the recovery of chlorine for synthesis, but also recovers the polymer backbone. Even complex brominated flame retardants such as HBCD can be converted into valuable cyclododecatriene.

Extension of the concept: from iodine to sulphur hexafluoride

Electrochemical processes are astonishingly versatile. In the case of iodinated contrast media such as iomeprol, almost complete deiodination is achieved with a recovery rate of over 95 per cent. Industrial partners such as Bayer AG are already testing this approach for its practical applicability. Even extremely stable compounds such as the insulating gas sulphur hexafluoride are transformed into building blocks for medical applications through combined light electrochemistry. To simplify the handling of reactive halogens, the researchers also developed innovative storage methods: storage in stable polyhalide ions or cyclodextrin-based carrier materials eliminates risks during transport and storage.

Prospects: circular economy and defossilisation

These electrochemical approaches pave the way for a sustainable 'halogen circular economy' with threefold benefits. Firstly, they reduce the burden on the environment by using pollutants such as lindane or PCBs as raw materials instead of sending them to landfill. Secondly, they conserve resources by substituting fossil halogen sources, such as rock salt. Thirdly, they generate added value by using carbon skeletons from PVC or lindane as non-fossil basic chemicals.

For large-scale implementation, researchers are working on standardised reactors and adapted process parameters, supported by projects such as the BMBF-funded future cluster 'ETOS' and the 'Halocycles' initiative of the Carl Zeiss Foundation. However, as Waldvogel emphasises, implementation requires joint efforts: 'Science, authorities and politics must work together to create the framework conditions for putting these technologies into practice.'

» Original publication

Source: Max Planck Institute for Chemical Energy Conversion (CEC)