Molecular Sorting

Turning residual waste into raw materials – recycling at the molecular level

About 60 billion tons of resources are currently consumed worldwide each year – with an upward trend. Resource efficiency is therefore one of the most important keys to sustainable development. As part of the sustainability concept, resource efficiency is an important element of national and international strategies, for example at the level of the United Nations, the European Union, and the German Federal Government. In technological terms, resource efficiency primarily takes the form of material substitution and closed-loop approaches in research, development, and everyday practice. In the research project Molecular Sorting as part of the Fraunhofer Future Topics scheme for the »Markets of the day after tomorrow,« the Fraunhofer-Gesellschaft is promoting methodically oriented development which in the medium to long term will enable the recycling and reprocessing of materials in new, efficient separation processes at a molecular level following the production or use of products. A total of seven Fraunhofer Institutes are pooling their resources for this closed-loop economy of the next generation with two aims: testing new methods on selected material flows, so-called demonstrators; and ensuring that the results are transferable to further substances and sectors of industry.

Life Cycle Assessment

The recovery of material resources from waste is fundamentally desirable in terms of the objective of resource conservation. However, the effort involved must stand in appropriate relation to the benefits – not only in economic, but also in ecological terms. Recycling is ecologically beneficial as long the environmental burden generated in preparing the secondary material is less than that for the primary material. It is worthwhile recycling materials that are difficult to produce but can be recovered in relatively minimalistic processes. Three aspects are of central importance here: first, the ecological profile of the primary materials to be replaced; second, the specific configuration of the processes for primary and secondary production, both now and in the future; and third, the multidimensional meaning of the concept of »ecological impact.« The ecological profile of primary materials is frequently indicated as a constant, for example as x kg CO2 equivalent per 1 kg of material; this represents the sum of the ecological impacts of the individual processing stages. The ecological profile is gradually increased from the natural resource to the final material or even workpiece. To recover materials, the composite into which these are incorporated must be dismantled and if necessary the material itself modified. Depending on the position in this upward cascade at which a secondary material is introduced, recycling can be either more or less worthwhile. The ecological profile of hybrid components, for example, is often due more to the processing stages than to provision of the individual materials. In the interest of ecologically favorable recycling processes, it can be more advantageous to replace intensively processed materials, or even entire workpieces, than the individual plastics used or even their monomers. This is only one side of the equation – the effort involved in the recycling process is initially not taken into consideration.

The details of the processes are modified over time. First, the molecular sorting methods to be developed are currently only at the prototype stage at best, and are thus not comparable with large-scale industrial processes. And second, existing processes that are already used on a large scale are subject to change. The efficiency of classic recycling methods (bulk sorting) is impaired with a greater variety of materials, and the primary provision of materials changes with the ongoing exploitation of the known deposits of input resources. The primary preparation of metals, for example, becomes increasingly laborious the deeper the deposits are located and the lower the typical metal content of the extracted ores, since this for example necessitates deeper excavation and further concentration of the material. A general tendency can therefore be expected for recycling to become increasingly worthwhile in future, even with processes that at first appear laborious. The concept of »ecological impact« is more complex than it may first appear. Reference was made above, for example, to the quantity »kg CO2 equivalent.« However, this only describes the effect of a product on anthropogenic climatic change. In the context of Life Cycle Assessments in molecular sorting, the focus is extended from the climate effect to acid rain, eutrophication, and summer smog. Use of resources is also considered, since the advantages of the recycling processes are not as clear-cut as described above. It is possible, although not probable, that intricate recycling processes indirectly consume more resources than they directly recover. Depending on the type of product system under evaluation, the different influences on the environment can correlate either more or less strongly, or in extreme cases even run contrary to one another. For a differentiated analysis, it is imperative to treat these influencing factors individually and to discuss the significance of tradeoffs together with the process developers.

For each process developed in molecular sorting, a Life Cycle Assessment model of the product system into which the process is integrated is prepared in parallel with the actual development of the process. The information thereby gained is relayed back to the developers in several iterative loops. The end result comprises processes that are not only awarded a »Life Cycle Assessment seal« but for which the ecological analysis is an integral component of the development process.