Molecular Sorting

Turning residual material into raw material - recycling on a molecular level

At present, some 60 billion tons of resources are consumed worldwide every year - and the trend is growing. Resource efficiency is therefore a key factor when it comes to sustainable development. As part of the sustainability concept, resource efficiency is an important constituent of national and international strategies, such as those implemented by the United Nations, the European Union and the German Federal Government. Technically, resource efficiency is primarily achieved in research, development and practice through the use of substitute or recycled materials. To this end, within the scope of the Fraunhofer Future Topics for the “Markets of Tomorrow”, with its Molecular Sorting research project the Fraunhofer-Gesellschaft is funding a method-driven development. New, high-performance separation processes right down to the molecular level will enable materials from the manufacture or utilization of products to be recovered and reused in the mid- to long term. A total of seven Fraunhofer Institutes have joined forces to work on this next-generation closed-loop economy. Besides testing new methods on selected material flows - so-called demonstrators - they are also aiming at transferring the results to other materials and other branches of industry.

Life cycle assessment

In principle, in order to conserve resources, it makes sense to recover materials from waste. However, the associated costs must be in reasonable proportion to the benefit, not only in economic but also in ecological terms. Recycling becomes ecologically beneficial when the environmental impact of obtaining the secondary material is less than that of its primary supply. It is worth recycling materials that are recovered relatively easily but are expensive and complex to produce. Three aspects are of key relevance. First, the ecological profile of the primary materials to be replaced. Second, the concrete design of the processes for primary and secondary supply now and in the future. Third, the multidimensional meaning of the term “environmental impact”. The ecological profile of primary materials is often expressed as a fixed value, for example as x kg CO2 equivalent per 1 kg of material. This is the sum of the environmental impact of the various processing steps. From the basic resource to the finished material or even workpiece, the ecological profile gradually increases. In order to recover a material, the compound in which it is bound has to be broken down and, if necessary, the material itself also modified. Depending on at which point in this upward cascade a secondary material is added, recycling makes more or less ecological sense. For example, the ecological profile of hybrid parts is often more due to the processing steps involved than to the steps taken to obtain the various materials. In terms of ecologically advantageous recycling processes, it is usually better to replace heavily processed materials or even entire workpieces than the plastics or even their monomers used. However, this is only one side of the equation. The cost of the recycling process has not yet been taken into account at this point.

Process design changes over time. On the one hand, the processes under development in the Molecular Sorting project are at best at the prototype stage, i.e. they cannot be compared with large-scale industrial processes. On the other hand, existing processes that are already in use on a large scale are changing. Traditional recycling processes (bulk sorting) become less efficient the more materials they contain, and the primary supply of materials changes with the gradual exploitation of known deposits of the resources required. For instance, the primary supply of metals becomes more and more costly the deeper the deposits are located and the lower the average metal content in the mined ores becomes, due to the fact that the ores have to be extracted from a greater depth and that the mined material has to be concentrated more before it can be used. As a general tendency, it is therefore to be expected that recycling will become increasingly worthwhile in the future, even with processes that initially appear to be costly. The term “environmental impact” is more complex than it seems. The value “kg CO2 equivalent” was mentioned before as an example but this only describes the effect of a product on climate change driven by man. When assessing the life cycle in Molecular Sorting, the scope is extended to include acid rain, over-fertilization and summer smog as well as the impact on the climate. The use of resources is also considered because the benefits of recycling processes are not as clear as described above. Although unlikely, it could be the case that a costly recycling process indirectly uses more resources than it recovers. Depending on the type of product system under consideration, the effects on the environment may correlate more or less strongly or, in extreme cases, even diverge. To enable a differentiated view, these must be discussed individually and the significance of trade-offs must be assessed with process developers.

For each process developed in the Molecular Sorting project, alongside the actual process development a life cycle assessment model of the product system in which the process is embedded is also made. The information gained is fed back to the developers in several iteration loops. As a result, processes are developed which are not only given a “life cycle assessment stamp”, but which have also been analyzed from an ecological point of view at the same time.