Get into the loop!

What sounds simple is in fact a multi-layered concept: Loops can be closed at different stages, leading to a concentric scheme rather than one big cycle. As a rule of thumb, the smaller the circle, the less effort and resources are required to retain the value.

Repair / refit / remanufacture: Looking from the product perspective, these are the smallest loops. A piece of equipment can be repaired or updated so that it can be used even in a changing processing environment. One example for this is to fit an “analogue” compressor or mixer with data retrieval components in order to make it “smart” and usable in a more digital environment. This is a very important point for refitting brownfield plants. Another possibility would be to reassemble the modules of a pump to meet new requirements rather than buying a whole new pump.

Recycling: If a product or piece of equipment has reached the end of its lifespan, the next opportunity to close a loop is recycling. This means that the product is broken down into its components or, more drastically, the material is melted down or otherwise reshaped without affecting its chemical composition. While this is a well-established and proven process for glass, many metals and some other products, the case of plastics highlights its limits. They arise from several challenges at different points in the recycling system: Recycling requires sophisticated collection and sorting systems, demanding elaborate logistics. This becomes more complicated the more varieties of a material are on the market or, even worse, combined in a composite  material. While glass bottles differ mainly by colour, “plastic” can consist of a plethora of different materials that need to be correctly sorted to allow for recycling without loss of quality. Every impurity can cause problems in the process.

Chemical recycling: One work-around for this is chemical recycling. This process which is currently much discussed with regard to the use of bio-based waste streams and plastics relies on breaking down the material chemically, resulting in small  molecules such as monomers, oils and syngas. The range of waste streams that can be processed is wide and reaches from used cooking oils to polymers. They are broken down by pyrolysis, for example. The steps that follow are very similar to the processing of natural gas or fossil oil – a big advantage because it can be integrated into existing production landscapes. The downside is that this cycle is rather wide and contains many steps, each requiring resources and especially energy, first for breaking down, then for rebuilding the material.

Combustion: While CO₂ resulting from “thermal recycling” is also a small carbon molecule, it is much more difficult to convert back into materials. Thus, combustion should be restricted to waste streams that can not be recycled otherwise. Biology  offers one way for CO₂ usage by photosynthesis; another way is CO₂ capture and usage, which mainly relies on renewable hydrogen and sophisticated catalytic processes. The cycle is even wider than chemical recycling, and the energy demand especially is much higher.