10/06/2020 | Trends
Recycling schemes are in place in many countries, and for some materials such as glass or paper they are widely accepted and work well. But to achieve a true and comprehensive “circular economy”, a lot remains to be done – and soon.
If strictly applied, the concept of a circular economy goes far beyond the handling of products or the recycling of materials. It calls for a holistic view – the biggest conceivable loop is the one that is limited by planetary boundaries. Although this perspective might not be the best starting point for applicable concepts, it provides the most striking argument for why a circular economy is mandatory with regard to human survival: resources are limited. Short of mining on extraterrestrial celestial bodies, we have to work with what is here.
This is obvious for some metals or rare earth elements, but limitations also apply to other resources like carbon. We might feel that carbon is available in abundance, but we would rather limit the amount of carbon that resides as oxidized carbon in the atmosphere. Thus, climate change does not limit the amount of existing carbon, but it limits the amount of carbon we can convert from oil, gas or biomass to CO2.
On a more regional scale, resources are even more limited, and this applies not only to valuable metals or elements, but also to fresh water, which has also to be considered when speaking about closing loops.
Reusing what has already been collected instead of letting it dissipate is not only necessary due to environmental and sustainability concerns, but also economically viable: The available primary sources require ever more effort because they are not easily accessible or contain low amounts of the desired materials. Exploration and processing thus become ever more costly. Closing loops and implementing a circular economy is thus not only at the top of the agenda for national governments, the EU and the UN, but also of high interest to companies who want to ensure a sustainable supply of resources for their plants. All there is to do is collecting what has been used and reprocessing it to something new without any loss of quality or value.
This sounds simple, but the decision about which path to follow requires the consideration of many factors. A thorough holistic life cycle analysis can indicate whether closing a loop really is economically and ecologically feasible and should always be the first step when thinking about where to close 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.
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