Circular Economy

In the primary industry sector, functioning networks for using secondary raw materials are already in place. But to further close the cycle of materials and use raw materials in the most efficient way possible, new approaches for recovering and using secondary raw materials need developing.

Industrial symbiosis – example of integrated chemical parks

• Creates shorter transport routes by setting up the facilities needed to produce basic chemicals and manufactured chemical products. For example, chlor-alkali electrolysers need to be located at chemical facilities to avoid transporting the chlorine needed to produce polyvinyl chloride (PVC). In integrated chemical parks, operating gas, water and steam are made available centrally by a steam power plant supplying several companies via a pipeline network.
• Heat integration (i.e. using heat from cooling processes to provide heat for other processes) not only in-house but also between local companies via a heating grid.

Industrial symbiosis – example of the cement industry utilising waste from the steel industry

• Blast furnace slag, which arises as a non-metallic by-product of the steel industry and hence finds no application in this sector, is used as a raw material in the cement industry. The granulated slag it contains thus substitutes clinker, a carbon intensive by-product.
• The transformation of the steel sector with the transition to the DR-Verfahren (direct reduction process) and the expansion of steel recycling in electric furnaces results in the removal of blast furnace slag as a by-product. Potential ways of using electric furnace slag as a secondary raw material in the cement industry need further research.

Utilising secondary products – example from the chemical industry

When producing the base chemical chlorine using chlor-alkali electrolysis, sodium hydroxide (caustic soda) is accrued as a by-product and new processes have been developed to make use of this substance. Nowadays, sodium hydroxide is used in the chemical industry as a neutralising agent and in the production of aluminium and glass. Sodium hydroxide is also implemental in processing chlorine into polyurethanes and polyesters.

Closing carbon cycles is an essential aspect of the transition to a climate-neutral future. CO₂ has already been used for some time as a raw material in some processes in the primary sector, but in the context of industrial transformation new technologies and supply chains are being developed that could extend its fields of application. Recycling CO₂ (Carbon Capture and Utilisation – CCU) keeps this greenhouse gas in a closed loop and reduces the amount that requires storing.

One particular challenge lies in optimising the recovery of used materials because the quality of the materials needs to be maintained over a large number of cycles. Currently, it is not always possible to avoid lower quality materials being produced as secondary raw materials in the recycling process, which leads to what is termed “down cycling”. In this context, using primary raw materials to produce high quality products is indispensable. That is why existing processes in the field of mechanical recycling are being further developed for many materials such as plastics. Apart from this, the focus is on developing chemical recycling for products that have been impossible to recycle until now.

Reuse and recycling imply that the products can be separated according to the type of material. In the case of reuse, products need to be sorted according to type or product components, whereas with recycling it is necessary to dismantle products and sort them at the material or resource level in order to be able to produce items of similar quality. Within a materials group, items need to be separated further, e.g. glass has to be separated by colour. In the case of plastics, on the other hand, sorting involves not only taking different colours into account but also the different types of plastic (PET, PP and so on) and additives used for different product applications due to their properties.

When sorting products to reuse components or recycle materials, it is not only the sorting technique, the sensors used in the process and the methods of analysis that are critical. Targeted product design is another crucial element. This determines whether it is possible to separate the product components and materials and what effort is needed to do this. Alongside product design, digitalisation of industrial production, for instance tracking product components, is a key factor contributing to success. Tracking makes it possible to identify the individual components and thus makes it easier to separate them.

Once the waste products have been sorted, they are recycled using the various technologies in different sectors. Some of the technologies have been established for years already and are in need of optimisation regarding efficiency and reducing impurities. In other sectors, however, new procedures are being worked out and designed to be competitive.

In Germany, 47 per cent of plastic waste is currently recycled. However, new procedures are planned to expand the potential available and make use of prevailing material requirements: the recycled material retrieved equates to just 13.7 per cent of material requirements.

Of the remaining plastic waste, 34.3 per cent is converted into energy at waste incineration plants and 18.5 per cent is used as substitute fuel in industrial processes, generating CO₂. Plastic recycling, also known as material use, is mostly done by mechanical recycling, whereby the chemical structure (makeup) of single-variety plastics is preserved. For current standard material or chemical recycling processes, the reduced plastic needs a high level of purity. New recycling processes that can also treat mixed plastic waste have the potential to supplement the technologies previously used, since they help to minimise the percentage of plastic waste used to produce energy – and the associated volume of carbon emissions – and to use the recycled material as an alternative to fossil-based primary raw materials as a source of carbon for new products.

Unlike the CCU process, it is not necessary to first form chains of molecules from individual small molecules. On the contrary, components, monomers and short chain polymers are already gained from chemical recycling,

The Circular Economy working group set up by IN4climate.NRW has published a discussion paper called “Chemical Recycling for Plastics”, which gives an overview of the technologies involved in chemical recycling and the state of the art. The "ChemCycling" project provides an example of best practice in the chemical industry.