ALLOCATION
Understanding mass balance as used in chemical recycling
Tracking use of mechanically recycled material is straightforward — the recycled resin is simply used as supplied or blended in with virgin. It is not so easy in chemical recycling, where recycled content takes the form of basic hydrocarbons fed into complex cracking and polymerisation processes. Individual molecules cannot be tracked but have to be accounted using the principles of mass balance. The idea behind mass balance is to measure the
input of an individual component in a much larger manufacturing process and allocate its contribution to each unit of end product. In the case of chemical recycling, it aims to ensure that the amount of recycled feedstock entering a production plant equates to any claims made about the recycled content of products leaving it. It is not a new con- cept; the idea is already applied in sectors as varied as electricity marketing and Fair Trade agriculture. As with many ideas, however, the challenge is in implementation. Different approaches can be taken with regard to what to allocate and where to allocate it. For instance, the entire output of a chemical recycling process — including both fuels and feedstocks — could be allocated as a contribu- tor to any polymer or chemical production process, whether or not there is any direct link. This is called free-attribution. Alternatively, it may be decided to allocate only non-fuel components. Or, at its strictest, only those components used as a non-fuel contributor to production of a polymer. Trade association Chemical Recycling Europe
Chemical Recycling – Global Insight 2023
leans toward the free-attribution approach. In a white paper it says: “Our position is that all mass-balance interpretations should ensure that the full recycled output from chemical recycling finds a credible value and recognition though the system.” Others, however, take a different approach. Zero
Waste Europe, together with several other environ- mental NGOs, has published 10 recommendations it argues will ensure the use of mass balance does not undermine circularity goals. This involves only including post-consumer waste streams, not allowing trading of recycled content credits, and ensuring allocations are restricted only to processes where there is a direct link between feedstock and final product.
Mass balance will be essential in the develop-
ment of chemical recycling as an industrial process and to that end it is important it is seen to be transparent and trusted — consumers, for example, must understand the claims made and, more importantly, have confidence in them. A number of organisations are already running certification programmes, of which the best known are Interna- tional Sustainability and Carbon Certification (ISCC) and RedCert (both headquartered in Germany). In addition, the International Organisation for Standardisation (ISO) has started work on a global mass balance standard — ISO/AWA 13662 Chain of Custody-Mass Balance-Requirement and Guide- lines. This is currently in the preparatory stage. �
www.chemicalrecyclingeurope.eu
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Main image: How are inputs and outputs treated in a chemical recycling process?
IMAGE: SHUTTERSTOCK
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